Hypoxia-induciblefactors
Review
TIPS-1218;No.ofPages10
cells[1,2].Together,cancercellsandhostcellsforma
tumormicroenvironmentthatenablestumorinitiation
andprogression.Thedependenceofcanceronthehost
cellssuggeststhatthesehostcellscouldalsobetargeted
forcancertherapy.Again,becauseconventionalcancer
therapywasdevelopedwithoutemphasizingthetumor
microenvironment,amajornewfocusforcancertherapy
istolimitcancerdevelopmentbytargetingthismicroen-
vironment.
andactivityofpyruvatekinasemuscleisozyme2(PKM2),
HIF-1acanserveasamasterswitchforoxygenregulation
incellularmetabolism[17].
AsillustratedinFigure1,HIFisaheterodimercom-
prisingaandbsubunits.Theheterodimerstranslocate
intothenucleus,wheretheyinteractwithspecificDNA
sequencescalledHIF-responsiveelements(HREs).By
bindingtotheHRE,HIFmayeitheractivateorrepress
geneexpression.Atleastthreedifferentgeneshavebeen
identifiedthatencodeasubunitofHIF,namelyHIF1a,
HIF2aandHIF3a.AllthreeHIFasubunitsheterodimer-
izewithaHIF-1bsubunitandaresubjecttopost-
translationalregulationsthataredictatedbytheoxygen
concentrationintheenvironment.AlthoughHIF-3alacks
atransactivationdomainandisgenerallyconsideredtobe
anegativeregulatorforHIF-1aandHIF-2afunction,a
notableexceptionwasreportedrecently[18].Despitethe
0165-6147/
C2232015PublishedbyElsevierLtd.http://dx.doi.org/10.1016/j.tips.2015.03.003
Correspondingauthor:Liu,Y.(yaliu@cnmc.org).
Keywords:leukemia-initiatingcells;tumormicroenvironment;myeloid-derived
suppressorcells;dendriticcells;tumor-associatedmacrophages;cancerimmunother-
apy.
stemcellsandinflammatio
GongPeng
1
andYangLiu
1,2
1
InstituteofTranslationalMedicine,TheFirstHospital,JilinUniversity,
2
CenterforCancerandImmunologyResearch,Children’sResearch
USA
Hypoxia-induciblefactors(HIF)mediatemetabolic
switchesincellsinhypoxicenvironments,including
thoseinbothnormalandmalignanttissueswithlimited
suppliesofoxygen.Paradoxically,recentstudieshave
shownthatcancerstemcells(CSCs)andactivatedim-
muneeffectorcellsexhibithighHIFactivityinnormoxic
environmentsandthatHIFactivityiscriticalinthe
maintenanceofCSCsaswellasthedifferentiationand
functionofinflammatorycells.Giventhatinflammation
andCSCsaretwomajorbarrierstoeffectivecancer
therapy,targetingHIFmayprovideanewapproachto
developingsuchtreatments.
Challengesintargetingthetumormicroenvironment
Animportantparadigmshiftincancerresearchhasbeen
therealizationthatcancertissueisnotahomogenous
populationofclonallyexpandedcancercells[1–3].Ithas
beenestablishedinmultiplecancertypesthatcancercells
arehierarchical:whileasmallsubsetofCSCshaveahigh
capacityforself-renewalandareresponsibleforinitiating
cancer,thebulkofcancercellslackself-renewaland
cancer-initiatingcapacity[3,4].Perhapsbecauseconven-
tionaltherapeuticapproacheswerenotdevelopedtotarget
CSCs,manysuchcellsareenrichedbyconventionalcancer
therapy[5,6].TheineffectiveeliminationofCSCsiscon-
sideredamajorcauseofcancerrelapsefollowingconven-
tionaltherapyand,thus,isamajorbarriertoeffective
cancertreatment[7].
Inadditiontoheterogeneityamongtransformedcan-
cercells,cancertissuesalsocomprisenoncanceroushost
incancer
n
Changchun,China
Institute,Children’sNationalMedicalCenter,Washington,DC,
Basedontheseconsiderations,itwouldbeofinterestto
identifydruggabletargetsthatarecriticalforCSCsand
tumor-promotingmicroenvironments.Inthiscontext,
studieshavehighlightedtheselectiveactivationofthe
HIFpathwayandmetabolicswitchofCSCs[8–10].Re-
markably,recentstudiesdemonstratedthatHIFmayhave
amajorroleininflammation,includingtheadaptiveand
innateinflammatoryresponses[11–13].Thesharedre-
quirementforHIFinCSCsandinflammatorycellsraised
theinterestingprospectthatCSCsandinflammation,two
importantchallengesincancertherapy,maybeaddressed
bytargetingHIF.Here,wereviewthecriticalroleforHIF
inimmunologyandcancerbiology,withafocusonthe
potentialcross-fertilizationofHIFresearchoncancercells
andhostinflammatorycells.Wealsoexplorethetransla-
tionalpotentialofthisnewconcept.Readersarereferredto
outstandingrecentreviewsforthegeneralconceptand
involvementofHIFincancerbiologyandimmunology
[11,14,15].
HIFandcancer:anoverview
Themodesofenergyproductioninacellareusually
dictatedbytheoxygenlevelsintheenvironment:oxidative
phosphorylationoccursinawell-oxygenatedenvironment
(normoxia),whileglycolysisisswitchedonwhenoxygen
levelsdropbelow1%(hypoxia)[15].Inasearchforthe
fundamentalmechanismoftheoxygen-mediatedmetabol-
icswitch,GreggSemenzaandcolleaguesidentifiedHIF-1a
anoxygen-sensitivetranscriptionalactivator[16].Recent
studiessuggestthat,bydirectlyregulatingtheexpression
TrendsinPharmacologicalSciencesxx(2015)1–101
TIPS-1218;No.ofPages10
P
402OH
P
564OH
P
402
P
564
PHD1,2,3
VHL
O
2
O
2
UbUb
Proteasome
polyUb
HIF-1αHIF-2α
HIF-1β
HRE
P
405
P
531
P
405OH
P
531OH
O
2
TRENDSinPharmacologicalSciences
Figure1.Regulationofhypoxia-induciblefactors(HIF)activityinresponsetooxygen
levels.Underhypoxicconditions,stabilizedHIF-1aandHIF-2adimerizewithHIF-1b.
Theheterodimerstranslocateintothenucleustoregulategenetranscription.Inthe
presenceofoxygen,HIF-1aandHIF-2aproteinsarehydroxylatedbyprolyl
hydroxylasedomainproteins(PHD)1–3attheprolineresiduesindicated.
HydroxylatedHIFisrecognizedbyvonHippel-Lindautumorsuppressor,E3
ubiquitinproteinligase(VHL),whichcausespolyubiquitinylation(polyUb)and
Review
generalsimilarityinregulationandfunctionbetweenHIF-
1aandHIF-2a,theydifferintheirsensitivitytooxygen
deprivation,andtargetgenebindingandtissuedistribu-
tion[14].
ThecriticalroleofHIFincancerbiologywasestablished
whenamajorrenaltumorsuppressorgenevonHippel-
Lindautumorsuppressor,E3ubiquitinproteinligase
(VHL)wasidentifiedastheE3ligaseresponsibleubiqui-
tinylationofHIF-1aandHIF-2a[19–23].VHLrecognizes
hydroxylatedresiduesatPro402and/orPro562inHIF-1a
andPro405andPro531inHIF-2a,bymeansoftheprolyl
hydroxylasedomainprotein(PHD)[24].VHLisinacti-
vatedinmostrenalcancersamples,leadingtoincreased
expressionoftheHIF-1aandHIF-2aproteins[19–
23].MutationsofPHDprotein-encodinggenes,EGLN1
(PHD2),EGLN2(PHD1),andEGLN3(PHD3)havebeen
observedinvariouscancersatlowfrequency(http://www.
cbioportal.org/).ThefunctionofPHDisenhancedbyiso-
citratedehydrogenase1(IDH1)and/orIDH2[25,26],which
aremutatedatacombinedfrequencyofapproximately
15%inpatientswithacutemyeloidleukemia(AML)[27–
30]andlow-gradegliomaorglioblastoma[31].Tworeports
suggestedthatIDHmutationsleadtoincreaseinHIF-1a
accumulation[25,26],whileamorerecentstudysuggests
otherwise[32].
OverexpressionofHIF-1aand/orHIF-2aisamarkerfor
poorprognosisinmostcancertypestested,including
commoncancers,suchasbreast,prostate,colon,hepato-
cellular,pancreatic,brain,andovariancancers,aswellas
ahostoflesscommoncancers[14].Intransgenicmouse
proteasome-mediateddegradationofHIF.Abbreviation:HRE,HIF-responsive
element.
2
cancermodels,heterozygousdeletionofHif1areducedthe
growthofthymiclymphoma[33],whileshorthairpin
(sh)RNAsilencingofHif1aandoverexpressionofVHL
stronglyreducedleukemia-initiatingactivity[9].
DespitetheoverwhelmingassociationbetweenHIF
levelsincancertissueandpoorprognosisofpatientswith
cancer,conflictingreportshaveemergedinrenalcancer,
whereoverexpressionofHIF-1ahasbeenassociatedwith
eitherapoororfavorableprognosis,dependingonthe
methodsusedtoevaluateHIF-1alevels[34,35].Inmouse
cancermodels,recentstudiessuggestthat,whilelocal
deletionofHif1ainlungtissuehadnoimpactonKRas-
drivenlungcancer,deletionofHif2aparadoxicallyaccel-
eratedlungcancerdevelopment[36].Morerecently,broad
deletionofHif1ainadultmice,includinginthecellsthat
giverisetoleukemia,promoted,ratherthansuppressed
Mll-AF9a-inducedleukemia[37].Thesecontradicting
observationsmaybeexplainedbythebroadspectrumof
HIFtargetgenes:thecancer-promotingeffectisexempli-
fiedbyHIF-mediatedinductionandfunctionofPKM2,
vascularendothelialcellgrowthfactor(VEGF),andmulti-
drugresistancegene(MDR1),whileitsfunctionasatumor
suppressorcanbeexplainedbybothitstranscriptionaland
nontranscriptionalactivity.
PKM2andmetabolicswitchesincancercells
PKM2isthefinalenzymeinglycolysisandcomprisestwo
isoformsthatarisefromalternativesplicing.Mosttissues
expressthePKM1isoformwithproductsdirectedinto
oxidativephosphorylationtoefficientlyproduceATP.By
contrast,PKM2mayexisteitherintetramericordimeric
formstodirectoxidativephosphorylationorglycolysis,
respectively.GiventhatPKM2existspredominantlyin
itsdimericformincancercells,itcontributestoahigh
rateofaerobicglycolysisincancercellsregardlessof
hypoxia,aphenomenonknownastheWarburgeffect.
HIFregulatesPKM2throughtwomechanisms[17]:first,
HIF-1acanstimulateexpressionofPKM2.Second,
PKM2andHIF-1aformheterodimersandmigrateinto
thenuclei,wheretheyactasamasterswitchtoover-
expressgenescrucialforarobustglycolysisthatproduces
bothenergyandmetabolicintermediatesforbiosynthe-
sis.Therefore,HIF-1ahasacriticalroleinmetabolic
switchesincancercells.InadditiontoPKM2,HIF-1ahas
beenshowntoantagonizecMycactivitybyinducing
expressionofMXl1,thusreducingmitochondrialbiogen-
esis[38].
VEGFandcancerneoangiogenesis
Theincreaseintumorvolumedemandsacorresponding
increaseinangiogenesis.ByregulatingVEGFexpression,
bothcellularandviraloncogenesnotonlyregulatethe
growthofcancercells,butalsoallowcancerprogressionin
thehost.OptimalVEGFexpressionwasfoundtodepend
onbothhypoxiaandoncogenes[39].Theseobservations
ledtotheidentificationofHIF-1aasamajorregulator
ofVEGFexpression[40,41].TheHIF-1a–p300/CREB-
bindingprotein(CBP)complexbindstoaHIF-responsive
0
TrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
elementinthe5promoterregionofthegeneencoding
VEGF[40,41].ThisHREsequencewasspecificallytar-
getedbyechinomycin[9,42].
TIPS-1218;No.ofPages10
MDR1
ThelinkbetweenHIFandMDR1wasfirstreportedin
nontransformedendothelialandepithelialcelllines
[43].TheauthorsshowedthatHIF1awasresponsible
forhypoxia-inducedMDR1expressionthroughstimula-
tionoftheMDR1promotersequence.Subsequently,itwas
showninheadandneckcancercelllinesthatinhibitionof
HIF-1aincreasedcancercellsensitivitytopaclitaxel
[44].ThecontributionofHIFtomultidrugresistanceis
nowsubstantiatedinmanytypesofcancer,including
gastriccancer,coloncancer,multiplemyeloma,AML,
laryngealcancer,andsacralchordoma[45–51].These
observationsexplainthepoorprognosisofpatientswith
canceroverexpressingHIFandsuggestanimportantrole
forHIFinhibitorsincombinatorialcancertherapy.
TumorgrowthinhibitionbyHIF-1a
DespitecompellingevidencefortheoncogeniceffectofHIF
familymembers,overactivationofHIFmaycausegrowth
arrestand/orapoptosis.Atleastthreemechanismshave
beenproposedtoexplainthetumorsuppressoractivityof
HIF-1a.First,HIF-1ahasbeenshowntostabilizep53,
perhapsbybindingtoMousedoubleminute2homolog
(MDM2)[52].Second,amongHIF-1atargetsaregenes
capableofinducingapoptosis,includingRPT801[53],
NIP3[54,55],andNIX[55].Third,HIF-1ahasbeenshown
toantagonizeMycbypreventingitsrepressionofp21
[56].Incombination,thesemechanismsmayreconcile
theinconsistenciesinthemousegeneticdatathatsuggest
thatHif1aeitherpromotesorsuppressestumorgrowth
dependingonthetumortypesinvestigated[33,37].
HIFandCSCs
Animportantadvanceincancerbiologywasmadewiththe
demonstrationthatsomaticallytransformedcancercells
areheterogeneousinestablishingcancerinanewhost.In
manysolidandhematologicalcancers,asmallsubsetof
cancer-initiatingcellscanbeprospectivelyisolatedbased
oneithercellsurfacephenotypesortheirabilitytoexclude
fluorescentdyes(sidepopulation).Althoughithasbeen
suggestedthattherapeuticeliminationofCSCsholdsthe
keytoreducingcancerrelapseanddrugresistance,few
druggabletargetshavebeenidentifiedthatprovidea
meansfortheselectiveeliminationofCSCs[57–60].As
reviewedbelow,accumulatingdatasuggestthatHIFwill
emergeasalong-soughttarget.
GliomastemcellsandHIF
TheinvolvementoftheHIFpathwayingliomastemcells
wasfirstreportedbyLietal.[8].Usingxenograftglioma-
initiatingandinvitrotumorosphereformationassaysand
CD133astheCSCmarkers,theseauthorsobservedsig-
nificantenhancementofstemcellactivitywhenthestem
cellswereculturedunderahypoxicenvironment.Inter-
estingly,stemcellactivityunderbothnormoxicandhyp-
oxicenvironmentsisreducedwheneitherHIF1aorHIF2a
aresilencedbyshRNA.GiventhatHIF2amRNAlevels
correlatewithgliomaactivity,progression,andprognosis,
Review
theauthorsemphasizedthatHIF2aiscriticalforglioma
stemcellactivity.However,shRNAsilencingshowedan
equallyimportantroleforHIF1ainCSCactivity.Thelack
ofcorrelationbetweenHIF1amRNAlevelsandstemcell
activitymaysimplyreflectthefactthatHIF-1aprotein
levelsareregulatedbypost-transcriptionalmechanisms.
TheHIFtargetsresponsibleforCSCactivityremaintobe
identified.
Acutelymphocyticleukemia
EarlyworkonCSCswascriticizedforusingxenograft
transplantationbecausetheCSCactivity(i.e.,tumor-
initiatingactivity)assayedinthexenogeneichostmay
beartificiallyaffectedbyrejectionofhumancellsbythe
innateimmunityoftherecipientmice[61].Wangand
colleaguesusedasyngeneictransplantationmodeltodem-
onstratethatthec-Kit
+
Sca-1
+
populationintheirmouse
modelofacutelymphocyticleukemia(ALL)wereleuke-
mia-initiatingcells[9].Giventhatc-Kit
+
Sca-1
+
cellsarea
necessaryandsufficientpopulationforaninvitrocolony-
formingunit(CFU),theauthorsusedthismodeltoidentify
inhibitorsthatmaytargetALLstemcells.Theyfoundthat
echinomycin,anaturalproductthatbindstoHREand,
thus,inhibitsHIFactivity,efficientlyeliminatedCFUwith
anIC
50
of30–100pM.Invivo,low-doseadministrationof
echinomycin(10mg/kgor30mg/m
2
)cured100%ofsynge-
neicmicethathadreceivedlethaldosesofleukemiacells.
TheinvolvementofHIF-1aissubstantiatedbythreelines
ofevidence.First,Hif1a,butnotHif2a,isexpressedat
substantiallyhigherlevelsintheleukemiastemcell(LSC)
populationcomparedwiththebulkofleukemiablasts.
Second,shRNAsilencingofHif1areducedCFUandleu-
kemia-initiatingactivity.Third,Hif-1awasfoundtoen-
hanceNotchsignalingbypreventingnegativefeedback
regulationoftheHesfamilybHLHtranscriptionfactor1
(Hes1)gene,akeyNotchtargetknowntobeinvolvedin
stemcellself-renewal.However,itremainstobeestab-
lishedwhetherupregulationofHes1isresponsibleforHIF-
mediatedmaintenanceofLSC.
UsingaHIFreporter,Wangetal.showedthat,under
normoxicconditions,HIFisactiveexclusivelywithinthe
c-Kit
+
Sca-1
+
LSCsubset[9].ThishighHIFactivitywas
duetotheselectivelossofVHLexpressioninthestemcell
subset,whichiscriticalforLSCfunction,giventhatectopic
expressionofVhleliminatesLSC[9].
AML
Historically,theprospectiveidentificationofAMLstem
cellsbyJohnDickandcolleaguesin1994markedthe
revivaloftheCSCconcept[4].Severalgroupshaveshown
thattheabundanceofAMLstemcellsisabiomarkerfor
poorprognosis[62–64].Geneexpressionsignaturesde-
rivedfromthecomparisonofAMLstemcellsandAML
blastshaveprovenvaluableinpredictingtheoutcomeof
newlydiagnosedpatients[65].Animportantpredictionof
theCSCconceptisthattherapeuticsthatselectivelyelim-
inatestemcellsshouldpreventdrugresistanceandcancer
relapse,thetwomostpressingissuesincancertherapy.
GiventhatechinomycincanselectivelyeliminateAML
stemcells[9],theplannedclinicaltrialsusingechinomycin
[66]mayprovideanopportunitytotestthisconcept.
TrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
UsingtheAMLstemcellmarkersidentifiedbyDick’s
group,Wangandcolleagues[9]showedthatHIF1amRNA
andproteinareoverexpressedinhumanAMLstemcells
3
TIPS-1218;No.ofPages10
comparedwiththebulkofAMLblasts.Inbothna?¨veand
treatedAMLsamples,echinomycinefficientlyinhibited
CFUactivity,withanIC
50
ofapproximately100pM.More
importantly,echinomycinwas100–1000-foldmoreeffi-
cientininducingapoptosisofCD34
+
CD8
C0
AMLstemcells
comparedwiththebulkofAMLblasts.Totestthethera-
peuticpotential,theauthorsestablishedhumanAMLin
NOD.SCIDmiceaccordingtomethodsdescribedbythe
Dicklaboratory[4]andtreatedthemicewithalowdoseof
echinomycin[9].Short-termtreatmentwithechinomycin
notonlyreducedleukemiablastburden,butalsoprefer-
entiallyreducedthefrequencyofAMLstemcellswithin
theleukemiacells,markingamajordifferencecompared
withconventionaltherapeutics.Asevidenceoffunctional
inactivatingAMLstemcells,theremainingAMLblast(s)
couldnolongerinitiateAMLinthenewhost.
Totestwhetherechinomycincanbeusedtotreatre-
lapsedAML,Wangandcoworkers[67]usedtherelapsed
AMLfrommicewithheterozygousknock-insoftwogenes
thatarefrequentlymutatedinhumanAML:FLT3
ITD
and
MLL
PTD
(Mll
PTD/WT
:Flt3
ITD/WT
).TheMll
PTD/WT
:Flt3
ITD/WT
micedevelopedspontaneousAMLandrespondedtotreat-
mentwithaDNAhypomethylatingagentand/orahistone
deacetylase(HDAC)inhibitor;however,theAMLinvari-
ablyrelapsed[68].Theauthorstransplantedtherelapsed
AMLfromCD45.2miceintoCD45.1miceandfollowedthe
expansionandtherapeuticresponseusingCD45.2asa
leukemiamarker[64].Theyobservedthatshort-term
treatmentwithechinomycincured40–60%ofmicewith
ahighburdenofrelapsedAMLatthetimeoftreatment.
Again,thebonemarrowfromthecuredmicedidnot
harbordormantAMLstemcells,asevidencedbytheir
inabilitytoinitiateAMLinthenewhosts.Surprisingly,
echinomycin-treatedbonemarrowcellsarefullycompe-
tentinhematopoiesisintransplantation.Therefore,ther-
apeuticeliminationofCSCscanbeachievedinrelapsed
AMLwithoutsignificantadverseeffectsontissuestem
cells.Thus,althoughCSCsandtissuestemcellsmayshare
self-renewalprograms,thetherapeuticeliminationofCSCs
canbeachievedwithoutharmingtissuehomeostasis.
Chronicmyeloidleukemia
Chronicmyeloidleukemia(CML)isaclonalmyeloprolif-
erativedisorderthatresultsfromanacquiredgenetic
changeinasinglehemopoieticstemcell.Thehallmark
ofCMListhegenerationoftheBCR-ABLchimeraprotein,
aconstitutivelyactivetyrosinekinase,asaresultofgene
translocation[69].InductionofBCR-ABLinducesexpres-
sionofHIF-1aanditstargetgeneVEGF[70].Kinase
inhibitors(suchasimatinib)failtoeradicateCMLLSCs.
Instead,thetargetedtherapyselectedforimatinib-
resistantcellswithhighlevelsofBCR-ABLandactive
HIF-1a,resultinginanaerobicglycolysisandincreased
survivalinvitro[71].UsingamousemodelofCML,Zhang
etal.showedthatHif1a-deficientHSPCsexpressing
BCR-ABLfailedtogenerateCMLinsecondaryrecipients.
DeletionofHif1apreventsthepropagationofCMLby
impairingcellcycleprogressionandinducingapoptosis
Review
ofLSCs[72].Inaddition,recentstudiesalsoshowedthat
HIF-1asupportsthemaintenanceofCMLLSCsdespite
effectiveBCR-ABL1inhibitioninhypoxicenvironments
4
[73].TheseobservationsindicatedthatHif-1aiscrucialfor
themaintenanceofCMLLSCs.
Takentogether,theaboveexamplesillustratethatHIF
hasacriticalroleinstemcellsforbothsolidtumorsand
hematologicalmalignancies,servingasadruggabletarget
forthetherapeuticeliminationofCSCs.ThefactthatHIF
isactiveinCSCsregardlessofhypoxiasuggeststhatthese
cellshaveacquiredmechanismstoprotectHIFunder
normoxicconditions.
BreastCSCs
BreastcanceristhefirstsolidtumorinwhichCSCswere
prospectivelyisolated[3].Usingaxenograftmodelof
humanbreastcancercelllines,Conleyetal.observedthat
antiangiogenicagentsincreasedtheproportionofbreast
CSCs(BCSCs)byinducinghypoxia.Theimpactofhypoxia
ismediatedbyHIF-1a,butnotHIF-2a,andcorrelateswith
WntsignalinginBCSC[74].Usingthemousemammary
tumorviruspolyomavirusmiddleT(MMTV-PyMT)
oncogene-inducedbreastcancermodel,Schwabetal.[75]
demonstratedthatconditionaldeletionofHif1ainmamma-
ryepithelialcellscausesreducedtumorgrowthandmetas-
tasis.Interestingly,thisdepressedtumorgrowthand
metastasiscorrespondedtoareductioninthenumberand
functionofBCSC[75].
AkeyissueishowHIF-1ainducesBCSC.Onekey
regulatorofBCSCactivityisaHippopathwayeffector
moleculecalledTAZ[76].Bycomparinggeneexpression
profilesamong1600casesofhumanbreastcancersamples,
Xiangetal.[77]showedasignificantcorrelationbetween
knownHIFtargetgenesandTAZ,raisingtheintriguing
possibilitythatTAZisadirecttargetofHIF-1a.This
hypothesisisvalidatedbyshRNAsilencing,chromatin-
immunoprecipitation,promoteractivity,TAZtargetgene
co-expression,andhypoxiaresponses.Inadditiontocon-
trollingTAZexpression,HIF-1aalsoactivatestranscrip-
tionoftheSiahE3ubiquitinproteinligase1(SIAH1)gene,
whichencodesaubiquitinligasethatisrequiredfor
proteasome-dependentdegradationoflargetumorsup-
pressorkinase2(LATS2).DegradationofLATS2allowed
nuclearlocalizationofTAZ.Apartfromtheexpressionand
functionofTAZ,hypoxiaalsoregulatestheinteraction
betweenBCSCandmesenchymalstemcells(MSC)and
tumor-associatedmacrophages(TAM)throughtwofeed-
forwardmechanisms[78].First,HIF-1ainducesexpres-
sionofchemokine(C-X-Cmotif)ligand16(CXCL16)to
recruitMSC.Second,MSCsproducechemokine(C-Cmo-
tif)ligand5(CCL5)torecruitTAM.Therefore,BCSC-
intrinsicsignalingnotonlymaintainsthenumberand
functionoftheBCSC,butalsodrivesformationofthe
tumormicroenvironment.
HIFinadaptiveandinnateinflammation
Hypoxia-resistantHIFactivityisnotlimitedtocancer
cells.AccumulatingevidenceshowsthatHIFshavearole
intheregulationofinnateandadaptiveimmunecellsthat
normallyresideinnormoxicenvironments.Activated
TcellsexpresstwoisoformsofHIF-1a:ashortformcalled
TrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
1.1andalongerformcalled1.2[79].Theshorter1.1form
appearstosuppresstheproductionofinflammatorycyto-
kinesbyTcells[80].Accumulatingdatademonstratethat
TIPS-1218;No.ofPages10
HIFisakeyregulatorofregulatoryTcell(Treg)/Thelper
(TH)-17development,thedifferentiationandfunctionof
cytotoxicTlymphocytes,(CTL),andinnateimmuneeffec-
tors,suchasdendriticcells,neutrophils,andmyeloid-
derivedsuppressorcells(MDSCs).
Treg/TH17celldifferentiation
AlthoughTh17andTregcellsshareimportantpathwaysin
theirdifferentiationfromna?¨veTcells,theyeventually
bifurcateintodistinctphenotypeswithoppositeactivities,
withTH17cellsbeingpro-inflammatoryandTregsbeing
anti-inflammatory.Recentstudiessuggestthatthefunc-
tionalswitchbetweenthesecelltypesismediatedbyHIF-
1a.
HIF-1aactivatesRetinoid-AcidReceptor-relatedOr-
phanReceptor(ROR)-gttranscriptionandformsatertiary
complexwithRORgtandp300toactivatetheIL-17Agene.
Bycontrast,Hif-1abindstoforkheadboxP3(Foxp3)and
causesitsdegradation,resultinginablockadeofTreg
differentiation.AsaresultofalteredTh17/Tregdifferenti-
ation,micewithHIF-1a-deficientTregareresistantto
experimentalautoimmuneencephalomyelitis[81].When
na?¨veTcellswereculturedinthepresenceoftransforming
growthfactor(TGF)bandIL6,theyshowedupregulation
oftheglycolyticactivityandinductionofglycolytic
enzymes.AcriticalroleforglycolysisinTh17development
isalsosuggested,giventhatblockingglycolysiswith
2-dexoglucoseinhibitedTH17celldevelopment.Consis-
tentwithacriticalroleforHIFinTh17differentiation,
HIF-1awasselectivelyexpressedinTH17cells,while
Hif1adeficiencyinhibitedTH17differentiation[82].The
functionofHIF-1ainTH17wasnotrestrictedtoregulation
ofthemetabolicswitch.HIF-1aalsocontrolledtheexpres-
sionofantiapoptoticBcl-2familygenesincollaboration
withNotchsignalingand,thus,supportsTH17survivalin
humansamples[83].Takentogether,thesedatahighlight
HIF-1a-dependentpathwaysinregulatingthebalance
betweenthedifferentiationofTH17andTregcells.
DespitetheinvitroeffectofHIF-1aonTregdifferenti-
ation,theinhibitoryfunctionofHIFonTregfunctioninthe
tumormicroenvironmentremainstobesubstantiated.
Surprisingly,HIFpromotesdifferentiationofCD4
+
/
CD25
+
Tregcellsinthecaseofhypoxiacausedbyrapid
tumorprogression[84].Tregsmaybeenrichedincancer
tissuebyHIF-1a-dependentproductionofchemokines,
suchasCCL28[85].Additionalstudiesareneededto
determinewhethertheapparentcontradictionwasattrib-
utabletothetumormicroenvironment,andifso,howthe
tumormicroenvironmentalterstheroleofHIF-1ainTreg
differentiation.
CTLdifferentiationandfunction
CTLsarekeyadaptiveeffectorsintheeliminationof
intracellularpathogensandtumorcells.HIF-1adeter-
minesCTLfatebyregulatingtranscriptionofgenesencod-
ingglucosetransporters,rate-limitingglycolyticenzymes,
cytolyticeffectormolecules,andessentialchemokineand
adhesionreceptorsthatregulateTcelltrafficking[86].Ac-
Review
tivatedTcellsexpresshighlevelsofHIF-1aproteinseven
undernormoxia,althoughhypoxiafurtherelevatesHIF-1a
levels[86,87].TheinductionofHIF-1aiscontrolledby
mammaliantargetofrapamycincomplex1(mTORC1)
[86].Geneticstudiesinmicedemonstratedthatdeletion
ofVhlinCTLsinhibitedpersistentviralinfectionand
neoplasticgrowth,whilethatofHif1aattenuatedCTL
effectorfunctionduringviralinfection[87].Surprisingly,
deletionofHif1ainactivatedTcellsalsoenhancedpro-
ductionofinflammatorycytokines.Thesedataarguefora
negativeregulatoryroleforHIF-1ainTcell-mediated
inflammatoryresponses[80,88].Furtherstudiesareneed-
edtoshedlightonTcell-intrinsicHIF-1afunctioninthe
tumormicroenvironment.
Dendriticcellactivation
Astheprimaryantigen-presentingcells,dendriticcells
(DCs)haveacrucialroleinlinkingtheinnateandthe
adaptiveimmunesystems.LPSandhypoxialeadtoin-
creasedglycolyticactivityandincreasedDCmaturation.
TheroleforHIF-1ahasbeenconfirmed,giventhatknock-
ingdownofHIF-1ainDCssignificantlyreducedglucose
utilityandinhibitedDCmaturation,asevidencedby
reducedstimulationofallogeneicTcells[89].Whilearole
forHIF-1aintumor-infiltratingDChasnotbeeninvesti-
gated,theinductionofB7homolog1(B7H1/PD-L1)by
HIF-1a[90,91]andimmunesuppressionbyB7H1-expres-
singmyeloidDCinhumancancer[92]suggestthatHIF-1a
expressedintumor-infiltratingDCcontributestotheim-
mune-suppressivetumormicroenvironment.
Tumor-associatedmyeloidsuppressorcells
Tumorgrowthaltersmyeloiddevelopmentinthehost,
withsignificantphenotypicandfunctionalchangesin
themyeloidcompartment[93].Amajorchangeinthe
tumor-bearinghostandthetumormicroenvironmentis
theexpansionofmyeloidsuppressorcells,includingtu-
mor-associatedmacrophages(TAM),MDSC,andmyeloid
dendriticcells(mDC)[93].Accumulatingdatademonstrate
thatHIF-1acontributestotheexpansion,differentiation,
andeffectorfunctionofmyeloidsuppressorcellswithinthe
tumormicroenvironment.
Asdiscussedabove,HIF-1amaycontributetomDC-
mediatedimmunesuppressionbyregulatingtheexpres-
sionofB7H1/PD-L1.BothTAMandMDSCsuppresstumor
immunitybyproducingsolublefactorssuchasnitricoxide
(NO)andROS[93,94],andthroughexpressionofcell
surfaceproteins,suchasB7H1/PD-L1.HIF-1a,butnot
HIF-2a,upregulatestheexpressionofB7H1/PD-L1by
bindingtotheHREofthePD-L1proximalpromoterto
enhanceexpressionofPD-L1[90].Inaddition,HIF-1ais
necessaryfortheoptimalexpressionofarginaseandin-
duciblenitricoxidesynthase(iNOs)inbothTAMand
MDSCand,thus,isresponsibleforNOproduction[95].In-
terestingly,MDSChavebeenshowntodifferentiateinto
TAMinthetumormicroenvironment,andthisprocessis
requiresexpressionofHIF-1aMDSC[95].
ThecontributionofHIFtothetumormicroenvironment
hasbeendemonstratedmostlyusingtransplantabletumor
models.Asanotableexception,myeloid-specificHIF-1a
deletioninatransgenicmodelofbreastcancerreduced
TrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
tumorgrowthandprogression[96].Thiswasachieved
withoutalternationofVEGF-Alevelsandvascularization.
Totestwhetherthisdeletionaffectsmacrophagefunctions,
5
theauthorscomparedwildtypeandHif1a
C0/C0
bonemar-
row-derivedmacrophagesundernormoxicandhypoxic
cultureconditions.Theauthorsobservedthathypoxia
exacerbatedinhibitionofTcellproliferationandthatsuch
exacerbationwasHif1adependent.GiventhatTAMare
knowntoinhibitTcellfunction[93],itwouldbeofinterest
todeterminewhetherthedelayintumorgrowthwas
attributabletoHif1adeletioninTAM.
EpigeneticandgeneticmechanismsforHIFactivities
undernormoxia:cross-fertilizationbetweencancer
biologyandimmunology
ThecriticalroleforHIFincancercellmetabolism,CSC
function,andimmunityraisedafundamentalbutlargely
unansweredquestion:howisHIFactivitymaintainedin
circulatingLSCs,cancercells,andhematopoieticcellsina
normoxicenvironment?Accumulatingdataindicatethat
HIFactivationisstimulatedbyincreasedtranscription
andtranslationofHIF1aandinactivationofoxygen-
mediatedHIFdegradation,throughbothgeneticandepi-
geneticmechanisms.
Geneticmechanismstaughtbycancer:theAML
example
Review
TIPS-1218;No.ofPages10
TheaccumulationofHIF1aproteinanditstranscriptional
activityarestrictlyregulated.AsshowninFigure2,many
ofthesemechanismsaretargetedinAML,andseveral
genomicalterationsinAMLhaveeitherbeenshown,or
havethepotential,toenhanceHIFactivity.First,AML-
associatedmutationsseemtotargetthecanonicalHIF
degradationpathway.Undernormoxia,HIF-1aisdegrad-
edbyVHL,whichrecognizesHIF-1awhenitishydroxyl-
atedatPro402and/orPro562byPHD[24].Mutationsof
geneencodingPHDhavebeenobservedinAMLonlyatlow
Ub–HIF1α
Degradag415on
IHD
VHL
mIHD
2–HG
mTOR
PI3K/AKT
O2+
α
–KG
PhD
HIF1α
HydroxylatedHIF1α
p53MDM2
FLT3–ITD/TKD
NPM/p14ARF
10%
30%NCAML
25–35%
10–15%
Hd
HI
F1
mIH
Ub
2
d
ITD
TRENDSinPharmacologicalSciences
Figure2.Prevalentmutationsinacutemyeloidleukemia(AML)potentiallyaffect
hypoxia-induciblefactor(HIF)levelsincancercells.Mutationsofgenesencoding
isocitratedehydrogenase(IDH)1and2,whicharemutatedin10–15%ofAML
cases,inactivateprolylhydroxylasedomainprotein(PHD)tosuppressHIF
hydroxylation.Fms-relatedtyrosinekinase3(FLT3)mutations(foundin25–35%
ofAMLcases)stimulatesthephosphatidylinositol3-kinase(PI3K)/AKTpathwayto
enhanceHIFtranslation.Nucleophosmin(NPM)mutation,whichwasfoundin30%
ofAMLwithnormalkaryotype(NC),reducesp14ARF,andHIFinhibitors.TP53
mutationreducesexpressionofMousedoubleminute2homolog(MDM2),an
alternativeE3ubiquitinylation(Ub)ligaseE3forHIF.ThisinturnmayreduceHIF
ubiquitinylation.
6
frequency.However,thefunctionofPHDisenhancedby
IDH1and/orIDH2[25,26],whicharemutatedatacom-
binedfrequencyofapproximately15%inpatientswith
AML[27–30].OnestudyshowedthatIDHmutations
increaseHIF1aaccumulation[25,26],whilealaterstudy
suggestedanoppositeeffect[32].Thedifferencesbetween
thetworemaintobereconciled.Second,fms-relatedtyro-
sinekinase3(FLT3)-internaltandemrepeats(ITD)and
tyrosinekinasedomain(TKD)mutationsactivateFLT3
[97,98].GiventhatFLT3signalingactivatesthephospha-
tidylinositol3-kinase(PI3K)–mTORpathway[99]andthat
mTORactivationincreasesHIF1aproteinaccumulation
[100–103],itwouldbeintriguingtotestwhetherFLT3
mutationscauseHIFactivationinAML.Third,lossof
TP53functionintumorcellshasbeenshowntocause
defectiveMDM2-mediateddegradationofHIF-1a[104].
Inaddition,becausep53mutationsareobservedinap-
proximately10%ofAMLsamples,andthismutationis
associatedwithadevastatingprognosis[105],itwouldbe
ofinteresttodeterminewhetherthismutationcontributes
toincreasedHIF-1aaccumulationinAML.Giventhat
MDM2isanE3ligaseforHIF-1a[106,107],p53mutations
mayincreaseHIF-1alevelsbydecreasingMDM2.Fourth,
Nucleophosmin1(NPM1)ismutatedin30–40%ofAML
samplesthathaveanormalkaryotype[108,109].Inaddi-
tion,sinceNPM1sequestersandprotectsp14ARFagainst
degradation[110],NPMmutationsmaystimulateHIF
activitiesbyinactivatingthep14ARF-mediatedaberrant
delocalizationofHIF1a[111].
EpigeneticmechanismofHIF1aactivation:unanswered
questionsfromCSCsandimmuneeffectorcells
AstheoffspringofCSCs,cancercellsshouldhaveinherited
geneticalterationsthatenableoxygen-resistantHIFac-
tivity.Therefore,forcancersthatshowselectiveactivation
ofHIFwithintheCSCcompartment,includingAML,ALL,
CLL,andglioma,geneticalterationsinHIFregulatorsdo
notprovideafullexplanation.Thereareatleasttwo
mechanismsforselectiveHIF-1aactivationinmouseLSCs
[9]:increasedHif1amRNAaccumulationandlackofex-
pressionofVhl.BothHif1aupregulationandVhldown-
regulationarenecessaryforthemaintenanceofLSC.
GiventhatLSCsareaself-renewingpopulationthatalso
‘differentiates’intocancercells,itisofinteresttodeter-
minetheepigeneticmechanismthatensurestheheritable
geneexpressionpatternofHif1aandVhlandhowthis
patternislostwhentheLSCs‘differentiate’intocancer
cells.Elucidationofthismechanismwillalsohelpto
formallydemonstratetheexistenceofepigeneticprograms
thatmaintainLSCactivitybyselectiveactivationofHIF-
1ainthiscompartment.
Similarly,howoxygen-resistantHIF-1aactivityisin-
ducedintheimmuneeffectorcellsremainslargelyunex-
plained.Accumulatingdatasuggestthatactivationof
eitherTcellreceptor[81,82,112]orToll-likereceptors
(TLR)[113]induceaccumulationofHif1amRNA,perhaps
throughsuppressionofmiR-200[112].However,addition-
almechanismsareneededtoexplainoxygen-resistant
TrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
HIF-1aactivity.TheAKT-PI3Kpathwayinducesaccumu-
lationofHIF-1athroughactivationofmTORtoincrease
translationofHIF-1a[114].Inaddition,mTORactivation
ReviewTrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
TIPS-1218;No.ofPages10
HIF
CTL
Treg
Th17
DC
MDSC
TAM
CSC
CaC
EC
HIF
TRENDSinPharmacologicalSciences
Figure3.Acentralroleforhypoxia-induciblefactor(HIF)inthetumor
microenvironment.Inadditiontoitscriticalroleformaintenanceandproliferation
ofcancerstemcells(CSC)andcancercells(CaC),HIFpromotesthedifferentiation
and/orproliferationofhostcellswithinthetumormicroenvironment,including
endothelialcells(EC),dendriticcells(DC),tumor-associatedmacrophages(TAM),
andmyeloid-derivedsuppressorcells(MDSC).Apartfromregulatingcellsthataffect
Tcellfunction,HIFalsodirectlyregulatestheactivationanddifferentiationofvarious
functionalsubsetsofTcells,includingcytolyticTlymphocytes(CTL),regulatoryT
cells(Treg),andinterleukin(IL)-17-producingTcells(Th17).
preventsoxygen-inducedHIF-1adegradation[102].Inthe
lattercase,mTOR-inducedHIFprotectionagainstdegra-
dationrequiresfunctionalinteractionbetweenmTORand
theHIF-1adomainthatisalsoinvolvedinhydroxylationof
HIF-1a.Therefore,mTORmayinhibitHIFdegradation
throughanasyetundefinedmechanism.
Recentstudiesdemonstratedthat,similartoadaptive
immunity,innateeffectorcellsmaybealsocapableof
immunememory,thatis,theycanbetrainedtomount
amorerobustormuchreducedrecallresponse[12,13].For
instance,stimulationofmonocyteswithglucantrainedthe
monocytestomountamorerobustinnateimmunere-
sponsetosecondarystimulationinvitroandincreased
hostresistancetoinfectionsbyCandidaalbicansand
Staphylococcusaureus[12].Thistrainingisassociated
withextensiveepigeneticalterationsinthemonocytes
[13].Surprisingly,thetrainingisalsoassociatedwitha
metabolicswitchfromoxidativephosphorylationtoglycol-
ysis[12].GiventhecriticalroleofHIF-1ainthemetabolic
switch,researchersusedageneticmodeltodetermine
theinvolvementofHIF-1aintherecallresponseofinnate
effectors[12].Indeed,targetedmutationofHif1ain
myeloidcellswassufficienttoablatetrainedimmunity.
ThecriticalroleforHIF-1aintrainedimmunityandthe
extensiveepigeneticreprogrammingduringtheprocess
raisedaninterestingissueastowhetherepigeneticmech-
anismsmaybedirectlyresponsibleforoxygen-resistant
HIFactivationinmonocytes.
Takentogether,inbothimmuneeffectorsandCSCs,a
steadystateofoxygen-resistantHIF-1aaccumulationhas
beenachieved.Amajorchallengeremainsindefininghow
thiscrucialstateisachievedthroughnongenetic,perhaps
epigenetic,mechanisms.
Concludingremarks
HIFwasdiscoveredintheprocessofinvestigatinghow
livingorganismsadjusttoavaryingoxygenenvironment
[15].Morerecentstudieshavedemonstratedthatthis
pathwayisoperativeevenundernormoxicenvironment
andthatsuchoxygen-resistantfunctioniscriticalincancer
biologyandimmunology.HIFactivationisresponsiblefor
ametabolicswitchthatallowsmoresustainedprolifera-
tionwithlessDNAdamage.Thesefeaturesareimportant
forthemaintenanceofCSCs.Intheimmunesystem,
activationand/orfunctionreprogrammingofimmune
effectorsisoftenimprintedthroughoxygen-resistant
HIFaccumulation.Theconvergingfeaturesuggeststhat
cross-fertilizationbetweencancerbiologistsandimmunol-
ogistsmaybringnewinsightsintothemechanismofHIF
regulationandnewapproachesforcancertherapy.
AssummarizedinFigure3,cancercellsandimmune
effectorsaremajorcomponentsofthetumormicroenviron-
ment.Inthisenvironment,theimmunesystemnotonly
failstodefendthehostagainstcancer,butalsooften
activelyaidscarcinogenesis,withfunctionsrangingfrom
promotingCSCactivity[115,116]andangiogenesis[117],
tofacilitatingmalignanttransformation[118]andmetas-
tasis[119].Therefore,effectivecontrolofthetumormicro-
environmentwilllikelycomplementthetraditional
approachofcancertherapy,aimingateliminatingcancer
cells.Giventhatmostcontributorstothetumor-promoting
microenvironmentrelyonHIF,itislikelythattargeting
HIFwillnotonlyaidinthetherapeuticeliminationof
CSCs,butalsoresultindeprivingcancercellsofahabit-
ablemicroenvironment.
Acknowledgments
WethankChristopherBaileyforeditorialassistance.Thisworkis
supportedbyJilinUniversityFirstHospitalandgrantsfromNational
CancerInstitute,USA(CA183030andCA171972toY.L.).
References
1Hanahan,D.andWeinberg,R.A.(2000)Thehallmarksofcancer.Cell
100,57–70
2Hanahan,D.andWeinberg,R.A.(2011)Hallmarksofcancer:thenext
generation.Cell144,646–674
3Al-Hajj,M.etal.(2003)Prospectiveidentificationoftumorigenic
breastcancercells.Proc.Natl.Acad.Sci.U.S.A.100,3983–3988
4Lapidot,T.etal.(1994)Acellinitiatinghumanacute
myeloidleukaemiaaftertransplantationintoSCIDmice.Nature
367,645–648
5Bao,S.etal.(2006)Gliomastemcellspromoteradioresistance
bypreferentialactivationoftheDNAdamageresponse.Nature
444,756–760
6Terpstra,W.etal.(1996)Fluorouracilselectivelysparesacutemyeloid
leukemiacellswithlong-termgrowthabilitiesinimmunodeficient
miceandinculture.Blood88,1944–1950
7Wicha,M.S.etal.(2006)Cancerstemcells:anoldidea–aparadigm
shift.CancerRes.66,1883–1890discussion1895–1886
8Li,Z.etal.(2009)Hypoxia-induciblefactorsregulatetumorigenic
capacityofgliomastemcells.CancerCell15,501–513
9Wang,Y.etal.(2011)TargetingHIF1alphaeliminatescancerstem
cellsinhematologicalmalignancies.CellStemCell8,399–411
10Wang,Y.H.etal.(2014)Cell-state-specificmetabolicdependencyin
hematopoiesisandleukemogenesis.Cell158,1309–1323
7
ReviewTrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
TIPS-1218;No.ofPages10
11Palazon,A.etal.(2014)HIFtranscriptionfactors,inflammation,and
immunity.Immunity41,518–528
12Cheng,S.C.etal.(2014)mTOR-andHIF-1alpha–mediatedaerobic
glycolysisasmetabolicbasisfortrainedimmunity.Science345,
1250684
13Saeed,S.etal.(2014)Epigeneticprogrammingofmonocyte-to–
macrophagedifferentiationandtrainedinnateimmunity.Science
345,1251086
14Keith,B.etal.(2012)HIF1alphaandHIF2alpha:siblingrivalryin
hypoxictumourgrowthandprogression.Nat.Rev.Cancer12,9–22
15Semenza,G.L.(2012)Hypoxia-induciblefactorsinphysiologyand
medicine.Cell148,399–408
16Wang,G.L.etal.(1995)Hypoxia-induciblefactor1isabasic-helix-
loop-helix-PASheterodimerregulatedbycellularO2tension.Proc.
Natl.Acad.Sci.U.S.A.92,5510–5514
17Luo,W.etal.(2011)PyruvatekinaseM2isaPHD3-stimulated
coactivatorforhypoxia-induciblefactor1.Cell145,732–744
18Zhang,P.etal.(2014)Hypoxia-induciblefactor3isanoxygen-
dependenttranscriptionactivatorandregulatesadistinct
transcriptionalresponsetohypoxia.CellRep.6,1110–1121
19Kondo,K.etal.(2002)InhibitionofHIFisnecessaryfor
tumorsuppressionbythevonHippel-Lindauprotein.CancerCell1,
237–246
20Latif,F.etal.(1993)IdentificationofthevonHippel-Lindaudisease
tumorsuppressorgene.Science260,1317–1320
21Maranchie,J.K.etal.(2002)ThecontributionofVHLsubstrate
bindingandHIF1-alphatothephenotypeofVHLlossinrenalcell
carcinoma.CancerCell1,247–255
22Pereira,T.etal.(2003)Identificationofresiduescriticalforregulation
ofproteinstabilityandthetransactivationfunctionofthehypoxia-
induciblefactor-1alphabythevonHippel-Lindautumorsuppressor
geneproduct.J.Biol.Chem.278,6816–6823
23Zbar,B.(1995)VonHippel-Lindaudiseaseandsporadicrenalcell
carcinoma.CancerSurv.25,219–232
24Semenza,G.L.(2010)HIF-1:upstreamanddownstreamofcancer
metabolism.Curr.Opin.Genet.Dev.20,51–56
25Xu,W.etal.(2011)Oncometabolite2-hydroxyglutarateisa
competitiveinhibitorofalpha-ketoglutarate-dependentdioxygenases.
CancerCell19,17–30
26Zhao,S.etal.(2009)Glioma-derivedmutationsinIDH1dominantly
inhibitIDH1catalyticactivityandinduceHIF-1alpha.Science324,
261–265
27Ward,P.S.etal.(2010)Thecommonfeatureofleukemia-associated
IDH1andIDH2mutationsisaneomorphicenzymeactivity
convertingalpha-ketoglutarateto2-hydroxyglutarate.CancerCell
17,225–234
28Pardanani,A.etal.(2010)IDH1andIDH2mutationanalysisin
chronic-andblast-phasemyeloproliferativeneoplasms.Leukemia24,
1146–1151
29Abbas,S.etal.(2010)AcquiredmutationsinthegenesencodingIDH1
andIDH2botharerecurrentaberrationsinacutemyeloidleukemia:
prevalenceandprognosticvalue.Blood116,2122–2126
30Paschka,P.etal.(2010)IDH1andIDH2mutationsarefrequent
geneticalterationsinacutemyeloidleukemiaandconferadverse
prognosisincytogeneticallynormalacutemyeloidleukemiawith
NPM1mutationwithoutFLT3internaltandemduplication.
J.Clin.Oncol.28,3636–3643
31Yan,H.etal.(2009)IDH1andIDH2mutationsingliomas.N.Engl.J.
Med.360,765–773
32Koivunen,P.etal.(2012)Transformationbythe(R)-enantiomerof
2-hydroxyglutaratelinkedtoEGLNactivation.Nature483,484–488
33Bertout,J.A.etal.(2009)Heterozygosityforhypoxiainduciblefactor
1alphadecreasestheincidenceofthymiclymphomasinap53mutant
mousemodel.CancerRes.69,3213–3220
34Lidgren,A.etal.(2005)Theexpressionofhypoxia-induciblefactor
1alphaisafavorableindependentprognosticfactorinrenalcell
carcinoma.Clin.CancerRes.11,1129–1135
35Klatte,T.etal.(2007)Hypoxia-induciblefactor1alphainclearcell
renalcellcarcinoma.Clin.CancerRes.13,7388–7393
36Mazumdar,J.etal.(2010)HIF-2alphadeletionpromotesKras-driven
lungtumordevelopment.Proc.Natl.Acad.Sci.U.S.A.107,
14182–14187
8
37Velasco-Hernandez,T.etal.(2014)HIF-1alphacanactasa
tumorsuppressorgeneinmurineacutemyeloidleukemia.Blood124,
3597–3607
38Zhang,H.etal.(2007)HIF-1inhibitsmitochondrialbiogenesisand
cellularrespirationinVHL-deficientrenalcellcarcinomaby
repressionofC-MYCactivity.CancerCell11,407–420
39Mazure,N.M.etal.(1996)Oncogenictransformationandhypoxia
synergisticallyacttomodulatevascularendothelialgrowthfactor
expression.CancerRes.56,3436–3440
40Arany,Z.etal.(1996)Anessentialroleforp300/CBPinthe
cellularresponsetohypoxia.Proc.Natl.Acad.Sci.U.S.A.93,
12969–12973
41Forsythe,J.A.etal.(1996)Activationofvascularendothelialgrowth
factorgenetranscriptionbyhypoxia-induciblefactor1.Mol.Cell.Biol.
16,4604–4613
42Kong,D.etal.(2005)Echinomycin,asmall-moleculeinhibitorof
hypoxia-induciblefactor-1DNA-bindingactivity.CancerRes.65,
9047–9055
43Comerford,K.M.etal.(2002)Hypoxia-induciblefactor-1-dependent
regulationofthemultidrugresistance(MDR1)gene.CancerRes.62,
3387–3394
44Ricker,J.L.etal.(2004)2-methoxyestradiolinhibitshypoxia-
induciblefactor1alpha,tumorgrowth,andangiogenesisand
augmentspaclitaxelefficacyinheadandnecksquamouscell
carcinoma.Clin.CancerRes.10,8665–8673
45Zhang,H.etal.(2014)Kruppel-likefactor8contributestohypoxia-
inducedMDRingastriccancercells.CancerSci.105,1109–1115
46Ria,R.etal.(2014)HIF-1alphaofbonemarrowendothelialcells
impliesrelapseanddrugresistanceinpatientswithmultiple
myelomaandmayactasatherapeutictarget.Clin.CancerRes.
20,847–858
47Li,D.W.etal.(2013)Hypoxiainducedmultidrugresistanceof
laryngealcancercellsviahypoxia-induciblefactor-1alpha.Asian
Pac.J.CancerPrev.14,4853–4858
48Wang,H.etal.(2014)Wogoninreverseshypoxiaresistanceofhuman
coloncancerHCT116cellsviadownregulationofHIF-1alphaand
glycolysis,byinhibitingPI3K/Aktsignalingpathway.Mol.Carcinog.
53(Suppl.1),E107–E118
49Cui,X.Y.etal.(2013)Hypoxiainfluencesstemcell-likepropertiesin
multidrugresistantK562leukemiccells.BloodCells.Mol.Dis.51,
177–184
50Ji,Z.etal.(2010)ExpressionofMDR1,HIF-1alphaandMRP1in
sacralchordomaandchordomacelllineCM–319.J.Exp.Clin.Cancer
Res.29,158
51Ding,Z.etal.(2010)Expressionandsignificanceofhypoxia-inducible
factor-1alphaandMDR1/P-glycoproteininhumancoloncarcinoma
tissueandcells.J.CancerRes.Clin.Oncol.136,1697–1707
52An,W.G.etal.(1998)Stabilizationofwild-typep53byhypoxia-
induciblefactor1alpha.Nature392,405–408
53Shoshani,T.etal.(2002)Identificationofanovelhypoxia-inducible
factor1-responsivegene,RTP801,involvedinapoptosis.Mol.Cell.
Biol.22,2283–2293
54Bruick,R.K.(2000)Expressionofthegeneencodingtheproapoptotic
Nip3proteinisinducedbyhypoxia.Proc.Natl.Acad.Sci.U.S.A.97,
9082–9087
55Sowter,H.M.etal.(2001)HIF-1-dependentregulationofhypoxic
inductionofthecelldeathfactorsBNIP3andNIXinhuman
tumors.CancerRes.61,6669–6673
56Koshiji,M.etal.(2004)HIF-1alphainducescellcyclearrestby
functionallycounteractingMyc.EMBOJ.23,1949–1956
57Jin,L.etal.(2006)TargetingofCD44eradicateshumanacute
myeloidleukemicstemcells.Nat.Med.12,1167–1174
58Jin,L.etal.(2009)Monoclonalantibody-mediatedtargetingof
CD123,IL-3receptoralphachain,eliminateshumanacutemyeloid
leukemicstemcells.CellStemCell5,31–42
59Kikushige,Y.etal.(2010)TIM-3isapromisingtargettoselectively
killacutemyeloidleukemiastemcells.CellStemCell7,708–717
60Guzman,M.L.etal.(2007)Anorallybioavailableparthenolideanalog
selectivelyeradicatesacutemyelogenousleukemiastemand
progenitorcells.Blood110,4427–4435
61Kelly,P.N.etal.(2007)Tumorgrowthneednotbedrivenbyrare
cancerstemcells.Science317,337
ReviewTrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
TIPS-1218;No.ofPages10
62Wang,L.etal.(2013)FISH+CD34+CD38–cellsdetectedinnewly
diagnosedacutemyeloidleukemiapatientscanpredicttheclinical
outcome.J.Hematol.Oncol.6,85
63Witte,K.E.etal.(2011)Highproportionofleukemicstemcellsat
diagnosisiscorrelatedwithunfavorableprognosisinchildhoodacute
myeloidleukemia.Pediatr.Hematol.Oncol.28,91–99
64vanRhenen,A.etal.(2005)Highstemcellfrequencyinacutemyeloid
leukemiaatdiagnosispredictshighminimalresidualdiseaseand
poorsurvival.Clin.CancerRes.11,6520–6527
65Gentles,A.J.etal.(2010)Associationofaleukemicstemcellgene
expressionsignaturewithclinicaloutcomesinacutemyeloid
leukemia.JAMA304,2706–2715
66(2014)NIHClinicalCenteropentocoll-aboration.CancerDiscovery4,
752
67Wang,Y.etal.(2014)Echinomycinprotectsmiceagainstrelapsed
acutemyeloidleukemiawithoutadverseeffectonhematopoieticstem
cells.Blood124,1127–1135
68Bernot,K.M.etal.(2013)TowardpersonalizedtherapyinAML:in
vivobenefitoftargetingaberrantepigeneticsinMLL-PTD-associated
AML.Leukemia27,2379–2382
69Sloma,I.etal.(2010)Insightsintothestemcellsofchronicmyeloid
leukemia.Leukemia24,1823–1833
70Mayerhofer,M.etal.(2002)BCR/ABLinducesexpressionofvascular
endothelialgrowthfactoranditstranscriptionalactivator,hypoxia
induciblefactor-1alpha,throughapathwayinvolvingphosphoinositide
3-kinaseandthemammaliantargetofrapamycin.Blood100,
3767–3775
71Zhao,F.etal.(2010)ImatinibresistanceassociatedwithBCR-ABL
upregulationisdependentonHIF-1alpha-inducedmetabolic
reprograming.Oncogene29,2962–2972
72Zhang,H.etal.(2012)HIF1alphaisrequiredforsurvival
maintenanceofchronicmyeloidleukemiastemcells.Blood119,
2595–2607
73Ng,K.P.etal.(2014)Physiologichypoxiapromotesmaintenanceof
CMLstemcellsdespiteeffectiveBCR-ABL1inhibition.Blood123,
3316–3326
74Conley,S.J.etal.(2012)Antiangiogenicagentsincreasebreastcancer
stemcellsviathegenerationoftumorhypoxia.Proc.Natl.Acad.Sci.
U.S.A.109,2784–2789
75Schwab,L.P.etal.(2012)Hypoxia-induciblefactor1alphapromotes
primarytumorgrowthandtumor–initiatingcellactivityinbreast
cancer.BreastCancerRes.14,R6
76Cordenonsi,M.etal.(2011)TheHippotransducerTAZconfers
cancerstemcell-relatedtraitsonbreastcancercells.Cell147,
759–772
77Xiang,L.etal.(2014)Hypoxia-induciblefactor1mediatesTAZ
expressionandnuclearlocalizationtoinducethebreastcancer
stemcellphenotype.Oncotarget5,12509–12527
78Chaturvedi,P.etal.(2014)Hypoxia-induciblefactor-dependent
signalingbetweentriple-negativebreastcancercellsand
mesenchymalstemcellspromotesmacrophagerecruitment.Proc.
Natl.Acad.Sci.U.S.A.111,E2120–E2129
79Lukashev,D.etal.(2001)Differentialregulationoftwoalternatively
splicedisoformsofhypoxia-induciblefactor-1alphainactivated
Tlymphocytes.J.Biol.Chem.276,48754–48763
80Lukashev,D.etal.(2006)Cuttingedge:hypoxia-induciblefactor
1alphaanditsactivation-inducibleshortisoformI.1negatively
regulatefunctionsofCD4+andCD8+Tlymphocytes.J.Immunol.
177,4962–4965
81Dang,E.V.etal.(2011)ControlofT(H)17/T(reg)balancebyhypoxia-
induciblefactor1.Cell146,772–784
82Shi,L.Z.etal.(2011)HIF1alpha-dependentglycolyticpathway
orchestratesametaboliccheckpointforthedifferentiationofTH17
andTregcells.J.Exp.Med.208,1367–1376
83Kryczek,I.etal.(2011)HumanTH17cellsarelong–livedeffector
memorycells.Sci.Transl.Med.3,104ra100
84Ben-Shoshan,J.etal.(2008)HypoxiacontrolsCD4+CD25+
regulatoryT-cellhomeostasisviahypoxia-induciblefactor-1alpha.
Eur.J.Immunol.38,2412–2418
85Facciabene,A.etal.(2011)Tumourhypoxiapromotestolerance
andangiogenesisviaCCL28andT(reg)cells.Nature475,
226–230
86Finlay,D.K.etal.(2012)PDK1regulationofmTORandhypoxia-
induciblefactor1integratemetabolismandmigrationofCD8+Tcells.
J.Exp.Med.209,2441–2453
87Doedens,A.L.etal.(2013)Hypoxia-induciblefactorsenhancethe
effectorresponsesofCD8(+)Tcellstopersistentantigen.Nat.
Immunol.14,1173–1182
88Thiel,M.etal.(2007)TargeteddeletionofHIF–1alphageneinTcells
preventstheirinhibitioninhypoxicinflamedtissuesandimproves
septicmicesurvival.PLoSONE2,e853
89Jantsch,J.etal.(2008)Hypoxiaandhypoxia-induciblefactor-1alpha
modulatelipopolysaccharide-induceddendriticcellactivationand
function.J.Immunol.180,4697–4705
90Noman,M.Z.etal.(2014)PD-L1isanoveldirecttargetofHIF-1alpha,
anditsblockadeunderhypoxiaenhancedMDSC-mediatedTcell
activation.J.Exp.Med.211,781–790
91Barsoum,I.B.etal.(2014)Amechanismofhypoxia-mediatedescape
fromadaptiveimmunityincancercells.CancerRes.74,665–674
92Curiel,T.J.etal.(2003)BlockadeofB7-H1improvesmyeloid
dendriticcell-mediatedantitumorimmunity.Nat.Med.9,562–567
93Gabrilovich,D.I.andNagaraj,S.(2009)Myeloid-derivedsuppressor
cellsasregulatorsoftheimmunesystem.Nat.Rev.Immunol.9,162–174
94Talmadge,J.E.andGabrilovich,D.I.(2013)Historyofmyeloid-
derivedsuppressorcells.Nat.Rev.Cancer13,739–752
95Corzo,C.A.etal.(2010)HIF-1alpharegulatesfunctionand
differentiationofmyeloid-derivedsuppressorcellsinthetumor
microenvironment.J.Exp.Med.207,2439–2453
96Doedens,A.L.etal.(2010)Macrophageexpressionofhypoxia-
induciblefactor-1alphasuppressesT-cellfunctionandpromotes
tumorprogression.CancerRes.70,7465–7475
97Chen,W.etal.(2010)mTORsignalingisactivatedbyFLT3kinase
andpromotessurvivalofFLT3–mutatedacutemyeloidleukemia
cells.Mol.Cancer9,292
98Gilliland,D.G.andGriffin,J.D.(2002)TherolesofFLT3in
hematopoiesisandleukemia.Blood100,1532–1542
99Sathaliyawala,T.etal.(2010)Mammaliantargetofrapamycin
controlsdendriticcelldevelopmentdownstreamofFlt3ligand
signaling.Immunity33,597–606
100Brugarolas,J.etal.(2004)RegulationofmTORfunctioninresponse
tohypoxiabyREDD1andtheTSC1/TSC2tumorsuppressorcomplex.
GenesDev.18,2893–2904
101Brugarolas,J.B.etal.(2003)TSC2regulatesVEGFthroughmTOR-
dependentand-independentpathways.CancerCell4,147–158
102Hudson,C.C.etal.(2002)Regulationofhypoxia-induciblefactor
1alphaexpressionandfunctionbythemammaliantargetof
rapamycin.Mol.Cell.Biol.22,7004–7014
103VandeVelde,S.etal.(2011)mTORlinksincretinsignalingtoHIF
inductioninpancreaticbetacells.Proc.Natl.Acad.Sci.U.S.A.108,
16876–16882
104Huang,J.etal.(2009)Pivotalroleforglycogensynthasekinase-3in
hematopoieticstemcellhomeostasisinmice.J.Clin.Invest.119,
3519–3529
105Parkin,B.etal.(2010)Acquiredgenomiccopynumberaberrationsand
survivalinadultacutemyelogenousleukemia.Blood116,4958–4967
106Joshi,S.etal.(2014)MDM2regulateshypoxichypoxia-inducible
factor1alphastabilityinanE3ligase,proteasome,andPTEN-
phosphatidylinositol3-kinase-AKT-dependentmanner.J.Biol.
Chem.289,22785–22797
107Ravi,R.etal.(2000)Regulationoftumorangiogenesisbyp53-induced
degradationofhypoxia-induciblefactor1alpha.GenesDev.14,34–44
108Falini,B.etal.(2005)Cytoplasmicnucleophosmininacutemyelogenous
leukemiawithanormalkaryotype.N.Engl.J.Med.352,254–266
109Grisendi,S.andPandolfi,P.P.(2005)NPMmutationsinacute
myelogenousleukemia.N.Engl.J.Med.352,291–292
110Chen,D.etal.(2010)Transcription-independentARFregulationin
oncogenicstress-mediatedp53responses.Nature464,624–627
111Fatyol,K.andSzalay,A.A.(2001)Thep14ARFtumorsuppressor
proteinfacilitatesnucleolarsequestrationofhypoxia-induciblefactor-
1alpha(HIF-1alpha)andinhibitsHIF-1-mediatedtranscription.
J.Biol.Chem.276,28421–28429
112Wang,H.etal.(2014)NegativeregulationofHif1aexpressionand
TH17differentiationbythehypoxia-regulatedmicroRNAmiR-210.
Nat.Immunol.15,393–401
9
113Blouin,C.C.etal.(2004)Hypoxicgeneactivationbylipopolysaccharide
inmacrophages:implicationofhypoxia-induciblefactor1alpha.Blood
103,1124–1130
114Laughner,E.etal.(2001)HER2(neu)signalingincreasestherateof
hypoxia-induciblefactor1alpha(HIF-1alpha)synthesis:novel
mechanismforHIF-1-mediatedvascularendothelialgrowthfactor
expression.Mol.Cell.Biol.21,3995–4004
115Cui,T.X.etal.(2013)Myeloid-derivedsuppressorcellsenhance
stemnessofcancercellsbyinducingmicroRNA101andsuppressing
thecorepressorCtBP2.Immunity39,611–621
116Kryczek,I.etal.(2014)IL-22(+)CD4(+)Tcellspromotecolorectal
cancerstemnessviaSTAT3transcriptionfactoractivationand
inductionofthemethyltransferaseDOT1L.Immunity40,772–784
117Lin,E.Y.etal.(2006)Macrophagesregulatetheangiogenicswitchina
mousemodelofbreastcancer.CancerRes.66,11238–11246
118Ben-Neriah,Y.andKarin,M.(2011)Inflammationmeetscancer,with
NF-kappaBasthematchmaker.Nat.Immunol.12,715–723
119Lin,E.Y.andPollard,J.W.(2007)Tumor-associatedmacrophages
presstheangiogenicswitchinbreastcancer.CancerRes.67,
5064–5066
ReviewTrendsinPharmacologicalSciencesxxxxxxx,Vol.xxx,No.x
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