Heregulinβ activates storeoperated Ca2+ channels through cerbB2 receptor leveldependent pathway.docx
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Heregulinβ activates storeoperated Ca2+ channels through cerbB2 receptor leveldependent pathway.docx
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HeregulinβactivatesstoreoperatedCa2+channelsthroughcerbB2receptorleveldependentpathway
Heregulinβactivatesstore-operatedCa2+channelsthroughc-erbB2
receptorlevel-dependentpathwayinhumanbreastcancercells
Jie-YingLiaoa,b,1,Lin-LinLia,c,1,2,QunWeicandJia-ChangYuea,
aNationalLaboratoryofBiomacromolecules,InstituteofBiophysics,ChineseAcademyofSciences,15DatunRoad,ChaoyangDistrict,Beijing100101,China
bGraduateUniversityoftheChineseAcademyofSciences,Beijing100049,China
cTheSchoolofLifeScience,BeijingNormalUniversity,Beijing100875,China
Received26September2006;
revised23November2006.
Availableonline12December2006.
Abstract
Theheregulinβ(HRGβ)isaligandtoactivatec-erbB2/c-erbB3interactionandcansubsequentlyincreasescytosolic[Ca2+]i.Inthetwohumanbreastcancercelllines,MCF-7showsalowc-erbB2expressionlevel,whereasSK-BR-3overexpressc-erbB2receptor.Inthisarticle,wehavefoundthatinMCF-7,HRGβinducedCa2+releasefromtheendoplasmicreticulums(ER)andsubsequentlyactivatedCa2+entryviastore-operatedCa2+channel(SOC).However,inSK-BR-3,HRGβfailedtoinduceCa2+releaseandCa2+entry.RNAinterferencetodecreasec-erbB2levelinSK-BR-3resultedinreactivationofHRGβ-evokedCa2+releaseandCa2+entryviaSOC,whichwassimilartothatofMCF-7.Inaddition,intheabsenceofHRGβ,aconstitutiveactivationofSOCwasobservedinSK-BR-3ratherthaninMCF-7andc-erbB2-siRNAtreatedSK-BR-3.Comparedtothecellswithlowc-erbB2level,c-erbB2mighttendtointeractwithc-erbB3intherestingstateinthecellswithhighc-erbB2level,whichresultedindifferent[Ca2+]iresponsestoHRGβ.InSK-BR-3,theCa2+mobilizationinthepresenceorintheabsenceofHRGβwascompletelyblockedbyPLCinhibitorU73122.Insummary,ourresultsindicatethatHRGβ-inducedSOCwasregulatedbyc-erbB2levelanddependentonactivationofPLCinhumanbreastcancercells.
Keywords:
HRGβ;Store-operatedCa2+channel(SOC);C-erbB2;PLC;Human
breastcancer
cells
ArticleOutline
Materialsandmethods
Materials
Cellculture
[Ca2+]imeasurements
Mn2+quenchingmeasurements
RNAinterference(RNAi)
Westernblotting
Statisticalanalysis
Results
EffectofHRGβon[Ca2+]iinhumanbreastcancerwithdifferentexpressionlevelsofc-erbB2
SOCwasresponsibleforCa2+entryinthepresenceorintheabsenceofHRGβ
HRGβ-inducedCa2+mobilizationwasdependentonPLC
Discussion
Acknowledgements
References
CytosolicCa2+signalsrepresentaconvergentpointofmanysignaltransductionpathwaysandmodulateadiversearrayofcellularactivitiesrangingfromshort-termresponsessuchascontractionandsecretion,tolonger-termcontroloftranscription,celldivision,andcelldeath.Innon-excitablecells,intracellularcalciummobilizationgenerallyinvolvesinternalCa2+releasefromendoplasmicreticulums(ER)andfollowingCa2+entryacrosstheplasmamembrane[1]and[2].Thestimulationoftyrosinekinasereceptorbymanyhormonesleadstostimulationofreceptortyrosinekinase-PLC-γpathwaystoproduceinositol1,4,5-trisphosphate(IP3).IP3couplestotheIP3receptor(IP3R)3locatedonERandinducesCa2+release[3]and[4].ThesubsequentCa2+entryinthisprocessisgenerallyknownasstore-operatedorcapacitativeCa2+entrythroughaspecifictypeofCa2+channeltermedstore-operatedCa2+channel(SOC)[1],[2]and[5].Previousstudieshavedemonstratedthatepidermalgrowthfactor(EGF)inducesCa2+signalsviadifferentmechanismsindifferentcelllines.Zhangetal.foundthatinhumansalivarycells,EGFstimulatedCa2+influxbyalternativemechanismsdistinctfromCa2+entryviaSOC[6]andanotherlaboratoryprovidedevidencethatEGF-activatedSOCviaaPLC-dependentbutIP3Rindependentpathwayinhumanglomerularmesangialcells[7].
TheerbB/epidermalgrowthfactorreceptor(EGFR)familyconsistsoffourproteins:
EGFR(c-erbB1),c-erbB2,c-erbB3andc-erbB4,whichareinvolvedinsignaltransductionpathwaysthatregulatecellgrowthanddifferentiation.Overexpressionoramplificationofepidermalgrowthfactorreceptorisassociatedwithmalignancyandapoorprognosisinbreastcancer.Inthefourreceptors,c-erbB2isoverexpressedinabout30%ofhumanbreastcancerpatients[8],[9],[10]and[11].Heregulinβ(HRGβ)isamemberofEGF-likeligandstoleadtoerbB-receptorinteraction[11].Inthevariousheterodimersandhomodimers,thec-erbB2/c-erbB3dimerconstitutesahighestaffinityco-receptorforHRGβ[12],[13],[14],[15]and[16],whichresultsinactivationofPLCsignalpathwayandsubsequentmobilizationof[Ca2+]i[3],[4],[17]and[18].EGF-inducedrisein[Ca2+]iviaactivationofEGFRisderivedfromtheactivationofbothreleasefromER(triggeredbyIP3)andCa2+influxviaSOClocatedonplasmamembrane[19],[20]and[21].However,whetherCa2+influxstimulatedbyHRGβisthroughSOCandthecorrelationbetweenthec-erbB2receptorlevelandsignaltransductionpathwaymodulatedbycellular[Ca2+]iarestillunknown.
Here,weinvestigatedtheeffectsofc-erbB2receptorathighandlowlevelsonCa2+mobilization.OurstudyfocusedonMCF-7andSK-BR-3humanbreastcancercelllines,representingmodelswithdifferentc-erbB2expressionlevel:
MCF-7showsalowc-erbB2level,whereasSK-BR-3isobservedtooverexpressc-erbB2[22]and[23].Inthepresentstudy,weprovidedevidencesthatinthecellswithlowc-erbB2level(MCF-7andc-erbB2-siRNAtreatedSK-BR-3),HRGβ-evokedintracellularCa2+mobilizationinvolvedtwophases(i.e.,aninitialrapidrisefollowedbyasustainedplateau).InSK-BR-3cellswithhighlevelofc-erbB2receptor,HRGβfailedtoactivatefurtherincreaseofintracellular[Ca2+]ialthoughconstitutiveactivationofSOCwasmeasuredwithoutHRGβaddition.Inaddition,Ca2+mobilizationinthecellseitherwithlowc-erbB2levelorwithhighc-erbB2levelwasviaaPLC-dependentmechanism.Thus,c-erbB2receptorlevelhasanessentialroleinregulationofPLC-dependentCa2+mobilizationpathwayinhumanbreastcancercells.
Materialsandmethods
Materials
Heregulinβ(HRGβ),1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione(U73122),Fura-2acetoxymethylester(Fura-2/AM)andthapsigargin(Tg)wereobtainedfromSigma.c-erbB2monoclonalantibodywaspurchasedfromNeomarkers.Allotherreagentswereofanalyticalgrade.2-Aminoethoxydiphenylborate(2-APB)wasagiftfromProf.JianwenChen(TheNationalLaboratoryofBiomacromolecules,InstituteofBiophysics,ChineseAcademyofSciences,China).
Cellculture
TheMCF-7humanbreastcancercelllinewaskindlyprovidedbyProf.JianwenChen.SK-BR-3wasobtainedfromAmericanTypeCultureCollection(Rockville,MD).CellsweremaintainedinDulbecco’smodifiedEagle’smedium(Sigma)supplementedwith10%fetalbovineserum(PAA)at37 °Cinahumidified5%CO2incubator.
[Ca2+]imeasurements
Thecells(2 × 105cells)wereplantedatlowdensityincompletemediumformorethan24 honglassbottomdishesandwerestarvedfor4–6 hinserum-freeDMEMbeforetheexperiments.[Ca2+]iwasmonitoredwithdualexcitationwavelengthfluorescencemicroscopyusingFura-2/AM.Inbrief,cellswereloadedwithFura-2/AM(1 μM)byincubationfor40 minin5%CO2incubatorinCa2+buffer(145 mMNaCl,5 mMKCl,1 mMMgCl2,2 mMCaCl2,10 mMglycose,10 mMHepes,pH7.4)andthenrinsedwithnominallyCa2+-freebuffer(145 mMNaCl,5 mMKCl,3 mMMgCl2,10 mMglycose,10 mMHepes,0.01 mMEGTA,pH7.4)nolessthan20 mintoremoveextracellularfreecalcium.Fura-2/AMwasexcitedwithlightfromamercurylampalternatelyfilteredto340or380 nm.Ina37 °Cenvironmentalchamber,thefluorescenceimagesoftheattachedcellsonthebottomglass(40×objective)werecapturedevery5 satemissionof510 nmonanNikonDiaphot300invertedmicroscopeequippedwithAquaCosmosMicroscopicImageAcquisition.AnalysissystemwasprovidedbyHamamatsuPhotonicsK.K.(Japan).Thedigitizedfluorescenceratio(R340/R380)imagesofthecellsandthekineticchangeoftheratioineachcellwereprocessedonlineonaPCcomputer.Intheimagingsystemusedinthisinvestigation,theexcitationlightilluminatescellsonlyforveryshorttime(112 ms)duringacquisitionofeachimage,butwasshutdownbeforenextimaging(5 sapart).Therefore,thephotobleachingoftheCa2+indicatorisnegligible.
Mn2+quenchingmeasurements
TherateofMn2+entry,asmeasuredbythequenchingofcellularFura-2/AMfluorescenceafteradditionofMn2+(0.2 mMMnCl2),hasbeenusedasameasureofstore-operatedCa2+influx.ThecellswereloadedwithFura-2/AMinCa2+bufferasdescribedaboveandthenrinsedwithnominallyCa2+-freebuffernolessthan20 min.Thefluorescencewasexcitedat360 nmandmeasuredat510 nm.TheattachedcellsonthebottomglasswerestimulatedbyagonistsbeforeMn2+addition.TheslopeofMn2+entry-inducedreductionofFura-2/AMfluorescenceinitiatedbyadditionofTgorHRGβwasestimatedasdescribedbyCohenetal.[24].TheinitialslopesofthelineardeclineinFura-2fluorescencewereduringthe30 simmediatelyafteradditionofMn2+.
RNAinterference(RNAi)
c-erbB2-siRNAwasasfollows:
sense:
5′-GGAGCUGGCGGCCUUCAUG,antisense:
5′-GCACAAGGCCGCCAGCUCC;negativecontrolsiRNAwasasfollows:
sense:
5′-AAUAGUGUAUACGGCAUGC,antisense:
5′-CGAUGCCGUAUACACUAUU.Onedaybeforetransfection,cells(2 × 105cells)wereplatedin1 mlofgrowthmediumsothattheywillbe30–50%confluentatthetimeoftransfection.Transfectionof100 nMsiRNAduplexeswascarriedoutusinglipofectamine2000transfectionreagent(Invitrogen)accordingtothemanufacturer’sinstructions.S
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