自噬与核糖体的关系

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BoththeautophagyandproteasomalpathwaysfacilitatetheUbp3p-dependentdepletionofasubsetoftranslationandRNAturnoverfactorsduringnitrogenstarvationinSaccharomycescerevisiae

SHANEP.KELLY1andDAVIDM.BEDWELL1,2

1

DepartmentofCell,DevelopmentalandIntegrativeBiology,2DepartmentofMicrobiology,UniversityofAlabamaatBirmingham,Birmingham,Alabama35294,USA

ABSTRACT

Proteinturnoverisanimportantregulatorymechanismthatfacilitatescellularadaptationtochangingenvironmentalconditions.Previousstudieshaveshownthatribosomeabundanceisreducedduringnitrogenstarvationbyaselectiveautophagymechanismtermedribophagy,whichisdependentuponthedeubiquitinaseUbp3p.Inthisstudy,weaskedwhethertheabundanceofvarioustranslationandRNAturnoverfactorsarereducedfollowingtheonsetofnitrogenstarvationinSaccharomycescerevisiae.Wefounddistinctdifferencesintheabundanceoftheproteinstestedfollowingnitrogenstarvation:(1)Thelevelofsomedidnotchange;(2)otherswerereducedwithkineticssimilartoribophagy,and(3)afewproteinswererapidlydepleted.Furthermore,differentpathwaysdifferentiallydegradedthevariousproteinsuponnitrogenstarvation.ThetranslationfactorseRF3andeIF4GI,andthedecappingenhancerPat1p,requiredanintactautophagypathwayfortheirdepletion.Incontrast,thedeadenylasesubunitPop2pandthedecappingenzymeDcp2pwererapidlydepletedbyaproteasome-dependentmechanism.Theproteasome-dependentdepletionofDcp2pandPop2pwasalsoinducedbyrapamycin,suggestingthattheTOR1pathwayinfluencesthispathway.Likeribophagy,depletionofeIF4GI,eRF3,Dcp2p,andPop2pwasdependentuponUbp3ptovaryingextents.Together,ourresultssuggestthattheautophagyandproteasomalpathwaysdegradedistincttranslationandRNAturnoverfactorsinaUbp3p-dependentmannerduringnitrogenstarvation.Whileribophagyisthoughttomediatethereutilizationofscarceresourcesduringnutrientlimitation,ourresultssuggestthattheselectivedegradationofspecificproteinscouldalsofacilitateabroaderreprogrammingofthepost-transcriptionalcontrolofgeneexpression.Keywords:autophagy;proteasome;nitrogenstarvation;translationfactors;RNAturnoverfactors

INTRODUCTION

Macroautophagy(hereafterreferredtoasautophagy)isanimportantmechanismusedbyeukaryoticcellstodegradecy-tosoliccontentsandrecycletheresultingbuildingblocksforthesynthesisofnewmacromoleculesduringstresscon-ditions.Autophagyinyeastoccursmainlyinresponsetonu-trientlimitation(Takeshigeetal.1992).Inthisprocess,portionsofthesubcellularenvironmentaresequesteredintodenovoformeddoublemembranevesiclesandroutedtotheyeastvacuole(ormammalianlysosome)wherethecontentsaredegraded.Theresultingdegradativeproductsaretransportedbackintothecytoplasmthroughvacuolarpermeasestofacilitatetheirreuseinbiosyntheticpathways.Inthisway,autophagymaintainscytoplasmicaminoacidlev-elsandbasalproteinsynthesisduringstarvationconditions

Correspondingauthor:dbedwell@uab.edu

Articlepublishedonlineaheadofprint.Articleandpublicationdateareat/cgi/doi/10.1261/rna.045211.114.

(OnoderaandOhsumi2005;Yangetal.2006;YangandKlionsky2007).

Thetargetofrapamycin(TOR1)kinasefunctionsasanimportantsensorofnitrogenandaminoacidavailabilityineukaryoticcells.AdditionoftheTOR1inhibitor,rapamycin,inducesautophagyduringnutrient-richgrowth(NodaandOhsumi1998).TOR1regulatestheautophagypathwaybydi-rectphosphorylationofAtg13p(Kamadaetal.2010).TOR1kinaseactivityisrapidlyinhibitedunderstarvationcondi-tions,allowingdephosphorylatedAtg13ptoaccumulateandinductionofautophagytooccur.However,TOR1func-tionisgraduallyreactivatedinanautophagy-dependentmannerduringprolongedstarvationinbothyeastandmam-maliancells,suggestingthatTOR1reactivationmayplaya

©2015KellyandBedwellThisarticleisdistributedexclusivelybytheRNASocietyforthefirst12monthsafterthefull-issuepublicationdate(see/site/misc/terms.xhtml).After12months,itisavailableunderaCreativeCommonsLicense(Attribution-NonCommercial4.0Inter-national),asdescribedat/licenses/by-nc/4.0/.

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RNA21:898–910;PublishedbyColdSpringHarborLaboratoryPressfortheRNASociety