The ubiquitin-like modifier FAT10 in antigen processing and antimicrobial defense

(1)

The ubiquitin-like modiﬁer FAT10 in antigen processing and antimicrobial defense

Michael Basler

^a,b,∗

, Stefanie Buerger

^a

, Marcus Groettrup

^a,b,∗∗

aDivisionofImmunology,DepartmentofBiology,UniversityofKonstanz,D-78457Konstanz,Germany

bBiotechnologyInstituteThurgau(BITg)attheUniversityofKonstanz,CH-8280Kreuzlingen,Switzerland

Keywords:

Antigenpresentation Antigenprocessing Ubiquitin-likemodiﬁer FAT10

a b s t r a c t

Theubiquitin-likemodiﬁer(ULM)HLA-Fadjacenttranscript10(FAT10)isencodedintheMHClocus, isup-regulatedduringdendriticcellmaturation,ishighlyexpressedinlymphoidtissues,andstrongly inducedbyinterferon(IFN)-␥andtumornecrosisfactor(TNF)-␣.FAT10istheonlyULMknowntodate whichdirectlytargetsitshundredsofsubstratesfordegradationbytheproteasome.Thisimpliesarole forFAT10inantigenpresentation.Indeed,fusionofFAT10toviralproteinsenhancedtheirpresentation alongtheproteasomedependentMHCclassIpresentationpathway.InthisreviewwediscusstheFAT10 conjugationsystemasanalternativeanddistinctpathwayforMHCclassIandIIantigenprocessing.

Furthermore,wereviewtherecentﬁndingthatFAT10playsaroleinantimicrobialdefenseagainst intracellularpathogens.

1. Introduction

Ubiquitin-likemodiﬁers(ULM)post-translationallymodifycel- lular targets in pathwaysthat are parallel tobut distinct from theubiquitinsystemand inﬂuencediversebiologicalprocesses.

Thecovalentmodiﬁcationwiththecytokine-inducibleULMHLA-F adjacent transcript 10 (FAT10) targets proteins in a ubiquitin- independent mannerfor proteasomal degradation (Raasi et al., 2001;Hippetal.,2005;Schmidtkeetal.,2009).AsotherULMs, FAT10isconjugatedtoitssubstratesviaisopeptidelinkagemedi- atedbyanE1,E2,andpossiblyE3enzymecascade,whereUBA6 (alsotermedUBE1L2,E1-L2,orMOP-4)andUSE1(UBA6-speciﬁc E2enzyme)serveasE1-typeactivatingandE2-typeconjugating enzymes,respectively(Aichemetal.,2010;PelzerandGroettrup, 2010;Chiuetal.,2007).FAT10hasbeenimplicatedinmultiplecel- lularprocesseslikeapoptosis,spindlecheckpointcontrolduring mitoticcellcycle,andNF-␬Bactivation.BasalFAT10expressionis mostprominentinorgansoftheimmunesystem,likethymus,fetal

∗Correspondingauthorat:DepartmentofBiology,DivisionofImmunology,Uni- versityofKonstanz,P1101Universitätsstrasse10,D-78457Konstanz,Germany.

Tel.:+497531882258;fax:+497531883102.

∗∗Correspondingauthorat:DepartmentofBiology,DivisionofImmunology,Uni- versityofKonstanz,P1101Universitätsstrasse10,D-78457Konstanz,Germany.

Tel.:+497531882130;fax:+497531883102.

E-mailaddresses:Michael.Basler@uni-konstanz.de(M.Basler), Marcus.Groettrup@uni-konstanz.de(M.Groettrup).

liver,lymphnodes,andspleen.Inaddition,expressionofFAT10 canbesynergisticallyinducedbythepro-inﬂammatorycytokines IFN␥andTNF␣anditisup-regulatedduringdendriticcellmaturation (summarized in (Schmidtke et al.,2014)). Micelacking FAT10areviableandfertile,indicatingthathousekeepingfunctions arenotgrosslyinﬂuencedbyFAT10(Canaanetal.,2006).Never- theless,lymphocytesofFAT10knockoutmicearemoreproneto spontaneousapoptoticdeathandmicedemonstratedahighlevel ofsensitivitytowardsendotoxinchallenge(Canaanetal.,2006).

Furthermore,FAT10-deﬁcientmicehaveanextendedlifespanand reducedadiposity(Canaanetal.,2014).

2. FAT10inantigenprocessing

Themajorhistocompatibilitycomplex(MHC)class-Irestricted pathwayofantigenprocessingallowsthepresentationofintra- cellularantigenstocytotoxicTlymphocytes.Themainprotease involvedinthisprocessistheproteasome(Basleretal.,2009).Pro- teinsdestinedfordegradationbythe26Sproteasomeareusually markedwithubiquitin,whichrequiresthecoordinatedactivities ofubiquitin-activating(E1),-conjugating(E2),and-ligating(E3) enzymes.Itisgenerallyassumedthatubiquitinisthemaindriver forproteasomaldegradationinMHC-Iantigenprocessing,although experimentalevidence for a role ofubiquitin inthis process is ratherlimitedandcontradictory(Michaleketal.,1993;Coxetal., 1995).Inarecentstudy,theknockdownofubiquitin,expression ofalysine48(K48)ubiquitinmutant,orinhibitionofproteasome

Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-0-313521 Erschienen in: Molecular Immunology ; 68 (2015), 2. - S. 129-132

https://dx.doi.org/10.1016/j.molimm.2015.04.012

(2)

130

Fig.1. FAT10inMHCclassIandMHCclassIIantigenpresentation.FAT10conjugationoccursinacatalyticalcascadeviaanE1enzyme(UBA6),E2enzyme(USE1)andso farunidentiﬁedE3enzymes.ThisresultsintheformationofanisopeptidebondbetweenFAT10andalysineofthesubstrateprotein.DockingofFAT10anditssubstrate proteintotheproteasomeoccursviatheVWAdomainofthe19SproteasomeregulatorsubunitRpn10.FAT10anditssubstrateproteinaredegradedbytheproteasome.The peptidesaresubsequentlytransferredintotheER-lumenviathetransporterassociatedwithantigenprocessing(TAP)wheretheyareloadedonemptyMHCclassImolecules.

Theassembledpeptide–MHCcomplexesarethentransportedtothecellsurfaceviatheER-GolginetworkwheretheyarepresentedtoCD8⁺Tcells.Thesofarhypothetical involvementofFAT10intheMHCclassIIantigenpresentationpathwayinvolvesbindingofFAT10ylatedsubstrateproteinstotheautophagyadapterp62.Interactionof p62withLC3leadstoautophagosomeformationandsubsequentfusionwithlysosomes.MHCclassIImoleculescontaininganinvariantchainblockingthepeptidebinding grooveareexportedviatheER-Golginetwork.Uponfusionofthevesicleswiththeautophagolysosomes,lysosomalproteasesdegradetheinvariantchainaswellasthe FAT10substrate.PeptidesderivedfromFAT10substrateproteinscanthenbindtoMHC-IIandpeptide–MHCcomplexareexportedtothecellsurfaceforpresentationto CD4⁺Tcells.

associateddeubiquitinasessigniﬁcantlyimpairedantigenpresen- tation(Fiebigeretal., 2015).The authorssuggesteda model in which thebindingof the antigensubstrate by anadaptorpro- teinleadstoK48-poly-ubiquitylationoftheadaptor(butnotthe antigen)andthesubsequentdeliveryoftheantigencargofordegra- dationbythe26Sproteasome.Inanotherstudy,usinganinducible vacciniavirus systemoverexpressing wildtype and dominant- negativelysinelessformsofubiquitininmammaliancellstherole of ubiquitin in antigen processing was assessed (Huang et al., 2011).Thereby,ubiquitin-dependentdegradationappearedtoplay amajorroleintheprocessingofER-targetedproteins,butthere wasaratherrestrictedroleintheprocessingofcytosolicproteins.

Thepresenceofsuchfunctionallydistinctpathwayssuggeststhe existenceofalternativeproteasomaltargetingsystems,likeULM, involvedinantigenpresentation.SinceFAT10istheonlyULMable todirectlytargetproteinsforproteasomaldegradation,itislikely thatFAT10mightbeinvolvedinanalternativeproteasomaltar- getingforMHC-Irestrictedpresentation.Furthermore,likeseveral componentsinvolvedinantigenpresentationFAT10isencodedin theMHClocus.Therefore,itseemslikelythatFAT10-mediatedpro- teasomaldegradationmightinﬂuenceMHC-Iantigenpresentation (Fig.1).

FAT10 was described as a ubiquitin-independent signal for proteasomaldegradationthatdirectlytargetsproteinsfordegra- dation by theproteasome (Hippet al., 2005; Schmidtke et al., 2009).ThedegradationofFAT10-linkedproteinsbytheproteasome isstronglyacceleratedbytheubiquitin-like-ubiquitin-associated proteinNEDD8ultimatebuster-1long(NUB1L)(Hippetal.,2004).

ToinitiateproteolysisbothFAT10andNUB1Ldocktothe26Spro- teasome.DockingofFAT10tothe26Sproteasomeoccursviathe VWAdomainofthe19Scapofthe26SproteasomesubunitRpn10 (S5a),whereasNUB1Lcanbindtoboth19ScapsubunitsRpn10 andRpn1/S2(Ranietal.,2012).Hence,inprinciple,FAT10isable totargetpotentialantigensforproteasomaldegradation.Indeed,a roleofFAT10inMHCantigenpresentationhasbeendemonstrated (Ebstein etal.,2012;Schlieheetal.,2012).Ebsteinetal.(2012) expressedfusionproteinsconsistingofthehumancytomegalovirus (HCMV)-derivedpp65antigenN-terminallytaggedwitheitherubi- quitin orFAT10 inHeLa cells and analyzed thepresentationof theimmunodominantpp65495–503epitopeinthesecells.Incom- parison to the untagged pp65, the FAT10-pp65 fusion protein enhancedantigenpresentationapproximatelytwofold,asimilar extentasthatseenwiththeubiquitin-pp65fusionprotein.The improvedpp65_495–503presentationobtainedwithubiquitin-pp65

(3)

131

wassubstantially reducedwhenallthesevenlysineresiduesof thefusedubiquitinmoietywerechangedintoarginineresidues indicatingthatUb-pp65reliesonthepoly-ubiquitylationofitsN- terminalubiquitin.Nevertheless,itwasnotaddressedwhetherthe enhanced FAT10-inducedantigen presentation isdependent on poly-FAT10ylation.However,inadifferentstudy,notaddressing antigenpresentation,FAT10withitstwoubiquitin-likedomains served as a degradation signal with no need for chain forma- tion(Ranietal.,2012).Rpn10knockdownwasassociatedwitha signiﬁcantlyimpairedpp65_495–503epitopepresentationfromthe FAT10-pp65fusionprotein,indicatingthatdockingofFAT10tothe 26SproteasomeoccursviaRpn10(Ebsteinetal.,2012).Interest- ingly,FAT10-pp65processingisnotalteredbyimmunoproteasome subunitsandPA28␣/␤,theIFN␥induciblecomponentsofthepro- teasome.AninvolvementofFAT10inMHCantigenpresentation wasalsodemonstratedbySchlieheetal.(2012).N-terminalfusion ofthelymphocyticchoriomeningitisvirus(LCMV)nucleoprotein (NP) withubiquitin(Ub-NP)or FAT10(FAT10-NP)enhanced its degradationrate.TheN-terminalfusionoftheNPtoeitherubiqui- tinorFAT10convertedthelong-livedNPintoarapidlydegraded FAT10-NP fusion protein. Transfection of cells with these con- structsincreasedthedegradationrateofFAT10-NPleadingtoa 2–3foldenhancedpresentationofthenucleoprotein-derivedMHC classIepitopesNP_396–404orNP_118–126.Additionally,infectionof cellswitha recombinantvacciniavirusexpressingFAT10-NPin vitro strongly increased the presentation of the LCMV-derived NP_396–404 orNP_118–126.Interestingly,theenhancedpresentation didnotimprovethecytotoxicTcell(CTL)responsetotheseepitopes inmiceimmunizedwithFAT10-NP,neitherinaDNAimmuniza- tionset-upnorafterinfectionwithrecombinantvacciniaviruses.

Instead,theNPspecificCTLresponsecorrelatedpositivelywiththe stabilityoftheantigen,withstableantigensshowingthestrongest CTLresponse.Asstableantigeninantigendonorcellsisrequired forefficientcross-presentation,thisresultwasinterpretedasevi- denceforcross-presentationforprimingNP-specificCTLresponses.

Takentogether,theseresultsstronglysuggestthatlinkagetoFAT10 canfeedantigensintotheMHCclassIantigenprocessingpathway.

DCaggresome-likestructures(DALIS)containpoly-ubiquitylated proteins. These transient aggresome-like structures function as storagecompartmentsofantigenicproteinsduringthematuration ofdendriticcellsandpeptidesderivedfromDALIScanbepresented byMHCclass Imolecules(Pierre,2005).Kalverametal.(2008) reportedthatFAT10interactswiththecytoplasmicproteinhistone deacetylase6(HDAC6)andlocalizestoaggresomesunderproteasomeinhibition.Hence,itremainstobedeterminedwhetherFAT10 isalsoinvolvedintheformationofDALISandtherebyinﬂuences classIpresentation.

ApartfromaroleinMHCclassIantigenpresentation,FAT10 mightinﬂuenceclassIIpresentation(Fig.1).Classically,endocyto- sisdeliversnonself-antigenstoMHC-IImolecules,butasubstantial portionofMHCclassIIligandsoriginatesfromcytosolicandnuclear antigens.Autophagyisanevolutionarilyconservedpathwaywith nutrient-recyclingfunctionsduringstarvation,however,inhigher eukaryotesthispathwayisalsousedtopresentpeptidesonMHC classIImoleculestoCD4⁺Tcells(Munz,2012).Ithasbeendemon- stratedthattheautophagosomalreceptorp62/SQSTM1becomes covalentlymono-FAT10ylatedatseverallysines,andthatFAT10 co-localizeswithp62inp62bodies(Aichemetal.,2012).Further- more,FAT10isinvolvedintheformationofMallory-Denkbodies, whichareaggresome-likestructuresinhepatocellularcarcinoma cells composedof ubiquitylated proteins (French et al., 2012).

Additionally,FAT10decoratesautophagy-targetedSalmonellaand contributestoSalmonellaresistanceinmice(Spinnenhirnetal., 2014)(seebelow).Hence,theassociationofFAT10withautophago- somal markers indicates that FAT10 might, similar to class I presentation,beinvolvedinMHCclassIIpresentation.Supporting

thisideaisthefactthatFAT10ishighlyexpressedinthethymus (Lukasiaketal.,2008),anorganinwhichautophagyisanessential processinmediatingtoleranceofCD4⁺Tcells.Inhumansandinrats type1diabetes(T1D)isstronglyassociatedwithapermissiveclass IIMHChaplotype,indicatingthatclassIIantigenpresentationplays acrucialroleinthisautoimmunedisease.Recently,thefat10gene (alsocalledubiquitinD(ubd)gene)couldbelinkedtoenhanced susceptibilitytovirus-triggeredautoimmunediabetesinrats(Cort etal.,2014).Geneexpressionproﬁlingofpancreaticlymphnodes insusceptibleandresistantratsduringdiseaseinductionshowed differencesinfat10transcriptabundance.Furthermore,LEW.1WR1 ratslackingFAT10expressionshowedareducedsusceptibilityto virus-inducedT1D.Theseresultsstronglysupportthenotionofa roleforFAT10inclassIIantigenpresentation.

3. FAT10inantimicrobialdefense

Invasionofbacteriaintoeukaryoticcellsiscounteractedbycell autonomous innate immune mechanisms includingxenophagy.

The initiation of the destruction of intracellular bacteria by xenophagy is mediated by the decoration of cytosolic bacteria withubiquitinandbindingofgalectin-8.Whetherpathogensare eitherdirectlyubiquitylatedorwhetherubiquitylatedhostpro- teins accumulate on theirsurface to initiate xenophagy is still a matter of debate. Ubiquitin decoration of cytosolic bacteria leadstotherecruitmentofautophagyadaptorslikep62,NDP52, and optineurin. FAT10, via an UBA-domain independent cova- lentinteraction,canbeconjugatedtotheautophagyadaptorp62 (Aichemetal.,2012).Additionally,astrongnon-covalentinterac- tionbetweenFAT10andp62hasbeendescribed (Aichemetal., 2012).Functioningasanautophagosomaladaptorbetweenubi- quitinonbacteriaandthenascentautophagosome-linkedprotein LC3,p62hasbeenimplicatedinthecaptureofcytosolicbacteria.

ThisindicatesthatFAT10might,analogoustoubiquitin,beinvolved intargetingpathogensfor autophagosomaldegradation.Indeed, FAT10decoratedcytosolicSalmonellatyphimuriumwhichweretar- getedforautophagy(Spinnenhirnetal.,2014).Similartoubiquitin, FAT10decorationandautophagosomaltargetingofS.typhimurium occurredwiththesamekinetics.Nevertheless,thepercentageof ubiquitinand FAT10decoratedbacteria markedlydiffered, sug- gesting that theFAT10-targetedstructures arenot thesameas the ubiquitylatedones. Unexpectedly,neither FAT10deﬁciency noroverexpressiondidsigniﬁcantlychangebacterialreplication invitro.Nevertheless,infectionofamousestrainsusceptibleto S.typhimuriumrevealedaroleofFAT10inantimicrobialdefense.

14dayspostinfection,asignificantlyenhancedbacterialloadin mesentericlymphnodesfromFAT10-deficientmiceascomparedto wildtypemicewasobserved(Spinnenhirnetal.,2014).Addition- ally,FAT10-deficientmiceshowedatendencytolosemorebody weightthan theirFAT10-proficientwild type controls.Further- more,survivalexperimentsfollowingS.typhimuriuminfectionof susceptiblewildtypeandFAT10-deficientmiceresultedinahigher rateofdeatheventsinmicelackingFAT10.ThelateeffectofFAT10 deficiencyonSalmonellainfectioninmicecouldalsoindicatearole inadaptiveimmunity,butthisremainstobedetermined.Taken together,FAT10decoratesS.typhimuriumincellsandcontributes totheprotectionofmiceagainstthispathogen.

4. Conclusions

TheFAT10axiswasdescribedasanovelrouteforMHCclass Iantigenpresentation(Ebsteinetal.,2012;Schlieheetal.,2012).

FAT10istheonlyubiquitin-likemodiﬁerknowntodate,which, likepoly-ubiquitinchains,candirectly targetseveralsubstrates fordegradationbythe26Sproteasome(Schmidtkeetal.,2014).

(4)

132

Althoughthe ubiquitin-like modifier FAT10is in many aspects similartoubiquitin,theexpressionofFAT10uponcytokinestim- ulationsuggeststhatthisnovelroutemayallowpresentationof differentantigenicpeptidesorincreasedamountsofpeptidesin inflamedtissue comparedtotheclassical ubiquitinconjugation system.E3ligasesarecrucialindeterminingsubstratespecificity intheubiquitin–proteasomesystem.Hence,E3ligasesexclusively involvedinFAT10conjugationcouldtargetadifferentpoolofpro- teinsfordegradationandtherebyalterthepeptidespresentedon MHC-I.However,sofar,noE3ligasesintheFAT10conjugation machineryhavebeenidentified.ToinvestigatewhetherFAT10E3 ligases,comparedtoubiquitin,targetdifferentproteins,thedis- coveryof E3ligases intheFAT10 conjugationprocessis highly warranted.DockingofFAT10tothe26S proteasomeoccursvia theVWAdomainofRpn10(S5a)whilepoly-ubiquitinbindstothe ubiquitin-interactionmotifsofRpn10aswellasthesubunitRpn13 (Ranietal.,2012;Ebsteinetal.,2012).Thismightresultinadif- ferentialprocessingofFAT10ascomparedtoubiquitin-conjugated proteinsbythe26Sproteasome.Furthermore,FAT10mighttarget short-livedproteinsfordegradation,andtherebybeinvolved in thepresentationofdefectiveribosomal products(DRIPs). Taken together,it seemsthattheFAT10-conjugationmachinerymight representa complementarypathwaywhenubiquitinbecomesa rate-limitingfactor.Iftheproteasomeisoverwhelmedorinhibited, bothubiquitinand FAT10accumulatein aggresomes(Kalveram etal., 2008).Additionally, FAT10interacts withtheautophago- somalreceptorp62/SQSTM1(Aichemetal.,2012).Thissuggests thatFAT10mightbeinvolvedinMHCclassIIpresentation.How- ever,furtherexperimentsareneededtoelucidatetheexact role ofFAT10inclassIIpresentation.FAT10-deficientmicehaveapart fromminoralterationsnoobviousphenotype(Canaanetal.,2006, 2014).Nevertheless,FAT10-deficientmicerevealedahighersus- ceptibilityforS.typhimuriumsuggestinga roleforFAT10inthe intracellulardefense againstbacteria(Spinnenhirnetal., 2014).

Hence,furtherinvestigationswithdifferentpathogensarewarr- antedtoclarifythebiologicalroleoftheubiquitin-likemodiﬁer FAT10.

Conﬂictofinterest

Theauthorshavenoﬁnancialconﬂictsofinterest.

Acknowledgments

ThisworkwasfundedbytheGermanResearchFoundationgrant Nr.BA4199/2-1toM.B.and GR1517/2.4 and GR1517/10-2to M.G.

References

Aichem,A.,Pelzer,C.,Lukasiak,S.,Kalveram,B.,Sheppard,P.W.,Rani,N.,Schmidtke, G.,Groettrup,M.,2010.USE1isabispeciﬁcconjugatingenzymeforubiquitin andFAT10,whichFAT10ylatesitselfincis.Nat.Commun.1,13.

Aichem,A.,Kalveram,B.,Spinnenhirn,V.,Kluge,K.,Catone,N.,Johansen,T.,Groet- trup,M.,2012.TheproteomicanalysisofendogenousFAT10substratesidentiﬁes p62/SQSTM1asasubstrateofFAT10ylation.J.CellSci.125,4576–4585.

Basler,M.,Lauer,C.,Beck,U.,Groettrup,M.,2009.Theproteasomeinhibitorborte- zomibenhancesthesusceptibilitytoviralinfection.J.Immunol.183,6145–6150.

Canaan,A.,Yu,X.,Booth,C.J.,Lian,J.,Lazar,I.,Gamﬁ,S.L.,Castille,K.,Kohya,N., Nakayama,Y.,Liu,Y.C.,etal.,2006.FAT10/diubiquitin-likeprotein-deﬁcient miceexhibitminimalphenotypicdifferences.Mol.Cell.Biol.26,5180–5189.

Canaan,A.,DeFuria,J.,Perelman,E.,Schultz,V.,Seay,M.,Tuck,D.,Flavell,R.A.,Snyder, M.P.,Obin,M.S.,Weissman,S.M.,2014.Extendedlifespanandreducedadiposity inmicelackingtheFAT10gene.Proc.Natl.Acad.Sci.U.S.A.111,5313–5318.

Chiu,Y.H.,Sun,Q.,Chen,Z.J.,2007.E1-L2activatesbothubiquitinandFAT10.Mol.

Cell27,1014–1023.

Cort,L.,Habib,M.,Eberwine,R.A.,Hessner,M.J.,Mordes,J.P.,Blankenhorn,E.P., 2014.Diubiquitin(Ubd)isasusceptibilitygeneforvirus-triggeredautoimmune diabetesinrats.GenesImmun.15,168–175.

Cox,J.H.,Galardy,P.,Bennink,J.R.,Yewdell,J.W.,1995.Presentationofendogenous andexogenousantigensisnotaffectedbyinactivationofE1ubiquitin-activating enzymeintemperature-sensitivecelllines.J.Immunol.154,511–519.

Ebstein,F.,Lehmann,A.,Kloetzel,P.M.,2012.TheFAT10-andubiquitin-dependent degradationmachineriesexhibitcommonanddistinctrequirementsforMHC classIantigenpresentation.Cell.Mol.LifeSci.69,2443–2454.

Fiebiger,B.M.,Pﬁster,H.,Behrends,U.,Mautner,J.,2015.Polyubiquitinationof lysine-48isanessentialbutindirectsignalforMHCclassIantigenprocessing.

Eur.J.Immunol.45,716–727.

French,S.W.,French,B.A.,Oliva,J.,Li,J.,Bardag-Gorce,F.,Tillman,B.,Canaan,A., 2012.FAT10knockoutmiceliversfailtodevelopMallory–Denkbodiesinthe DDCmousemodel.Exp.Mol.Pathol.93,309–314.

Hipp,M.S.,Raasi,S.,Groettrup,M.,Schmidtke,G.,2004.NEDD8ultimatebuster-1L interactswiththeubiquitin-likeproteinFAT10andacceleratesitsdegradation.

J.Biol.Chem.279,16503–16510.

Hipp,M.S.,Kalveram,B.,Raasi,S.,Groettrup,M.,Schmidtke,G.,2005.FAT10,a ubiquitin-independentsignalforproteasomaldegradation.Mol.Cell.Biol.25, 3483–3491.

Huang,L.,Marvin,J.M.,Tatsis,N.,Eisenlohr,L.C.,2011.Cuttingedge:selectiverole ofubiquitininMHCclassIantigenpresentation.J.Immunol.186,1904–1908.

Kalveram,B.,Schmidtke,G.,Groettrup,M.,2008.Theubiquitin-likemodiﬁerFAT10 interactswithHDAC6andlocalizestoaggresomesunderproteasomeinhibition.

J.CellSci.121,4079–4088.

Lukasiak,S.,Schiller,C.,Oehlschlaeger,P.,Schmidtke,G.,Krause,P.,Legler,D.F., Autschbach,F.,Schirmacher,P.,Breuhahn,K.,Groettrup,M.,2008.Proinﬂam- matorycytokinescauseFAT10upregulationincancers ofliverandcolon.

Oncogene27,6068–6074.

Michalek,M.T.,Grant,E.P.,Gramm,C.,Goldberg,A.L.,Rock,K.L.,1993.Arolefor theubiquitin-dependentproteolyticpathwayinMHCclassI-restrictedantigen presentation.Nature363,552–554.

Munz,C.,2012.AntigenprocessingforMHCclassIIpresentationviaautophagy.

Front.Immunol.3,9.

Pelzer,C.,Groettrup,M.,2010.FAT10:activatedbyUBA6andfunctioninginprotein degradation.Subcell.Biochem.54,238–246.

Pierre,P.,2005.Dendriticcells,DRiPs,andDALISinthecontrolofantigenprocessing.

Immunol.Rev.207,184–190.

Raasi,S.,Schmidtke,G.,Groettrup,M.,2001.Theubiquitin-likeproteinFAT10forms covalentconjugatesandinducesapoptosis.J.Biol.Chem.276,35334–35343.

Rani,N.,Aichem,A.,Schmidtke,G.,Kreft,S.G.,Groettrup,M.,2012.FAT10andNUB1L bindtotheVWAdomainofRpn10andRpn1toenableproteasome-mediated proteolysis.Nat.Commun.3,749.

Schliehe,C.,Bitzer,A.,vandenBroek,M.,Groettrup,M.,2012.Stableantigenismost effectiveforelicitingCD8+T-cellresponsesafterDNAvaccinationandinfection withrecombinantvacciniavirusinvivo.J.Virol.86,9782–9793.

Schmidtke,G.,Kalveram,B.,Groettrup,M.,2009.DegradationofFAT10bythe26S proteasomeisindependentofubiquitylationbutreliesonNUB1L.FEBSLett.583, 591–594.

Schmidtke,G.,Aichem,A.,Groettrup,M.,2014.FAT10ylationasasignalforprotea- somaldegradation.Biochim.Biophys.Acta1843,97–102.

Spinnenhirn,V.,Farhan,H.,Basler,M.,Aichem,A.,Canaan,A.,Groettrup,M.,2014.

Theubiquitin-likemodiﬁerFAT10decoratesautophagy-targetedSalmonella andcontributestoSalmonellaresistanceinmice.J.CellSci.127,4883–4893.