SensingSelfandForeignCircularRNAsbyIntronIdentityY.GraceChen1,MyoungjooV.Kim2,XingqiChen1,PedroJ.Batista1,SaekoAoyama2,JeremyE.Wilusz3,AkikoIwasaki2,andHowardY.Chang1,4,*1CenterforPersonalDynamicRegulomesandPrograminEpithelialBiology,StanfordUniversitySchoolofMedicine,Stanford,CA94305,USA2DepartmentofImmunobiology,HowardHughesMedicalInstitute,YaleSchoolofMedicine,NewHaven,CT06519,USA3DepartmentofBiochemistryandBiophysics,UniversityofPennsylvania,PerelmanSchoolofMedicine,Philadelphia,PA19104,USASUMMARYCircularRNAs(circRNAs)aresingle-strandedRNAsthatarejoinedheadtotailwithlargelyunknownfunctions.HereweshowthattransfectionofpurifiedinvitrogeneratedcircRNAintomammaliancellsledtopotentinductionofinnateimmunitygenesandconfersprotectionagainstviralinfection.ThenucleicacidsensorRIG-IisnecessarytosenseforeigncircRNA,andRIG-IandforeigncircRNAco-aggregateincytoplasmicfoci.CircRNAactivationofinnateimmunityisindependentofa5′triphosphate,double-strandedRNAstructure,ortheprimarysequenceoftheforeigncircRNA.Instead,self-nonselfdiscriminationdependsontheintronthatprogramsthecircRNA.UseofahumanintrontoexpressaforeigncircRNAsequenceabrogatesimmuneactivation,andmaturehumancircRNAisassociatedwithdiverseRNAbindingproteinsreflectingitsendogenoussplicingandbiogenesis.TheseresultsrevealinnateimmunesensingofcircRNAandhighlightintrons—thepredominantoutputofmammaliantranscription—asarbitersofself-nonselfidentity.InBrief*Correspondence:howchang@stanford.edu.4LeadContactSUPPLEMENTALINFORMATIONSupplementalInformationincludessixfiguresandthreetablesandcanbefoundwiththisarticleonlineathttp://dx.doi.org/10.1016/j.molcel.2017.05.022.AUTHORCONTRIBUTIONSConceptualization:Y.G.C.andH.Y.C.;Methodology:Y.G.C.andH.Y.C.;Investigation:Y.G.C.(allexceptforwithHEK293TandMEFs),M.V.K.,S.A.,andA.I.(293TandMEFs),X.C.(microscopy),andJ.E.W.(ChIRP-MSdesign);Analysis:Y.G.C.(allexceptforRNA-seqdata)andP.J.B.(RNA-seqdata);Resources:J.E.W.(ZKSCAN1andlaccase2plasmids);Writing:Y.G.C.andH.Y.C.HHSPublicAccessAuthormanuscr...
