SET-18 Regulates The Unfolded Protein Response Of Mitochondria And Endoplasmic Reticulum In Caenorhabditis Elegans

A large amount of misfolded or unfolded proteins are accumulated in cells,while they are infected by viruses and damaged by oxidative stress.In order to maintain protein homeostasis,the unfolded proteins of cells are cleared by enhancing protein folding,accelerating degradation of unfolded proteins,which process is well-known as unfolded protein response?UPR?.This response mainly occurs in two organelles,mitochondria and endoplasmic reticulum,which are namely asUPR^mt?mitochondrial unfolded protein response?and UPR^ER?endoplasmic reticulum unfolded protein response?,respectively.Evidence shows that UPR^mt and UPR^ER are closely related to aging.During aging,the ability of UPR^mt or UPR^ER decreases.Activation of UPR^mt or UPR^ERis reported to extend lifespan.Caenorhabditis elegans?C.elegans?is one of classic model to study agingcontrol.Previous studies in our laboratory have found that a C.elegans histone H3K36dimethyltransferase SET-18 promotes aging by Insulin/IGF-1 pathway,which is highly conserved to mammals.SET-18 inhibits FOXO transcription factor daf-16a transcription by H3K36me2 modification ondaf-16a promoter,thereby shorten the lifespan of worms.However,which cellular activities are modulated bySET-18 in aging processremains unclear.SET-18 is specifically expressed in muscle,where UPR^mtt and UPR^ER are activated.Moreover,evidence shows that mammalian SET-18 homologous SMYD1 is involved in UPR^ER control.Therefore,it is proposed that SET-18 play roles in regulating UPR^mt and UPR^ER.HSP-6 and HSP-60 are two marker genes that respond to UPR^mt.To explore the role of SET-18 in regulatingUPR^mt,We first constructed two strains that expressing hsp-6::GFPor hsp-60::GFPon set-18?gk334?mutant background by using genetic crossing.The genotypes of these two strains were identified by PCR.Fluorescence microscopy results showed that loss of set-18 did not change the expression levels of HSP-6 and HSP-60.When UPR^mtwas activated by inhibition of cytochrome c oxidase cco-1 byRNAi,the expression levels of HSP-6 and HSP-60 in wild-type N2 worms are similar to those of set-18?gk334?mutants.These suggest that SET-18 has no effect on UPR^mtregulation.HSP-4 is a marker genethatresponds to UPR^ER,which is activated byheat shock and TM?tunicamycin?treatment.Using the worms expressinghsp-4::GFP on set-18?gk334?mutant background,we found that both heat shock and TM treatmentincreased HSP-4 expression level in day 1?the first day of adult worms?N2worms,but not in set-18?gk334?mutant worms.These suggest that loss of set-18changes the response of UPR^ER.To explore whether the effect of SET-18 on UPR^ER is changed in aging process,HSP-4 expression level was examined from the day 3to day 11 of set-18?gk334?mutant worms.Results showed that the response ability of ER stressinduced by TM treatment decreases in wild-type N2 worms during aging.However,HSP-4 expression was failed to activate by TM treatment inset-18?gk334?mutantsfrom day 1,day 3,day 7,to day 11.These indicate that the effect of SET-18 on UPR^ER regulation is not changed in aging process.In addition,we treated set-18?gk334?mutants upondaf-16RNAi,and found that daf-16 RNAi did not changed the effect of set-18 on UPR^ERprocess.These findingssuggest that histone H3K36me2 methyltransferase SET-18 play key roles in regulating UPR^ER,but not UPR^mt.The function of SET-18 in UPR^ERcontrol is not changedduring aging,and independent on DAF-16activity.These laid a foundation for further exploration of cytological mechanism by which histone H3K36me2 modification promotes aging.