Ubiquitin-dependent Degradation And Stability Of GASZ Protein And Underlying Mechanism

GASZ is a germ cell specific protein,which contains four Ankyrin repeats(ANK),a Sterile alpha motif(SAM),and a basic leucine Zipper(bZIP).GASZ is largely localized at the outer membrane of mitochondria via its C-terminal mitochondrial localization signal(MLS).In addition,GASZ participates in the formation of inter-mitochondrial cement(IMC,a specific type of nuage in germ cells)with PIWI family members(including MIWI,MIWI2 and MILI in mice)for piRNA biosynthesis,TDRD1,TDRD2,and MVH/VASA.Our previous studies showed that GASZ promoted the formation of primordial germ cells(PGCs)from both human and murine embryonic stem cells(ESCs).Loss of function of GASZ or its dislocation from mitochondria lead to disrupted formation of nuage,defective piRNA biosynthesis,upregulated transposon expression,blocked development of spermatocytes,and male infertility.Therefore,it is important to understand how the stability of GASZ is regulated during spermatogenesis.In this study,we explored the molecular mechanisms that degradation of GASZ protein was associated with its self-interaction and mitochondrial localization.We found that the region between SAM and bZIP domain was essential for both self-interaction and maintaining stability of GASZ.In addition,dislocation from mitochondria decreased the stability of GASZ as well,and thereby suggesting that the MLS was also important for regulating its stability.Finally,we identified two lysines in bZIP domain of GASZ,which were essential for the protein degradation of GASZ.