title: CRMP5-associated GTPase (CRAG) protein protects neuronal cells against cytotoxicity of expanded polyglutamine protein partially via c-Fos-dependent activator protein-1 activation.
abstract: We previously demonstrated that CRAM (CRMP5)-associated GTPase (CRAG), a short splicing variant of centaurin-γ3/AGAP3, facilitated degradation of expanded polyglutamine protein (polyQ) via the nuclear ubiquitin-proteasome pathway. Taking advantage of this feature, we also showed that lentivirus-mediated CRAG expression in the Purkinje cells of mice expressing polyQ resulted in clearance of the polyQ aggregates and rescue from ataxia. However, the molecular basis of the function of CRAG in cell survival against polyQ remains unclear. Here we report that CRAG, but not centaurin-γ3, induces transcriptional activation of c-Fos-dependent activator protein-1 (AP-1) via serum response factor (SRF). Mutation analysis indicated that the nuclear localization signal and both the N- and C-terminal regions of CRAG are critical for SRF-dependent c-Fos activation. CRAG knockdown by siRNA or expression of a dominant negative mutant of CRAG significantly attenuated the c-Fos activation triggered by either polyQ or the proteasome inhibitor MG132. Importantly, c-Fos expression partially rescued the enhanced cytotoxicity of CRAG knockdown in polyQ-expressing or MG132-treated cells. Finally, we suggest the possible involvement of CRAG in the sulfiredoxin-mediated antioxidant pathway via AP-1. Taken together, these results demonstrated that CRAG enhances the cell survival signal against the accumulation of unfolded proteins, including polyQ, through not only proteasome activation, but also the activation of c-Fos-dependent AP-1.
authors.affiliation: Laboratory of Molecular Biochemistry, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, USA.
authors.forename: Shun
authors.initials: S
authors.lastname: Nagashima
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Fukuda
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kubota
authors.forename: Ayumu
authors.initials: A
authors.lastname: Sugiura
authors.forename: Mitsuyoshi
authors.initials: M
authors.lastname: Nakao
authors.forename: Ryoko
authors.initials: R
authors.lastname: Inatome
authors.forename: Shigeru
authors.initials: S
authors.lastname: Yanagi
mesh_terms: D000818:Animals; D001259:Ataxia / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D004789:Enzyme Activation / Q000235:genetics; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000235:genetics; D055785:Gene Knockdown Techniques; D051379:Mice; D009154:Mutation; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D011689:Purkinje Cells / Q000378:metabolism* / Q000473:pathology; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D010455:Peptides; D016760:Proto-Oncogene Proteins c-fos; D026362:Serum Response Factor; D018808:Transcription Factor AP-1; C097188:polyglutamine; D050862:Oxidoreductases Acting on Sulfur Group Donors; C529381:sulfiredoxin protein, mouse; D046988:Proteasome Endopeptidase Complex; C530558:CRAG protein, mouse; D020558:GTP Phosphohydrolases