title: MM-1 facilitates degradation of c-Myc by recruiting proteasome and a novel ubiquitin E3 ligase.
abstract: We have reported that a novel c-Myc-binding protein, MM-1, repressed the E-box-dependent transcription activity of c-Myc by recruiting the HDAC1 complex via TIF1beta/KAP1, a transcriptional corepressor. We have also reported that a mutation of A157R in MM-1, which is often observed in patients with leukemia or lymphoma, abrogated all of the repressive activities of MM-1 toward c-Myc, indicating that MM-1 is a novel tumor suppressor. In this study, we found that MM-1 was bound to a component of proteasome and stimulated degradation of c-Myc in human cells. Knockdown of endogenous MM-1 in human HeLa cells by introduction of siRNA against MM-1 stabilized the endogenous c-Myc. To identify proteins that participate in c-Myc degradation by MM-1, in vivo and in vitro binding assays were carried out. The results showed that MM-1 directly bound to Rpt3, a subunit of 26S proteasome, and that c-Myc directly bound to Skp2, which recruited ElonginC, ElonginB and Cullin2, thereby forming a novel ubiquitin E3 ligase. Knockdown of endogenous Cullin2 stabilized the endogenous c-Myc. Thus, MM-1 is a factor that connects c-Myc to the ubiquitin E3 ligase and the proteasome.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Kimura
authors.forename: Arisa
authors.initials: A
authors.lastname: Nagao
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fujioka
authors.forename: Akiko
authors.initials: A
authors.lastname: Satou
authors.forename: Takahiro
authors.initials: T
authors.lastname: Taira
authors.forename: Sanae M M
authors.initials: SM
authors.lastname: Iguchi-Ariga
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Ariga
mesh_terms: D044842:Cullin Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000075065:Elongin; D006367:HeLa Cells; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*