title: MafB protein stability is regulated by the JNK and ubiquitin-proteasome pathways.
abstract: MafB is a basic leucine zipper transcription factor that plays important roles in development and differentiation processes. During osteoclastogenesis, its expression is downregulated at the transcriptional level via the JNK and p38 MAP kinase pathways. In the present study, we demonstrated that MafB protein stability is regulated by JNK and identified a phosphorylation site, Thr62. The expression of a constitutively active form of JNK (a fusion protein MKK7alpha1-JNK1beta1) promoted the degradation of MafB in COS7 cells, and a T62A substitution significantly reduced the instability of MafB. The introduction of a fourfold (T58A/T62A/S70A/S74A) substitution in an acidic transcription-activating domain almost protected the instability resulting from the activation of JNK. Furthermore, treatment with proteasome inhibitors increased the MafB level, and a high-molecular-weight smear, characteristic of polyubiquitination, was observed in lysates from cells in which MafB, ubiquitin, and MKK7alpha1-JNK1beta1 were co-expressed. These results suggest that phosphorylation of MafB by JNK confers susceptibility to proteasomal degradation.
authors.affiliation: Department of Neuroplasticity, Research Institute on Aging and Adaptation, Shinshu University Graduate School of Medicine, 3-1-1 Asahi, Matsumoto, Japan. tanahasi@shinshu-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tanahashi
authors.forename: Keiji
authors.initials: K
authors.lastname: Kito
authors.forename: Takashi
authors.initials: T
authors.lastname: Ito
authors.forename: Katsuji
authors.initials: K
authors.lastname: Yoshioka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D006801:Humans; D047468:Immunoprecipitation; D048670:MAP Kinase Kinase 4 / Q000378:metabolism*; D051258:MafB Transcription Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: C490407:MAFB protein, human; D051258:MafB Transcription Factor; D011994:Recombinant Proteins; D025801:Ubiquitin; D048670:MAP Kinase Kinase 4; D046988:Proteasome Endopeptidase Complex