title: p38alpha antagonizes p38gamma activity through c-Jun-dependent ubiquitin-proteasome pathways in regulating Ras transformation and stress response.
abstract: p38 MAPK family consists of four isoform proteins (alpha, beta, gamma, and delta) that are activated by the same stimuli, but the information about how these proteins act together to yield a biological response is missing. Here we show a feed-forward mechanism by which p38alpha may regulate Ras transformation and stress response through depleting its family member p38gamma protein via c-Jun-dependent ubiquitin-proteasome pathways. Analyses of MAPK kinase 6 (MKK6)-p38 fusion proteins showed that constitutively active p38alpha (MKK6-p38alpha) and p38gamma (MKK6-p38gamma) stimulates and inhibits c-Jun phosphorylation respectively, leading to a distinct AP-1 regulation. Depending on cell type and/or stimuli, p38alpha phosphorylation results in either Ras-transformation inhibition or a cell-death escalation that invariably couples with a decrease in p38gamma protein expression. p38gamma, on the other hand, increases Ras-dependent growth or inhibits stress induced cell-death independent of phosphorylation. In cells expressing both proteins, p38alpha phosphorylation decreases p38gamma protein expression, whereas its inhibition increases cellular p38gamma concentrations, indicating an active role of p38alpha phosphorylation in negatively regulating p38gamma protein expression. Mechanistic analyses show that p38alpha requires c-Jun activation to deplete p38gamma proteins by ubiquitin-proteasome pathways. These results suggest that p38alpha may, upon phosphorylation, act as a gatekeeper of the p38 MAPK family to yield a coordinative biological response through disrupting its antagonistic p38gamma family protein.
authors.affiliation: Department of Pharmacology and Toxicology, Zablocki Department of Veterans Affairs Medical Center, Wisconsin 53226, USA.
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Qi
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Pohl
authors.forename: Mathew
authors.initials: M
authors.lastname: Loesch
authors.forename: Songwang
authors.initials: S
authors.lastname: Hou
authors.forename: Rongshan
authors.initials: R
authors.lastname: Li
authors.forename: Jian-Zhong
authors.initials: JZ
authors.lastname: Qin
authors.forename: Ana
authors.initials: A
authors.lastname: Cuenda
authors.forename: Guan
authors.initials: G
authors.lastname: Chen
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004622:Embryo, Mammalian; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D016758:Genes, jun; D011905:Genes, ras; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000166:cytology; D051379:Mice; D048291:Mitogen-Activated Protein Kinase 12 / Q000037:antagonists & inhibitors*; D048308:Mitogen-Activated Protein Kinase 14 / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D013312:Stress, Physiological; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; D025801:Ubiquitin; D048291:Mitogen-Activated Protein Kinase 12; D048308:Mitogen-Activated Protein Kinase 14; D046988:Proteasome Endopeptidase Complex