p38 Antagonizes p38 Activity through c-Jun-dependent Ubiquitin-proteasome Pathways in Regulating Ras Transformation and Stress Response

University of Dundee, Dundee, Scotland, United Kingdom
Journal of Biological Chemistry (Impact Factor: 4.57). 11/2007; 282(43):31398-408. DOI: 10.1074/jbc.M703857200
Source: PubMed


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.

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    • "Few reports addressed the p38γ and p38δ isoforms. Recent studies indicated that the Ras oncogene positively regulated the expression of p38γ, which increases Ras-dependent growth or inhibits stress induced cell-death independent of phosphorylation26. This role that p38 played may be achieve by up-regulation of ERK (extracellular signal-regulated kinase) expression or banding with PTPH1 (Protein-tyrosine phosphatase H1)1327. "
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