%0 Journal Article
%T p38¦Â MAPK upregulates atrogin1/MAFbx by specific phosphorylation of C/EBP¦Â
%A Zhang Guohua
%A Li Yi-Ping
%J Skeletal Muscle
%D 2012
%I BioMed Central
%R 10.1186/2044-5040-2-20
%X Background The p38 mitogen-activated protein kinases (MAPK) family plays pivotal roles in skeletal muscle metabolism. Recent evidence revealed that p38¦Á and p38¦Â exert paradoxical effects on muscle protein homeostasis. However, it is unknown why p38¦Â, but not p38¦Á, is capable of mediating muscle catabolism via selective activation of the C/EBP¦Â that upregulates atrogin1/MAFbx. Methods Tryptic phosphopeptide mapping was carried out to identify p38¦Á- and p38¦Â-mediated phosphorylation sites in C/EBP¦Â. Chromosome immunoprecipitation (ChIP) assay was used to evaluate p38¦Á and p38¦Â effect on C/EBP¦Â binding to the atrogin1/MAFbx promoter. Overexpression or siRNA-mediated gene knockdown of p38¦Á and p38¦Â, and site-directed mutagenesis or knockout of C/EBP¦Â, were used to analyze the roles of these kinases in muscle catabolism in C2C12 myotubes and mice. Results Cellular expression of constitutively active p38¦Á or p38¦Â resulted in phosphorylation of C/EBP¦Â at multiple serine and threonine residues; however, only p38¦Â phosphorylated Thr-188, which had been known to be critical to the DNA-binding activity of C/EBP¦Â. Only p38¦Â, but not p38¦Á, activated C/EBP¦Â-binding to the atrogin1/MAFbx promoter. A C/EBP¦Â mutant in which Thr-188 was replaced by alanine acted as a dominant-negative inhibitor of atrogin1/MAFbx upregulation induced by either p38¦Â or Lewis lung carcinoma (LLC) cell-conditioned medium (LCM). In addition, knockdown of p38¦Â specifically inhibited C/EBP¦Â activation and atrogin1/MAFbx upregulation induced by LCM. Finally, expression of active p38¦Â in mouse tibialis anterior specifically induced C/EBP¦Â phosphorylation at Thr-188, atrogin1/MAFbx upregulation and muscle mass loss, which were blocked in C/EBP¦Â-null mice. Conclusions The ¦Á and ¦Â isoforms of p38 MAPK are capable of recognizing distinct phosphorylation sites in a substrate. The unique capacity of p38¦Â in mediating muscle catabolism is due to its capability in phosphorylating Thr-188 of C/EBP¦Â.
%K Cachexia
%K E3 protein
%K Gene regulation
%K DNA-binding
%K Thr-188
%U http://www.skeletalmusclejournal.com/content/2/1/18