Journal Article

p38alpha MAPK disables KMT1A-mediated repression of myogenic differentiation program

Jothi, Mathivanan, Wolff, David W, Chatterjee, Biswanath, Mal, Munmun, Mal, Asoke K

2016

Overview

Master transcription factor MyoD can initiate the entire myogenic gene expression program which differentiates proliferating myoblasts into multinucleated myotubes. We previously demonstrated that histone methyltransferase KMT1A associates with and inhibits MyoD in proliferating myoblasts, and must be removed to allow differentiation to proceed. It is known that pro-myogenic signaling pathways such as PI3K/AKT and p38[alpha] MAPK play critical roles in enforcing associations between MyoD and transcriptional activators, while removing repressors. However, the mechanism which displaces KMT1A from MyoD, and the signals responsible, remain unknown. To investigate the role of p38[alpha] on MyoD-mediated differentiation, we utilized C2C12 myoblast cells as an in vitro model. p38[alpha] activity was either augmented via overexpression of a constitutively active upstream kinase or blocked via lentiviral delivery of a specific p38[alpha] shRNA or treatment with p38[alpha]/[beta] inhibitor SB203580. Overexpression of KMT1A in these cells via lentiviral delivery was also used as a system wherein terminal differentiation is impeded by high levels of KMT1A. The association of KMT1A and MyoD persisted, and differentiation was blocked in C2C12 myoblasts specifically after pharmacologic or genetic blockade of p38[alpha]. Conversely, forced activation of p38[alpha] was sufficient to activate MyoD and overcome the differentiation blockade in KMT1A-overexpressing C2C12 cells. Consistent with this finding, KMT1A phosphorylation during C2C12 differentiation correlated strongly with the activation of p38[alpha]. This phosphorylation was prevented by the inhibition of p38[alpha]. Biochemical studies further revealed that KMT1A can be a direct substrate for p38[alpha]. Importantly, chromatin immunoprecipitation (ChIP) studies show that the removal of KMT1A-mediated transcription repressive histone tri-methylation (H3K9me3) from the promoter of the Myogenin gene, a critical regulator of muscle differentiation, is dependent on p38[alpha] activity in C2C12 cells. Elevated p38[alpha] activity was also sufficient to remove this repressive H3K9me3 mark. Moreover, ChIP studies from C2C12 cells show that p38[alpha] activity is necessary and sufficient to establish active H3K9 acetylation on the Myogenin promoter. Activation of p38[alpha] displaces KMT1A from MyoD to initiate myogenic gene expression upon induction of myoblasts differentiation.

• Publisher: BioMed Central Ltd
• Subject: Gene expression / Genetic transcription / Methyltransferases