E47 phosphorylation by p38 MAPK promotes MyoD/E47 association and muscle-specific gene transcription

Abstract

Selective recognition of the E-box sequences on muscle gene promoters by heterodimers of myogenic basic helixloop-helix (bHLH) transcription factors, such as MyoD, with the ubiquitous bHLH proteins E12 and E47 is a key event in skeletal myogenesis. However, homodimers of MyoD or E47 are unable of binding to and activating muscle chromatin targets, suggesting that formation of functional MyoD/E47 heterodimers is pivotal in controlling muscle transcription. Here we show that p38 MAPK, whose activity is essential for myogenesis, regulates MyoD/E47 heterodimerization. Phosphorylation of E47 at Ser140 by p38 induces MyoD/E47 association and activation of muscle-specific transcription, while the nonphosphorylatable E47 mutant Ser140Ala fails to heterodimerize with MyoD and displays impaired myogenic potential. Moreover, inhibition of p38 activity in myocytes precludes E47 phosphorylation at Ser140, which results in reduced MyoD/E47 heterodimerization and inefficient muscle differentiation, as a consequence of the impaired binding of the transcription factors to the E regulatory regions of muscle genes. These findings identify a novel pro-myogenic role of p38 in regulating the formation of functional MyoD/E47 heterodimers that are essential for myogenesis. The EMBO Journal (2005) 24, 974-984.

E2A protein degradation by the ubiquitin-proteasome system is stage-dependent during muscle differentiation

“…MAP kinase-induced MyoD and E47 heterodimerization and muscle-specific gene transcription (Lluis et al, 2005). However, the evaluation of E47S133AHA stability revealed no correlation between Ser133 phosphorylation and E47 degradation.…”

“…This suggests that the E2A proteins may be relatively spared whereas forming active transcriptional complexes with muscle regulatory factors during the initiation and maintenance of muscle differentiation. Previous electrophoresis mobility shift analyses have shown that E2A/MyoD/Ebox-DNA complexes only form after the initiation of muscle differentiation (Lluis et al, 2005). In proliferating myoblasts, rapid turnover of the E2A proteins may prevent the cells from the commitment for differentiation.…”

“…Furthermore, assessment of the turnover of E47 phosphorylation site mutants also failed to provide any link between E47 phosphorylation and degradation (Figure 6b). Thus, in muscle cells, E2A protein phosphorylation may not relate to its degradation by the ubiquitin system, but likely relates to other aspects of function such as protein complex formation, as E47 phosphorylation by p38 MAP kinase promotes MyoD/E47 association and E2A protein degradation in muscle differentiation L Sun et al muscle-specific gene transcription (Lluis et al, 2005). It may be important to note here that whereas in muscle cells, MyoD/E47 heterodimer is the active transcription regulator that binds DNA, E47 forms DNA-binding homodimers in B cells.…”

Mixed Lineage Kinase Phosphorylates Transcription Factor E47 and Inhibits TrkB Expression to Link Neuronal Death and Survival Pathways

“…Previous work has demonstrated that p38 MAPK activates muscle-specific gene transcription. Phosphorylation of E47 at Ser 140 by p38 MAPK enhances MyoD/E47 heterodimerization and subsequent binding to E-box sequences (12). Other results may suggest that p38 MAPK could exert a negative effect by phosphorylating other residues in the N terminus of E47 (13).…”

“…It has been reported that phosphorylation status of E47 alters the DNA binding ability of E47 as homodimers or heterodimers in different cellular contexts (9 -11). Thus, p38 MAPK has been described to phosphorylate E47 at Ser 140 and promote MyoD/E47 association and muscle-specific gene transcription (12). On the other hand, it has also been observed that MEKK1 (MAPK/ERK kinase kinase 1) signaling through p38 leads to transcriptional inactivation of E47 (13).…”