Abstract

Skeletal muscle differentiation is well regulated by a series of transcription factors. We reported previously that enhancer of polycomb1 (Epc1), a chromatin protein, can modulate skeletal muscle differentiation, although the mechanisms of this action have yet to be defined. Here we report that Epc1 recruits both serum response factor (SRF) and p300 to induce skeletal muscle differentiation. Epc1 interacted physically with SRF. Transfection of Epc1 to myoblast cells potentiated the SRF-induced expression of skeletal muscle-specific genes as well as multinucleation. Proximal CArG box in the skeletal alpha-actin promoter was responsible for the synergistic activation of the promoter-luciferase. Epc1 knockdown caused a decrease in the acetylation of histones associated with serum response element (SRE) of the skeletal alpha-actin promoter. The Epc1.SRF complex bound to the SRE, and the knockdown of Epc1 resulted in a decrease in SRF binding to the skeletal alpha-actin promoter. Epc1 recruited histone acetyltransferase activity, which was potentiated by cotransfection with p300 but abolished by si-p300. Epc1 directly bound to p300 in myoblast cells. Epc1+/- mice showed distortion of skeletal alpha-actin, and the isolated myoblasts from the mice had impaired muscle differentiation. These results suggest that Epc1 is required for skeletal muscle differentiation by recruiting both SRF and p300 to the SRE of muscle-specific gene promoters.

Highlights

  • 2007-313-E00126. □S The on-line version of this article contains supplemental Figs

  • We observed that enhancer of polycomb1 (Epc1) is involved in skeletal muscle differentiation, which raised the possibility that Epc1 may interact with other muscle-specific transcription factors to regulate differentiation

  • We have shown here that Epc1 interacts with Serum response factor (SRF), a key regulator of diverse muscle differentiation and cell survival [1, 25]

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Summary

EXPERIMENTAL PROCEDURES

Plasmid Constructs—pCMV-myc-mouse Epc was described previously. pCMX-p300 was kindly provided by Prof. Error bars represent S.E. Epc and SRF synergistically induced the expression of myogenin (Fig. 2, B and D), a critical determinant of skeletal muscle differentiation and myotube formation [15]. We studied whether Epc potentiates the SRF-mediated expression of the muscle-specific structural genes as well as transcription factors in C2C12 myoblast cells after transient transfection of pCGN-HA-SRF or pCMV-myc-Epc. We studied whether Epc potentiates the SRF-mediated expression of the muscle-specific structural genes as well as transcription factors in C2C12 myoblast cells after transient transfection of pCGN-HA-SRF or pCMV-myc-Epc1 The expression level of skeletal ␣-actin, a primary component of skeletal muscle thin filament [16], was increased by transfection of SRF, which was further potentiated by cotransfection of Epc. Myogenin expression was increased by transfection of both genes (Fig. 3, A and B)

RESULTS
DISCUSSION
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