PC4 Coactivates MyoD by Relieving the Histone Deacetylase 4-Mediated Inhibition of Myocyte Enhancer Factor 2C

Abstract

Histone deacetylase 4 (HDAC4) negatively regulates skeletal myogenesis by associating with the myocyte enhancer factor 2 (MEF2) transcription factors. Our data indicate that the gene PC4 (interferon-related developmental regulator 1 [IFRD1], Tis7), which we have previously shown to be required for myoblast differentiation, is both induced by MyoD and potentiates the transcriptional activity of MyoD, thus revealing a positive regulatory loop between these molecules. Enhancement by PC4 of MyoD-dependent activation of muscle gene promoters occurs selectively through MEF2 binding sites. Furthermore, PC4 localizes in the nucleus of differentiating myoblasts, associates with MEF2C, and is able to counteract the HDAC4-mediated inhibition of MEF2C. This latter action can be explained by the observed ability of PC4 to dose dependently displace HDAC4 from MEF2C. Consistently, we have observed that (i) the region of PC4 that binds MEF2C is sufficient to counteract the inhibition by HDAC4; (ii) PC4, although able to bind HDAC4, does not inhibit the enzymatic activity of HDAC4; and (iii) PC4 overcomes the inhibition mediated by the amino-terminal domain of HDAC4, which associates with MEF2C but not with PC4. Together, our findings strongly suggest that PC4 acts as a coactivator of MyoD and MEF2C by removing the inhibitory effect of HDAC4, thus exerting a pivotal function during myogenesis.

ACKNOWLEDGMENTS

We are grateful to Guriqbal Basi for the gift of the rat EMBL-3 genomic library, to Stefano Lorenzetti for the construction of pcDNA3-HA-MEF2C, to Giuseppina Corrente for experiments regarding PC4 pull-down performed when she was undergraduate student, to Fabio Cavaliere for the production of constructs carrying PC4, and to the numerous colleagues who kindly provided reagents. We are indebted to Livio Baron for excellent technical assistance. F.T. gratefully remembers the late Franco Tatò for the encouragement he provided while this study was in progress.

This research was supported by Telethon (project A46), by Progetto Finalizzato CNR Terapia Preclinica Molecolare in Oncologia, by European Community Grant QLG3-CT-2000-00072, and by the Donazione Maria Bianchi, which was made possible thanks to Roberto Salmoiraghi, mayor of Campione d'Italia.