Poly(ADP-ribose) Polymerase 1 (PARP1) restrains MyoD-dependent gene expression during muscle differentiation

The myogenic factor MyoD regulates skeletal muscle differentiation by interacting with a variety of chromatin-modifying complexes. Although MyoD can induce and maintain chromatin accessibility at its target genes, its binding and trans-activation ability can be limited by some types of not fully characterized epigenetic constraints. In this work we analysed the role of PARP1 in regulating MyoD-dependent gene expression. PARP1 is a chromatin-associated enzyme, playing a well recognized role in DNA repair and that is implicated in transcriptional regulation. PARP1 affects gene expression through multiple mechanisms, often involving the Poly(ADP-ribosyl)ation of chromatin proteins. In line with PARP1 down-regulation during differentiation, we observed that PARP1 depletion boosts the up-regulation of MyoD targets, such as p57, myogenin, Mef2C and p21, while its re-expression reverts this effect. We also found that PARP1 interacts with some MyoD-binding regions and that its presence, independently of the enzymatic activity, interferes with MyoD recruitment and gene induction. We finally suggest a relationship between the binding of PARP1 and the loss of the activating histone modification H3K4me3 at MyoD-binding regions. This work highlights not only a novel player in the epigenetic control of myogenesis, but also a repressive and catalytic-independent mechanisms by which PARP1 regulates transcription.