Role of Caspase 3/Caspase Activated DNase induced DNA Strand Breaks during Skeletal Muscle Differentiation.

Abstract

Cell fate decisions incorporate distinct and overlapping mechanisms. The activity of caspase 3 was initially understood to be a cell death restricted event, however numerous studies have implicated this enzyme in the regulation of both differentiation and proliferation. How the activity of caspase 3 promotes a non-death cell fate remains unclear. Here we examine the role caspase 3 activity plays during skeletal muscle differentiation; in particular we explore the hypothesis that the mechanism of inducing DNA strand breaks during cell death is also a key feature of differentiation, albeit with a distinctly different outcome. We delineate the transient formation of Caspase 3/Caspase activated DNase (CAD) dependent DNA strand breaks during differentiation. The formation of these breaks is essential for differentiation and the regulation of specific genes. In particular expression of the cell cycle inhibitor p21 is related to the formation of a DNA strand break within the gene’s promoter element. Further, we explored the genome wide association of CAD using Chromatin Immunoprecipitation coupled to high through put sequencing (ChIP-seq). This approach identified a potential role for Caspase3/CAD in regulating the expression of Pax7. Here, a CAD directed DNA strand break in the Pax7 gene is correlated with decreased Pax7 expression, an outcome that has been shown to be critical for progress of the myogenic differentiation program. The regulation of Pax7 expression through a CAD induced DNA strand break raises an intriguing connection between this regulation and oncogenic transformation observed in alveolar rhabdomyosarcoma. The putative site of CAD induced DNA strand breaks that promote decreased Pax7 expression during differentiation corresponds to site of chromosomal translocations responsible for Pax7 fusion events in alveolar rhabdomyosarcoma.