Regulation of Pax7 protein levels by caspase-3 and proteasome activity in differentiating myoblasts

Abstract

The transcription factor Pax7 negatively regulates the activity of the muscle regulatory transcription factor MyoD, preventing muscle precursor cells from undergoing terminal differentiation. In this context, the ratio between Pax7 and MyoD protein levels is thought to be critical in allowing myogenesis to proceed or to maintain the undifferentiated muscle precursor state. We have previously shown that Pax7 is subject to rapid down regulation in differentiating myoblasts, via a proteasome-dependent pathway. Here we present evidence indicating that Pax7 is also subject to caspase-3-dependent regulation. Furthermore, simultaneous inhibition of caspase-3 and proteasome activity induced further accumulation of Pax7 protein in differentiating myoblasts. These results suggest that at early stages of muscle differentiation, Pax7 levels are regulated by at least two independent mechanisms involving caspase-3 and proteasome activity.

Protective and Promising Myogenic Effect of Two Thymoquinone Formulations In Relation To the Hamster Buccal Pouch-Induced Carcinogenic Model

“…Alternatively, increased caspase-3 expression may lead to intracellular alterations, in turn activate a differentiation process (28). This effect was clear, in the present results, in early weeks of combined treatment groups, where the evidence of new muscle formation (central nuclei and multinucleated fibers) (49), near the necrotic mass was seen, i.e. dedifferentiation of degenerating cells to regenerate new cells.…”

“…Of interest was the contribution of caspase-3 to differentiation of various cells including muscle cells (49), which was explained as that differentiating myoblasts share a remarkable similarity with many key cellular alterations common for apoptosis (28). The role of caspase-3 was explained by Fernando et.…”

Caspase 3 cleavage of Pax7 inhibits self-renewal of satellite cells

“…Previous observations have suggested Pax7 is subjected to caspase/proteasome-dependent regulation (15). Here, we provide evidence that Pax7 is a direct target of caspase 3 at aspartic acid residues D187 and D208.…”

“…The mechanisms involved in the posttranslational regulation of Pax7 protein stability during myoblast differentiation has only been briefly analyzed (15). However, its close paralogue, Pax3, has been demonstrated to be regulated by ubiquitin-mediated degradation (30).…”

Regulation of Muscle Stem Cell Functions: A Focus on the p38 MAPK Signaling Pathway

“…Pax7 is expressed in quiescent satellite cells and is also critical for their cell cycle progression by regulating genes involved in cell proliferation, while preventing differentiation (Olguin et al, 2007; Soleimani et al, 2012a; von Maltzahn et al, 2013). Pax7-expressing quiescent satellite cells induce the expression of Myf5 and MyoD upon their activation (Mckinnell et al, 2008), thereby allowing successive rounds of cell proliferation (Olguin and Olwin, 2004); instead, downregulation of Pax7 prior to myogenin activation facilitates exit the cell cycle and differentiation entry (Olguin et al, 2007; Olguin, 2011; Bustos et al, 2015). Translational control of MRFs' expression also accounts for the transition through the sequential myogenic stages: (1) In quiescent satellite cells the expression of the Myf5 protein is avoided by sequestration of the Myf5 mRNA in messenger ribonucleoprotein granules and by the action of the microRNA-31, which blocks Myf5 translation (Crist et al, 2012); (2) MyoD protein expression is also prevented in quiescent satellite cells by the action of tristetraprolin (TTP), a protein that promotes the degradation of MyoD RNA (Hausburg et al, 2015); (3) Moreover, a global mechanism of repression of translation, mediated by the phosphorylation of the eukaryotic initiation factor eIF2α at serine 51, preserves the quiescent state of satellite cells, as cells that cannot phosphorylate eIF2α exit quiescence and activate the myogenic program (Zismanov et al, 2016).…”