Abstract

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Differentiation of skeletal myogenic cells into multinucleated myotubes involves several cellular events including survival, migration, and motility. The level of eukaryotic initiation factor 2 (eIF2)-associated glycoprotein p67 gradually increases during the differentiation of C2C12 myoblasts into myotubes. It not only suppresses the rates of global protein synthesis, it inhibits the activation and activity of extracellular signal-regulated kinases 1 and 2 (ERK1/2) when myoblasts are differentiating into myotubes. To explore whether p67 has additional roles in myoblasts’ survival, migration, and motility we examined p67’s effects on expression and activity of p21-activating kinase 1 (Pak1). Because Pak1 not only controls several cellular activities including glucose homeostasis, it is also involved in cytoskeleton dynamics by regulating cell migration and motility. We found that Pak1 level is increased by ~1.5 fold in rat p67-expressing myoblasts and its conserved D251 and H331 residues along with its N-terminal acidic residue-rich domain are involved in this process. On the other hand, the level of Pak1 is ~3.0-fold higher in rat p67-expressing myotubes and its N-terminal acidic residue-rich domain but not the lysine-rich domains 1 & II is involved in this process. P67 is also involved in the increased level of Cdc42 by proteolytic processing of the “pro” form of this protein, which is the upstream activator of Paks. Together, these results suggest that p67 is involved in the upregulated expression and activity of Pak1 in C2C12 myotubes and thus may be involved in the control of cytoskeleton dynamics including survival, migration, and motility of differentiated C2C12 myoblasts.

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