SHP-2 complex formation with the SHP-2 substrate-1 during C2C12 myogenesis

Myogenesis is a highly ordered process that involves the expression of musc le-specific genes, cell-cell recognition and multinucleated myotube formati on. Although protein tyrosine kinases have figured prominently in myogenesi s, the involvement of tyrosine phosphatases in this process is unknown. SHP -2 is an SH2 domain-containing tyrosine phosphatase, which positively regul ates growth and differentiation. We show that in C2C12 myoblasts, SHP-2 bec omes upregulated early on during myogenesis and associates with a 120 kDa t yrosyl-phosphorylated complex. We have identified that the 120 kDa complex consists of the SHP-2 substrate-1 (SHPS-1) and the Grb2-associated binder-1 (Gab-1), SHPS-1, but not Gab-1, undergoes tyrosyl phosphorylation and asso ciation with SHP-2 during myogenesis, the kinetics of which correlate with the expression of MyoD. Either constitutive expression or inducible activat ion of MyoD in 10T1/2 fibroblasts promotes SHPS-1 tyrosyl phosphorylation a nd its association with SHP-2. It has been shown that p38 mitogen-activated protein kinase (MAPK) activity is required for the expression/activation o f MyoD and MyoD-responsive genes. Inhibition of p38 MAPK by SB203580 in dif ferentiating C2C12 myoblasts blocks MyoD expression, SHPS-1 tyrosyl phospho rylation and the association of SHPS-1 with SHP-2. These data suggest that SHPS-1/SHP-2 complex formation is an integral signaling component of skelet al muscle differentiation.