Phosphorylation of integrin in differentiating ts-Rous sarcoma virus-infected myogenic cells.

The differentiation of primary myogenic cultures requires the attachment of the cells to an extracellular matrix substrate using an integrin family receptor. These integrin receptors can be phosphorylated on both their alpha and beta chains, and it has been postulated that phosphorylation regulates the receptor function. Quail myogenic clones transformed with ts-LA24A differentiated into mature myotubes following a temperature shift to nonpermissive temperature which inactivates the viral src kinas. Phosphorylation of integrin beta-1 chain and of at least one alpha chain was detected on both serine and tyrosine. An additional alpha chain(s) with a mobility similar to alpha 5 was not phosphorylated at either temperature. Following the induction of differentiation by a temperature shift, there was a marked decrease in integrin phosphorylation of both alpha and beta integrin chains. This decrease was more prominent for serine than for tyrosine, suggesting that src could not be the only kinase involved. The drop in integrin phosphorylation correlated with the initiation of differentiation, suggesting that integrin phosphorylation could be at least part of the mechanism by which myogenic differentiation is blocked by v-src.