Bovine skeletal growth factor stimulates protein phosphorylation of chicken bone cells in vitro.

1. Bovine skeletal growth factor (SGF), a potent bone cell mitogen, stimulated protein phosphorylation in cultured chicken calvarial cells. 2. SDS-PAGE followed by autoradiographic analysis of the cellular proteins indicated that [32P] incorporation was enhanced in several proteins in response to 10 ng/ml of SGF (the maximum stimulatory mitogenic dose for these cells). 3. Under conditions favoring tyrosine kinases, SGF stimulated phosphorylation of at least 6 proteins in crude calvarial cell membrane fraction, and caused a time-dependent stimulation of phosphorylation of angiotensin II by crude calvarial cell membrane fractions. 4. Thus, our data demonstrate that SGF stimulates protein phosphorylation in bone cells, and suggest that at least some of the protein phosphorylation involves tyrosine residues.