Figure 5.

Insulin-induced tyrosine phosphorylation of IRS-1 and IR in GSK-3-expressing cells. (A) CHO/IR/IRS-1 cells expressing WT GSK-3 or the S9A mutant were starved for 4 hr followed by stimulation with insulin (100 nM) for 15 min. Equal amount of protein from cell lysates were subjected to gel electrophoresis, transferred to polyvinylidene difluoride membrane, and immunoblotted with monoclonal antibodies to phosphotyrosine. Tyrosine phosphorylated IRS-1 and the β subunit of IR are indicated. (B) Image density of tyrosine phosphorylated IRS-1 and the β subunit of IR from A. Results are presented as percent of control cells and are the mean ± SE from three independent experiments.