Effect of IGF-1 on tyrosine phosphorylation of IRS-2 or IRS-1 and their association with PI-3K.

Cells were unstimulated (−) or stimulated (+) with IGF-I for 10 minutes after 18 hours of serum starvation. Cell lysates were immunoprecipitated with anti–IRS-2 (A) or anti–IRS-1 (B), subjected to SDS-PAGE, and blotted with the indicated antibodies. Mouse plasmacytoma line 12.2 (A) and 32D cells transfected with IRS-1 (B) were used as positive controls for IRS-2 and IRS-1, respectively. Positions of IRS-2, IRS-1, and the p85 subunit of PI-3K are as indicated.