Figure 4

Retroviral expression of wild-type and mutant IGF-IRs in U87 glioma cells. U87 cells stably infected with pseudotyped retroviruses expressing β-galactosidase (LacZ), wild-type IGF-IR (WT) or kinase defective IGF-IR (MK) were rendered quiescent by serum-starvation then stimulated with IGF-I (10 or 100 ng/ml) for 5 min. Whole cell extracts were immunoblotted for phosphotyrosine. The positions of the β-subunit of the IGF-IR and the IRS proteins are indicated.