Figure 1
Expression of a kinase inactive IGF-IR impairs tumorigenesis. CHO cells express 5 × 104 IGF-IRs, CHO-WT cells express 2 × 105 wild-type IGF-IRs, and the CHO-MK cells express 2 × 105 mutant IGF-IRs that contain a Lysine to Methionine point mutation in the ATP-binding site (MK1003). Panel A: IGF-I stimulated whole cell tyrosine phosphorylation. Serum-starved cells were stimulated with IGF-I (10 or 100 ng/ml) for 5 min and whole cell extracts immunoblotted for phosphotyrosine. The positions of the β-subunit of the IGF-IR and IRS-1 are indicated. Panel B: Serum-starved CHO or CHO-MK cells were stimulated with increasing concentrations of IGF-I for 18 h then pulsed with 3H-thymidine for 1 h. DNA was precipitated with TCA and counted. Panel C: ten thousand cells were plated in soft agar in complete medium for 14–21 days. Colonies > 125 μm in diameter were counted after staining with crystal violet. Panel D: ten million cells were injected subcutaneously into the rear flank of athymic nude mice. Tumor size was measured with calipers every few days. Graph shows mean tumor volume (± SEM) as a function of time. Panel E: Mice were euthanized after 21 days and the tumors excised, weighed and fixed for staining. Graph shows mean tumor weight (± SEM).