TEL/PDGFβR activates PI3 kinase.

Parental Ba/F3 cells (lanes 1-5) or transformed Ba/F3-TEL/PDGFβR cells (lanes 6-11) were analyzed during log phase growth (lanes 1,6) or after treatment with DMSO alone (lanes 4,7) or the PI3 kinase inhibitor, LY294002 (lanes 5,8,9) for 4 hours. LY294002 was dissolved in DMSO and used at a concentration of 25 μM to obtain complete inhibition. As a positive control, Ba/F3 cells were deprived of IL-3 for 4 hours and then restimulated with IL-3 at 50 ng/mL (lane 3). To demonstrate a necessity for the kinase activity of TEL/PDGFβR for activation of PI3 kinase, cells were treated with STI571 at 1 μM in dH20 for 4 hours (lane 10). As a control for the specificity of STI571, Ba/F3-TEL/PDGFβR cells were treated with STI571 for 4 hours and then stimulated with IL-3 50 ng/mL for 10 minutes (lane 11). All experiments were performed in the presence of 10% fetal calf serum.