Isolation of PI3K-C2β, SOS, and EGFR in anti-Grb2 immunoprecipitates (ippt). Confluent and quiescent cultures of human renal epithelial cells (HKC-8) and breast cancer cells (HTM3551, T47D, and SKBr3) were incubated with (+) or without (−) EGF (100 nM) for 10 min. Lysates were prepared to which anti-Grb2 antibody (Santa Cruz C-23) was added for 4 h at 4°C. Immune complexes were isolated following addition of protein A-Sepharose and centrifugation. Proteins were extracted, fractionated by SDS-PAGE, and Western blotted with antisera to PI3K-C2β (upper panels), SOS 1/2 (D21; Santa Cruz) (middle panels), and EGFR (1005; Santa Cruz) (lower panels).