(A) IRS-1 and IRS-2 but not IRS-3 suppress apoptosis of Ba/F3 cells deprived of IL-3. Stable transfectants of IRS-1, IRS-2, IRS-3, 4F-IRS-1, Bcl-2, and mock cells were deprived of IL-3 and cultured in RPMI 1640 medium containing 5% FCS. FCS used in this study contained 15 nM insulin quantified by IRMA. (B) PI3K activity of insulin-stimulated cell lines. Stable transfectants of IRS-1, IRS-2, IRS-3, 4F-IRS-1, and mock cells treated with or without insulin were lysed and immunoprecipitated with 4G10. The immunoprecipitates were subjected to the PI3K assay. (C) Survival rate of stable transfectants expressing deletion mutants of IRS-1, C-1, C-2, C-3, and C-4.