Overexpression of p85β regulatory subunit of class I_A PI3K inhibits BMMC growth and maturation. (A) Deficiency of p85α and p85β alters the maturation of BMMCs. LDMNCs from WT, P85α^−/−, and P85β^−/− mice were cultured in the presence of IL-3 (10 ng/mL) for 4 weeks. At the indicated time points, maturation was analyzed by staining the cells with antibodies that recognize KIT and IgE receptor followed by flow cytometry. Shown is dot blot profile from one of 4 independent experiments. (B) Reduced growth of WT MCps overexpressing p85β. WT and P85α^−/− MCps transduced with vector, p85α, or p85β were sorted to homogeneity and cultured in the presence of IL-3 (10 ng/mL). Cells were starved for 6 hours in serum- and cytokine-free media and cultured in the presence or absence of SCF (50 ng/mL). After 48 hours, proliferation was evaluated by a [³H]thymidine incorporation assay. Bars represent the mean [³H]thymidine incorporation in BMMCs (CPM + SD) from one representative experiment performed in quadruplicate. Similar results were observed in 3 or 4 additional independent experiments. *P < .01, WT-vector versus WT-p85β, WT-vector versus P85α^−/−-vector, and WT-vector versus P85α^−/− p85β. (C) Overexpression of p85β in WT MCps results in reduced differentiation. WT and P85α^−/− MCps transduced with vector, p85α, or p85β were sorted to homogeneity and cultured in the presence of IL-3 (10 ng/mL). Cells were harvested at indicated time points, and maturation was analyzed by staining the cells with antibodies to detect the expression of KIT and IgE receptor by flow cytometry. Shown is a dot blot profile of an independent experiment. Similar findings were observed in 2 to 4 additional independent experiments.