p110β inhibition suppresses response to growth factor stimulation. A-C) Cells were serum-starved for 16-24 h, then pretreated with 1 μM GSK2636771 for 1 h followed by stimulation with heregulin (Hrg) +/− GSK2636771. Protein lysates were analyzed by immunoblot. D) RPPA measurements of ER, PTEN, and P-AKTT308 levels in 248 luminal breast tumors were extracted from refs. (5, 36) and compared by Spearman correlation. E) Cells were treated as indicated. Medium and drug were refreshed every 2-3 d, and protein lysates were analyzed as above.