Figure 5

Inhibition of PI3K, not MEK1/2, prevents proliferation of MDA-MB-231 cells. (A) LY294002 and U0126 effectively inhibit Akt and Erk1/2 activation in MDA-MB-231 cells. Serum-starved shCTL and shSRBI MDA-MB-231 cells were incubated with or without the inhibitors LY294002 (15 μM) or U0126 (10 μM) for 2 hours. Medium containing 10% FBS was added for 30 minutes, cells were lysed, and whole-cell lysates were analyzed by Western blot for the indicated proteins. GAPDH was used as a loading control. (B) PI3K inhibition reduces cellular proliferation of shCTL MDA-MB-231 cells. shCTL and shSRBI MDA-MB-231 cells were incubated with culture media containing either LY294002 (15 μM) or U0126 (10 μM) and ³H-thymidine for 6 hours, at which time, the assay was stopped, and lysates were collected. Columns represent the mean [³H]thymidine incorporation (cpm/μg protein); bars represent ± SD. Results obtained from vehicle-treated (CTL) shCTL MDA-MB-231 cells are significantly different from those obtained with shSRBI MDA-MB-231 cells (**P < 0.001, one-way ANOVA with Tukey's post-test analysis). Results obtained from vehicle-treated shCTL MDA-MB-231 cells (CTL) are significantly different from those obtained with shCTL MDA-MB-231 cells treated with LY294002. Note that proliferation of shCTL MDA-MB-231 cells treated with U0126 was not significantly different from that observed with vehicle-treated shCTL MDA-MB-231 cells. Proliferation of shSRBI MDA-MB-231 cells treated with LY294002 or U0126 was also not significantly different from that observed with vehicle-treated shCTL MDA-MB-231 cells. Results are representative of three independent experiments.