Knockdown of the HDL receptor, SR-BI, inhibits proliferation, migration, and invasion of MDA-MB-231 cells. (A) Cholesterol content of shCTL and shSRBI MDA-MB-231 cells. Cholesterol was extracted from cells with isopropanol, and total cholesterol was measured enzymatically by using a colorimetric assay. Protein concentration was also determined, and total cellular cholesterol content was expressed as the amount of cholesterol per milligram of protein. Columns represent the mean cholesterol content, and bars represent ± SD. shCTL MDA-MB-231 cells display significantly more cholesterol than shSRBI MDA-MB-231 cells (**P < 0.01 by Student's t test). (B) Knockdown of SR-BI inhibits proliferation of MDA-MB-231 cells. MDA-MB-231 cells containing control shRNA (shCTL) or shSRBI were incubated in the presence of 3H-thymidine for 6 hours in DMEM containing 10% FBS. Proliferation was measured by 3H-thymidine incorporation. Columns represent the mean 3H-thymidine incorporation (cpm/μg protein); bars represent ± (SD). The results obtained for shCTL and shSRBI cells are significantly different (*P < 0.01 by Student's t test). Results are representative of three independent experiments. (C) Knockdown of SR-BI reduces cellular migration. Cellular migration of shCTL and shSRBI MDA-MB-231 cells was assessed for 24 hours in a Boyden chamber by using 1% FBS as a chemoattractant. Columns represent the mean number of migrated cells from three independent experiments, and bars represent ± standard deviation (SD), (n = 12). The results obtained from the shCTL and shSRBI groups are significantly different (*P < 0.05 versus shCTL, as determined with Student's t test). (D) Knockdown of SR-BI leads to a marginally significant reduction in cellular invasion. Invasion of shCTL and shSRBI MDA-MB-231 cells was assessed by Matrigel-coated Boyden chamber assays by using 1% FBS as a chemoattractant. Columns represent the mean number of invaded cells from three separate experiments (n = 12); bars represent ± SD (P = 0.0517, Student's t test).