Berberine downregulates RAD51 in tumor cells.

<p>(A), The levels of DNA repair proteins in esophageal cancer cells treated with berberine. Cells were treated with berberine at the indicated concentrations and for the indicated duration before cells were prepared for cell extracts. (B), Decrease in <i>RAD51</i> mRNA levels after berberine exposure. Cells were exposed to berberine (15 µM) for 24 h for KYSE30 cells (48 h for KYSE450 cells), and collected for quantitative real-time PCR analysis of the RAD51/GAPDH mRNA ratios. (C), <i>RAD51</i> promoter activity was suppressed by berberine in KYSE30 and KYSE450 cells. The pGL3-RAD51p luciferase (firefly) reporter plasmids were transiently transfected into human esophageal cancer cells. Four h later, the cells were treated with berberine for 24 h, and then assayed for luciferase activity. Firefly luciferase values were normalized to Renilla luciferase activity from a co-transfected pRL-SV40 control vector. Each value represents the mean SE for three independent experiments. Statistical analysis was performed using unpaired Student's <i>t test. *</i>, P<0.05 as compared with control values. (D), Lack of RAD51 downregulation in nonmalignant cells. Cells were exposed to berberine (15 µM) for the specified time period and collected for immunoblot analysis. (E), Downregulation of RAD51 in other types of cancer cells. Cells were exposed to the designated berberine concentration for 48 h and collected for immunoblot analysis. The immunoblots shown in A, D, and E are representative of at least two independent experiments with GAPDH serving as a protein loading control. C indicates cultures exposed to the vehicle control DMSO.