β -Elemene Inhibits Cell Proliferation by Regulating the Expression and Activity of Topoisomerases I and II α in Human Hepatocarcinoma HepG-2 Cells

Objective. To investigate the effects of beta-Elemene (beta-ELE) on the proliferation, apoptosis, and topoisomerase I (TOPO I) and topoisomerase II alpha (TOPO II alpha) expression and activity of human hepatocarcinoma HepG-2 cells. Methods. After treatment with beta-ELE, morphological alterations of HepG-2 cells were observed under an inverted microscope. Cell proliferation was assessed using an MTT assay, cell cycles were analyzed using flow cytometry, and apoptosis was detected by Annexin V/PI staining. The expression of TOPO I and TOPO II alpha was analyzed by Western blot techniques, and their activity was measured using the TOPO I-mediated, supercoiled pBR322 DNA relaxation and TOPO II alpha-mediated Kinetoplast DNA (kDNA) decatenation assays, respectively. Supercoiled pBR322 and kDNA were also used to determine the direct effect of beta-ELE on DNA breaks. Results beta-ELE significantly inhibited HepG-2 cell proliferation in a dose- and time-dependent manner beta-ELE also induced tumor cell arrest at S phase, induced cell apoptosis, and downregulated the protein expression of TOPO I and TOPO II alpha in a dose-dependent manner beta-ELE also inhibited TOPO I- and TOPO II alpha-mediated DNA relaxation but did not directly induce DNA breakage at any concentration. Conclusion. beta-ELE could inhibit the proliferation of HepG-2 cells and interfere with the expression and activity of TOPO I and TOPO II alpha.