cytochrome-c-t and embelin

Pseudolaric acid B (PAB) is a diterpene acid isolated from the root and trunk bark of Pseudolarix kaempferi Gordon (Pinaceae). Recent studies have reported that PAB exhibits cytotoxic effects in several cancer cell lines. In the present study, we assessed its antitumor activity and molecular mechanisms in HO-8910 and A2780 ovarian cancer cells in vitro. We found that PAB reduced cell viability and induced apoptosis in a dose- and time-dependent manner in HO-8910 and A2780 human ovarian cancer cells. The induction of apoptosis was also accompanied by the regulation of Bcl-2 and XIAP family proteins, cytochrome c and Apaf-1. Moreover, we observed that PAB treatment resulted in the activation of caspase-3 and -9, which may partly explain the anticancer activity of PAB. Collectively, the present study for the first time suggests that PAB enhances apoptosis of HO-8910 and A2780 cells through regulation of Bcl-2 and IAP family proteins. Moreover, the triggering of caspase-3 and -9 activation mediated apoptotic induction. Our results suggest that PAB may be a new therapeutic option for the treatment of ovarian cancers.

Topics: Apoptosis; Apoptotic Protease-Activating Factor 1; Benzoquinones; Caspase 3; Caspase 9; Caspase Inhibitors; Cell Line, Tumor; Cell Survival; Cytochromes c; Diterpenes; Enzyme Activation; Female; Humans; Microscopy, Electron, Transmission; Mitochondria; Oligopeptides; Ovarian Neoplasms; Proto-Oncogene Proteins c-bcl-2; X-Linked Inhibitor of Apoptosis Protein

Molecular mechanism(s) responsible for drug resistance of non-small cell lung cancer (NSCLC) cells to cisplatin was investigated. Results showed that cisplatin (50muM)-induced cell death (apoptosis) was more significant in CH27 and A549 cell lines than in H460. The high protein levels of X-linked inhibitor-of-apoptosis protein (XIAP) observed in H460 cells appeared to play a key role in the regulation of cisplatin resistance of H460 cells. XIAP can bind to and suppress the activities of caspase 3 in H460 cells and lead to apoptosis inhibition of these cells. Blockade of XIAP activity by Embelin (XIAP inhibitor) or siRNA has increased caspase 3 activities and promoted cisplatin-induced cell death of H460 cells. The results indicate a therapeutic value of Embelin and/or XIAP siRNA in the control of cisplatin-resistant NSCLC cells (H460).

Topics: Apoptosis; Benzoquinones; Carcinoma, Non-Small-Cell Lung; Caspase 3; Cell Line, Tumor; Cisplatin; Cytochromes c; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Gene Knockdown Techniques; Humans; Lung Neoplasms; Membrane Potential, Mitochondrial; Mitochondria; RNA, Small Interfering; Time Factors; X-Linked Inhibitor of Apoptosis Protein

XIAP is an important antiapoptotic protein capable of conferring resistance to cancer cells. Embelin, the small molecular inhibitor of XIAP, possesses wide spectrum of biological activities with strong inhibition of nuclear factor kappa B and downstream antiapoptotic genes. However, the mechanism of its cell death induction is not known. Our studies using colon cancer cells lacking p53 and Bax suggest that both lysosomes and mitochondria are prominent targets of embelin-induced cell death. Embelin induced cell-cycle arrest in G(1) phase through p21, downstream of p53. In the absence of p21, the cells are sensitized to death in a Bax-dependent manner. The loss of mitochondrial membrane potential induced by embelin was independent of Bax and p53, but lysosomal integrity loss was strongly influenced by the presence of p53 but not by Bax. Lysosomal role was further substantiated by enhanced cathepsin B activity noticed in embelin-treated cells. p53-dependent lysosomal destabilization and cathepsin B activation contribute for increased sensitivity of p21-deficient cells to embelin with enhanced caspase 9 and caspase 3 activation. Cathepsin B inhibitor reduced cell death and cytochrome c release in embelin-treated cells indicating lysosomal pathway as the upstream of mitochondrial death signaling. Deficiency of cell-cycle arrest machinery renders cells more sensitive to embelin with enhanced lysosomal destabilization and caspase processing emphasizing its potential therapeutic importance to address clinical drug resistance.

Topics: Apoptosis; bcl-2-Associated X Protein; Benzoquinones; Caspases; Cathepsin B; Cell Line, Tumor; Cyclin-Dependent Kinase Inhibitor p21; Cytochromes c; Dose-Response Relationship, Drug; Enzyme Activation; HCT116 Cells; Humans; Lysosomes; Membrane Potential, Mitochondrial; Mitochondria; Tumor Suppressor Protein p53