Autophagy Fails to Alter Withaferin A-Mediated Lethality in Human Breast Cancer Cells
Authors
Eun-Ryeong Hahm
Department of Pharmacology & Chemical Biology, and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA
Shivendra Singh
Department of Pharmacology & Chemical Biology, and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA
Keywords:
Withaferin A, Breast Cancer, MDA-MB-231, MCF-7, Autophagy, Atg5, Beclin1
Abstract
We have shown previously that withaferin A (WA), which is a highly promising anticancer constituent of Ayurvedic medicine plant Withania somnifera, inhibits viability of cultured breast cancer cells in association with reactive oxygen species (ROS)-dependent apoptosis induction. Because ROS production is implicated in induction of autophagy, which is an evolutionary conserved process for bulk degradation of cellular components including organelles (e.g., mitochondria) and considered a valid cancer chemotherapeutic target, we questioned whether WA treatment resulted in autophagy induction. Indeed exposure of MDA-MB-231 and MCF-7 human breast cancer cells as well as a spontaneously immortalized and non-tumorigenic normal human mammary epithelial cell line (MCF-10A) to pharmacologic concentration of WA resulted in autophagy as evidenced by transmission electron microscopy, cleavage of microtubule-associated protein 1 light chain 3 isoform B (LC3B-II), and/or acridine orange staining. Inhibition of MDA-MB-231 xenograft growth in vivo by WA administration was also associated with a significant increase in level of total LC3 protein in the tumor. However, WA-mediated inhibition of MDA-MB-231 and MCF-7 cell viability was not compromised either by pharmacological suppression of autophagy using 3-methyl adenine or genetic repression of autophagy by RNA interference of Atg5, a critical component of the autophagic machinery. Finally, Beclin1 was dispensable for WA-mediated autophagy as well as inhibition of MDA-MB-231 cell viability. Based on these observations we conclude that autophagy induction fails to have any meaningful impact on WA-mediated lethality in breast cancer cells, which may be a therapeutic advantage because autophagy serves to protect against apoptosis by several anticancer agents.
Keywords: Withaferin A, Breast Cancer, MDA-MB-231, MCF-7, Autophagy, Atg5, Beclin1
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