Autophagy Fails to Alter Withaferin A-Mediated Lethality in Human Breast Cancer Cells
Shivendra V. Singh.
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, processing of microtubuleassociated
protein 1 light chain 3 isoform B, 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 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: Autophagy, Atg5, Beclin1, breast cancer, MCF-7, MDA-MB-231, withaferin A.
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