Atg7- and Keap1-dependent autophagy protects breast cancer cells against mitoquinone-induced oxidative stress

Wednesday, November 06, 2013 — Poster Session I
4:00 p.m. – 6:00 p.m.	FAES Academic Center (Upper-Level Terrace)	FDA/CBER	CANCER-3

Authors

Y Gonzalez-Berrios
B Aryal
L Chehab
VA Rao

Abstract

Mitoquinone (MitoQ), a mitochondrially-targeted redox-active ubiquinone agent, selectively killed breast cancer cells compared to healthy mammary epithelial cells. MitoQ, although a synthetic derivative of the antioxidant ubiquinone, generated superoxide in MDA-MB-231 cells. Investigation into the cytotoxicity mechanism of MitoQ showed that a greater number of cells undergo autophagy than apoptosis. Drug treatment increased protein levels of the autophagosome-associated light chain 3 (LC3-II) that is responsible for the formation and nucleation of the autophagy bodies. However, the relationship between mitoquinone-induced oxidative stress and autophagy as a primary cellular response is not well characterized. We found that MitoQ induces Atg7-dependent autophagy independent of Beclin-1. Cancer cells and mouse embryonic fibroblast lacking the Atg7 had lower levels of autophagy after MitoQ treatment. Autophagy-deficient cells showed higher dihydroethidium levels, an indicator of one-electron oxidation of hydroethidine. Keap1, an oxidative stress sensor protein that regulates an antioxidant response via the transcription factor Nrf2, underwent oxidation and degradation in drug-treated cells. Autophagy deficient cells Keap1 degradation decreased. Moreover, downregulation of Keap1 decreased autophagy levels, increased Nrf2 activation, and caused accumulation of p62. We provided evidence for an Atg7- and Keap1- dependent autophagy as one of the mechanisms that respond to the oxidative stress by Mito-Q.