Suppression of basal autophagy reduces lung cancer cell proliferation and enhances caspase-dependent and -independent apoptosis by stimulating ROS formation

Abstract

Autophagy is a catabolic process involved in the turnover of organelles and macromolecules which, depending on conditions, may lead to cell death or preserve cell survival. We found that some lung cancer cell lines and tumor samples are characterized by increased levels of lipidated LC3. Inhibition of autophagy sensitized non-small cell lung carcinoma (NSCLC) cells to cisplatin-induced apoptosis; however, such response was attenuated in cells treated with etoposide. Inhibition of autophagy stimulated ROS formation and treatment with cisplatin had a synergistic effect on ROS accumulation. Using genetically encoded hydrogen peroxide probes directed to intracellular compartments we found that autophagy inhibition facilitated formation of hydrogen peroxide in the cytosol and mitochondria of cisplatin-treated cells. The enhancement of cell death under conditions of inhibited autophagy was partially dependent on caspases, however, antioxidant NAC or hydroxyl radical scavengers, but not the scavengers of superoxide or a MnSOD mimetic, reduced the release of cytochrome c and abolished the sensitization of the cells to cisplatin-induced apoptosis. Such inhibition of ROS prevented the processing and release of AIF (apoptosis-inducing factor) and HTRA2 from mitochondria. Furthermore, suppression of autophagy in NSCLC cells with active basal autophagy reduced their proliferation without significant effect on the cell-cycle distribution. Inhibition of cell proliferation delayed accumulation of cells in the S phase upon treatment with etoposide that could attenuate the execution stage of etoposide-induced apoptosis. These findings suggest that autophagy suppression leads to inhibition of NSCLC cell proliferation and sensitizes them to cisplatininduced caspase-dependent and -independent apoptosis by stimulation of ROS formation.

The roles of oxidative stress, endoplasmic reticulum stress, and autophagy in aldosterone/mineralocorticoid receptor-induced podocyte injury

“…51 Furthermore, autophagy inhibition led to enhanced ROS generation in several cell lines. 52,53 Therefore, the crosstalk among ROS, ER stress, and autophagy is quite complex. Elucidating the correlation represents a major area for our future research.…”

Life in the balance – a mechanistic view of the crosstalk between autophagy and apoptosis

“…Consequently, pharmacological inhibition of autophagy under these conditions, particularly in combination with other chemotherapeutic agents, might lead to a favourable outcome, compromising the ability of tumour cells to adapt to stress, thus driving apoptotic-competent cells towards cell cycle arrest or programmed cell death (Carew et al, 2007;Jin et al, 2007;Maycotte and Thorburn, 2011). Other recent work suggested that suppression of autophagy leads to inhibition of cell proliferation in non-small-cell lung carcinoma (NSCLC) and sensitises cells to cisplatin-induced apoptosis by stimulation of reactive oxygen species (ROS) formation (Kaminskyy et al, 2012). By contrast, the inhibition of autophagy in apoptosis-deficient tumours, such as those overexpressing BCL2, might have detrimental effects.…”

Peneciraistin C induces caspase‐independent autophagic cell death through mitochondrial‐derived reactive oxygen species production in lung cancer cells

“…(10,15,16) However, it seems somewhat controversial that ROS is instrumental in inducing autophagy under stress conditions. (17)(18)(19)(20) In this regard, it is of interest to determine the role of ROS and autophagy in A549 cell death induced by the novel compound Pe-C.In the present study, we investigated the mechanism underlying the novel compound Pe-C in lung cancer cells. We found that Pe-C elicited autophagic cell death independent of caspase activation and apoptosis in a variety of lung cancer cells, which was mediated by the accumulation of mitochondrialderived ROS.…”

“…(10,15,16) However, it seems somewhat controversial that ROS is instrumental in inducing autophagy under stress conditions. (17)(18)(19)(20) In this regard, it is of interest to determine the role of ROS and autophagy in A549 cell death induced by the novel compound Pe-C.…”