Mcl-1 regulates reactive oxygen species via NOX4 during chemotherapy-induced senescence

Abstract

// Abeba Demelash 1 , Lukas W. Pfannenstiel 1 , Li Liu 1 , Brian R. Gastman 1, 2 1 Department of Immunology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA 2 Institutes of Head and Neck, Dermatology and Plastic Surgery, Taussig Cancer Center, Cleveland Clinic, Cleveland, OH, USA Correspondence to: Brian R. Gastman, email: gastmab@ccf.org Keywords: senescence, cancer therapy, Mcl-1, reactive oxygen species, NOX4 Received: December 21, 2016      Accepted: February 27, 2017      Published: March 07, 2017 ABSTRACT Mcl-1, a Bcl-2 family member, is highly expressed in a variety of human cancers and is believed to enhance tumorigenic potential and chemotherapy resistance through the inhibition of apoptosis and senescence. We previously reported that Mcl-1’s regulation of chemotherapy-induced senescence (CIS) is dependent on its ability to prevent reactive oxygen species (ROS) generation. In this report, we demonstrate that Mcl-1-regulated CIS requires not only ROS, but specifically mitochondrial ROS, and that these events are upstream of activation of the DNA damage response, another necessary step toward senescence. Mcl-1’s anti-senescence activity also involves the unique ability to inhibit ROS formation by preventing the upregulation of pro-oxidants. Specifically, we found that NADPH oxidases (NOXs) are regulated by Mcl-1 and that NOX4 expression in particular is a required step for CIS induction that is blocked by Mcl-1. Lastly, we illustrate that by preventing expression of NOX4, Mcl-1 limits its availability in the mitochondria, thereby lowering the production of mitochondrial ROS during CIS. Our studies not only define the essential role of Mcl-1 in chemoresistance, but also for the first time link a key pro-survival Bcl-2 family member with the NOX protein family, both of which have significant ramifications in cancer progression.