Role of oxidative/nitrosative stress-mediated Bcl-2 regulation in apoptosis and malignant transformation

Bcl-2 is a key apoptosis regulatory protein of the mitochondrial death pathway. The oncogenic potential of Bcl-2 is well established, with its overexpression reported in various cancers. The antiapoptotic function of Bcl-2 is closely associated with its expression levels. Reactive oxygen and nitrogen species (ROS/RNS) are important intracellular signaling molecules that play a key role in various physiological processes including apoptosis. We have recently reported that ROS and RNS can regulate Bcl-2 expression levels, thereby impacting its function. Superoxide anion (·O₂^-) plays a proapoptotic role by causing downregulation and degradation of Bcl-2 protein through the ubiquitin-proteasomal pathway. In contrast, nitric oxide (NO)-mediated S-nitrosylation of Bcl-2 prevents its ubiquitination and subsequent proteasomal degradation, leading to inhibition of apoptosis. Interestingly, NO-mediated S-nitrosylation and stabilization of Bcl-2 protein was the primary mechanism involved in the malignant transformation of nontumorigenic lung epithelial cells in response to long-term carcinogen exposure. We describe a novel mechanism of Bcl-2 regulation by ·O ₂^- and NO, providing a new dimension to reactive species-mediated Bcl-2 stability, apoptotic cell death, and cancer development.