Role of ERK1/2 Signaling in Cinnabarinic Acid-Driven Stanniocalcin 2-Mediated Protection against Alcohol-Induced Apoptosis.

We have previously shown that a bona fide aryl hydrocarbon receptor (AhR) agonist, cinnabarinic acid (CA), protects against alcohol-induced hepatocyte apoptosis via activation of a novel AhR target gene, stanniocalcin 2 (Stc2). Stc2 translates to a secreted disulfide-linked hormone, STC2, known to function in cell development, calcium and phosphate regulation, angiogenesis, and antiapoptosis-albeit the comprehensive mechanism by which the CA-AhR-STC2 axis confers antiapoptosis is yet to be characterized. In this study, using RNA interference library screening, downstream antiapoptotic molecular signaling components involved in CA-induced STC2-mediated protection against ethanol-induced apoptosis were investigated. RNA interference library screening of kinases and phosphatases in Hepa1 cells and subsequent pathway analysis identified mitogen-activated protein kinase (MAPK) signaling as a critical molecular pathway involved in CA-mediated protection. Specifically, phosphorylation of ERK1/2 was induced in response to CA treatment without alterations in p38 and JNK signaling pathways. Silencing Stc2 in Hepa1 cells and in vivo experiments performed in Stc2 (Stc2 knockout) mice, which failed to confer CA-mediated protection against ethanol-induced apoptosis, showed abrogation of ERK1/2 activation, underlining the significance of ERK1/2 signaling in CA-STC2-mediated protection. In conclusion, activation of ERK1/2 signaling in CA-driven AhR-dependent Stc2-mediated protection represents a novel mechanism of protection against acute alcohol-induced apoptosis. SIGNIFICANCE STATEMENT: Previous studies have shown the role of stanniocalcin 2 (Stc2) in cinnabarinic acid (CA)-mediated protection against alcohol-induced apoptosis. Here, using RNA interference library screening and subsequent in vivo studies, the functional significance of ERK1/2 activation in CA-induced Stc2-mediated protection against acute ethanol-induced apoptosis was identified. This study is thus significant as it illustrates a comprehensive downstream mechanism by which CA-induced Stc2 protects against alcoholic liver disease.