Atypical G Protein β5 Promotes Cardiac Oxidative Stress, Apoptosis, and Fibrotic Remodeling in Response to Multiple Cancer Chemotherapeutics.

The clinical use of multiple classes of cancer chemotherapeutics is limited by irreversible, dose-dependent, and sometimes life-threatening cardiotoxicity. Though distinct in their mechanisms of action, doxorubicin, paclitaxel, and 5-FU all induce rapid and robust upregulation of atypical G protein Gβ in the myocardium correlating with oxidative stress, myocyte apoptosis, and the accumulation of proinflammatory and profibrotic cytokines. In ventricular cardiac myocytes (VCM), Gβ deficiency provided substantial protection against the cytotoxic actions of chemotherapeutics, including reductions in oxidative stress and simultaneous attenuation of ROS-dependent activation of the ATM and CaMKII proapoptotic signaling cascades. In addition, Gβ loss allowed for maintenance of Δψ, basal mitochondrial calcium uniporter expression, and mitochondrial Ca levels, effects likely to preserve functional myocyte excitation-contraction coupling. The deleterious effects of Gβ are not restricted to VCM, however, as Gβ knockdown also reduces chemotherapy-induced release of proinflammatory cytokines (e.g., TNFα), hypertrophic factors (e.g., ANP), and profibrotic factors (e.g., TGFβ1) from both VCM and ventricular cardiac fibroblasts, with the most dramatic reduction occurring in cocultured cells. Our experiments suggest that Gβ facilitates the myofibroblast transition, the persistence of which contributes to pathologic remodeling and heart failure. The convergence of Gβ-mediated, ROS-dependent signaling pathways in both cell types represents a critical etiological factor in the pathogenesis of chemotherapy-induced cardiotoxicity. Indeed, intracardiac injection of Gβ-targeted shRNA allowed for heart-specific protection against the damaging impact of chronic chemotherapy. Together, our results suggest that inhibition of Gβ might represent a novel means to circumvent cardiotoxicity in cancer patients whose treatment regimens include anthracyclines, taxanes, or fluoropyrimidines. These findings suggest that inhibiting an atypical G-protein might provide a strategy to limit the cardiotoxicity in cancer patients treated with anthracyclines, taxanes, or fluoropyrimidines. .