G-protein Inactivator RGS6 Mediates Myocardial Cell Apoptosis and Cardiomyopathy Caused By Doxorubicin

Abstract

Clinical use of the widely used chemotherapeutic agent doxorubicin is limited by life-threatening cardiotoxicity. The mechanisms underlying Dox-induced cardiomyopathy and heart failure remain unclear, but are thought to involve p53-mediated myocardial cell apoptosis. The tripartite G protein inactivating protein RGS6 has been implicated in reactive oxygen species (ROS) generation, ATM/p53 activation and apoptosis in Dox-treated cells. Thus, we hypothesized that RGS6, the expression of which is enriched in cardiac tissue, might also be responsible for the pathological effects of Dox treatment in heart. In this study, we show that RGS6 expression is induced strongly by Dox in the ventricles of mice and isolated ventricular myocytes (VCM) via a post-transcriptional mechanism. While Dox-treated wild type (WT) mice manifested severe left ventricular dysfunction, loss of heart and body mass, along with decreased survival five days after Dox administration, mice lacking RGS6 were completely protected against these pathogenic responses. Activation of ATM/p53-apoptosis signaling by Dox in ventricles of WT mice was also absent in their RGS6−/− counterparts. Dox-induced ROS generation was dramatically impaired in both the ventricles and VCM isolated from RGS6−/− mice, and the apoptotic response to Dox in VCM required RGS6-dependent ROS production. These results identify RGS6 as an essential mediator of the pathogenic responses to Dox in heart, and they argue that RGS6 inhibition offers a rational means to circumvent Dox cardiotoxicity in human cancer patients.

Regulator of G protein signaling 6 is a critical mediator of both reward-related behavioral and pathological responses to alcohol

“…We have previously shown that cardiotoxic stimuli can induce up-regulation of RGS6 in heart (39). A transient rise in RGS6 protein levels was observed in the heart after 2 wk of EtOH exposure, which returned to baseline by 1 mo (Fig.…”

“…Although the exact pathogenic ROS source remains unclear, scavenging or inhibition of superoxide anion generation from activated NADPH oxidase (Nox) complexes protects against EtOH-induced tissue injury (36,37). Although originally discovered as a G-protein regulator with the demonstrated capacity to modulate multiple GPCR-dependent physiological processes (28,29,38), our recently published studies have shown that RGS6 is also involved in ROSdependent cardiomyopathy induced by doxorubicin (Dox) (39), and promotes ROS generation and ROS-mediated apoptosis in cancer cells through G protein-independent mechanisms (40). Both Dox-and EtOH-induced cardiomyopathies require Noxdependent ROS generation (37,41), leading us to the novel hypothesis that RGS6 also promotes EtOH-induced, ROS-mediated apoptosis, and subsequent pathology.…”

“…Having established a critical role for RGS6 in promoting alcohol-seeking behaviors, we next sought to investigate the involvement of RGS6 in the pathogenesis of cardiac damage induced by EtOH. We reasoned that, given the ability of RGS6 to promote ROS-dependent apoptosis in the Dox-treated myocardium (39) and studies implicating ROS in the development of alcoholic cardiomyopathy (37), RGS6 might mediate oxidative stress-induced cytotoxicity in alcohol-exposed hearts. To test this hypothesis, we used a "forced" EtOH feeding paradigm, which eliminates genotype effects on EtOH seeking and reward behaviors and has been shown to cause detectable loss of cardiac contractility in addition to compromising liver function after 2 mo (36,37).…”

“…Primary neonatal VCM were isolated from 2-to 3-d-old WT and RGS6 −/− mice according to our previously published protocol (39). Twenty-four hours after isolation and plating, cells were treated with 200 mM EtOH (24 h) in the presence or absence of DPI (1 μM, 1.5-h pretreatment) where indicated.…”

Letter by Patanè Regarding Article, “Early Detection of Anthracycline Cardiotoxicity and Improvement With Heart Failure Therapy”

“…The ability of RGS6 to promote p53 activation in response to anthracycline is independent of RGS6 interaction with G proteins but requires ataxia telangiectasia-mutated serine/threonine protein kinase and exhibits a reactive oxygen species-dependent, DNA damage-independent, and GGL and DEP domain-dependent mechanism. [2][3][4] These results identify the GGL and DEP domains of RGS6 as essential mediators of the pathogenic responses to anthracycline in the heart, and they argue that the GGL and DEP domain inhibition of RGS6 offers a rational means to circumvent anthracycline cardiotoxicity in human patients with cancer 3 or that the presence of a GGL and DEP domain-altered mechanism could be a predictor of anthracycline-induced cardiotoxicity. I would like to observe that the authors have reported no relationships with RGS6, the GGL and DEP domains, ataxia telangiectasia-mutated serine/threonine protein kinase, p53, and reactive oxygen species.…”