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Gene 33 is a potential inducer of cardiomyocyte apoptosis
The 8th Annual Scientific Meeting
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HFSA
S61
158
159
HDAC Inhibitors Promote a More Differentiated and Physiologic Genotype in Cardiac Hypertrophy Sara O. Weiss,1 Carmen C. Sucharov,1 Carlin S. Long1; 1Department of Medicine, Division of Cardiology, University of Colorado Health Sciences Center, Denver, CO
Gene 33 Is a Potential Inducer of Cardiomyocyte Apoptosis Dazhong Xu,1 Richard D. Patten,1 John M. Kyriakis1; 1Molecular Cardiology Research Institute, Tufts-New England Medical Center, Boston, MA
Background: Pathologic cardiac hypertrophy and heart failure are characterized by the induction of fetal genes such as β-myosin heavy chain (βMHC), atrial natriuretic peptide (ANP) and skeletal actin. Less well studied, however, is the coordinate repression of adult genes such as α-myosin heavy chain (αMHC) and sarcoplasmic reticulum Ca2⫹-ATPase 2α (SERCA) that is also characteristic of a pathologic growth program. Although several specific transcription factors have been implicated in controlling the expression of these genes, recent studies have demonstrated that chromatin modification by histone deacetylases (HDACs) may also play a substantive role in their regulation. The ability of HDAC inhibitors to increase acetylation of histones and induce a differentiated gene program has, in fact, lead to clinical trials examining their utility as anti-cancer agents. It is tempting to speculate that these inhibitors could also be used to reverse the fetal gene program and cause re-differentiation to an adult cardiac genotype in the context of pathologic myocardial growth. Objective: To examine the response of the cardiac myocyte gene program to treatment with Trichostatin A (TSA), a potent and specific HDAC inhibitor. Methods and Results: Neonatal rat ventricular myocytes were treated with increasing concentrations of TSA (0-100nM) in the presence or absence of hypertrophic stimuli (phenylephrine or interleukin-1β) and their gene program evaluated by RNAse protection. As expected, both hypertrophic agonists induced myocyte growth and decreased expression of both αMHC and SERCA mRNAs, an effect that was largely reversed by TSA treatment. Notably, even under control conditions, TSA treated cells expressed higher levels of both SERCA and αMHC mRNAs. Conclusion: As seen with several tumor cell lines, HDACs play an important role in the regulation of the differentiated cardiomyocyte gene program. HDAC inhibitors appear to reverse the induction of the fetal gene program by hypertrophic agents such as PE and IL-1. This is exciting data because HDAC inhibitors may induce a more physiologic gene program and therefore could represent a new therapeutic option for patients with heart failure.
Apoptosis has been implicated in the cardiomyopathy associated with acute and chronic heart failure. Myocardial infarction, cardiac hypertrophy and especially ischemia/reperfusion have been shown to lead to cardiomyocyte apoptosis. Despite previous findings, the role of apoptosis in cardiomyopathy and the mechanism of apoptosis in cardiomyocytes are poorly understood. Gene 33 encodes a 50 kD polypeptide that in numerous tissues is inducible by a wide variety of stimuli. Although Gene 33′s molecular structure suggests it functions as an adaptor/scaffold protein, very little is known about the biological functions of Gene33. It has been shown that Gene 33 binds to EGF receptor family receptor tyrosine kinases and suppresses their downstream signaling. Gene 33, when over expressed, also binds GTP-bound Cdc42 and activates JNK. We find that Gene 33 inhibits EGFR tyrosine phosphorylation thus accounting for the mechanism by which Gene 33 suppresses EGF effectors such as ERK and Akt, as well as EGF-stimulated protein synthesis and DNA synthesis. Here we show that infection of neonatal rat cardiomyocytes with a recombinant adenovirus expressing Gene 33 is potently apoptogenic. Consistent with this, ectopic expression of Gene 33 results in activation of cardiomyocyte caspase 3. Western blot analysis reveals elevated levels of Gene 33 protein in a mouse model for myocardial infarction. Of note, both Western blot and immunohistochemistry indicate that expression of the Gene 33 polypeptide is higher in the infarct region compared to the none-infarct zone. These results strongly suggest a role of Gene 33 in cardiomyocyte apoptosis. We therefore propose a model in which Gene 33 is induced by stress conditions such as myocardial infarction, ischemia/reperfusion and possibly late-stage cardiac hypertrophy. Gene 33 then participates in triggering pathophysiologic cardiomyocyte apoptosis.
•
HFSA
S61
158
159
HDAC Inhibitors Promote a More Differentiated and Physiologic Genotype in Cardiac Hypertrophy Sara O. Weiss,1 Carmen C. Sucharov,1 Carlin S. Long1; 1Department of Medicine, Division of Cardiology, University of Colorado Health Sciences Center, Denver, CO
Gene 33 Is a Potential Inducer of Cardiomyocyte Apoptosis Dazhong Xu,1 Richard D. Patten,1 John M. Kyriakis1; 1Molecular Cardiology Research Institute, Tufts-New England Medical Center, Boston, MA
Background: Pathologic cardiac hypertrophy and heart failure are characterized by the induction of fetal genes such as β-myosin heavy chain (βMHC), atrial natriuretic peptide (ANP) and skeletal actin. Less well studied, however, is the coordinate repression of adult genes such as α-myosin heavy chain (αMHC) and sarcoplasmic reticulum Ca2⫹-ATPase 2α (SERCA) that is also characteristic of a pathologic growth program. Although several specific transcription factors have been implicated in controlling the expression of these genes, recent studies have demonstrated that chromatin modification by histone deacetylases (HDACs) may also play a substantive role in their regulation. The ability of HDAC inhibitors to increase acetylation of histones and induce a differentiated gene program has, in fact, lead to clinical trials examining their utility as anti-cancer agents. It is tempting to speculate that these inhibitors could also be used to reverse the fetal gene program and cause re-differentiation to an adult cardiac genotype in the context of pathologic myocardial growth. Objective: To examine the response of the cardiac myocyte gene program to treatment with Trichostatin A (TSA), a potent and specific HDAC inhibitor. Methods and Results: Neonatal rat ventricular myocytes were treated with increasing concentrations of TSA (0-100nM) in the presence or absence of hypertrophic stimuli (phenylephrine or interleukin-1β) and their gene program evaluated by RNAse protection. As expected, both hypertrophic agonists induced myocyte growth and decreased expression of both αMHC and SERCA mRNAs, an effect that was largely reversed by TSA treatment. Notably, even under control conditions, TSA treated cells expressed higher levels of both SERCA and αMHC mRNAs. Conclusion: As seen with several tumor cell lines, HDACs play an important role in the regulation of the differentiated cardiomyocyte gene program. HDAC inhibitors appear to reverse the induction of the fetal gene program by hypertrophic agents such as PE and IL-1. This is exciting data because HDAC inhibitors may induce a more physiologic gene program and therefore could represent a new therapeutic option for patients with heart failure.
Apoptosis has been implicated in the cardiomyopathy associated with acute and chronic heart failure. Myocardial infarction, cardiac hypertrophy and especially ischemia/reperfusion have been shown to lead to cardiomyocyte apoptosis. Despite previous findings, the role of apoptosis in cardiomyopathy and the mechanism of apoptosis in cardiomyocytes are poorly understood. Gene 33 encodes a 50 kD polypeptide that in numerous tissues is inducible by a wide variety of stimuli. Although Gene 33′s molecular structure suggests it functions as an adaptor/scaffold protein, very little is known about the biological functions of Gene33. It has been shown that Gene 33 binds to EGF receptor family receptor tyrosine kinases and suppresses their downstream signaling. Gene 33, when over expressed, also binds GTP-bound Cdc42 and activates JNK. We find that Gene 33 inhibits EGFR tyrosine phosphorylation thus accounting for the mechanism by which Gene 33 suppresses EGF effectors such as ERK and Akt, as well as EGF-stimulated protein synthesis and DNA synthesis. Here we show that infection of neonatal rat cardiomyocytes with a recombinant adenovirus expressing Gene 33 is potently apoptogenic. Consistent with this, ectopic expression of Gene 33 results in activation of cardiomyocyte caspase 3. Western blot analysis reveals elevated levels of Gene 33 protein in a mouse model for myocardial infarction. Of note, both Western blot and immunohistochemistry indicate that expression of the Gene 33 polypeptide is higher in the infarct region compared to the none-infarct zone. These results strongly suggest a role of Gene 33 in cardiomyocyte apoptosis. We therefore propose a model in which Gene 33 is induced by stress conditions such as myocardial infarction, ischemia/reperfusion and possibly late-stage cardiac hypertrophy. Gene 33 then participates in triggering pathophysiologic cardiomyocyte apoptosis.