Hrishikesh Thakur

Anchored p90 Ribosomal S6 Kinase 3 is Required for Cardiac Myocyte Hypertrophy

Rationale: Cardiac myocyte hypertrophy is the main compensatory response to chronic stress on the heart. p90 ribosomal S6 kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. Although increased RSK activity has been observed in stressed myocytes, the functions of individual RSK family members have remained poorly defined, despite being potential therapeutic targets for cardiac disease. Objective: To demonstrate that type 3 RSK (RSK3) is required for cardiac myocyte hypertrophy. Methods and Results: RSK3 contains a unique N-terminal domain that is not conserved in other RSK family members. We show that this domain mediates the regulated binding of RSK3 to the muscle A-kinase anchoring protein scaffold, defining a novel kinase anchoring event. Disruption of both RSK3 expression using RNA interference and RSK3 anchoring using a competing muscle A-kinase anchoring protein peptide inhibited the hypertrophy of cultured myocytes. In vivo, RSK3 gene deletion in the mouse attenuated the concentric myocyte hypertrophy induced by pressure overload and catecholamine infusion. Conclusions: Taken together, these data demonstrate that anchored RSK3 transduces signals that modulate pathologic myocyte growth. Targeting of signaling complexes that contain select kinase isoforms should provide an approach for the specific inhibition of cardiac myocyte hypertrophy and for the development of novel strategies for the prevention and treatment of heart failure.

The Scaffold Protein Muscle A-Kinase Anchoring Protein β Orchestrates Cardiac Myocyte Hypertrophic Signaling Required for the Development of Heart Failure

Background—Cardiac myocyte hypertrophy is regulated by an extensive intracellular signal transduction network. In vitro evidence suggests that the scaffold protein muscle A-kinase anchoring protein &bgr; (mAKAP&bgr;) serves as a nodal organizer of hypertrophic signaling. However, the relevance of mAKAP&bgr; signalosomes to pathological remodeling and heart failure in vivo remains unknown. Methods and Results—Using conditional, cardiac myocyte–specific gene deletion, we now demonstrate that mAKAP&bgr; expression in mice is important for the cardiac hypertrophy induced by pressure overload and catecholamine toxicity. mAKAP&bgr; targeting prevented the development of heart failure associated with long-term transverse aortic constriction, conferring a survival benefit. In contrast to 29% of control mice (n=24), only 6% of mAKAP&bgr; knockout mice (n=31) died in the 16 weeks of pressure overload (P=0.02). Accordingly, mAKAP&bgr; knockout inhibited myocardial apoptosis and the development of interstitial fibrosis, left atrial hypertrophy, and pulmonary edema. This improvement in cardiac status correlated with the attenuated activation of signaling pathways coordinated by the mAKAP&bgr; scaffold, including the decreased phosphorylation of protein kinase D1 and histone deacetylase 4 that we reveal to participate in a new mAKAP signaling module. Furthermore, mAKAP&bgr; knockout inhibited pathological gene expression directed by myocyte-enhancer factor-2 and nuclear factor of activated T-cell transcription factors that associate with the scaffold. Conclusions—mAKAP&bgr; orchestrates signaling that regulates pathological cardiac remodeling in mice. Targeting of the underlying physical architecture of signaling networks, including mAKAP&bgr; signalosome formation, may constitute an effective therapeutic strategy for the prevention and treatment of pathological remodeling and heart failure.

The Scaffold Protein mAKAPβ Orchestrates Cardiac Myocyte Hypertrophic Signaling Required for the Development of Heart Failure

Background—Cardiac myocyte hypertrophy is regulated by an extensive intracellular signal transduction network. In vitro evidence suggests that the scaffold protein muscle A-kinase anchoring protein &bgr; (mAKAP&bgr;) serves as a nodal organizer of hypertrophic signaling. However, the relevance of mAKAP&bgr; signalosomes to pathological remodeling and heart failure in vivo remains unknown. Methods and Results—Using conditional, cardiac myocyte–specific gene deletion, we now demonstrate that mAKAP&bgr; expression in mice is important for the cardiac hypertrophy induced by pressure overload and catecholamine toxicity. mAKAP&bgr; targeting prevented the development of heart failure associated with long-term transverse aortic constriction, conferring a survival benefit. In contrast to 29% of control mice (n=24), only 6% of mAKAP&bgr; knockout mice (n=31) died in the 16 weeks of pressure overload (P=0.02). Accordingly, mAKAP&bgr; knockout inhibited myocardial apoptosis and the development of interstitial fibrosis, left atrial hypertrophy, and pulmonary edema. This improvement in cardiac status correlated with the attenuated activation of signaling pathways coordinated by the mAKAP&bgr; scaffold, including the decreased phosphorylation of protein kinase D1 and histone deacetylase 4 that we reveal to participate in a new mAKAP signaling module. Furthermore, mAKAP&bgr; knockout inhibited pathological gene expression directed by myocyte-enhancer factor-2 and nuclear factor of activated T-cell transcription factors that associate with the scaffold. Conclusions—mAKAP&bgr; orchestrates signaling that regulates pathological cardiac remodeling in mice. Targeting of the underlying physical architecture of signaling networks, including mAKAP&bgr; signalosome formation, may constitute an effective therapeutic strategy for the prevention and treatment of pathological remodeling and heart failure.

p90 ribosomal S6 kinase 3 contributes to cardiac insufficiency in α-tropomyosin Glu180Gly transgenic mice

Myocardial interstitial fibrosis is an important contributor to the development of heart failure. Type 3 p90 ribosomal S6 kinase (RSK3) was recently shown to be required for concentric myocyte hypertrophy under in vivo pathological conditions. However, the role of RSK family members in myocardial fibrosis remains uninvestigated. Transgenic expression of α-tropomyosin containing a Glu180Gly mutation (TM180) in mice of a mixed C57BL/6:FVB/N background induces a cardiomyopathy characterized by a small left ventricle, interstitial fibrosis, and diminished systolic and diastolic function. Using this mouse model, we now show that RSK3 is required for the induction of interstitial fibrosis in vivo. TM180 transgenic mice were crossed to RSK3 constitutive knockout (RSK3(-/-)) mice. Although RSK3 knockout did not affect myocyte growth, the decreased cardiac function and mild pulmonary edema associated with the TM180 transgene were attenuated by RSK3 knockout. The improved cardiac function was consistent with reduced interstitial fibrosis in the TM180;RSK3(-/-) mice as shown by histology and gene expression analysis, including the decreased expression of collagens. The specific inhibition of RSK3 should be considered as a potential novel therapeutic strategy for improving cardiac function and the prevention of sudden cardiac death in diseases in which interstitial fibrosis contributes to the development of heart failure.

Bidirectional regulation of HDAC5 by mAKAPβ signalosomes in cardiac myocytes

Class IIa histone deacetylases (HDACs) are transcriptional repressors whose nuclear export in the cardiac myocyte is associated with the induction of pathological gene expression and cardiac remodeling. Class IIa HDACs are regulated by multiple, functionally opposing post-translational modifications, including phosphorylation by protein kinase D (PKD) that promotes nuclear export and phosphorylation by protein kinase A (PKA) that promotes nuclear import. We have previously shown that the scaffold protein muscle A-kinase anchoring protein β (mAKAPβ) orchestrates signaling in the cardiac myocyte required for pathological cardiac remodeling, including serving as a scaffold for both PKD and PKA. We now show that mAKAPβ is a scaffold for HDAC5 in cardiac myocytes, forming signalosomes containing HDAC5, PKD, and PKA. Inhibition of mAKAPβ expression attenuated the phosphorylation of HDAC5 by PKD and PKA in response to α- and β-adrenergic receptor stimulation, respectively. Importantly, disruption of mAKAPβ-HDAC5 anchoring prevented the induction of HDAC5 nuclear export by α-adrenergic receptor signaling and PKD phosphorylation. In addition, disruption of mAKAPβ-PKA anchoring prevented the inhibition by β-adrenergic receptor stimulation of α-adrenergic-induced HDAC5 nuclear export. Together, these data establish that mAKAPβ signalosomes serve to bidirectionally regulate the nuclear-cytoplasmic localization of class IIa HDACs. Thus, the mAKAPβ scaffold serves as a node in the myocyte regulatory network controlling both the repression and activation of pathological gene expression in health and disease, respectively.

Erratum to: CIP4 is required for the hypertrophic growth of neonatal cardiac myocytes

Correction In the published work [1], Figure three A panels e and f and Figure four B (Figure 1B here) panels b and f represent the same types of samples in two different experiments, i.e., CIP4 siRNA-transfected myocytes cultured in the absence and presence of phenylephrine, respectively. However, in the original version of Rusconi, et al. [1], the panels in Figure three A e and f were unintentionally duplicated in the panels in Figure four B (Figure 1B here) b and f, respectively. In this correction, a new Figure four (Figure 1 here) is provided with different panels for figure four B (Figure 1B) b and f. The interpretation and conclusion of the depicted experiments remain the same. Corrected Figure four (Figure 1 here):

Erratum: CIP4 is required for the hypertrophic growth of neonatal cardiac myocytes (Journal of Biomedical Science (2014) 21:45)

Correction In the published work [1], Figure three A panels e and f and Figure four B (Figure 1B here) panels b and f represent the same types of samples in two different experiments, i.e., CIP4 siRNA-transfected myocytes cultured in the absence and presence of phenylephrine, respectively. However, in the original version of Rusconi, et al. [1], the panels in Figure three A e and f were unintentionally duplicated in the panels in Figure four B (Figure 1B here) b and f, respectively. In this correction, a new Figure four (Figure 1 here) is provided with different panels for figure four B (Figure 1B) b and f. The interpretation and conclusion of the depicted experiments remain the same. Corrected Figure four (Figure 1 here):

Correction: CIP4 is required for the hypertrophic growth of neonatal cardiac myocytes.

Correction In the published work [1], Figure three A panels e and f and Figure four B (Figure 1B here) panels b and f represent the same types of samples in two different experiments, i.e., CIP4 siRNA-transfected myocytes cultured in the absence and presence of phenylephrine, respectively. However, in the original version of Rusconi, et al. [1], the panels in Figure three A e and f were unintentionally duplicated in the panels in Figure four B (Figure 1B here) b and f, respectively. In this correction, a new Figure four (Figure 1 here) is provided with different panels for figure four B (Figure 1B) b and f. The interpretation and conclusion of the depicted experiments remain the same. Corrected Figure four (Figure 1 here):