Abstract 9559: The Role of Myopalladin in the Interactions of ANKRD1/CARP with the Co-Activator p53 in Hypertrophic Cardiomyopathy

Abstract

Background: Myopalladin (MYPN), a member of the Z-disc that interacts with other Z-disc proteins, including the cardiac ankyrin repeat protein ANKRD1 (CARP). Mutations in MYPN and CARP genes cause human dilated (DCM) and hypertrophic cardiomyopathies (HCM). Both MYPN and CARP have dual distributions in the cytoplasm and nucleus. In the nucleus, CARP is a transcriptional co-activator of p53, repressing expression of the cardiac proteins in an in vitro system. A MYPN-dependent cytoplasmic anchoring for CARP is described although the molecular basis of the MYPN modulation of CARP gene transcription is unclear. Previously, our laboratory identified a novel MYPN variant (MYPN Y20C ) in DCM and HCM patients. A transgenic MYPN Y20C cardiac-restricted overexpression mouse model recapitulates the HCM phenotype.. Methods and Results: In vitro and in vivo studies demonstrated that the MYPN Y20C mutation resulted in perinuclear localization in myoblasts while CARP retained its cytoplasmic/nuclear dual distribution; as did wild-type MYPN. Co-immunoprecipitation revealed decreased association between CARP and MYPN Y20C suggesting a dissociation of the cellular distributions of CARP and MYPN Y20C . In transgenic MYPN Y20C hearts, perinuclear MYPN Y20C had increased association with p53, a co-activator for negative gene regulation of CARP. Nuclear localization of p53 is a critical element in the activation of its transcription. Its sequestration in the cytoplasm renders the protein non-functional. This resulted in a loss-of-function of CARP gene transcription as demonstrated by increased expression of the CARP-specific sarcomeric protein myosin heavy chain (MHC), and atrial natriuretic peptide (ANP), and brain natriuretic peptide (BNP) in vivo . CARP was serine phosphorylated and coexpression with MYPN led to suppression of CARP phosphorylation. Conclusion: Our study demonstrates a novel role for myopalladin in the development of HCM. The perinuclear/cytoplasmic sequestration of p53 by MYPN Y20C resulted in the inactivation of p53, which leads to loss-of-function of CARP gene regulation. Our data also suggests that myopalladin plays a pivotal role in relaying cardiac Z-disc signaling to those proteins involved in CARP phosphorylation/activation.