Abstract 15441: MURC/Cavin-4 Requires the Coiled-coil Domain for Membrane Trafficking of Caveolin-3 in Cardiomyocytes

Abstract

[Background] Muscle-restricted coiled-coil protein (MURC), also referred to as Cavin-4, is a member of the cavin family that is cooperated with caveolins in caveola formation and function. Cavins are cytoplasmic proteins that have coiled-coil domains and form heteromeric complexes, which are recruited to caveolae in cells expressing caveolins. Among caveolins, caveolin-3 (Cav3) is exclusively expressed in muscle cells, similar to MURC/Cavin-4. In the heart, Cav3 overexpression contributes to cardiac protection, while its deficiency leads to progressive cardiomyopathy. Mutations in the MURC/Cavin-4 gene have been identified in patients with dilated cardiomyopathy. MURC/Cavin-4 has the coiled-coil domain; however, its functional significance remains unknown. [Methods and Results] MURC/Cavin-4 was localized at the plasma membrane in H9c2 cells, while a MURC/Cavin-4 mutant lacking the coiled-coil domain (ΔCC) was primarily localized to the cytoplasm. ΔCC bound to Cav3 and impaired membrane localization of Cav3 in cardiomyocytes. In addition, although ΔCC did not influence Cav3 mRNA expression, it decreased the Cav3 protein level in cardiomyocytes. MURC/Cavin-4 and ΔCC similarly induced cardiomyocytes hypertrophy; however, ΔCC showed higher hypertrophy-related fetal gene expression, such as ANP, BNP, and skeletal α-actin (SkA) mRNA expression and the βMHC/αMHC ratio, than MURC/Cavin-4. ΔCC induced ERK activation in cardiomyocytes. Cardiac function assessed by echocardiography was significantly impaired in transgenic mice expressing ΔCC in the heart (ΔCC-Tg mice) compared with non-transgenic (NTg) mice (% FS; 24.6 ± 2.4 % in ΔCC-Tg mice vs. 48.8 ± 2.5 % in NTg mice, p<0.01), which was accompanied by cardiomyocyte hypertrophy, increased interstitial fibrosis, and the increase of lung weight-to-tibial-length ratio (LW/TL; 18.04 ± 2.41 in ΔCC-Tg mice vs. 7.51 ± 0.81 in NTg mice, p<0.01). ΔCC-Tg hearts showed reduction of the Cav3 protein level and the activation of ERK. [Conclusions] These results reveal that MURC/Cavin-4 requires its coiled-coil domain to target the plasma membrane and Cav3 trafficking to the plasma membrane of cardiomyocytes, and that MURC/Cavin-4 functions as a crucial caveolar component to regulate cardiac function.