Human Molecular Genetic and Functional Studies Identify TRIM63, Encoding Muscle RING Finger Protein 1, as a Novel Gene for Human Hypertrophic Cardiomyopathy

Abstract

Rationale: A delicate balance between protein synthesis and degradation maintains cardiac size and function. TRIM63 encoding Muscle RING Finger 1 (MuRF1) maintains muscle protein homeostasis by tagging the sarcomere proteins with ubiquitin for subsequent degradation by the Ubiquitin-Proteasome System (UPS).

Objective: To determine the pathogenic role of TRIM63 in human hypertrophic cardiomyopathy (HCM).

Methods and Results: Sequencing of TRIM63 gene in 302 HCM probands (250 Caucasians) and 339 controls (262 Caucasians) led to identification of two missense (p.A48V and p.I130M) and a deletion (p.Q247*) variants exclusively in the HCM probands. These three variants were absent in 751 additional controls screened by TaqMan assays. Likewise, rare variants were enriched in the Caucasian HCM population (11/250, 4.4% vs. 3/262, 1.1%, respectively, p=0.024). Expression of the mutant TRIM63 was associated with mislocalization of TRIM63 to sarcomere Z disks, impaired auto-ubiquitination, reduced ubiquitination and UPS-mediated degradation of myosin heavy chain 6, cardiac myosin binding protein C, calcineurin (PPP3CB), and p-MTOR in adult cardiac myocytes. Induced expression of the mutant TRIM63 in the mouse heart was associated with cardiac hypertrophy, activation of the MTOR-S6K and calcineurin pathways and expression of the hypertrophic markers, which were normalized upon turning off expression of the mutant protein.

Conclusions: TRIM63 mutations, identified in patients with HCM, impart loss-of-function effects on E3 ligase activity and are likely causal mutations in HCM. The findings implicate impaired protein degradation in the pathogenesis of HCM.