Effects of FHC-Related Troponin T Mutations on Proteasome Activity and Half-Life of Troponin T

Abstract

Familial hypertrophic cardiomyopathy (FHC) is a genetic disease of the heart muscle that can be caused by mutations in sarcomeric proteins such as cardiac troponin T (TnT), a thin filament regulator of muscle contraction. Results from our lab show that the ubiquitin proteasome system (UPS) is affected in TnT-related cardiomyopathies; in FHC mice expressing the I79N or R278C mutant forms of TnT, changes in proteasome subunit expression and gene expression of proteins in the ubiquitination pathway, increased levels of oxidized proteins, and decreases in proteasome activity in 3 month old I79N mice were observed, suggesting that UPS dysfunction may be an important contributing factor to the pathogenesis of this disease. Mutations in sarcomeric proteins can alter their rates of proteasomal degradation, and increased degradation may lead to proteasome functional insufficiency by competitively inhibiting breakdown of other proteasome substrates. To investigate whether the observed impairment of proteasome function was due to a change in the degradation rate of mutated TnT, the degradation rates of wild-type and mutated (I79N and R278C) TnT were determined in CV-1 cells. The half-life of TnT was not affected by either mutation, suggesting that the effects of these mutations on the proteasome are not due to a difference in the degradation rate of TnT. Experiments to determine the rate of degradation of the FHC mutant F110I are currently being carried out. Overall, our results suggest that the effects of FHC mutations on proteasome function are not due to the mutation directly affecting the proteasome. This work was supported by NIH Grant HL096819.