Cardiology
Ring Finger Protein may prevent Cardiac Hypertrophy
By Akanksha, Staff Reporter
Jan 9, 2005, 18:06

Muscle-specific RING finger protein 1 (MuRF1) is a sarcomere-associated protein that is restricted to cardiac and skeletal muscle.

In skeletal muscle, MuRF1 is up-regulated by conditions that provoke atrophy, but its function in the heart is not known. The presence of a RING finger in MuRF1 raises the possibility that it is a component of the ubiquitin�proteasome system of protein deg-radation.

Vishram Kedar, from the University of North Carolina at Chapel Hill, and colleagues performed a yeast two-hybrid screen to search for interaction partners of MuRF1 in the heart that might be targets of its putative ubiquitin ligase activity.

This screen identified troponin I as a MuRF1 partner protein. MuRF1 and troponin I were found to associate both in vitro and in vivo in cultured cardiomyocytes.

MuRF1 reduced steady-state troponin I levels when coexpressed in COS-7 cells and increased degradation of endogenous troponin I protein in cardiomyocytes.

The degradation of troponin I in cardiomyocytes was associated with the accumulation of ubiquitylated intermediates of troponin I and was proteasome-dependent.

In vitro, MuRF1 functioned as a ubiquitin ligase to catalyze ubiquitylation of troponin I through a RING finger-dependent mechanism.

In isolated cardiomyocytes, MuRF1 reduced indices of contractility.

In cardiomyocytes, these processes may determine the balance between hypertrophic and antihypertrophic signals and the regulation of myocyte contractile responses in the setting of heart failure.

It was hypothesized that MuRF1 may destabilize sarcomeres by binding to titin, which would in turn provide MuRF1 with access to its substrate troponin I. Troponin I could then be targeted for ubiquitylation and proteasome-dependent degradation by MuRF1. This activity of MuRF1 may be generalized to other sarcomere accessory proteins.





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