Muscle-specific RING finger 1 is a bona fide ubiquitin ligase that degrades cardiac troponin I

Abstract

Muscle-specific RING finger protein 1 (MuRF1) is a sarcomereassociated 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 degradation. We 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.

Regulation of Large Conductance Ca2+-activated K+ (BK) Channel β1 Subunit Expression by Muscle RING Finger Protein 1 in Diabetic Vessels

“…We believe that the coiled-coil region of MuRF1 is the structure required for recruiting BK-␤1 to MuRF1 because BK-␤1 can be detected in the pulldown of the MuRF1 coiled-coil region alone, but a direct protein binding experiment is required to further confirm our findings. Our results are similar to previous observations that the coiled-coil region is sufficient for MuRF1 binding to sarcomeric M-line titin and thick filament (63). Interestingly, partially deleting the RING finger domain or the family conserved region of MuRF1 interferes with the physical association with BK-␤1.…”

“…For instance, MuRF1 interacts with the hydrophobic amino acids of "Titin repeats" (61) and myosin heavy chain in skeletal muscles (62). The coiled-coil region of MuRF1 is responsible for the binding of troponin I in cardiomyocytes (63). The MuRF family conserved region is required for the interaction with phospho-c-Jun in the heart (64).…”

Effects of alfacalcidol on circulating cytokines and growth factors in rat skeletal muscle

“…MuRF-1 ubiquitinates myofibrillar and cytoskeleton proteins and metabolic enzymes in preparation for their subsequent breakdown in the proteasome [57][58][59][60]. In line with this role in muscle protein breakdown during fasting, we observed that MuRF-1 expression was increased substantially in the alfacalcidol group, without a change in MAFbx mRNA levels (see Fig.…”

Activation of AMPK inhibits cardiomyocyte hypertrophy by modulating of the FOXO1/MuRF1 signaling pathway in vitro

“…It has also recently been reported that myocardium lacking MuRF1 expression has exaggerated cardiac hypertrophy in response to prohypertrophic stimulation [13] . More recently, some other reports have demonstrated that MuRF1 inhibits cardiac hypertrophy by degrading sarcomeric proteins that constitute the bulk of cardiomyocyte mass [30] and interfering with prohypertrophic signaling [31] . In cardiomyocytes, these processes may determine the balance between prohypertrophic and antihypertrophic signals [30] .…”

“…More recently, some other reports have demonstrated that MuRF1 inhibits cardiac hypertrophy by degrading sarcomeric proteins that constitute the bulk of cardiomyocyte mass [30] and interfering with prohypertrophic signaling [31] . In cardiomyocytes, these processes may determine the balance between prohypertrophic and antihypertrophic signals [30] . As a sensor of cellular energy status, AMPK responds to an increase in the ratio of AMP to ATP, which can be observed in response to starvation, exercise, and muscle contraction [20,32] .…”