Muscle RING-Finger Protein-1 (MuRF1) as a Connector of Muscle Energy Metabolism and Protein Synthesis

Department of Enzymatic Regulation for Cell Functions (Calpain Project), Tokyo Metropolitan Institute of Medical Science (Rinshoken), Tokyo 113-8613, Japan.
Journal of Molecular Biology (Impact Factor: 3.96). 04/2008; 376(5):1224-36. DOI: 10.1016/j.jmb.2007.11.049
Source: PubMed

ABSTRACT During pathophysiological muscle wasting, a family of ubiquitin ligases, including muscle RING-finger protein-1 (MuRF1), has been proposed to trigger muscle protein degradation via ubiquitination. Here, we characterized skeletal muscles from wild-type (WT) and MuRF1 knockout (KO) mice under amino acid (AA) deprivation as a model for physiological protein degradation, where skeletal muscles altruistically waste themselves to provide AAs to other organs. When WT and MuRF1 KO mice were fed a diet lacking AA, MuRF1 KO mice were less susceptible to muscle wasting, for both myocardium and skeletal muscles. Under AA depletion, WT mice had reduced muscle protein synthesis, while MuRF1 KO mice maintained nonphysiologically elevated levels of skeletal muscle protein de novo synthesis. Consistent with a role of MuRF1 for muscle protein turnover during starvation, the concentrations of essential AAs, especially branched-chain AAs, in the blood plasma significantly decreased in MuRF1 KO mice under AA deprivation. To clarify the molecular roles of MuRF1 for muscle metabolism during wasting, we searched for MuRF1-associated proteins using pull-down assays and mass spectrometry. Muscle-type creatine kinase (M-CK), an essential enzyme for energy metabolism, was identified among the interacting proteins. Coexpression studies revealed that M-CK interacts with the central regions of MuRF1 including its B-box domain and that MuRF1 ubiquitinates M-CK, which triggers the degradation of M-CK via proteasomes. Consistent with MuRF1's role of adjusting CK activities in skeletal muscles by regulating its turnover in vivo, we found that CK levels were significantly higher in the MuRF1 KO mice than in WT mice. Glucocorticoid modulatory element binding protein-1 and 3-hydroxyisobutyrate dehydrogenase, previously identified as potential MuRF1-interacting proteins, were also ubiquitinated MuRF1-dependently. Taken together, these data suggest that, in a multifaceted manner, MuRF1 participates in the regulation of AA metabolism, including the control of free AAs and their supply to other organs under catabolic conditions, and in the regulation of ATP synthesis under metabolic-stress conditions where MuRF1 expression is induced.

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Available from: Stephanie H Witt, Jul 25, 2015
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    • "The levels of mRNA expression were normalized by those of housekeeping Hprt because its expression was stable during fasting in all tested tissues. As the ubiquitin–proteasome system marker, we examined the expression of Atrogin-1 (also known as MAFbx [Muscle Atrophy F-box]) and MuRF1 (Muscle RING Finger 1; also known as Trim63 [Muscle Atrophy F-box]), the two E3 ubiquitin ligases involved in skeletal muscle atrophy [9] [10]. The expression of Atrogin-1 was significantly upregulated upon fasting in skeletal muscle >> small intestine, thymus > heart, colon, lung > spleen, kidney > stomach (Fig. 2A). "
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    FEBS Open Bio 04/2015; 5. DOI:10.1016/j.fob.2015.04.012 · 1.52 Impact Factor
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    • "However, given the normal hypertrophic response to FO in the MuRF1 KO mice, it seems that MuRF1 is not essential for muscle growth. Considering that protein synthesis is higher in MuRF1 KO mice under atrophy conditions (Koyama et al., 2008; Baehr et al., 2011), it may be that the major role of MuRF1 in skeletal muscle is to suppress protein synthesis. Thus, deletion of MuRF1 is advantageous to muscle growth and consequently, the MuRF1 KO mice maintain an ability to hypertrophy throughout their lifetime. "
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    ABSTRACT: The regulation of skeletal muscle mass depends on the balance between protein synthesis and degradation. The role of protein degradation and in particular, the ubiquitin proteasome system, and increased expression of the E3 ubiquitin ligases, MuRF1 and MAFbx/atrogin-1, in the regulation of muscle size in response to growth stimuli is unclear. Thus, the aim of this study was to measure both proteasome activity and protein synthesis in mice over a 14-day period of chronic loading using the functional overload (FO) model. Further, the importance of MuRF1 and MAFbx expression in regulating muscle hypertrophy was examined by measuring muscle growth in response to FO in mice with a null deletion (KO) of either MuRF1 or MAFbx. In wild type (WT) mice, the increase in muscle mass correlated with significant increases (2-fold) in protein synthesis at 7 and 14 days. Interestingly, proteasome activity significantly increased in WT mice after one day, and continued to increase, peaking at 7 days following FO. The increase in proteasome activity was correlated with increases in the expression of the Forkhead transcription factors, FOXO1 and FOXO3a, which increased after both MuRF1 and MAFbx increased and returned to baseline. As in WT mice, hypertrophy in the MuRF1 and MAFbx KO mice was associated with significant increases in proteasome activity after 14 days of FO. The increase in plantaris mass was similar between the WT and MuRF1 KO mice following FO, however, muscle growth was significantly reduced in female MAFbx KO mice. Collectively, these results indicate that muscle hypertrophy is associated with increases in both protein synthesis and degradation. Further, MuRF1 or MAFbx expression is not required to increase proteasome activity following increased loading, however, MAFbx expression may be required for proper growth/remodeling of muscle in response to increase loading.
    Frontiers in Physiology 02/2014; 5:69. DOI:10.3389/fphys.2014.00069 · 3.50 Impact Factor
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    • "This is the first report showing the inhibitory effects of COMMD6 on CK activities; it will be of particular interest to determine if this is also true for COMMD6 in other organisms. Interestingly, recent studies have shown that muscle RING-finger protein-1 (MuRF1) and ycaC-related protein (ycaCR) are also able to interact with CK (Jiang et al., 2008; Koyama et al., 2007). These results and ours together suggest that CK activity may be regulated by multiple factors. "
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