title: Developmental regulation of MURF ubiquitin ligases and autophagy proteins nbr1, p62/SQSTM1 and LC3 during cardiac myofibril assembly and turnover.
abstract: The striated muscle-specific tripartite motif (TRIM) proteins TRIM63/MURF1, TRIM55/MURF2 and TRIM54/MURF3 can function as ubiquitin E3 ligases in ubiquitin-mediated muscle protein turnover. Despite their well-characterised roles in muscle atrophy, the dynamics of MURF expression in the development and early postnatal adaptation of striated muscle is largely unknown. Here, we show that MURF2 is expressed at the very onset of mouse cardiac differentiation at embryonic day 8.5, and represents a sensitive marker for differentiating myocardium. During cardiac development, expression shifts from the 50 kDa to the 60 kDa A-isoform, which dominates postnatally. In contrast, MURF1 shows strong postnatal upregulation and MURF3 is not significantly expressed before birth. MURF2 expression parallels that of the autophagy-associated proteins LC3, p62/SQSTM1 and nbr1. SiRNA knockdown of MURF2 in neonatal rat cardiomyocytes disrupts posttranslational microtubule modification and myofibril assembly, and is only partly compensated by upregulation of MURF3 but not MURF1. Knockdown of both MURF2 and MURF3 severely disrupts the formation of ordered Z- and M-bands, likely by perturbed tubulin dynamics. These results suggest that ubiquitin-mediated protein turnover and MURF2 in particular play an unrecognised role in the earliest steps of heart muscle differentiation, and that partial complementation of MURF2 deficiency is afforded by MURF3.
authors.affiliation: King's College London BHF Centre of Research Excellence, Randall Division for Cell and Molecular Biophysics and Cardiovascular Division, New Hunt's House, Guy's Campus, London SE1 1UL, UK.
authors.forename: Sue
authors.initials: S
authors.lastname: Perera
authors.forename: Mark R
authors.initials: MR
authors.lastname: Holt
authors.forename: Baljinder S
authors.initials: BS
authors.lastname: Mankoo
authors.forename: Mathias
authors.initials: M
authors.lastname: Gautel
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D018507:Gene Expression Regulation, Developmental; D006321:Heart / Q000196:embryology*; D006360:Heat-Shock Proteins / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D008870:Microtubules / Q000502:physiology; D009124:Muscle Proteins / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism; D009210:Myofibrils / Q000502:physiology*; D011506:Proteins / Q000502:physiology*; D051381:Rats; D000071456:Sequestosome-1 Protein; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D006360:Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D009124:Muscle Proteins; C486326:Nbr1 protein, mouse; D011506:Proteins; C413644:Rnf30 protein, mouse; D000071456:Sequestosome-1 Protein; C101343:Sqstm1 protein, mouse; C485888:TRIM54 protein, human; D000070584:Tripartite Motif Proteins; C499086:Trim63 protein, rat; D044767:Ubiquitin-Protein Ligases