Muscle-specific RING finger-1 interacts with titin to regulate sarcomeric M-line and thick filament structure and may have nuclear functions via its interaction with glucocorticoid modulatory element binding protein-1

Abigail S. McElhinny, Kazumi Kakinuma, Hiroyuki Sorimachi, Siegfried Labeit, Carol Gregorio

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The COOH-terminal A168-170 region of the giant sarcomeric protein titin interacts with muscle-specific RING finger-1 (MURF-1). To investigate the functional significance of this interaction, we expressed green fluorescent protein fusion constructs encoding defined fragments of titin's M-line region and MURF-1 in cardiac myocytes. Upon expression of MURF-1 or its central region (containing its titin-binding site), the integrity of titin's M-line region was dramatically disrupted. Disruption of titin's M-line region also resulted in a perturbation of thick filament components, but, surprisingly, not of the NH2-terminal or I-band regions of titin, the Z-lines, or the thin filaments. This specific phenotype also was caused by the expression of titin A168-170. These data suggest that the interaction of titin with MURF-1 is important for the stability of the sarcomeric M-line region. MURF-1 also binds to ubiquitin-conjugating enzyme-9 and isopeptidase T-3, enzymes involved in small ubiquitin-related modifier-mediated nuclear import, and with glucocorticoid modulatory element binding protein-1 (GMEB-1), a transcriptional regulator. Consistent with our in vitro binding data implicating MURF-1 with nuclear functions, endogenous MURF-1 also was detected in the nuclei of some myocytes. The dual interactions of MURF-1 with titin and GMEB-1 may link myofibril signaling pathways (perhaps including titin's kinase domain) with muscle gene expression.

Original languageEnglish (US)
Pages (from-to)125-136
Number of pages12
JournalJournal of Cell Biology
Issue number1
Publication statusPublished - Apr 1 2002



  • Cardiac myocyte
  • GMEB-1
  • MURF-1
  • SUMO-3
  • Titin

ASJC Scopus subject areas

  • Cell Biology

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