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.
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.
McElhinny
Abigail S
AS
Department of Cell Biology and Anatomy, University of Arizona, Tucson, AZ 85724, USA.
Kakinuma
Kazumi
K
Sorimachi
Hiroyuki
H
Labeit
Siegfried
S
Gregorio
Carol C
CC
D000818:Animals; D019759:Carbon-Nitrogen Lyases / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D064211:Connectin; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression / Q000502:physiology; D049452:Green Fluorescent Proteins; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D008164:Luminescent Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology; D009210:Myofibrils / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012518:Sarcomeres / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D000070584:Tripartite Motif Proteins; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9
D064211:Connectin; D004268:DNA-Binding Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D009124:Muscle Proteins; C577285:TTN protein, human; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; C400298:p96 subunit, parvovirus initiation factor; D049452:Green Fluorescent Proteins; D044763:Ubiquitin-Conjugating Enzymes; C440908:TRIM63 protein, human; C499086:Trim63 protein, rat; D044767:Ubiquitin-Protein Ligases; D011494:Protein Kinases; D019759:Carbon-Nitrogen Lyases; C034300:isopeptidase; D008025:Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9