title: Regulation of pre-fusion events: recruitment of M-cadherin to microrafts organized at fusion-competent sites of myogenic cells.
abstract: BACKGROUND
  Previous research indicates that the membrane ruffles and leading edge of lamellipodia of myogenic cells contain presumptive fusion sites. A micrometer-sized lipid raft (microraft) is organized at the presumptive fusion site of mouse myogenic cells in a cell-contact independent way and serves as a platform tethering adhesion proteins that are relevant to cell fusion. However, the mechanisms underlying recruitment of adhesion proteins to lipid rafts and microraft organization remain unknown.
  
  
  RESULTS
  Here we show that small G-protein Rac1 was required for microraft organization and subsequent cell fusion. However, Rac1 activity was unnecessary for recruitment of M-cadherin to lipid rafts. We found that p120 catenin (p120) binds to M-cadherin exclusively in lipid rafts of differentiating myogenic cells. The Src kinase inhibitor SU6656 prevented p120 binding to M-cadherin and their recruitment to lipid rafts, then suppressed microraft organization, membrane ruffling, and myogenic cell fusion. Suppression of membrane ruffling in SU6656-treated cells was partially restored by pretreatment with the protein tyrosine phosphatase inhibitor vanadate. The present analyses using an antibody to tyrosine phosphorylated p120 suggest that Src family kinases play a role in binding of p120 to M-cadherin and the recruitment of M-cadherin to lipid rafts through phosphorylation of putative substrates other than p120.
  
  
  CONCLUSIONS
  The present study showed that the procedure establishing fusion-competent sites consists of two sequential events: recruitment of adhesion complexes to lipid rafts and organization of microrafts. The recruitment of M-cadherin to lipid rafts depended on interaction with p120 catenin, whereas the organization of microrafts was controlled by a small G protein, Rac1.
authors: Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 35 Gengo, Morioka, Oobu, Aichi 474-8522, Japan. nao@ncgg.go.jp.
authors: Atsushi
authors: A
authors: Mukai
authors: Naohiro
authors: N
authors: Hashimoto
mesh_terms: D000818:Animals; D015820:Cadherins / Q000235:genetics* / Q000378:metabolism; D051177:Catenins / Q000235:genetics / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects; D002459:Cell Fusion; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D007211:Indoles / Q000494:pharmacology; D021962:Membrane Microdomains / Q000187:drug effects; D051379:Mice; D024510:Muscle Development / Q000235:genetics*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics*; D013449:Sulfonamides / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D000095002:Delta Catenin
chemical_list: D015820:Cadherins; D051177:Catenins; D007211:Indoles; D009479:Neuropeptides; C484602:Rac1 protein, mouse; C416927:SU 6656; D013449:Sulfonamides; C070896:M-cadherin; D014638:Vanadates; D017027:Protein Tyrosine Phosphatases; D020830:rac1 GTP-Binding Protein; D000095002:Delta Catenin; C000722349:Ctnnd1 protein, mouse
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