title: Characterization of novel complexes on the cell surface between integrins and proteins with 4 transmembrane domains (TM4 proteins).
abstract: Here we identified several new integrin/TM4 protein complexes on the cell surface. By immunoprecipitation using nonstringent conditions, and by reciprocal immunoprecipitation, we found that alpha 3 beta 1 and alpha 6 beta 1 integrins but not alpha 2 beta 1, alpha 5 beta 1, or alpha 6 beta 4 integrins associated with CD9 and CD81 in alpha 3 beta 1/CD81, alpha 3 beta 1/CD9, alpha 6 beta 1/CD81, and alpha 6 beta 1/CD9 complexes. Also, cross-linking experiments established that alpha 3 beta 1/CD81, alpha 3 beta 1/CD9, and alpha 3 beta 1/CD63 associations occur on the surface of intact cells and suggested that a critical interaction site is located within extracellular domains. Cross-linking in conjunction with reimmunoprecipitation indicated that larger multi-component alpha 3 beta 1/TM4/TM4 complexes (alpha 3 beta 1/CD9/CD63, alpha 3 beta 1/CD81/CD63, and alpha 3 beta 1/CD9/CD81) also could be detected on the cell surface. Immunofluorescent staining showed redistribution of alpha 3 beta 1/TM4 complexes toward the periphery of cells plated on various extracellular matrix substrates and also showed that these complexes were localized in cell footprints. Staining of human tissues yielded additional results consistent with co-localization of alpha 3 beta 1 and CD9, CD63, and CD81 proteins. In conclusion we suggest that the prevalence of integrin/TM4 complexes in diverse cellular environments is indicative of their general physiological importance.
authors.affiliation: Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: F
authors.initials: F
authors.lastname: Berditchevski
authors.forename: M M
authors.initials: MM
authors.lastname: Zutter
authors.forename: M E
authors.initials: ME
authors.lastname: Hemler
mesh_terms: D015703:Antigens, CD / Q000378:metabolism*; D000954:Antigens, Surface / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D039201:Integrin alpha3beta1; D039121:Integrin alpha6beta1; D039161:Integrin alpha6beta4; D016023:Integrins / Q000378:metabolism*; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011485:Protein Binding; D060225:Tetraspanin 28; D060245:Tetraspanin 29; D060149:Tetraspanin 30; D014407:Tumor Cells, Cultured
chemical_list: D015703:Antigens, CD; D000954:Antigens, Surface; C554586:CD63 protein, human; C554798:CD81 protein, human; C554869:CD9 protein, human; D039201:Integrin alpha3beta1; D039121:Integrin alpha6beta1; D039161:Integrin alpha6beta4; D016023:Integrins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010980:Platelet Membrane Glycoproteins; D060225:Tetraspanin 28; D060245:Tetraspanin 29; D060149:Tetraspanin 30