EWI-2 Is a Major CD9 and CD81 Partner and Member of a Novel Ig Protein Subfamily
A novel Ig superfamily protein, EWI-2, was co-purified with tetraspanin protein CD81 under relatively stringent Brij 96 detergent conditions and identified by mass spectrometric protein sequencing. EWI-2 associated specifically with CD9 and CD81 but not with other tetraspanins or with integrins. Immunodepletion experiments indicated that EWI-2–CD9/CD81 interactions are highly stoichiometric, with ∼70% of CD9 and CD81 associated with EWI-2 in an embryonic kidney cell line. The EWI-2 molecule was covalently cross-linked (in separate complexes) to both CD81 and CD9, suggesting that association is direct. EWI-2 is part of a novel Ig subfamily that includes EWI-F (F2α receptor regulatory protein (FPRP), CD9P-1), EWI-3 (IgSF3), and EWI-101 (CD101). All four members of this Ig subfamily contain a Glu-Trp-Ile (EWI) motif not seen in other Ig proteins. As shown previously, the EWI-F molecule likewise forms highly proximal, specific, and stoichiometric complexes with CD9 and CD81. Human and murine EWI-2 protein sequences are 91% identical, and transcripts in the two species are expressed in virtually every tissue tested. Thus, EWI-2 potentially contributes to a variety of CD9 and CD81 functions seen in different cell and tissue types. A novel Ig superfamily protein, EWI-2, was co-purified with tetraspanin protein CD81 under relatively stringent Brij 96 detergent conditions and identified by mass spectrometric protein sequencing. EWI-2 associated specifically with CD9 and CD81 but not with other tetraspanins or with integrins. Immunodepletion experiments indicated that EWI-2–CD9/CD81 interactions are highly stoichiometric, with ∼70% of CD9 and CD81 associated with EWI-2 in an embryonic kidney cell line. The EWI-2 molecule was covalently cross-linked (in separate complexes) to both CD81 and CD9, suggesting that association is direct. EWI-2 is part of a novel Ig subfamily that includes EWI-F (F2α receptor regulatory protein (FPRP), CD9P-1), EWI-3 (IgSF3), and EWI-101 (CD101). All four members of this Ig subfamily contain a Glu-Trp-Ile (EWI) motif not seen in other Ig proteins. As shown previously, the EWI-F molecule likewise forms highly proximal, specific, and stoichiometric complexes with CD9 and CD81. Human and murine EWI-2 protein sequences are 91% identical, and transcripts in the two species are expressed in virtually every tissue tested. Thus, EWI-2 potentially contributes to a variety of CD9 and CD81 functions seen in different cell and tissue types. heparin binding-epidermal growth factor 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid F2α receptor regulatory protein dithiobis(succinimidylpropionate) glutamine-tryptophan-isoleucine horseradish peroxidase phosphate-buffered saline with 0.1% Tween 20 hepatitis C virus human Ig superfamily monoclonal antibody polyacrylamide gel electrophoresis high performance liquid chromatography human Tetraspanin proteins contain cytoplasmic N and C termini, four transmembrane domains, one small and one large extracellular loop, and at least 30 amino acids distributed throughout the molecule that are highly conserved among most family members (1Wright M.D. Tomlinson M.G. Immunol. Today. 1994; 15: 588-594Abstract Full Text PDF PubMed Scopus (332) Google Scholar, 2Maecker H.T. Todd S.C. Levy S. FASEB J. 1997; 11: 428-442Crossref PubMed Scopus (809) Google Scholar, 3Hemler M.E. Mannion B.A. Berditchevski F. Biochim. Biophys. Acta. 1996; 1287: 67-71PubMed Google Scholar). Conserved cysteines within the large extracellular loop stabilize the folding of five α-helical domains (4Kitadokoro K. Bordo D. Galli G. Petracca R. Falugi F. Abrignani S. Grandi G. Bolognesi M. EMBO J. 2001; 20: 12-18Crossref PubMed Scopus (225) Google Scholar). Tetraspanins may be molecular facilitators (2Maecker H.T. Todd S.C. Levy S. FASEB J. 1997; 11: 428-442Crossref PubMed Scopus (809) Google Scholar) that organize other tetraspanins and other cell surface proteins into a network of complexes described as the tetraspan web (5Rubinstein E. Le Naour F. Lagaudriere-Gesbert C. Billard M. Conjeaud H. Boucheix C. Eur. J. Immunol. 1996; 26: 1665-2657Crossref Scopus (330) Google Scholar). Indeed, tetraspanins form extensive complexes with each other and with other proteins such as integrins (5Rubinstein E. Le Naour F. Lagaudriere-Gesbert C. Billard M. Conjeaud H. Boucheix C. Eur. J. Immunol. 1996; 26: 1665-2657Crossref Scopus (330) Google Scholar, 6Berditchevski F. Zutter M.M. Hemler M.E. Mol. Biol. Cell. 1996; 7: 193-207Crossref PubMed Scopus (251) Google Scholar, 7Mannion B.A. Berditchevski F. Kraeft S.K. Chen L.B. Hemler M.E. J. Immunol. 1996; 157: 2039-2047PubMed Google Scholar, 8Serru V. Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Crossref PubMed Scopus (202) Google Scholar, 9Berditchevski F. Bazzoni G. Hemler M.E. J. Biol. Chem. 1995; 270: 17784-17790Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar, 10Fitter S. Sincock P.M. Jolliffe C.N. Ashman L.K. Biochem. J. 1999; 338: 61-70Crossref PubMed Scopus (99) Google Scholar, 11Sincock P.M. Fitter S. Parton R.G. Berndt M.C. Gamble J.R. Ashman L.K. J. Cell Sci. 1999; 112: 833-844Crossref PubMed Google Scholar, 12Indig F.E. Diaz-Gonzalez F. Ginsberg M.H. Biochem. J. 1997; 327: 291-298Crossref PubMed Scopus (72) Google Scholar, 13Hasegawa H. Nomura T. Kishimoto K. Yanagisawa K. Fujita S. J. Immunol. 1998; 161: Google Scholar, Cell 1996; PubMed Scopus Google Scholar, K. R. E. J. Cell Biol. 1995; PubMed Scopus Google Scholar, J. J. Immunol. 1996; 157: Google Scholar, E. Le Naour F. Billard M. M. Boucheix C. Eur. J. Immunol. 1994; PubMed Scopus Google (5Rubinstein E. Le Naour F. Lagaudriere-Gesbert C. Billard M. Conjeaud H. Boucheix C. Eur. J. Immunol. 1996; 26: 1665-2657Crossref Scopus (330) Google Scholar, J. V. S. J. Immunol. 1996; 157: Google Scholar, Levy S. J. Immunol. Google Scholar, V. 1994; PubMed Scopus Google and T. J. Immunol. Google and Levy S. J. Immunol. Google Scholar, G. V. D. Billard M. Boucheix C. Rubinstein E. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google and growth and R. S. T. M. E. EMBO J. 1994; PubMed Scopus Google Scholar, S. R. K. G. M. E. J. Cell Biol. 1995; PubMed Scopus Google Scholar). The large of proteins and may be by tetraspanin complexes with to four detergent and complexes are in conditions that other tetraspanin and at least of is associated with under conditions Berditchevski F. J. Hemler M.E. Mol. Biol. Cell. 1998; PubMed Scopus Google Scholar). of to that and are associated Hemler M.E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). in and growth to a and Hemler M.E. J. Cell Sci. PubMed Google Scholar). other tetraspanin are the stringent Brij detergent tetraspanin complexes in Brij 96 a C. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google such as may tetraspanin complexes in of PubMed Scopus Google tetraspanin complexes in Brij 96 are and not C. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google tetraspanin complexes with protein be in Brij 96 and tetraspanin in Brij 96 to be CD81 contributes to Hemler M.E. J. Cell Sci. PubMed Google Scholar) and to G. V. D. Billard M. Boucheix C. Rubinstein E. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, Sci. S. 1997; PubMed Scopus Google Scholar). The tetraspanin CD81 is expressed by virtually every cell CD9 is As seen in at least one cell the of CD9 may be in a with CD81. with in Brij 96 CD81 and CD9 complexes other but other tetraspanin complexes D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). CD9 an in K. G. S. H. F. K. K. K. M. E. PubMed Scopus Google Scholar, Naour F. Rubinstein E. C. M. Boucheix C. PubMed Scopus Google Scholar) and as a the and of J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, K. T. T. T. E. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google CD81 to the hepatitis C virus protein S. Galli G. Falugi F. Petracca R. M. D. Grandi G. Abrignani S. 1998; PubMed Scopus Google Scholar) and may as a a virus that and is a of and K. Biol. PubMed Scopus Google Scholar). CD81 and CD9 in and virus into T. J. Immunol. Google Scholar, S. Galli G. Falugi F. Petracca R. M. D. Grandi G. Abrignani S. 1998; PubMed Scopus Google Scholar, M. J. J. 1997; PubMed Scopus Google Scholar, 1994; Google Scholar, J. 1997; PubMed Google Scholar). CD9 and CD81 are in into Hemler M.E. J. Cell Biol. 1999; PubMed Scopus Google Scholar). cell CD9 and CD81 in cell Hemler M.E. J. Cell Sci. PubMed Google Scholar, V. Mol. Biol. Cell. 1997; PubMed Scopus Google Scholar, M. M. M. S. J. PubMed Scopus Google Scholar, M. K. S. 1999; Google Scholar, M. K. S. H. S. 2001; PubMed Scopus Google Scholar, K. S. M. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, M. C. M. R. Ashman L.K. F. J. Cell Biol. 1998; PubMed Scopus Google Scholar). CD9 in may cell in a variety of S. M. M. R. M. J. PubMed Scopus Google Scholar, M. T. M. T. K. M. 1995; Google Scholar, M. K. T. T. 1996; Google Scholar, T. 1997; Google Scholar, M. H. M. H. H. T. PubMed Scopus Google Scholar, S. G. T. M. M. J. 1999; PubMed Scopus Google Scholar, M. K. T. M. H. T. 1998; Google Scholar, M. K. M. S. T. T. 1995; Google Scholar). identified as the of an antibody R. S. C. Levy R. Levy S. Mol. Cell. Biol. PubMed Scopus Google as a of S. Levy S. C. Mol. Cell. 2001; PubMed Scopus Google Scholar) and of and of cell Levy S. J. Immunol. Google Scholar, Sci. S. 1997; PubMed Scopus Google Scholar, R. S. C. Levy R. Levy S. Mol. Cell. Biol. PubMed Scopus Google Scholar, R. M. 1996; PubMed Scopus Google Scholar, T. EMBO J. 1997; PubMed Scopus Google Scholar, H.T. Levy S. J. 1997; PubMed Scopus Google Scholar, H.T. Levy S. Sci. S. 1998; PubMed Scopus Google Scholar). the large of CD9 and CD81 to a of and to CD9 and CD81 protein that are specific, highly proximal, and highly stoichiometric, to into the functions of CD9 and CD81 in and this a mass protein to proteins that with CD81 Brij 96 a novel Ig superfamily protein, EWI-2, that with CD81 and CD9 with high and the CD9 and one other molecule to a of and with that seen EWI-2 D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). that molecule to the novel subfamily of proteins as EWI-2 in this S. R. F. Hemler M.E. Cell 1994; PubMed Scopus Google M.E. F. J. Immunol. Google and Berditchevski F. Hemler M.E. 1995; PubMed Scopus Google Scholar). K. M. T. M. S. J. PubMed Google Scholar) and T. J. Immunol. Google and Berditchevski F. J. Hemler M.E. Mol. Biol. Cell. 1998; PubMed Scopus Google Scholar). The or to was peroxidase antibody and and to to and embryonic kidney in with and with acid into and with C. PubMed Google Scholar). proteins as described D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). CD81 complexes a Brij 96 of and protein proteins in 0.1% by and by at with and at to in gel and As described D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google sequences by chromatography to a mass with a of the mass of the was by in the and by with the B.A. 1998; PubMed Scopus Google Scholar, J. 1994; PubMed Scopus Google Scholar). EWI-2 with a was by EWI-2 The the an that was by the and the and The was and and of the The was by the into the cell was a with and to by in The in as A tissue was with EWI-2 or to the EWI-2 was by of with and gel of a of EWI-2 by with with to the with in 20 at with by into Brij 96 or in with 20 and a at with was by and at with protein with protein and complexes at with to with four with complexes by in by and to with in phosphate-buffered saline with 0.1% Tween 20 with and by CD81 as by and to with in the with the by and and as with and 30 with with a to by and cell and in Brij 96 as described The was into and of or in The into four and by as Brij 96 of by two of at and with the indicated of the or dithiobis(succinimidylpropionate) at by at with was to to cross-linked and a of the and with the indicated and by by as described Cell surface in Brij 96 as was in with and to a that in Brij 96 in at 96 at of the of the to the of this was with of Brij 96 in a of and with of and in at in a at of the of the The was in the of Brij 96 in was to each and CD81 complexes and by with as described of proteins Brij 96 detergent and that detergent conditions of CD81 complexes D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). CD81 complexes cell embryonic kidney and CD9 as as species identified as a of and a novel Ig superfamily protein D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google All cell a species of the protein, CD81 complexes a Brij 96 of and by The was and with by liquid chromatography and by mass A of the and are in mass A other to proteins CD81 association not be and M. the most species was a protein into with The five in to an described as to a surface The in this of one an of with an to the M. 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J. Mol. Biol. 1994; PubMed Scopus Google Scholar, Immunol. PubMed Scopus Google Scholar). A of the Ig proteins with to proteins is a CD9 and CD81 D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google as as and four proteins are to each other to other Ig protein the the Ig domains of each protein to the shown in and in The of the in each Ig C. J. Mol. Biol. 1994; PubMed Scopus Google Scholar, Immunol. PubMed Scopus Google Scholar). The most is among the two Ig domains of each of other Ig domains is the Ig domains to each other to the Ig a is a a protein motif within the loop in the Ig of each protein the protein the Ig protein EWI-2, and the of the family members to each other and within the two Ig domains EWI-3 and EWI-101 are to each other to the other two members of the and in in the human EWI-2 protein, to a and to this of the of the murine of the human and EWI-2 proteins 91% and throughout the within the two Ig The human EWI-2 protein to at in the the to within a that the The of the human and EWI-2 and of a tissue with human EWI-2 high in human and with in other in EWI-2 is a expressed of a novel Ig subfamily and may conserved functions in the association of EWI-2 with CD9 and an EWI-2 with a was into a was to EWI-2 and cell with and in or Brij of EWI-2 but not the a of as of and in may be of the EWI-2 protein The in EWI-2 may contain EWI-F but may contain of EWI-2 are under T. and M. Brij 96 a to with both CD81 and CD9 to CD9 and CD81 with EWI-2 CD9 CD81 in or The with CD9 and CD81 in and the seen in CD9 and CD81 and may be the of the of the protein of complexes with CD9 and CD81 are highly stoichiometric and EWI-F EWI-2 cell with and in Brij of the with or with or by and with The and of EWI-F with CD81 and CD9 with or a Brij 96 of was by A was by CD81 complexes each and by by with of to EWI-2 and EWI-F in by the of the cell in CD9 and CD81 Brij 96 of EWI-2 with an monoclonal EWI-2 was specifically in CD9 and CD81 but not in or the CD81 with CD9 and EWI-2 but not with or the highly association of EWI-2 with CD9 and CD81. The of EWI-2 in a of the of EWI-2 in the a of EWI-2 was with an a Brij 96 that the and as species in contain the are of the EWI-2 with CD81. that the within the of the EWI-2 molecule may not the Ig domains of the The in the of to EWI-2 seen in A is by the in seen with the antibody in the of CD9 and CD81 to EWI-2, a of a Brij 96 of EWI-2 was with the the of and The by and CD81 to an in both the CD81 and the that was not in the of and or in the and CD81 is of a with one molecule of CD81 cross-linked to one molecule of in the of CD81 of a with a of CD81. Indeed, of the CD81 large loop that CD81 is to form a (4Kitadokoro K. Bordo D. Galli G. Petracca R. Falugi F. Abrignani S. Grandi G. Bolognesi M. EMBO J. 2001; 20: 12-18Crossref PubMed Scopus (225) Google Scholar). that EWI-2 be cross-linked to CD81 CD9, a Brij 96 of EWI-2 was with of the was to and a of and was by with an As shown in as of with CD9 and CD81 to in to the EWI-2 be cross-linked to CD81 CD9 and in a separate a of EWI-2 was cross-linked to CD81 and to a to CD9 A indicated that the of EWI-2 cross-linked to CD9 CD81 and was the of EWI-2 that with CD81 in Brij 96 and to or was that the is highly and to be direct. The be but cross-linked at a the of the EWI-2 with CD9 and a Brij 96 of cell EWI-2 was with with or with and and each shown in and that of the EWI-2 the and of CD9 and a of ∼70% the EWI-2 with CD9 and CD81. was with the and EWI-2, CD9, or CD81 the A separate EWI-2 of CD9 and is EWI-F D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). the and Brij 96 cell chromatography a CD81 complexes was by and CD81 complexes each As shown in and in EWI-2 and EWI-F associated with CD81 but with EWI-2 of the the was in but in EWI-2 and EWI-F complexes was antibody of CD9 and of the EWI-F associated with CD9 and CD81 complexes may contain both EWI-2 and a of complexes into the functions of tetraspanins CD9 and to associated protein Brij 96 detergent the a protein of identified mass as a novel Ig superfamily protein, and EWI-2 is the protein that a The human EWI-2 protein is 91% to suggesting a highly conserved EWI-2 is Human and a of tissue and human and EWI-2 transcripts in every tissue and and and J. J. 11: PubMed Scopus Google Scholar). The of in of domains in CD81 A of EWI-2 both to with CD81 and cytoplasmic that the two Ig domains are not CD81 is with molecular Ig domains and CD81. a of J. Immunol. 1998; PubMed Scopus Google the Ig domains of EWI-2 the domains be to with the large extracellular loop of may the cell surface (4Kitadokoro K. Bordo D. Galli G. Petracca R. Falugi F. Abrignani S. Grandi G. Bolognesi M. EMBO J. 2001; 20: 12-18Crossref PubMed Scopus (225) Google Scholar). A of protein a highly EWI-2 and other Ig superfamily and and the of by high of is with the of seen within other of Ig proteins with and The most to EWI-2 is the with an of As a an motif by four family and and EWI-F in this of the motif other Ig superfamily proteins this The of and EWI-F previously, EWI-3 was as part of a S. G. M. S. K. 1998; PubMed Scopus Google Scholar). the other are by family The of proteins are of Ig domains, an Ig superfamily proteins in All highly cytoplasmic and family the two Ig domains are the of to the other proteins in the to a potentially domains, to EWI-F identified as a CD9 and CD81 D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). is not EWI-3 and EWI-101 are CD9 and CD81 to EWI-2 and the EWI-3 and EWI-101 proteins both contain cysteines to Ig of EWI-101 cysteines C. S. E. M. Immunol. 1994; PubMed Scopus Google Scholar). the CD9 and CD81 EWI-2 and EWI-F as the most specific, and highly stoichiometric identified to EWI-2 and EWI-F highly complexes with CD9 and CD81 in the relatively stringent Brij other CD9 and proteins such as and and growth in relatively such as or Brij or in detergent conditions S. Sincock P.M. Jolliffe C.N. Ashman L.K. Biochem. J. 1999; 338: 61-70Crossref PubMed Scopus (99) Google Scholar, 11Sincock P.M. Fitter S. Parton R.G. Berndt M.C. Gamble J.R. Ashman L.K. J. Cell Sci. 1999; 112: 833-844Crossref PubMed Google Scholar, 12Indig F.E. Diaz-Gonzalez F. Ginsberg M.H. Biochem. J. 1997; 327: 291-298Crossref PubMed Scopus (72) Google Scholar, 13Hasegawa H. Nomura T. Kishimoto K. Yanagisawa K. Fujita S. J. Immunol. 1998; 161: Google Scholar, J. J. Immunol. 1996; 157: Google Scholar, R. S. T. M. E. EMBO J. 1994; PubMed Scopus Google Scholar, H. R. J. Cell Biol. PubMed Scopus Google Scholar). EWI-2 and other Brij CD9 CD81 complexes with and and other tetraspanins such as and among EWI-2 and EWI-F with CD9 and CD81 with EWI-2 and EWI-F D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar) with at and other tetraspanins F. Zutter M.M. Hemler M.E. Mol. Biol. Cell. 1996; 7: 193-207Crossref PubMed Scopus (251) Google G. V. D. Billard M. Boucheix C. Rubinstein E. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google and T. M. M. J. Immunol. 1995; Google of in or in interactions are F. Zutter M.M. Hemler M.E. Mol. Biol. Cell. 1996; 7: 193-207Crossref PubMed Scopus (251) Google the to an extensive such that and with CD9 and CD81 at a D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google and EWI-2 or EWI-F association with or be D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google and EWI-2 and EWI-F with CD9 and CD81 in suggesting that interactions are a network of an of are to are as a protein in the and mass the EWI-2 protein as by the most protein different to in that may be a and this in experiments and the of with complexes or EWI-2 and of that and complexes are be in Brij 96 are with a and a S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). a that an protein EWI-2 be relatively stringent detergent to CD9 or CD81 but not to EWI-F S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). the of EWI-2 and of EWI-F that and complexes in the of of EWI-2 Brij 96 a large of CD9 and CD81 but a of the and a and complexes be at least to be complexes may be a gel complexes to be complexes D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google with the of the two proteins. that and complexes may a of EWI-2 to the the two of protein Indeed, experiments as as (4Kitadokoro K. Bordo D. Galli G. Petracca R. Falugi F. Abrignani S. Grandi G. Bolognesi M. EMBO J. 2001; 20: 12-18Crossref PubMed Scopus (225) Google Scholar) that CD81 as a and that the of CD9 in is with CD81 D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). as and complexes shown to D. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Le Naour F. M. Billard M. G. Boucheix C. Rubinstein E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google that and complexes may Indeed, of CD81 or both of CD9, a protein EWI-2 Hemler M.E. J. Cell Sci. PubMed Google Scholar, C. Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). a that CD9 may be associated with was is that CD9 association within a this to be to EWI-2 and other proteins may be cross-linked to CD9 CD81. CD9, and integrins F. Zutter M.M. Hemler M.E. Mol. Biol. Cell. 1996; 7: 193-207Crossref PubMed Scopus (251) Google Scholar, K. R. E. J. Cell Biol. 1995; PubMed Scopus Google CD81 and protein Hemler M.E. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google and CD9 and R. S. T. M. E. EMBO J. 1994; PubMed Scopus Google suggesting in each a of was with the and cross-linked complexes of and protein not to the of the molecular was to covalently to CD9 K. R. E. J. Cell Biol. 1995; PubMed Scopus Google but in EWI-F with may the protein CD9 CD81 in cell cell and cell the that a expressed protein such as EWI-2 a in of the CD81 large extracellular loop is in S. Galli G. Falugi F. Petracca R. M. D. Grandi G. Abrignani S. 1998; PubMed Scopus Google may be T. J. PubMed Scopus Google Scholar, M. M. Levy S. C. J. E. J. PubMed Scopus Google Scholar, R. D. J. E. J. 2001; PubMed Scopus Google Scholar). a protein such as the EWI-2 molecule an this EWI-2 transcripts are in the J. J. 11: PubMed Scopus Google and The murine EWI-2 within a that J. J. 11: PubMed Scopus Google at D. 1998; PubMed Scopus Google Scholar). EWI-2, expressed in both the and is a not the J. J. 11: PubMed Scopus Google Scholar, 2001; PubMed Scopus Google Scholar). within the in the in the human within a that associated with a variety of J. J. 11: PubMed Scopus Google Scholar). identified a novel protein, EWI-2, as a CD9 and CD81 EWI-2 a subfamily of Ig proteins that includes CD9 and CD81. EWI-2 and EWI-F other and proteins are highly stoichiometric, and by of EWI-2 is an in the functions to CD9 CD81 such as cell cell and and of EWI-2 and at CD9 and CD81 as as or into CD9 and CD81 S. R. and K. of the in mass and with of Ig domains, M. E. and a of the and the sequencing.