The Tetraspan Protein Epithelial Membrane Protein-2 Interacts with β1 Integrins and Regulates Adhesion

The growth arrest-specific-3 (GAS3)/PMP22 proteins are members of the four-transmembrane (tetraspan) superfamily. Although the function of these proteins is poorly understood, GAS3/PMP22 proteins have been implicated in the control of growth and progression of certain cancers. Epithelial membrane protein-2 (EMP2), a GAS3/PMP22 family member, was recently identified as a putative tumor suppressor gene. Here, we addressed the normal function of EMP2 by testing the prediction that it influences integrin-related cell functions. We observed that EMP2 associates with the β1 integrin subunit. Co-immunoprecipitation and immunodepletion experiments indicated that ∼60% of β1integrins and EMP2 can be isolated in common protein complexes. Whereas this association between EMP2 and β1 integrin may be direct or indirect, it has features of integrin heterodimer selectivity. Thus, by laser confocal microscopy, EMP2 colocalized with α6β1 but not α5β1 integrin. Increased expression of EMP2 also influenced the integrin heterodimer repertoire present on the plasma membrane. EMP2 specifically increased the surface expression of the α6β1 integrin while decreasing that of the α5β1 protein. Reciprocally, reduction in EMP2 expression using a specific ribozyme decreased surface expression of α6β1 integrin. Accordingly, these EMP2-mediated changes resulted in a dramatic alteration in cellular adhesion to extracellular matrix proteins. This study demonstrates for the first time the interaction of a GAS3/PMP22 family member with an integrin protein and suggests that such interactions and their functional consequences are a physiologic role of GAS3/PMP22 proteins. The growth arrest-specific-3 (GAS3)/PMP22 proteins are members of the four-transmembrane (tetraspan) superfamily. Although the function of these proteins is poorly understood, GAS3/PMP22 proteins have been implicated in the control of growth and progression of certain cancers. Epithelial membrane protein-2 (EMP2), a GAS3/PMP22 family member, was recently identified as a putative tumor suppressor gene. Here, we addressed the normal function of EMP2 by testing the prediction that it influences integrin-related cell functions. We observed that EMP2 associates with the β1 integrin subunit. Co-immunoprecipitation and immunodepletion experiments indicated that ∼60% of β1integrins and EMP2 can be isolated in common protein complexes. Whereas this association between EMP2 and β1 integrin may be direct or indirect, it has features of integrin heterodimer selectivity. Thus, by laser confocal microscopy, EMP2 colocalized with α6β1 but not α5β1 integrin. Increased expression of EMP2 also influenced the integrin heterodimer repertoire present on the plasma membrane. EMP2 specifically increased the surface expression of the α6β1 integrin while decreasing that of the α5β1 protein. Reciprocally, reduction in EMP2 expression using a specific ribozyme decreased surface expression of α6β1 integrin. Accordingly, these EMP2-mediated changes resulted in a dramatic alteration in cellular adhesion to extracellular matrix proteins. This study demonstrates for the first time the interaction of a GAS3/PMP22 family member with an integrin protein and suggests that such interactions and their functional consequences are a physiologic role of GAS3/PMP22 proteins. Connexins, tetraspanins, and GAS3/PMP22 1The abbreviations used are: GAS3, growth arrest-specific-3; ECM, extracellular matrix; EMP2, epithelial membrane protein-2; PBS, phosphate-buffered saline; FITC, fluorescein isothiocyanate; MFI, mean fluorescence intensity; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid. comprise the major families of tetraspan proteins. Functionally, the best understood tetraspan proteins are connexins, which form the major structural elements of gap junctions. On the other hand, tetraspanins have recently gained prominence for their role as “molecular facilitators” in the assembly of mixed protein signaling complexes, including those involving integrins (1Berditchevski F. Odintsova E. J. Cell Biol. 1999; 146: 477-492Google Scholar, 2Maecker H.T. Todd S.C. Levy S. FASEB J. 1997; 11: 428-442Google Scholar). Functionally, tetraspanins have been shown to influence integrin-mediated events such as cell proliferation, migration, and tumor cell invasion in a variety of cell types (3Berditchevski F. Bazzoni G. Hemler M.E. J. Biol. Chem. 1995; 270: 17784-17790Google Scholar, 4Berditchevski F. Tolias K.F. Wong K. Carpenter C.L. Hemler M.E. J. Biol. Chem. 1997; 272: 2595-2598Google Scholar, 5Fitter S. Sincock P.M. Jolliffe C.N. Ashman L.K. Biochem. J. 1999; 338: 61-70Google Scholar, 6Mannion B.A. Berditchevski F. Kraeft S.K. Chen L.B. Hemler M.E. J. Immunol. 1996; 157: 2039-2047Google Scholar, 7Serru V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google Scholar, 8Yauch R.L. Berditchevski F. Harler M.B. Reichner J. Hemler M.E. Mol. Biol. Cell. 1998; 9: 2751-2765Google Scholar). Currently, there are at least six known members of the GAS3/PMP22 family: PMP22, EMP1 (or TMP), EMP2 (or XMP), EMP3 (or YMP), PERP, and brain cell membrane protein 1 (9Attardi L.D. Reczek E.E. Cosmas C. Demicco E.G. McCurrach M.E. Lowe S.W. Jacks T. Genes Dev. 2000; 14: 704-718Google Scholar, 10Ben Porath I. Benvenisty N. Gene (Amst.). 1996; 183: 69-75Google Scholar, 11Taylor V. Suter U. Gene (Amst.). 1996; 175: 115-120Google Scholar, 12Christophe-Hobertus C. Szpirer C. Guyon R. Christophe D. Genomics. 2001; 2: 3-10Google Scholar). These genes share ∼30–40% amino acid identity (11Taylor V. Suter U. Gene (Amst.). 1996; 175: 115-120Google Scholar, 13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). All GAS3/PMP22 members are predicted to contain two extracellular loops and a small cytoplasmic tail, but beyond this structural information, little is known about the endogenous function(s) associated with most of the family members. What is known is that many of these proteins appear to be involved with cell proliferation, cell-cell, and cell-matrix interactions and/or myelin formation. Dysregulation of certain family members has been linked with disease (11Taylor V. Suter U. Gene (Amst.). 1996; 175: 115-120Google Scholar, 14Naef R. Suter U. Microsc. Res. Tech. 1998; 41: 359-371Google Scholar). For example, PMP22 has gained prominence due to the fact that genetic alterations in this gene (e.g. mutations, deletions, or duplications) lead to peripheral neuropathies such as Charcot-Marie-Tooth type 1A and Dejerrine Sottas syndrome (14Naef R. Suter U. Microsc. Res. Tech. 1998; 41: 359-371Google Scholar, 15Dackovic J. Rakocevic-Stojanovic V. Pavlovic S. Zamurovic N. Dragasevic N. Romac S. Apostolski S. Eur. J Neurol. 2001; 8: 689-692Google Scholar, 16Fabbretti E. Edomi P. Brancolini C. Schneider C. Genes Dev. 1995; 9: 1846-1856Google Scholar, 17Snipes G.J. Suter U. Shooter E.M. J. Neurochem. 1993; 61: 1961-1964Google Scholar). Epithelial membrane protein-2 (EMP2) was first identified based on its homology to PMP22 (11Taylor V. Suter U. Gene (Amst.). 1996; 175: 115-120Google Scholar). Our laboratory initially encountered EMP2 as part of a search for genes involved in the malignant progression of B cell lymphomas using suppression subtractive hybridization (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). Disruption of EMP2 yielded dramatic phenotypes. Specifically, in a model of B cell lymphoma progression, EMP2 appears to act as a tumor suppressor (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). Moreover, ectopic overexpression of in cultured cells promoted stress-induced apoptosis (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). In this study, we begin to address the biochemical function of GAS3/PMP22 family members. We test the idea that they may share with tetraspanins the capacity to interact with integrins (1Berditchevski F. Odintsova E. J. Cell Biol. 1999; 146: 477-492Google Scholar, 18Sugiura T. Berditchevski F. J. Cell Biol. 1999; 146: 1375-1389Google Scholar, 19Penas P.F. Garcia-Diez A. Sanchez-Madrid F. Yanez-Mo M. J. Invest. Dermatol. 2000; 114: 1126-1135Google Scholar). Integrins are αβ heterodimeric receptors that bind and organize cellular responses to ECM proteins and cellular receptors (21Shimizu Y. Hum. Cell. 1996; 9: 175-180Google Scholar, 22Dedhar S. Curr. Opin. Hematol. 1999; 6: 37-43Google Scholar). There is exceptional combinatorial diversity in this receptor system, with 16 α and 9 β subunits and alternate splicing of individual subunits (11Taylor V. Suter U. Gene (Amst.). 1996; 175: 115-120Google Scholar, 23Meredith Jr., J.E. Kiosses W.B. Takada Y. Schwartz M.A. J. Biol. Chem. 1999; 274: 8111-8116Google Scholar). Individual integrin αβ heterodimers display distinct specificities for various ECM proteins and cell surface receptors, so changes in the expression of these various integrins have profound effects on the repertoire of cell proliferation, survival, adhesion, and migration (12Christophe-Hobertus C. Szpirer C. Guyon R. Christophe D. Genomics. 2001; 2: 3-10Google Scholar, 14Naef R. Suter U. Microsc. Res. Tech. 1998; 41: 359-371Google Scholar, 24Keely P. Parise L. Juliano R. Trends Cell Biol. 1998; 8: 101-106Google Scholar). The present study tests whether EMP2 phenotypic effects are mediated through its interaction with integrins. We show that EMP2 associates with the β1 integrin subunit and appears to have a selective effect on the surface expression of the α6β1 integrin heterodimer. This change in integrin expression mediated by EMP2 confers unique binding properties onto the cell, namely adhesion to the ECM component laminin. These observations reflect an important role for EMP2 in the regulation of an integrin-mediated cellular phenotype. An EMP2-specific hammerhead ribozyme was constructed and used to decrease the endogenous expression of EMP2 in NIH3T3 cells (25McCall M.J. Hendry P. Jennings P.A. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 5710-5714Google Scholar). Briefly, two complementary 42-bp oligonucleotides, EMP2Rz1a and EMP2Rz1s, were synthesized by Invitrogen. The sequences were as follows: EMP2Rz1a, 5′-TCATCATTGTTTCGTCCTTTCGGACTCATCAGTTCCACATCG-3′; EMP2Rz1s, 5′-CGATGTGGAACTCAGGAGTCCGAAAGGACGAAACAATGATGA-3′. Incorporated into these oligonucleotides was the 22 bases of the hammerhead ribozyme conserved catalytic core (underlined) and two 10 nucleotide EMP2-specific recognition domains (GenBankTMaccession number AF346627; nucleotides 204–224 of the murine the the two oligonucleotides were to and into the unique in the of the protein gene in NIH3T3 cells were cultured in with 1 and NIH3T3 cells a murine EMP2 to as or an control to as were as (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). NIH3T3 cells were also with the EMP2-specific ribozyme using the were using NIH3T3 cells with the ribozyme were to as and of All cells were at in a In ribozyme of EMP2 was by was isolated NIH3T3 or cells using an was to to a membrane by and by EMP2 was using with as (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). were with for 1 and with for at were with a and and to were as (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). The used were cell and The integrin and were integrin was by D. of was by J. of J. Immunol. Scholar). An was or were used as NIH3T3 or cells were two with PBS, in 10 10 10 and 10 and for at were for and the were at for 10 The cell were by with protein were into and with to an or control The were or in and in were the using EMP2 (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar). In to EMP2 in were using were as the at for proteins were by and to a membrane were with to were with in and with an integrin or EMP2 were using a by were at least NIH3T3 or cells were and as was into to be using EMP2 or protein an integrin were and the was This was in and for were with as for EMP2 were to by expression was using the and was by the and immunodepletion as by D. Hemler M.E. J. Biol. Chem. 2001; Scholar). were adhesion was as R. Takada Y. Hemler M.E. J. Biol. Chem. 1993; Scholar). Briefly, were with the ECM or For or were as the were onto the ECM in and at cells were cells were with and using The was by the at to ECM was in was at least An test was used to between and as as between and In cells were with various of or integrin for at were into a with or and to for cells were and cells were as was or cells were onto were and in for at and with normal for were at in a with the and with were with a fluorescein and at in a were with with and onto using a confocal was used to the and of proteins. were using a confocal and were with and at and between and or was for or were at experiments were in and using the In cells were observed using a was at least The membrane expression of and β1 integrin subunits was by were in in for on were with for on in two and with for on control cells were with the two cells were in and with a expression were as mean were In to the cellular function of EMP2, we first a number of cell to of the gene. We on the fact that type NIH3T3 cells of EMP2, so we that (3Berditchevski F. Bazzoni G. Hemler M.E. J. Biol. Chem. 1995; 270: 17784-17790Google or this gene with the type The was through the of an EMP2-specific hammerhead ribozyme M. Cell Mol. Sci. 1998; which EMP2 expression by specific of its was used to that the EMP2-specific ribozyme the EMP2 type NIH3T3 cells yielded a EMP2 at 1 NIH3T3 cells with an EMP2 ribozyme a for the normal and an the EMP2 The EMP2 ribozyme expression in this We used to the protein of EMP2 in control NIH3T3 cells cells a EMP2 and cells the EMP2-specific ribozyme 1 with EMP2 protein were in cells and in was also to the of an tetraspan protein of were the cell 1 These observations indicated that cell were as for EMP2 expression and that the was specific for these NIH3T3 we the normal cellular function of we a on the that members of the tetraspanins associated with integrin the β1 subunit (12Christophe-Hobertus C. Szpirer C. Guyon R. Christophe D. Genomics. 2001; 2: 3-10Google Scholar, 13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar, 22Dedhar S. Curr. Opin. Hematol. 1999; 6: 37-43Google Scholar). Specifically, we to whether EMP2 associated with integrins and/or In to whether EMP2 and the β1 integrin subunit a was were NIH3T3 (or and with an integrin to this and to using EMP2 shown in that EMP2 with the β1 integrin subunit. The with an EMP2 β1 integrin protein in which EMP2 and were for the protein and that a of these proteins were in a common the of the β1 integrin subunit that associates with EMP2, immunodepletion experiments were to the of D. Hemler M.E. J. Biol. Chem. 2001; and of or cell were with integrin or EMP2 and the with proteins was using protein The of EMP2 and β1 integrin in the and immunodepletion were by and and these were used to the of protein in the and and integrin of their and β1 of the β1 integrin subunit cells and integrin of EMP2 in cell these that ∼60% of β1 integrin and EMP2 of the are present in a common This association between EMP2 and may be direct or it be that the interaction between EMP2 and β1 integrin was in the of which certain other most interactions observed such V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google Scholar, 8Yauch R.L. Berditchevski F. Harler M.B. Reichner J. Hemler M.E. Mol. Biol. Cell. 1998; 9: 2751-2765Google Scholar, R.L. Hemler M.E. J. Biol. Chem. 2000; Scholar). appears that the association was not due to this type of We the association and of EMP2 and the β1 integrin subunit using confocal or cells were with integrin and and laser confocal were and using In NIH3T3 or cells EMP2 expression is with an component of and of plasma membrane The is with and L. and J. of EMP2 in cells resulted in increased EMP2 on the plasma membrane. cells were with and there was a of in the and cytoplasmic In β1 integrin colocalized with EMP2 on the plasma membrane. These were specific for was observed between EMP2 and tetraspan in or cells not We whether the association of EMP2 with the β1 integrin subunit functional Specifically, we whether of EMP2 expression the binding of cells to the and cells were for in with various ECM proteins and were used as and cells were and the cells were with and as and the cells that EMP2 an in binding with cells and a in binding with In to the with EMP2 expression with Specifically, the cells with of EMP2 binding to with or cells the of the cell binding to or in the of which is known to integrin-mediated adhesion A. E.E. J. Cell. 1998; not binding is not mediated by the α6β1 integrin M.A. Microsc. Res. Tech. 2000; Scholar). that binding in and cells was mediated by we whether an integrin this were with integrin or with integrin as a control and to to a for integrin but not integrin specifically binding of and cells to and We that EMP2 with the β1 integrin subunit and that EMP2 binding to through the expression and/or of the integrin subunit. we whether EMP2 colocalized with the integrin subunit and whether protein of EMP2 the cellular of the integrin protein. or cells were with and and for cellular and using confocal shown in EMP2 colocalized with the integrin subunit in and to the β1 integrin the of the integrin subunit on the cell surface with increased expression of EMP2 in cells In to the integrin EMP2 not with the integrin In the integrin subunit was present on the plasma overexpression of EMP2 not appear to surface expression of the but increased integrin in the and cytoplasmic was used to the surface expression of the and β1 integrin subunits in and were with or β1 and by for of surface expression using a shown in the of the integrin subunit on the plasma membrane with the of cells integrin on their surface with cells or cells In the expression of integrin protein on the cell surface was with the of EMP2, with cells integrin on their surface with cells and cells Whereas EMP2 or the plasma membrane expression of and integrin the surface of the β1 integrin subunit in and cells Moreover, the of EMP2 expression effect on the surface expression of membrane not These that EMP2 expression can or the surface repertoire of integrin EMP2 to the GAS3/PMP22 family of tetraspan of which to little is known function or we show for the first time a binding for a GAS3/PMP22 family We by and immunodepletion that the of EMP2 and the β1 integrin subunit in common protein complexes. laser confocal microscopy, EMP2 colocalized with α6β1 but not α5β1 that EMP2 associates with a of integrins. Moreover, EMP2 expression the surface expression of α6β1 and with a alteration in cell adhesion to ECM proteins. These observations that EMP2 associates with certain integrin and that EMP2 in effect integrin surface expression and The association of EMP2 and β1 integrins Our that the of the EMP2 and can be isolated in complexes. The association of EMP2 and β1 integrin is not a for two The interaction between EMP2 and was observed in the of a that types of interactions observed with other for tetraspan proteins V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google Scholar, 8Yauch R.L. Berditchevski F. Harler M.B. Reichner J. Hemler M.E. Mol. Biol. Cell. 1998; 9: 2751-2765Google Scholar, R.L. Hemler M.E. J. Biol. Chem. 2000; Scholar, C. S. Edomi P. E. C. Schneider C. Mol. Biol. Cell. 1999; Scholar). In we not an association between EMP2 and a distinct using biochemical or laser confocal Our not the of proteins in these so we the of EMP2 and β1 integrin in these complexes. it is not whether the of EMP2 and the β1 integrin a direct association of these proteins or an association involving of a For example, various tetraspanins appear to form and as as integrins and other protein F. Tolias K.F. Wong K. Carpenter C.L. Hemler M.E. J. Biol. Chem. 1997; 272: 2595-2598Google Scholar, 6Mannion B.A. Berditchevski F. Kraeft S.K. Chen L.B. Hemler M.E. J. Immunol. 1996; 157: 2039-2047Google Scholar, 7Serru V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google Scholar, 8Yauch R.L. Berditchevski F. Harler M.B. Reichner J. Hemler M.E. Mol. Biol. Cell. 1998; 9: 2751-2765Google Scholar). Thus, it is that the EMP2 and β1 integrins other tetraspan and of membrane proteins. of this and the of is to the structural of the Our laser confocal that EMP2 associates with certain integrins but not α5β1 This suggests that the and β1 integrin may in part α6β1 and between certain integrins and family proteins are integrins have including interactions with and (1Berditchevski F. Odintsova E. J. Cell Biol. 1999; 146: 477-492Google Scholar, 18Sugiura T. Berditchevski F. J. Cell Biol. 1999; 146: 1375-1389Google Scholar, 19Penas P.F. Garcia-Diez A. Sanchez-Madrid F. Yanez-Mo M. J. Invest. Dermatol. 2000; 114: 1126-1135Google Scholar, R.L. Hemler M.E. J. Biol. Chem. 2000; Scholar, C. Hemler M.E. J. Biol. Chem. 2001; Scholar, J. A. J. Cell Biol. 2000; Scholar, J.E. Res. 1999; Scholar, M. A. C. M. R. M.A. Ashman L.K. Sanchez-Madrid F. J. Cell Biol. 1998; Scholar). tetraspanins form complexes, it is which tetraspanins are associated with this integrin. For example, using V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google observed a selective association of with EMP2, also appears to with α6β1 integrins V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google and proteins share a functional (13Wang C.X. Wadehra M. Fisk B.C. Goodglick L. Braun J. Blood. 2001; 97: 3890-3895Google Scholar, J. A. J. Cell Biol. 2000; Scholar). NIH3T3 cells not we not address in the present study whether EMP2 this with an biochemical study recently has direct for binding of and involving the extracellular of and amino of the subunit R.L. Hemler M.E. J. Biol. Chem. 2000; Scholar). β1 integrin association has been to be a J. A. J. Cell Biol. 2000; and experiments are to tetraspan involved in the interaction J. A. J. Cell Biol. 2000; Scholar, Le Naour F. C. Billard M. Boucheix C. Eur. J. Immunol. 1996; Scholar). These and be in whether EMP2 with α6β1 integrins and whether it with these proteins involved in and/or β1 interaction and selectivity. The present study demonstrates that EMP2 the of cell adhesion to ECM and this to changes in α6β1 integrin surface it be that other integrin heterodimers also can to and binding R. Takada Y. Hemler M.E. J. Biol. Chem. 1993; Scholar, Y. N. A. K. J. Cell Sci. 2000; Scholar, Juliano R.L. J. Biol. Chem. 1999; 274: Scholar). For example, the and subunits are part of heterodimer that are known to also bind as as and Juliano R.L. J. Biol. Chem. 1999; 274: Scholar). In is known to to binding M.A. Microsc. Res. Tech. 2000; Scholar, Y. N. A. K. J. Cell Sci. 2000; Scholar). by EMP2 of these integrin subunits little binding to or was that and subunit expression is in integrin protein not be in these cells by not We are whether EMP2 with and/or influences the expression of other integrin are in their association with integrins and of integrin-mediated cell proliferation, survival, migration, and tumor cell invasion (3Berditchevski F. Bazzoni G. Hemler M.E. J. Biol. Chem. 1995; 270: 17784-17790Google Scholar, 4Berditchevski F. Tolias K.F. Wong K. Carpenter C.L. Hemler M.E. J. Biol. Chem. 1997; 272: 2595-2598Google Scholar, 5Fitter S. Sincock P.M. Jolliffe C.N. Ashman L.K. Biochem. J. 1999; 338: 61-70Google Scholar, 6Mannion B.A. Berditchevski F. Kraeft S.K. Chen L.B. Hemler M.E. J. Immunol. 1996; 157: 2039-2047Google Scholar, 7Serru V., Le Naour F. Billard M. Azorsa D.O. Lanza F. Boucheix C. Rubinstein E. Biochem. J. 1999; 340: 103-111Google Scholar, 8Yauch R.L. Berditchevski F. Harler M.B. Reichner J. Hemler M.E. Mol. Biol. Cell. 1998; 9: 2751-2765Google Scholar). The present study that EMP2 also such properties but is distinct in its integrin and functional Thus, it appears that tetraspanins and EMP2 of other GAS3/PMP22 share the structural features integrin association but in integrin and/or We that the tetraspanins and GAS3/PMP22 proteins complementary and/or in and/or of integrin to the cell expression of the various and GAS3/PMP22 proteins may an important role in a repertoire of integrin-mediated functions. The by which EMP2 the surface expression of α6β1 integrin to be Integrins are in a which the for through is this is in a through certain signaling and cell Juliano R.L. Curr. Opin. Cell Biol. 1999; 11: Scholar, Juliano R.L. Mol. Biol. Cell. 1995; 6: Scholar, Juliano R.L. J. Biol. Chem. 1999; 274: Scholar). for may be that the association of EMP2 and α6β1 the of this integrin R. E. N. A. M. J. Cell Biol. 1999; Scholar). EMP2 may the heterodimer of the β1 integrin subunit with the integrin EMP2 may function in the of specific proteins the to the plasma membrane. EMP2 appears to the association of a of proteins and with R. L. and J. for The of these interactions may a into the surface receptor expression and the consequences for cellular functional phenotype. of such may on the function of GAS3/PMP22 proteins as as on the cell of integrins. We and for