CD9, CD63, CD81, AND CD82 ARE COMPONENTS OF A SURFACE TETRASPAN NETWORK CONNECTED TO HLA-DR AND VLA INTEGRINS

CD9, CD63, CD81, and CD82 are glycoproteins of unknown function which belong to the tetraspan superfamily. These molecules have short cytopl asmic sequences, four transmembrane domains and two unequal extracellu lar regions. Here, we show that these molecules are associated with ea ch other on cell surface and with other glycoproteins such as very lat e antigen (VLA) integrins and HLA-DR antigens. Moreover, the VLA integ rins and HLA-DR antigens were also found to be associated. The interac tions of these molecules were analyzed by transfection experiments. It is demonstrated that overexpression of CD9 antigen in Raji cells lead s to a lower efficiency of precipitation of CD81 and CD82, suggesting a direct interaction between these molecules. In these cells, the copr ecipitation of CD81 and CD82 was not modified, suggesting that these t etraspans did not compete for association. However, in COS-7 cells, tr ansfection of both CD81 and CD82 led to a marked reduction of the numb er of CD9/CD81 or CD9/CD82 complexes compared to single-transfected ce lls, and this was associated with the appearance of CD81/CD82 complexe s. Therefore,in this cellular system, CD9 competes with CD81 and CD82 for association with the other tetraspan proteins. Finally, the tetras pans do not compete for the association with integrins or HLA-DR. Inde ed, when CD9 was expressed in Raji cells, it was incorporated into the pre-existing complexes of these molecules with CD81 and CD82. These d ata suggest the existence of a tetraspan network which, by connecting several molecules, may organize the positioning of cell surface protei ns and play a role in signal transduction, cell adhesion, and motility .