Tetraspanins in intercellular adhesion of polarized epithelial cells: spatial and functional relationship to integrins and cadherins

The subcellular distribution of tetraspanin molecules and their functional relationship with integrins in cell-cell adhesion was studied in detail in different polarized epithelial cell models. CD9, CD81 and CD151 tetraspanin s were localized at lateral cell-cell contact sites in a similar distributi on to E-cadherin, Interestingly, CD9 was partially localized at the apical microvillae of Madin-Darby canine kidney cells forming multimolecular compl exes distinct from those found on the basolateral membrane, suggesting the coexistence of differential tetraspanin webs with different subcellular loc alization. We found that tetraspanin-associated beta1 integrins at cell-to- cell contacts were in a low-affinity conformational state, and that their l ocalization at intercellular contacts was independent of cadherin expressio n and adhesion. Furthermore, integrin-tetraspanin complexes were functional ly relevant in cell-cell adhesion in a cadherin-independent manner, without requiring a conformational change of the integrin moiety, Nevertheless, th e integrin alpha3 beta1 was ligand-binding competent and this binding did n ot disrupt association to tetraspanins. Moreover, Chinese hamster ovary cel ls treated with anti-tetraspanin mAbs or activatory anti-beta1 integrin mAb s were able to develop tubule-like structures, Together, these data support tetraspanin association as a new regulatory mechanism of integrin function and suggest a role for tetraspanins-integrin complexes in providing the ce ll with the spatial cues necessary for their proper polarization.