Selective tetraspan-integrin complexes (CD81/alpha 4 beta 1, CD151/alpha 3beta 1, CD151/alpha 6 beta 1) under conditions disrupting tetraspan interactions

The tetraspans are molecules with four transmembrane domains which are enga ged in multimolecular complexes (the tetraspan web) containing a subset of beta 1 integrins tin particular alpha 3 beta 1, alpha 4 beta 1 and alpha 6 beta 1), MHC antigens and several unidentified molecules. The molecules ass ociated with tetraspans are readily detected after immunoprecipitation perf ormed in mild detergents such as Brij 97 or CHAPS. In this study we show th at another classical mild detergent, digitonin, dissociated most of these a ssociated molecules, including integrins, from the tetraspans CD9, CD37, CD 53, CD63, CD82, Co-029, Talla-1 and NAG-2. In contrast, reciprocal immunopr ecipitations from various cell lines demonstrated that two other tetraspans , CD81 and CD151, formed complexes with integrins not disrupted by digitoni n. These complexes were CD81/alpha 4 beta 1, CD151/alpha 3 beta 1 and CD151 /alpha 6 beta 1. Furthermore, a new anti-CD151 monoclonal antibody (mAb), T S151r, was shown to have a restricted pattern of expression, inversely rela ted to the sum of the levels of expression of alpha 6 beta 1 and alpha 3 be ta 1. This mAb was unable to co-precipitate integrins in digitonin, suggest ing that its epitope is blocked by the association with integrins. Indeed, the binding of TS151r to the cell surface was quantitatively diminished fol lowing alpha 3 beta 1 overexpression. Altogether, these data suggest that, among tetraspans, CD81 interacts directly with the integrin alpha 4 beta 1, and CD151 interacts directly with integrins alpha 3 beta 1 and alpha 6 bet a 1. Because all tetraspan-tetraspan associations are disrupted by digitoni n, it is likely that the other tetraspans interact indirectly with integrin s, through interactions with CD81 or CD151.