Selective tetraspan-integrin complexes (CD81/α4β1, CD151/α3β1, CD151/α6β1) under conditions disrupting tetraspan interactions

The tetraspans are molecules with four transmembrane domains which are engaged 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 associated with tetraspans are readily detected after immunoprecipitation performed in mild detergents such as Brij 97 or CHAPS. In this study we show that another classical mild detergent, digitonin, dissociated most of these associated molecules, including integrins, from the tetraspans CD9, CD37, CD53, CD63, CD82, Co-029, Talla-1 and NAG-2. In contrast, reciprocal immunoprecipitations from various cell lines demonstrated that two other tetraspans, CD81 and CD151, formed complexes with integrins not disrupted by digitonin. 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), TS151r, was shown to have a restricted pattern of expression, inversely related to the sum of the levels of expression of alpha 6 beta 1 and alpha 3 beta 1. This mAb was unable to co-precipitate integrins in digitonin, suggesting that its epitope is blocked by the association with integrins. Indeed, the binding of TS151r to the cell surface was quantitatively diminished following 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 beta 1. Because all tetraspan-tetraspan associations are disrupted by digitonin, it is likely that the other tetraspans interact indirectly with integrins, through interactions with CD81 or CD151.