Transmembrane-4-superfamily proteins CD151 and CD81 associate with alpha 3beta 1 integrin, and selectively contribute to alpha 3 beta 1-dependent neurite outgrowth

Proteins in the transmembrane-4-superfamily (TM4SF) form many different com plexes with proteins in the integrin family, but the functional utility of these complexes has not yet been demonstrated. Were we show that TM4SF prot eins CD151, CD81, and CD63 co-distribute with alpha 3 beta 1 integrin on ne urites and growth cones of human NT2N cells. Also, stable CD151-alpha 3 bet a 1 and CD81-alpha 3 beta 1 complexes were recovered in NT2N detergent lysa tes, Total NT2N neurite outgrowth on laminin-5 (a ligand for alpha 3 beta 1 integrin) was strongly inhibited by anti-CD151 and -CD81 antibodies either together (similar to 85% inhibition) or alone (similar to 45% inhibition). Notably, these antibodies had no inhibitory effect on NT2N neurites formed on laminin-l or fibronectin, when alpha 3 beta 1 integrin was not engaged. Neurite number, length, and rate of extension were all affected by anti-TM 4SF antibodies. In summary: (1) these substrate-dependent inhibition result s strongly suggest that CD151 and CD81 associations with alpha 3 beta 1 are functionally relevant, (2) TM4SF proteins CD151 and CD81 make a strong pos itive contribution toward neurite number, length, and rate of outgrowth, an d (3) NT2N cells, a well-established model of immature central nervous syst em neurons, can be a powerful system for studies of integrin function in ne urite outgrowth and growth cone motility.