IDENTIFICATION OF A LARGE COMPLEX CONTAINING THE INTEGRIN ALPHA(6)BETA(1) LAMININ RECEPTOR IN NEURAL RETINAL CELLS

Integrin alpha(6) beta(1) is a laminin receptor involved in adhesion a nd neurite extension of retinal neurons on laminin, The present study was carried out to identify potential interactions between the alpha(6 ) beta(1) receptor and cellular proteins that may be involved in integ rin signaling and function, For this purpose we have used a biochemica l approach based on the solubilization of retinal neurons cultured on laminin with nonionic detergents, followed by centrifugation on sucros e velocity gradients, Analysis of the distribution of the alpha(6) and beta(1) integrin subunits in the gradients showed that they migrate a s a large complex after extraction of cells with octylglucoside, but n ot after Triton X-100 extraction, Cytoskeletal proteins known to local ize in adhesion plaques did not comigrate with alpha(6) beta(1) in oct ylglucoside gradients, while a set of polypeptides whose tyrosine phos phorylation was enhanced by culture on laminin colocalized with alpha( 6) beta(1) on the gradients after octylglucoside solubilization. Cultu re of retinal neurons on bovine serum albumin, a nonadhesive substratu m, partially affected the gradient distribution of the receptor after octylglucoside extraction, Furthermore, analysis of the gradient distr ibution of two alternatively spliced isoforms of the alpha(6) subunit, alpha(6)-cytoA and alpha(6)-cytoB, showed that the effect of non-adhe sion on the sedimentation properties of the two integrin alpha(6) isof orms was more dramatic for alpha(6)-cytoB than alpha(6)-cytoA. These d ifferences in the sedimentation behaviour indicate distinct biochemica l properties of the two alpha(6) isoforms that, together with previous observations on their differential distribution in the developing ret ina, may reflect functional specificities.