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 and 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 integrin signaling and function. For this purpose we have used a biochemical approach based on the solubilization of retinal neurons cultured on laminin with nonionic detergents, followed by centrifugation on sucrose velocity gradients. Analysis of the distribution of the alpha 6 and beta 1 integrin subunits in the gradients showed that they migrate as a large complex after extraction of cells with octylglucoside, but not after Triton X-100 extraction. Cytoskeletal proteins known to localize in adhesion plaques did not comigrate with alpha 6 beta 1 in octylglucoside gradients, while a set of polypeptides whose tyrosine phosphorylation was enhanced by culture on laminin colocalized with alpha 6 beta 1 on the gradients after octylglucoside solubilization. Culture of retinal neurons on bovine serum albumin, a nonadhesive substratum, partially affected the gradient distribution of the receptor after octylglucoside extraction. Furthermore, analysis of the gradient distribution of two alternatively spliced isoforms of the alpha 6 subunit, alpha 6-cytoA and alpha 6-cytoB, showed that the effect of non-adhesion on the sedimentation properties of the two integrin alpha 6 isoforms was more dramatic for alpha 6-cytoB than alpha 6-cytoA. These differences in the sedimentation behaviour indicate distinct biochemical properties of the two alpha 6 isoforms that, together with previous observations on their differential distribution in the developing retina, may reflect functional specificities.
de Curtis
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Department of Biological and Technological Research (DIBIT), HS Raffaele, Milano, Italy.
Gatti
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G
D017398:Alternative Splicing; D000818:Animals; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D002642:Chick Embryo; D003094:Collagen / Q000378:metabolism; D014644:Genetic Variation; D039121:Integrin alpha6beta1; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D007797:Laminin / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism; D017474:Receptors, Laminin / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
D039121:Integrin alpha6beta1; D016023:Integrins; D007797:Laminin; D011506:Proteins; D017474:Receptors, Laminin; D014443:Tyrosine; D003094:Collagen