Characterization of a novel set of membrane antigens associated with axonal growth. I. Biochemical and functional studies.

Cranin, a prominent 120 kDa laminin-binding protein of cell membranes, was originally identified and characterized by virtue of its ability to bind laminin directly in ligand-blotting assays. We have now raised polyclonal ('3070') and monoclonal antibodies (MAbs 4 and 199) against a partially purified preparation of cranin, and have characterized the properties and expression of the corresponding antigens in further detail. In immunoblots of E14 chick brain membranes, these antibodies all recognized a single major band migrating at approximately 125 kDa, with minor bands at 115 kDa and 170/180 kDa. The major 125 kDa antigen bound to laminin affinity beads in a divalent cation- and conformation-dependent manner. The 125 and 115 kDa bands were also the most prominent HNK-1 positive proteins detected overall within E14 chick brain membranes. MAbs 4 and 199 specifically inhibited the attachment of NG108-15 cells to low, but not high amounts of substratum-bound laminin. While the relation of 3070/MAb 4 antigens to cranin requires further elucidation, these data, together with evidence presented in the companion papers and elsewhere, suggest that the antigens are important in neural development by mediating at least some of the responses of neural cells to laminin--for example, by acting as a laminin receptor guiding axonal outgrowth and neuronal migration, or by involvement in the transport and binding of laminin to the surface of neurons and reactive glial cells that synthesize laminin.