Identification and partial characterization of laminin binding proteins in immature rat Sertoli cells

Laminin, a major component of basement membrane extracellular matrices, promotes differentiation in a number of cell types, including Sertoli cells. We have identified and characterized Sertoli cells. We have identified and characterized Sertoli cell surface molecules which interact with laminin. Using laminin-Sepharose affinity chromatography and [125I]laminin binding to Sertoli cell plasma membranes, binding proteins have been identified with the Mr 110,000, 67,000, 55,000, 45,000, 36,000, and 25,000. In addition, the Mr 110,000 and 67,000 laminin binding proteins were phosphorylated. The 67,000, 45,000, and 36,000 react with antibodies to the previously characterized laminin receptor and these antibodies stain the basolateral surface of Sertoli cells in vivo. Cultured Sertoli cells stain for laminin receptor both on the cell surface and within the cells. Antiserum to the 32,000 and 67,000 laminin binding proteins partially inhibited spreading of Sertoli cells on a laminin-coated culture dish, suggesting a functional importance of those proteins in Sertoli cell differentiation. The 25,000 and 45,000 laminin binding proteins reacted with integrin antibodies, but no high-molecular-weight forms could be detected. Integrin was localized to the cell surface and intracellularly but antibodies did not block Sertoli cell spreading on laminin. This work represents the first identification and characterization of extracellular matrix binding proteins in an endocrine organ and suggests an important role for the nonintegrin 32/67 laminin binding proteins.