Production of laminin and fibronectin by Schwannoma cells: cell-protein interactions in vitro and protein localization in peripheral nerve in vivo

We studied a rat Schwannoma cell line (RN22F) to determine if it produced the basement membrane glycoproteins laminin and fibronectin, and how it interacted with these proteins in vitro. We used antisera to laminin and fibronectin for immunoprecipitation experiments and immunocytochemical localization at the electron microscope level. Polyacrylamide gels of antilaminin immunoprecipitates of conditioned medium and solubilized Schwannoma cells contained bands of reduced Mr 200,000 and 150,000. Antilaminin immunoprecipitates of conditioned medium contained nonreduced bands of 850,000 daltons and 150,000, and immunoprecipitates of solubilized cells contained nonreduced bands of 850,000, 400,000, 200,000, and 150,000 daltons. Antifibronectin immunoprecipitates of conditioned medium contained a reduced band of 220,000 daltons, and nonreduced bands of 440,000 and 220,000 daltons. Radio-labeled protein was not detected in antifibronectin immunoprecipitates of solubilized cells. By immunocytochemistry, laminin was found along the cell surface in a continuous band, whereas fibronectin was only sparsely distributed along the cell surface. In cell adhesion assays, Schwannoma cells bound preferentially to laminin- coated substrates as compared to fibronectin or noncoated substrates. A number of Schwannoma cells displayed a curved and elongated morphology on laminin substrates, as compared to a uniformly spread morphology on fibronectin, and a round, nonspread morphology on noncoated substrates. Immunofluorescent staining showed laminin in the endoneurium and perineurium and fibronectin predominantly in the perineurium of mouse sciatic nerve in vivo. The production of laminin and fibronectin by Schwann cells may be important in the development and myelination of peripheral nerves, and the proper regeneration of axons following nerve injury.