Biosynthesis of type IV collagen by cultured rat Schwann cells.

Abstract

Evidence was obtained that rat Schwann cells synthesize and secrete type IV procollagen. Metabolic labeling of primary cultures of Schwann cells plus neurons and analysis by SDS PAGE [sodium dodecyl sulfate polyacrylamide gel electrophoresis] revealed the presence of a closely spaced pair of polypeptides in the medium of these cultures that were susceptible to digestion by purified bacterial collagenase, that co-migrated with type IV procollagen secreted by rat parietal endoderm cells, and were specifically immunoprecipitated by antibodies against mouse type IV collagen. Limited pepsin digestion of metabolically labeled medium or cell layers produced a pepsin-resistant fragment characteristic of pro-.alpha.1(IV) chains. Removal of neuronal cell bodies from the cultures immediately before labeling did not reduce the amount of type IV procollagen detected in the medium. This indicated that Schwann cells, not neurons, were responsible for synthesis of type IV procollagen. Apparently, type IV procollagen is a major constituent of the Schwann-cell extracellular matrix based upon its presence in a detergent-insoluble matrix preparation, its presence in the cell layer of the cultures in a state in which it can be removed by brief treatment with bacterial collagenase or tryspin, and by positive immunofluorescence of Schwann cell-neuron cultures with anti-type-IV collagen antibodies. Secretion of type IV procollagen was substantially reduced when Schwann cells were maintained in the absence of neurons. This observation may account for the previously reported finding that Schwann cells assemble a basal lamina only when co-cultured with neurons.