LAMININ, A NONCOLLAGENOUS COMPONENT OF EPITHELIAL BASEMENT-MEMBRANES SYNTHESIZED BY A RAT YOLK-SAC TUMOR

Abstract

Laminin, a glycoprotein antigenically similar or identical to a component of epithelial basement membranes, was a major component of the abundant extracellular matrix synthesized by an experimentally induced rat yolk sac tumor. Immunocytochemical staining revealed laminin in cultured tumor cells. The presence of soluble laminin in the culture media of the tumor cells was demonstrated using metabolic labeling followed by immunoprecipitation and sodium dodecyl sulfate:polyacrylamide gel electrophoresis. This revealed 2 polypeptides with MW of .apprx. 200,000 and 400,000. These comigrated with the polypeptides of mouse laminin. The yolk sac tumor tissue grown in vivo contained laminin in the tumor cells and in the extracellular material as evidenced by immunofluorescence and immunoperoxidase staining. Immunization with the tumor matrix resulted in an antiserum that contained antilaminin and antifibronectin and was made specific for laminin by adsorption with fibronectin. This antiserum precipitated laminin polypeptides from culture medium of yolk sac tumor cells and stained basement membranes in rat tissues in a manner indistinguishable from antilaminin. The presence of laminin in rat yolk sac cells, the presumed origin of this yolk sac tumor, was studied in some detail. Laminin was present in normal cells of the visceral and the parietal yolk sac layer and in their basement membranes suggesting that both types of cells can synthesize laminin. Production of laminin and the presence of laminin-containing basement membrane material may be important for the biological behavior of the yolk sac tumor. This tumor will be a useful source of laminin for chemical and biological characterization of this basement membrane protein.