Characterization of the fibronectin synthesized by human germ cell tumors

The ability of the human germ cell tumor cell lines Tera 1, Tera 2, PA-1, LICR LON HT 39/7, LICR LON HT3B1, and LICR LON HT 53 to synthesize and secrete fibronectin has been studied. The presence of cellular fibronectin was examined using indirect immunofluorescence, whereas the synthesis and secretion of the protein were studied using specific immunoprecipitation from cultures radioactively labeled with [35S]methionine. Two of the cell lines, LICR LON HT 39/7 and Tera 1, did not synthesize fibronectin, whereas all the other cell lines did. Plasma membrane fibronectin could not be demonstrated on any of the cell lines, although cytoplasmic fibronectin was easily demonstrable. The cells appear therefore to synthesize fibronectin but not retain it. Sodium dodecyl sulfate:polyacrylamide gel electrophoresis of the secreted fibronectin produced by the human teratoma cell lines showed that it had an apparent molecular weight greater than that produced by adult human breast fibroblasts or human plasma fibronectin. Peptide mapping of this secreted germ cell tumor fibronectin, by partial proteolytic cleavage, yielded peptide patterns similar to those obtained from either human plasma fibronectin or adult human breast fibroblast fibronectin. The difference in molecular weight between the fibronectins may therefore be due to changes in their patterns of glycosylation.