Expression of type C viral glycoproteins on P815 cells: higher expression of Mr 70,000 glycoprotein-containing glycoprotein on immunogenic variants.

Cells from P815 mastocytoma, a methylcholanthrene-induced tumor, were investigated for the presence of type C viral proteins on their surface. Little or no precipitation of purified Rauscher murine leukemia virus Mr 70,000 glycoprotein was observed with sera of mice immunized with P815 cells. However, a significant precipitation was obtained with sera from syngeneic or allogeneic mice immunized with P815 tumor cell variants obtained by mutagenesis. This difference was not detected when the sera were tested for precipitation of a pure Rauscher murine leukemia virus Mr 30,000 protein. The positive sera also precipitated a Mr 90,000 glycoprotein present on the membrane of all P815 cells. This glycoprotein was shown to contain endogenous ecotropic murine leukemia virus Mr 70,000 glycoprotein. On the membrane, a separate glycoprotein with a molecular weight of 90,000 containing gag gene products was also detected with a panel of reference antibodies. The level of glycoprotein containing Mr 70,000 glycoprotein on the cell membrane of the mutagenized cell variants was higher compared to the original P815 cells. The level of expression of the glycosylated gag precursor was the same on the original P815 cells and on the mutagenized cell variants.