Characterization of a secreted glycoprotein of the immunoglobulin superfamily inducible by mitogen and oncogene

Abstract

The T1 gene is transiently activated by the Ha-ras (EJ) or v-mos oncoproteins and by mitogens in NIH3T3 fibroblasts. Its primary gene product of 337 amino acids (38 kDa) undergoes extensive post-translational modification. For biochemical analysis, the T1 gene product was over-expressed in a vaccinia virus system. Cells infected with a recombinant T1-vaccinia virus produce and secrete multiple proteins of 60-70 kDa which react with polyclonal antisera raised against two T1-specific peptides. Two lines of evidence suggest that the apparent size heterogeneity of the T1 protein is due to a variable carbohydrate content of 40-50% of the total molecular mass. First, in the presence of an inhibitor of N-glycosylation (tunicamycin), a single 38-kDa protein is detected by the antisera in the cells infected with T1-vaccinia virus. Second, glycosidase digestions show that T1 protein maturation involves glycosylation and sialylation. These post-translational modification steps appear to be similar in different types of cells.