The structural relationships between 54,000-molecular-weight cellular tumor antigens detected in viral- and nonviral-transformed cells

Abstract

SV40-transformed mouse cells and murine embryonal carcinoma cells contain a 54,000 MW cellular tumor antigen which was detected with antibodies from animals bearing SV40-induced tumors ( D. I. H. Linzer and A. J. Levine, 1979, Cell, 17, 43–52). An antigen with a similar molecular weight has been detected in a variety of transformed mouse cell lines employing an antisera raised against a chemically induced murine sarcoma ( A. B. DeLeo et al., 1979 , Proc. Nat. Acad. Sci. USA, 76, 2420–2424). To examine the structural relationships between these cellular tumor antigens, the 54,000 MW proteins from a variety of murine transformed cell lines have been analyzed by chromatography of the methionine-containing tryptic peptides derived from these proteins. The results of this analysis demonstrate: (1) SV40 tumor sera and a monoclonal antibody, directed against a cellular tumor antigen of a chemically transformed cell line, each immuno-precipitated the same 54,000 MW protein from SV40-transformed cells as shown by the fact that each protein had an identical peptide map. (2) The 54,000 MW proteins obtained from (a) murine embryonal carcinoma cells, (b) 3T12 cells, (c) chemically transformed cell lines, and (d) an in vitro translation of m-RNA from SV40-transformed cells, all had similar or identical peptide maps. The 54,000 MW proteins from all these sources had eight methionine-containing peptides in common with the 54,000 MW protein obtained after in vivo labeling of SV40-transformed cells in cell culture. However, the 54,000 MW protein derived from SV40-transformed cells labeled in vivo produced a variable number (3–5) of additional methionine-containing tryptic peptides not detected in the other cell lines or with the 54,000 MW protein translated in vitro. These additional peptides may be the result of a post-translational modification of the 54,000 MW protein that is specific to SV40-transformed cells. The results of these experiments demonstrate the structural similarity or identity of the cellular 54,000 MW tumor antigens derived from a variety of murine cell lines transformed by diverse agents.