SV40 T antigen and the exocytotic pathway.
A chimeric gene consisting of DNA coding for the 15-amino acid signal peptide of influenza virus hemagglutinin and the C-terminal 694 amino acids of SV40 large T antigen was inserted into a bovine papilloma virus (BPV) expression vector and introduced into NIH-3T3 cells. Cell lines were obtained that express high levels (approximately 5 X 10(6) molecules/cell) of the chimeric protein (HA-T antigen). The biochemical properties and intracellular localization of HA-T antigens were compared with those of wild-type T antigen. Wild-type T antigen. Wild-type T antigen is located chiefly in the cell nucleus, although a small fraction is detected on the cell surface. By contrast, HA-T antigen is found exclusively in the endoplasmic reticulum (ER). During biosynthesis, HA-T antigen is co-translationally translocated across the membrane of the ER, the signal peptide is cleaved and a mannose-rich oligosaccharide is attached to the polypeptide (T antigen contains one potential N-linked glycosylation site at Asn154). HA-T antigen does not become terminally glycosylated or acylated and little or none reaches the cell surface. These results suggest that T antigen is incapable of being transported along the exocytotic pathway. To explain the presence of wild-type T antigen on the surface of SV40-transformed cells, an alternative route is proposed involving transport of T antigen from the nucleus to the cell surface.
D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005089:Exocytosis; D005453:Fluorescence; D005822:Genetic Vectors; D006056:Golgi Apparatus / Q000378:metabolism; D008668:Metallothionein / Q000235:genetics; D051379:Mice; D010766:Phosphorylation; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D014764:Viral Proteins; D008668:Metallothionein