Cell surface T antigen in cells infected with simian virus 40 or an adenovirus-simian virus 40 hybrid, Ad2+D2

Fine mapping two distinct antigenic sites on simian virus 40 (SV40) T antigen reactive with SV40-specific cytotoxic T-cell clones by using SV40 deletion mutants

The existence of two distinct antigenic sites at the surface of simian virus 40 (SV40)-transformed H-2b cells has been previously demonstrated (A. E. Campbell, L. F. Foley, and S. S. Tevethia, J. Immunol. 130:490-492, 1983) by using two independently isolated SV40-specific cytotoxic T-lymphocyte (CTL) clones, K11 and K19. We identified amino acids in the amino-terminal half of SV40 T antigen that are essential for the recognition of antigenic sites by these CTL clones by using H-2b cells transformed by mutants that produce T antigen truncated from the amino-terminal or carboxy-terminal end or carrying overlapping internal deletions in the amino-terminal regions of SV40 T antigen. The results show that CTL clone K11 failed to recognize and lyse target cells missing SV40 T-antigen amino acids 189 to 211, whereas CTL clone K19 lysed these cells. The cell lines missing SV40 T-antigen amino acids 220 to 223 and 220 to 228 were not lysed by CTL clone K19 but were susceptible to lysis by CTL clone K11. Two other cell lines missing amino acids 189 to 223 and 189 to 228 of SV40 T antigen were not lysed by either of the CTL clones but were lysed by SV40-specific bulk-culture CTL if sufficient amounts of relevant restriction elements were expressed at the cell surface. The SV40 T-antigen amino acids critical for the recognition of an antigenic site by CTL clone K11 were identified to be 193 to 211; 220 to 223 were identified as critical for recognition by CTL clone K19. The deletion of these amino acids from the T antigen resulted in the loss of antigenic sites specific for CTL clones K11 and K19.

Recognition of simian virus 40 T antigen synthesized during viral lytic cycle in monkey kidney cells expressing mouse H-2Kb- and H-2Db-transfected genes by SV40-specific cytotoxic T lymphocytes leads to the abrogation of virus lytic cycle

Simian virus 40 (SV40)-encoded tumor or T antigen localizes in the membranes in addition to the nucleus of SV40-infected permissive monkey cells and SV40-transformed nonpermissive cells. The surface T antigen in SV40-transformed mouse cells provides a target for the cytotoxic T lymphocytes (CTL) which recognize SV40 T antigen in association with murine K/D, class I H-2 antigens. In order to demonstrate that SV40 T antigen synthesized in SV40-infected permissive monkey kidney cells (TC-7) may also function as a target for CTL, cloned murine H-2Db and H-2Kb genes were expressed in TC-7 cells by DNA transfection and TC-7 cell lines expressing high levels of either H-2Kb or H-Db antigens were established after cell sorting. SV40-infected TC-7/H-2Kb and TC-7/H-2Db cells became susceptible to lysis by SV40-specific H-2b restricted CTL. The susceptibility of these transfected SV40-infected monkey cells to anti-SV40 bulk culture CTL and SV40-specific H-2Db- and H-2Db-restricted CTL clones depended upon the synthesis of SV40 T antigen and the expression of the appropriate H-2Kb or H-2Db restriction elements. Treatment of SV40-infected TC-7/H-2Db and TC-7/H-2Kb with CTL clones abrogated the virus lytic cycle indicating that CTL may play an important role in limiting papovavirus infection in the natural host.

Glycosylation of simian virus 40 T antigen and localization of glycosylated T antigen in the nuclear matrix

Evidence has been obtained for the glycosylation of simian virus 40 (SV40) T antigen in SV40-infected TC7 cells. Both [3H]mannose and [3H]glucosamine are incorporated into T antigen in cells grown and labeled in medium containing fructose instead of glucose. In addition, T antigen is visualized by a carbohydrate stain specific for mannose and/or glucose residues. Finally, lectin binding studies suggest that T antigen contains galactose and/or galactosamine, since T antigen is specifically eluted from soybean lectin by 0.2 M galactose. When gel-purified, [3H]glucosamine-labeled T antigen is subjected to tryptic peptide mapping, label is found in only one peptide, thought to correspond to the methionine-containing peptide extending from Asn-653 to Arg-691, near the carboxy-terminal end of T antigen. Insensitivity to tunicamycin and the localization of the glycosylation site in the carboxy-terminus of T antigen, and not at Asn-153, suggest that T antigen is not N-glycosylated. Cell fractionation studies show that [3H]glucosamine-labeled T antigen is preferentially associated with the nuclear matrix of SV40-infected TC7 cells.

Plasma membrane orientation of simian virus 40 T antigen in three transformed cell lines mapped with monoclonal antibodies

Simian virus 40 large T antigen transforms cells from several species. Recent studies show that it is present on the cell surface. As in other tumor virus systems, this may be important for transformation. We have used a radioimmunoassay to map antigenic determinants on living and formaldehyde-fixed transformed cells with six different monoclonal antibodies to T antigen. Nonrelevant monoclonal antibodies of the same subclasses served as controls. With the transformed mouse line SVT2, antibody PAb 101, which reacts with the C-terminal region of T antigen, and PAb 1700, which is directed against an internal region of T, reacted with both formaldehyde-fixed and living cells. Antibodies PAb 402 (C terminus) and 419 (N terminus) reacted only with living cells, their determinants being destroyed upon formaldehyde fixation. Antibodies PAb 405 (C terminus) and 100 (internal) fail to react on either fixed or living cells. Similar results were obtained on the simian virus 40-transformed human line SV80 and the fixed hamster line CHLwt23, although all antibodies failed to react with living CHLwt23 cells. The data suggest that T antigen is inserted into the plasma membrane of transformed cells in a specific, nonrandom manner, with the C and N termini exposed on the cell surface and the midportion either buried in the lipid bilayer, hidden by the tertiary structure of T antigen, or masked by a post-translational modification such as fatty acid acylation.

Antigenic structure of simian virus 40 large tumor antigen and association with cellular protein p53 on the surfaces of simian virus 40-infected and -transformed cells

The antigenic structure of simian virus 40 (SV40) large tumor antigen (T-ag) in the plasma membranes of SV40-transformed mouse cells and SV40-infected monkey cells was characterized as a step toward defining possible biological function(s). Wild-type SV40, as well as a deletion mutant of SV40 (dl1263) which codes for a truncated T-ag with an altered carboxy terminus, was used to infect permissive cells. Members of a series of monoclonal antibodies directed against antigenic determinants on either the amino or the carboxy terminus of the T-ag polypeptide were able to precipitate surface T-ag (as well as nuclear T-ag) from both SV40-transformed and SV40-infected cells. Cellular protein p53 was coprecipitated with T-ag by all T-ag-reactive reagents from the surface and nucleus of SV40-transformed cells. In contrast, T-ag, but not T-ag-p53 complex, was recovered from the surface of SV40-infected cells. These results confirm that nuclear T-ag and surface T-ag are highly related molecules and that a complex of SV40 T-ag and p53 is present at the surface of SV40-transformed cells. Detectable levels of such a complex do not appear to be present on SV40-infected cells. Both the carboxy and amino termini of T-ag are exposed on the surfaces of SV40-transformed and -infected cells. The possible relevance of the presence of a T-ag-p53 complex on the surface of SV40-transformed cells and its absence from SV40-infected cells is considered.

Cell-mediated immune reaction against BK virus-transformed cells

Syngeneic or allogeneic cells transformed by BK virus (BKV) were used to immunize C57BL/6J mice. After in vitro stimulation, lymphocytes prepared from the spleens of immunized mice were used in in vitro cytotoxicity tests. The results of these tests revealed the presence of a cell surface antigen, presumably corresponding to the viral transplantation antigen, common to all tested BKV- and SV40-transformed cell lines of C57BL/6J origin. An allogeneic cell line transformed by BKV also contained the same antigen. Immunization, i.e., in vivo priming, did not require syngeneic transformed cells, whereas cytolysis was only observed when the virus-specific antigen on target cells was associated with the same H2 haplotype as was expressed by effector cells. An additional unidentified antigen was shared by some of the BKV-transformed cell lines and cell lines transformed by simian adenovirus SA7.