Monoclonal antibodies against simian virus 40 tumor antigens: analysis of antigenic binding sites, using adenovirus type 2-simian virus 40 hybrid viruses

The antigenic binding sites of two monoclonal antibodies are located in the COOH-terminal region (clone 412) and probably in an internal region (clone 7) of simian virus 40 large T antigen. A third monoclonal antibody (clone 122), which has been shown to bind nonviral T antigen, does not react with HeLa cells infected with nondefective adenovirus type 2 (Ad2)-simian virus 40 hybrid viruses Ad2+ND1, Ad2+ND2, or Ad2+ND4.

Simian virus 40 T-antigen-related cell surface antigen: serological demonstration on simian virus 40-transformed monolayer cells in situ

Simian virus 40 (SV40)-transformed monolayer cells were analyzed in situ by indirect immunofluorescence microscopy for the postulated cell surface location of SV40 T-antigen-related molecules. With antisera prepared against purified, sodium dodecyl sulfate-denatured SV40 T-antigen, positive surface staining was obtained when the cells had been treated with formaldehyde before immunofluorescence analysis. In contrast, living SV40-transformed cells analyzed in monolayer were surface fluorescence negative. The fixation procedure developed in this study combined with a double staining immunofluorescence technique allowed the simultaneous analysis of the same cells for the expression of both SV40 T-antigen-related surface antigen and nuclear T-antigen. The localization of SV40 T-antigen-related surface antigen on the outer surface of the plasma membrane of formaldehyde-fixed SV40-transformed cells was demonstrated directly by the protein A-mediated binding of Staphylococcus aureus bacteria on formaldehyde-fixed SV40-transformed cells precoated with antiserum against sodium dodecyl sulfate-denatured T-antigen. Both cell surface staining and S. aureus binding were found to be highly specific for SV40 T-antigen-related binding sites. These results indicate that T-antigen-related molecules in a cryptic form are located on the surface of SV40-transformed monolayer cells and can be detected in situ after modification of the cell surface architecture.

Cell surface location of simian virus 40-specific proteins on HeLa cells infected with adenovirus type 2-simian virus 40 hybrid viruses Ad2+ND1 and Ad2+ND2

HeLa cells infected with the nondefective adenovirus type 2-simian virus 40 hybrid viruses Ad2+ND1 or Ad2+ND2 were analyzed for cell surface location of the SV40-specific hybrid virus proteins by indirect immunofluorescence microscopy. Two different batches of sera from SV40 tumor-bearing hamsters, serum from SV40 tumor-bearing mice, or two different antisera prepared against purified sodium dodecyl sulfate-denatured SV40 T-antigen, respectively, were used. All sera were shown to exhibit comparable T- and U-antibody titers and to specifically immunoprecipitate the SV40-specific proteins from cell extracts of Ad2+ND2-infected cells. Whereas analysis of living, hybrid virus-infected HeLa cells did not yield conclusive results, analysis of Formalin-fixed cells resulted in positive cell surface fluorescence with both Ad2+ND1- and Ad2+ND2-infected HeLa cells when antisera prepared against sodium dodecyl sulfate-denatured SV40 T-antigen were used as first antibody. In contrast, sera from SV40 tumor-bearing animals were not or only very weakly able to stain the surfaces of these cells. The fact that the tumor sera had comparable or even higher T- and U-antibody titers than the antisera against sodium dodecyl sulfate-denatured T-antigen but were not able to recognize SV40-specific proteins on the cell surface suggests that SV40 tumor-specific transplantation antigen may be an antigenic entity different from T- or U-antigen.

Simian virus 40 T- and U-antigens: immunological characterization and localization in different nuclear subfractions of simian virus 40-transformed cells

Simian virus 40 (SV40)-transformed cells and cells infected by the nondefective adenovirus 2(Ad2)-SV40 hybrid viruses Ad2+ND1 and Ad2+ND2 were analyzed for SV40 T- and U-antigens, respectively, using individual hamster SV40 tumor sera or serum for which U-antibodies were removd by absorption. These studies showed that (i) T- and U-antigens can be defined by separate classes of antigenic determinants and (ii) the U-antigenic determinants in SV40-transformed cells and in hybrid virus-infected cells are similar. The apparent discrepancy in the subcellular location of U-antigen in SV40-transformed cells (nuclear location) and in hybrid virus-infected cells (perinuclear location) as determined by immunofluorescence staining of methanol/acetone-fixed cells could be resolved by treating hybrid virus-infected cells with a hypotonic KCl solution before fixation. Upon this treatment hybrid virus-infected cells also showed nuclear U-antigen staining. The possibility of an association of T- and U-antigens with different nuclear subfractions in SV40-transformed cells was investigated. Detergent-cleaned nuclei of SV40-transformed cells were fractionated into nuclear matrices and a DNase-treated, high-salt nuclear extract. Analysis of the nuclear matrices by immunofluorescence microscopy with T+U+ and T+U- hamster SV40 tumor serum revealed that U-antigen remained associated with the nuclear matrices, whereas T-antigen could not be detected in this nuclear subfraction. T-antigen, however, could be immunoprecipitated from nuclear extracts of the SV40-transformed cells.

Simian virus 40 (SV40)-specific proteins associated with the nuclear matrix isolated from adenovirus type 2-SV40 hybrid virus-infected HeLa cells carry SV40 U-antigen determinants

The distribution of simian virus 40 (SV40)-specific proteins in nuclear subfractions of pulse-chase-labeled HeLa cells infected with nondefective adenovirus type 2 (Ad2)-SV40 hybrid viruses was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The SV40-specific proteins of Ad2+ND1, Ad2+ND2, and Ad2+ND5 specifically associate with the nuclear matrix and are virtually absent from the high-salt nuclear extract. In Ad2+ND4-infected HeLa cells, the SV40-specific proteins with molecular weights of 64,000 (64K) and lower also specifically associate with the nuclear matrix. The SV40-specific 72K, 74K, and 95K proteins were found both in the nuclear matrix and in the high-salt nuclear extract. Analyses of the nuclear matrices isolated from hybrid virus-infected cells by immunofluorescence microscopy showed that SV40 U-antigen-positive sera from SV40 tumor-bearing hamsters react with SV40-specific proteins integrated into nuclear matrices of HeLa cells infected by Ad2+ND1, Ad2+ND2, and Ad2+ND4, but not with nuclear matrices of HeLa cells infected by Ad2+ND5. This suggests that SV40-specific proteins of Ad2+ND1, Ad2+ND2, and Ad2+ND4 integrated into the nuclear matrix carry SV40 U-antigen determinants. The apparent discrepancy in the subcellular localization of SV40-specific proteins in hybrid virus-infected cells when analyzed by biochemical cell fractionation procedures and when analyzed by immunofluorescence staining is discussed.

Simian virus 40 tumor-specific proteins: subcellular distribution and metabolic stability in HeLa cells infected with nondefective adenovirus type 2-simian virus 40 hybrid viruses

HeLa cells infected with adenovirus type 2 (Ad2)-simian virus 40 (SV40) hybrid viruses produce several SV40-specific proteins. These include the previously reported 28,000-dalton protein of Ad2+ND1, and 42,000- and 56,000-dalton proteins of Ad2+ND2, the 56,000-dalton protein of Ad2+ND4, and the 42,000-dalton protein of Ad2+ND5. In this report, we extend the list of SV40-specific proteins induced by Ad2+ND4 to include proteins of apparent molecular weights of 28,000 42,000, 60,000, 64,000, 72,000, 74,000, and a doublet of 95,000. Cell fractionation studies demonstrate that the SV40-specific proteins are detectable in the nuclear, cytoplasmic, and plasma membrane fractions. By pulse-chase and cell fractionation experiments, three classes of SV40-specific proteins can be distinguished with regard to metabolic stability: (i) unstable in the cytoplasmic but stable in the nuclear and plasma membrane fractions; (ii) stable in the nuclear, cytoplasmic, and plasma membrane fractions; and (iii) unstable in all subcellular fractions. Immunoprecipitation of infected cell extracts demonstrates that most of the above proteins share antigenic determinants with proteins expressed in hamsters bearing SV40-induced tumors. Only the 42,000-dalton protein of Ad2+ND5 is not immunoprecipitable.

Phosphohydrolases on the cell surface of BHK cells: loss during long term culture

Low passage BHK 21/13 cells contain two cell surface enzymes, a nucleotide pyrophosphatase and a monophosphoester hydrolase, which together hydrolyze exogenous UDP-galactose to free galactose. During serial passage, BHK cells successively lose both enzymes. Concomitant with the loss of these enzymatic activities, changes in cell morphology, as well as in the serum requirement for the initiation of DNA synthesis, were observed. Clonal sublines of BHK cells were isolated, which differed qualitatively in their ability to hydrolyze UDP-galactose. Clonal BHK sublines, which exhibited both enzymatic activities on their cell surface, resembled low passage BHK cells in morphology and serum requirement for the initiation of DNA synthesis. Sublines not containing these enzymes resembled BHK cells of high passage cultures. The ability of intact BHK cells to hydrolyze exogenous nucleotide sugars may serve as an indicator for the progression of BHK cells from a normal to a more transformed state.

Simian virus to (SV40) tumor-specific proteins in nucleus and plasma membrane of HeLa cells infected by adenovirus 2-SV40 hybrid virus Ad2+ND2

HeLa cells infected with the nondefective adenovirus 2-SV40 hybrid virus (Ad2+ND2) have previously been shown to synthesize two SV40-specific proteins with molecular weights of 56,000 (56 K protein) and 42,000 (42 K protein). The present study demonstrates that these proteins are immunoprecipitable with serum from hamsters bearing SV40 tumors. By peptide analysis, it is shown that the 56 K and 42 K proteins share common amino acid sequences. Both proteins are metabolically stable in nuclei and plasma membranes but unstable in the cytoplasm, as shown by pulse-chase experiments and cell fractionation studies.

Differentiation between intracellular and cell surface glycosyl transferases: galactosyl transferase activity in intact cells and in cell homogenate

Intact BHK (baby hamster kidney) cells catalyze the hydrolysis of UDP-galactose to free galactose. The generation of galactose from UDP-galactose and its intracellular utilization impede the detection of possible galactosyl transferases on the cell surface of intact cells. Several independent procedures have been used to distinguish between intracellular and cell surface glycosyl transferases. With these procedures, no evidence was obtained for the presence of detectable amounts of galactosyl transferase activity on the surface of BHK cells. The data suggest that galactosyl transferases do not play a general role in the phenomena of cell adhesion and contact inhibition.