Induction of cellular DNA synthesis by the nondefective Adenovirus 2-Simian virus 40 hybrid viruses

The release of growth arrest by microinjection of adenovirus E1A DNA

The induction of DNA synthesis in growth-arrested mouse fibroblasts (NIH 3T3) was studied by microinjection of different constructs of adenovirus DNA using SV40 DNA and plasmid DNA as positive and negative controls. The E1A region of adenovirus types 2 and 12 appears to be sufficient to induce cellular DNA synthesis after growth arrest in approximately 30% of the cells and both 13S and 12S cDNA constructs mediate this effect. The presence of the E1A protein products as assayed by immunofluorescence does not strictly correlate with the induction of DNA synthesis in microinjected cells in contrast to the SV40 large T-antigen. Microinjection of truncated fragments of the Ad12 E1A region suggests, however, that the protein products of 12S and 13S may be involved in the induction process. A sequence comparison of the SV40 T-antigen and the adenovirus E1A products identified a region of significant homology providing a basis for a hypothesis concerning the evolution of T-antigen genes in DNA viruses.

Identification of adenovirus 2 early genes required for induction of cellular DNA synthesis in resting hamster cells

tsAF8 cells are temperature-sensitive (ts) mutants of BHK-21 cells that arrest at the nonpermissive temperature in the G1 phase of the cell cycle. When made quiescent by serum restriction, they can be stimulated to enter the S phase by 10% serum at 34 degrees C, but not at 40.6 degrees C. Infection by adenovirus type 2 or type 5 stimulates cellular DNA synthesis in tsAF8 cells at both 34 and 40.6 degrees C. Infection of these cells with deletion Ad5dl312, Ad5dl313, Ad2 delta p305, and Ad2+D1) and temperature-sensitive (H5ts125, H5ts36) mutants of adenovirus indicates that the expression of both early regions 1A and 2 is needed to induce quiescent tsAF8 cells to enter the S phase at the permissive temperature. This finding has been confirmed by microinjection of selected adenovirus DNA fragments into the nucleus of tsAF8 cells. In addition, we have shown that additional viral functions encoded by early regions 1B and 5 are required for the induction of cellular DNA synthesis at the nonpermissive temperature.

Induction of human cell DNA synthesis by herpes simplex virus type 2

The effect of herpes simplex virus type 2 (HSV-2) infection on the synthesis of DNA in human embryonic fibroblast cells was determined at temperatures permissive (37 C) and nonpermissive (42 C) for virus multiplication. During incubation of HSV-2 infected cultures at 42 C for 2 to 4 days or after shift-down from 42 to 37 C, incorporation of (3H)TdR into total DNA was increased 2-to 30-fold as compared with mock-infected cultures. Analysis of the (3H)DNA suggested that host cell DNA synthesis was induced by HSV-2 infection. Induction of host cell DNA synthesis by HSV-2 also occurred in cells arrested in DNA replication by low serum concentration. The three strains of HSV-2 tested were capable of stimulating cellular DNA synthesis. Virus inactivated by UV irradiation, heat, or neutral red dye and light did not induce cellular DNA synthesis, suggesting that an active viral genome is necessary for induction.

Studies of nondefective adenovirus 2-simian virus 40 hybrid viruses. Transformation of hamster kidney cells by adenovirus 2 and the nondefective hybrid viruses

Nonhybrid adenovirus 2 (Ad2) and five nondefective Ad2-simian virus 40 (SV40) hybrids (Ad2(+)ND(1)-Ad2(+)ND(5)) failed to produce tumors when injected into newborn hamsters. However, each of these agents transformed hamster kidney cells in vitro, and the transformed cell lines produced tumors when injected into suckling hamsters. Foci of cells transformed by the hybrids could not be distinguished from foci of cells transformed by nonhybrid Ad2. Histopathologically, tumors induced by the nondefective hybrid-transformed lines were of the adenovirus type with no areas of SV40-type fibrosarcoma. All of the cell lines studied contained Ad2 T antigen and Ad2 RNA. Only the B55HK(1) line contained the three early SV40 antigens, U, TSTA, and T. The ND(4)HK(1) line contained SV40 T and TSTA antigens (the latter antigen being detected only after 48 to 49 tissue culture passages) and SV40 RNA. The ND(2)HK(2) line contained SV40 RNA but no detectable SV40 antigens; the other hybrid-transformed lines contained no SV40 RNA. The transformation of hamster cells by the nondefective Ad2-SV40 hybrids seemed to be caused by the Ad2 genome and could not be attributed to the regions of the SV40 genome contained within the hybrids. Additionally, these results indicate that interactions between the genomes of the nondefective hybrid viruses and the hamster cells they transform are complex and could involve the site of integration, the size of the incorporated viral genome, the transcription or translation of the viral genome, or various combinations of these processes.