Variants of Defective Simian Papovavirus 40 (PARA) Characterized by Cytoplasmic Localization of Simian Papovavirus 40 Tumor Antigen

Abstract

Three isolates of PARA (particle aiding replication of adenovirus)-adenovirus 7 out of a total of 112 clonal progeny derived by two successive plaque purifications in green monkey kidney cells (GMK) were found to induce the synthesis of simian papovavirus40 (SV 40) tumor (T) antigen in the cytoplasm of infected cells. The variant viruses induced plaque formation in human embryonic kidney cells which followed one-hit kinetics. In GMK cells, plaque formation followed two-hit kinetics which converted to first-order kinetics in the presence of additional helper adenovirus type 7. Analysis of plaque progeny from human cells showed that the progeny could replicate only in human cells, whereas progeny from monkey cells could multiply in both human and monkey cells. Heterologous human adenoviruses were able to enhance plaque formation by the variant viruses in monkey kidney cells. Neutralization tests indicated that both components of the populations had a type 7 adenovirus capsid. All three viruses were capable of inducing SV40 transplantation immunity in weanling hamsters. These results indicate the three variants are PARA-adenovirus 7 populations. Response of the induction of the synthesis of the cytoplasmic antigen to metabolic inhibitors was the same as for the synthesis of the nuclear SV40 T antigen. Different pools of sera which reacted with the intranuclear SV40 T antigen also detected the cytoplasmic antigen induced by the variant viruses. An adsorption experiment with cells containing either nuclear or cytoplasmic T antigen to remove tumor antibody from hamster sera also indicated that it is probably SV40 T antigen which is responsible for the cytoplasmic reaction. The species of the host cell—human, simian, or rabbit—appeared to play no role in the altered localization of this antigen. It is postulated that these PARA variants are further defective in some virus-mediated transport mechanism which shifts the T antigen from the cytoplasm to the nucleus.