Binding of p53 and p105-RB is not sufficient for oncogenic transformation by a hybrid polyomavirus-simian virus 40 large T antigen

Immortalization of primary cells is a multistep process. The adenovirus EIA 12S gene product is a member of the class of oncoproteins that have the ability to establish primary cells as cell lines in culture. It is encoded by two exons. Extensive mutational analysis demonstrates that four regions of the ElA 12S gene, encoded by both exons, are necessary for immortalization of primary epithelial cells. Expression of two regions is necessary to activate quiescent cells into the cell cycle but is unable to extend the life span of these cells in culture and thus cannot immortalize them. These regions are encoded by the first exon. A third first-exon region, for which no function has yet been identified, is also required. These three regions are also required for 12S to cooperate with an activated ras gene to bring about tumorigenic transformation. The fourth region is required to maintain the cells in a proliferative mode, extend their life span in culture, and induce an autocrine growth factor. These functions are encoded by the second exon. The cells immortalized by wild-type 12S and immortalizationcompetent mutants retain their epithelial morphology and expression of keratin and vimentin intermediate filament proteins.

Section: Discussionmentioning

confidence: 99%

Immortalization of primary epithelial cells requires first- and second-exon functions of adenovirus type 5 12S

Quinlan

Douglas

1992

“…Recent studies have shown that binding of Rb by T antigen is essential for transformation of established rodent cells but is not necessary for immortalization of primary rodent cells (7, 50). However, binding to Rb is by itself not sufficient to transform and immortalize human or mouse cells in culture (31,41). Binding of p53 by T antigen has also been suggested by Tevethia et al (47)(48)(49) to also be necessary for transformation by SV40.…”

mentioning

confidence: 96%

The ability of large T antigen to complex with p53 is necessary for the increased life span and partial transformation of human cells by simian virus 40

Lin

Simmons

1991

Simian virus 40 (SV40) T antigen binds to the tumor suppressor p53 protein, and this association may contribute to oncogenic transformation by the virus. We investigated the importance of this binding on transformation by examining three replication-competent mutants of SV40 (402DE, 402DN, and 402DH). These mutants express T antigens defective in binding to human and monkey pS3s but retain some binding with mouse p53. All showed significant reduction in their ability to induce transformed cell foci of two normal human cell lines as well as a slight reduction with mouse embryo cells. Other comparable mutants which express T antigens retaining the ability to complex with p53 were able to induce foci at wild-type levels in both human and mouse cells. Further studies were performed with five T-antigen-positive clones isolated from the few human cell foci that appeared after transfection with 402 mutant DNAs. All five clones reached senescence at about the same point as did the parental untransformed cells. However, six other human cell clones obtained after transfection with DNA from nondefective mutants or wild-type virus were still growing well at more than 10 passages beyond their expected life span. These results suggest that the ability of T antigen to form stable complexes with p53 is necessary for SV40 to extend the life span and partially transform human cells in culture.

“…Our in vitro studies indicate that p53, but not pRb, would be active after a temperature shift of cells transformed by appropriate ts T antigens. Furthermore, in addition to binding to pRb and p53, T antigen appears to have a third function in the immortalization and transformation of cells (6,22,25,37,38). Although the nature of this function is unknown, it maps N terminal to the pRb binding region and is unlikely to be ts in any of the ts T antigens described here.…”

Section: Fig 3 P53 Inactivation By Ts T Antigensmentioning

confidence: 84%

Differential interaction of temperature-sensitive simian virus 40 T antigens with tumor suppressors pRb and p53

Ray

Anderson

Tegtmeyer

1996

Previous studies have shown that simian virus 40 large T antigen transforms cells by binding and inactivating suppressors of cell cycle progression and tumor formation. Here, we characterize the interactions of five temperature-sensitive T antigens with the tumor suppressor proteins pRb and p53. All five mutant T antigens bind pRb at the nonpermissive temperature with efficiencies similar to that of wild-type T antigen. A single transformation-competent mutant, with a substitution of amino acid 186, binds p53 at the nonpermissive temperature. Four transformation-defective mutants, with a substitution at T antigen position 357, 422, 427, or 438, are temperature sensitive for the binding and inactivation of p53. Our findings provide a basis for understanding the behavior of cells transformed by temperature-sensitive T antigens.