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Regions and Activities of Simian Virus 40 T Antigen That Cooperate with an Activated ras Oncogene in Transforming Primary Rat Embryo Fibroblasts

Tina M. Beachy,^1, Sara L. Cole,¹ Jane F. Cavender,² and Mary J. Tevethia^1*

Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033,¹ Department of Biology, Elizabethtown College, Elizabethtown, Pennsylvania 17022²

Received 20 September 2001/ Accepted 19 December 2001

Prolonged expression of a ras oncogene in primary cells accelerates the natural process of senescence. This ras-induced permanent growth arrest is bypassed in cells expressing the simian virus 40 large T antigen. Previously we showed that two regions of T antigen, a region consisting of the N-terminal 147 amino acids and a region consisting of amino acids 251 to 708 (T251-708), independently overcome ras-induced senescence. Coexpression of either T-antigen fragment and Ras results in the appearance of dense foci of transformed cells. Using a series of mutants that produce shorter T-antigen fragments, we show that the C-terminal limit of the N-terminal T-antigen fragment that cooperates with Ras lies between amino acids 83 and 121. The N-terminal limit of the C-terminal T-antigen fragment lies between amino acids 252 and 271. In addition, we present evidence that cooperation between the N-terminal fragment and Ras depends upon an intact T-antigen J domain and the ability of the T antigen to bind and inactivate the growth-suppressive effect of the tumor suppressor Rb. Introduction of specific amino acid substitutions surrounding residue 400 into T251-708 prevented the fragment from cooperating with Ras. T251-708 proteins with these same substitutions inhibited the transcriptional transactivating potential of p53 as effectively as did the wild-type protein. Thus, at least one activity contained within T251-708, other than inactivating p53 as a transcriptional transactivator, is likely to be required to bypass Ras-induced senescence.

Present address: Department of Biology, Bowdoin College, Brunswick, ME 04011.

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