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The Bovine Papillomavirus E5 Oncogene Can Cooperate with ras: Identification of p21 Amino Acids Critical for Transformation by c-rasH but Not v-rasH

par Willumsen, Berthe Marie;Vass, William W.C.;Velu, Thierry ;Papageorge, Alex A.G.;Schiller, John J.T.;Lowy, Douglas D.R.
Référence Molecular and cellular biology, 11, 12, page (6026-6033)
Publication Publié, 1991-12

Article révisé par les pairs

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Résumé :

We have previously used a series of insertion-deletion mutants of the mutationally activated v-rasH gene to identify several regions of the encoded protein that are dispensable for cellular transformation (B. M. Willumsen, A. G. Papageorge, H.-F. Kung, E. Bekesi, T. Robins, M. Johnsen, W. C. Vass, and D. R. Lowy, Mol. Cell. Biol. 6:2646-2654, 1986). To determine if some of these amino acids are more important for the biological activity of c-rasH, we have now tested many of the same insertion-deletion mutants in the c-ras form for their ability to transform NIH 3T3 cells. Since the transforming activity of c-rasH is low, we have used cotransfection with the bovine papillomavirus (BPV) genome to develop a more sensitive transformation assay for c-rasH mutants. The increased sensitivity of the assay, which is seen both in focal transformation and in anchorage-independent growth, is mediated by cooperation between the BPV E5 gene and ras. E5-dependent cooperation was seen for v-rasH as well as for c-rasH, which suggests that the major effect of E5 was to increase the susceptibility of the cell to transformation to a given level of ras activity. The cooperation assay was used to test the potential importance, in c-rasH, of codons 93 to 108, 123 to 130, and 166 to 183, which were nonessential for v-rasH transformation. Relative to the respective transforming activity of wild-type c-ras and v-rasH, mutants with lesions in codons 102 and 103 were significantly less active in their c-ras forms than in their v-rasH forms. We conclude that a region including amino acids 102 and 103 encodes a function that is more critical to c-rasH than to v-rasH. Guanine nucleotide exchange is one function that is compatible with such a phenotype.