The bovine papillomavirus E5 oncogene can cooperate with ras: identification of p21 amino acids critical for transformation by c-rasH but not v-rasH.
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-rasH 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-rasH and v-rasH, mutants with lesions in codons 102 and 103 were significantly less active in their c-rasH 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.
Willumsen
B M
BM
University Microbiology Institute, Copenhagen, Denmark.
Vass
W C
WC
Velu
T J
TJ
Papageorge
A G
AG
Schiller
J T
JT
Lowy
D R
DR
D016475:3T3 Cells; D000818:Animals; D052688:Bovine papillomavirus 1 / Q000235:genetics*; D002471:Cell Transformation, Neoplastic; D002472:Cell Transformation, Viral; D003001:Cloning, Molecular; D011905:Genes, ras; D051379:Mice; D009856:Oncogene Proteins, Viral / Q000235:genetics; D009857:Oncogenes; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D014162:Transfection
D009856:Oncogene Proteins, Viral; C054304:oncogene protein E5, Bovine papillomavirus type 1; D016283:Proto-Oncogene Proteins p21(ras)