LOW INCIDENCE OF POINT MUTATIONS DETECTED IN THE P53 TUMOR-SUPPRESSORGENE FROM CHEMICALLY-INDUCED RAT RENAL MESENCHYMAL TUMORS

Previous studies have shown renal mesenchymal tumors (RMTs) induced in rats hy a single intrarenal injection of nickel subsulfide and iron a re more pleomorphic and metastatically aggressive than RMTs induced by a single ip injection of methyl(methoxymethyl)nitrosamine (DMN-OMe). While both RMT types contain high levels of K-ras activation, the spec ific mutational spectra within codon 12 of K-ras are quite different. Nickel subsulfide and iron-induced tumors exhibited codon 12 GGT-->GTT transversions exclusively, while DMN-OMe RMTs showed a wide array of codon 12 mutations, as well as mutations within codons 61 and 63 [K. G . Higinbotham, J. M. Rice, B. A. Diwan, K. S. Kasprzak, C. D. Reed, an d A. O. Perantoni, Cancer Res., 52: 4747-4751, 1992; K. G. Higinbotham , J. M. Rice, and A. O. Perantoni, Mol. Carcinog., 5: 136-139, 1992]. In an effort to further correlate carcinogen-specific molecular events in renal tumors, we investigated the p53 tumor suppressor gene in RMT s induced by these two carcinogens for the presence of point mutations . The evolutionarily conserved portion of the coding region of the gen e, including part of exon 4 through exon 10, was surveyed for point mu tations utilizing single-strand conformation polymorphism and chemical cleavage of mismatches analyses. None (0 of 10) of the nickel subsulf ide and iron-induced RMTs and only 1 of 10 DMN-OMe-induced tumors that were evaluated contained point mutations within this portion of the p 53 gene. Direct sequencing of the one single-strand conformation polym orphism and chemical cleavage of mismatches-''positive'' DMN-OMe-induc ed RMT revealed a GCC-->GTC (Ala-Val) transition in codon 345 within e xon 10. These results suggest that the different tumorigenic phenotype s exhibited by these two RMTs are not the result of specific mutations or patterns of mutations within the portion of the p53 gene examined and that the mutated p53 tumorigenic pathway, whereby p53 plays a majo r role in many human neoplasms, does not function in RMTs induced by e ither agent.