Mutations in ras genes in cells cultured from mouse skin tumors induced by ultraviolet irradiation.

Abstract

Mutations in ras oncogenes were detced in cultured cells of mouse skin tumors induced by near-UV irradiation. DNA extracted from the UV-induced tumor cells was transfected to golden hamster embryo cells, and focusforming ability was confirmed in 22 of 26 cell strains, 15 of which had the repetitive mouse sequence. Mouse ras genes were detected in 10 of these 22 cell strains. Point mutations in the ras genes were at Ha-ras codon 13 (GGC --GTC in two strains, GGC -* AGC in one strain), Ki-ras codon 61 (CAA --GAA in two strains), and N-ras codon 61 (CAA --CAT in two strains, CAA --AAA in two strains). In one tumor cell strain no base change was deteted. Most mutations occurred at dipyrimidine sites. Pyrimidine dimers or pyrimidine(6-4)pyrimldone photoproducts are the likely cause of the skin cancers. The base change occurred preferentially at G-C base pairs, and transversions predominated. Solar UV light is important in the development of melanoma (1) and nonmelanoma skin cancers (2) in sun-exposed areas of human skin. Cyclobutane pyrimidine dimer and pyrimidine(6-4)pyrimidone photoproducts, which have cytotoxic and mutagenic effects, are the major types of DNA damage induced by far UV (3). The action spectrum for skin carcinogenesis is in the near-UV (UVB) range (4), but the nature and repair of the primary types of DNA damage caused by UVB in vivo have been little investigated. Unrepaired or misrepaired UV-induced DNA damage that leads to mutations and alterations in DNA structure during replication may trigger carcinogenesis if it occurs in specific target genes.Members of the ras gene family (c-Ha-ras, c-Ki-ras, and N-ras) are activated in human colon (5) and skin (6) cancers, as well as in animal skin cancers induced by chemicals (7,8). In human skin cancers, point mutations in codon 61 of the N-ras gene have been reported in patients with xeroderma pigmentosum who show defective repair of UV damages (9, 10) as well as in skin cancer patients without xeroderma pigmentosum (11).Point mutation in codons 12, 13, and 61 of the ras genes have been found preferentially in tumor cells that have activated transforming ability. Such mutations are suggested to be a cause of ras-related carcinogenesis, including skin cancers, or at the least as being part ofthe multistage process in carcinogenesis (12). We produced skin tumors on the backs of hairless mice using UVB irradiation (13). We report here results of detailed molecular analyses of the activation of and mutations in ras genes of cells cultured from UVB-induced mouse skin tumors. The cause-effect relationship in the development of skin cancers also is discussed. MATERIALS AND METHODSInduction of UVB-caused tumors and establishment of the tumor cell strains have been described (13). Specificpathogen-free albino hairless mice were irradiated with UVB light from six sun lamps (Toshiba FL-20 SE).Extraction of DNA from Tumors and Tumor Cells. Highmolecular-weight genomic DNA was extracted as described (14) from frozen tumor tissue samples and from cultured cell...

8-Oxoguanine Formation Induced by Chronic UVB Exposure Makes Ogg1 Knockout Mice Susceptible to Skin Carcinogenesis

“…8-Oxoguanine induces GC!TA transversions by mispairing with A as well as C. GC!TA transversions have been observed in the ras and p53 genes in UVB-induced mice skin cancers as well as in human nonmelanoma skin cancers of sun-exposed areas, which implies that 8-oxoguanine plays an important role in UV-related skin carcinogenesis (6,13,14). Previously it has been shown that UVB exposure increases the amount of 8-oxoguanine formations in epidermal cells (8).…”

P16 UV mutations in human skin epithelial tumors

“…The two transversions could also correspond to the mutation spectrum of UV light although they are less frequent (Nishigori et al, 1994). This is the ®rst indication of p16 inactivation by UV radiation in non melanoma skin cancers, although such mutations were previously reported in melanoma cell lines and sporadic melanoma (Maestro et al, 1995;Pollock et al, 1995;Healy et al, 1996).…”

Pathogenetic mechanisms and treatment options for ophthalmic pterygium: Trends and perspectives (Review)

“…Apart from TSGs, proto-oncogene (POG) sequences may also be affected by UVR (51,52). Mutations in genes of the ras family POGs, including Harvey-Ras (H-ras), Kirsten-Ras (K-ras) and Neuroblastoma-ras (N-ras), have been detected in cultured cells of mouse skin tumors following exposure to near-UVR (51) and are also frequently detected in human neoplastic conditions of sun-exposed body areas, such as cutaneous melanomas (52).…”