Combined subcarcinogenic benzo[a]pyrene and UVA synergistically caused high tumor incidence and mutations in H-ras gene, but not p53, in SKH-1 hairless mouse skin.
Combined subcarcinogenic doses of benzo[a]pyrene (BaP) and UVA induced H-ras, but not p53, gene mutations 8 weeks before tumor emergence in SKH-1 mice. Neither UVA (40 kJ/m2) nor BaP (8 nmol) induced any tumors after mice were topically treated 3 times/week for 25 weeks. However, combined BaP-UVA treatment synergistically increased tumor incidence and multiplicity. All tumors induced by BaP-UVA were malignant. The epidermis was collected from mice treated for 2, 6 and 10 weeks. DNA from UVB- (0.3 kJ/m2) or BaP-UVA-(8 nmol and 40 kJ/m2-induced tumors was isolated and screened for H-ras and p53 mutations. Four types of point mutation, GGC-->GAC, GCC, GTC and CGC, occurred in UVB-induced tumors at H-ras codon 13; and one type of point mutation, GGA-->GAA, at codon 12. Treatment with either BaP alone or BaP-UVA for 10 weeks caused GGA-->GAA mutation at codon 12 or GGC-->GAC mutation at codon 13 in nontumor skin, respectively, as well as in tumors induced by BaP-UVA. All of the 10-week samples treated with either BaP or BaP-UVA showed detectable mutations at codons 12 and 13, but the genetic load was significantly higher in BaP-UVA-treated mice than in those exposed only to BaP. UVA alone induced mutations at codon 12 in only one-third of samples. G-->A mutations induced by BaP or BaP-UVA at position 38 of codon 13 have not been reported previously. C-->T transitions were detected in p53 hot spots of exon 8 in 2 of 19 BaP-UVA-induced tumors but were not found in nontumor skin.
Wang
Yongyin
Y
Department of Dermatology, Mount Sinai School of Medicine, New York, NY 10029, USA.
Gao
Dayuan
D
Atencio
David P
DP
Perez
Evangeline
E
Saladi
Rao
R
Moore
Julian
J
Guevara
Denise
D
Rosenstein
Barry S
BS
Lebwohl
Mark
M
Wei
Huachen
H
D000818:Animals; D001564:Benzo(a)pyrene / Q000633:toxicity*; D003062:Codon; D004252:DNA Mutational Analysis; D005260:Female; D016158:Genes, p53; D011905:Genes, ras; D051379:Mice; D017354:Point Mutation; D012878:Skin Neoplasms / Q000209:etiology* / Q000473:pathology / Q000662:veterinary; D014466:Ultraviolet Rays / Q000009:adverse effects*
D003062:Codon; D001564:Benzo(a)pyrene