ULTRAVIOLET-B LIGHT-INDUCED MUTAGENESIS OF P53 HOTSPOT CODON-248 AND CODON-249 IN HUMAN SKIN FIBROBLASTS

Mutations in the p53 tumor suppressor gene are detected in approximately half of non-melanoma skin cancers. The type of base-pair changes observed strongly suggests solar radiation as the causative mutagen. Mutations are distributed nonrandomly and form moderate hotspots. We studied the capacity of ultraviolet B light (UVB, 280-320 nm) to induce base-pair changes into the p53 exon 7 sequence extending from nt 14067 to 14075 in human skin fibroblasts. This sequence contains hotspot codon 248. UVB induced mostly C-->A and G-->T transversions. The base-pair change with the highest relative abundance was C-->A in the fi rst position of codon 250 (CCC-->($) under bar ACC), followed by (in diminishing relative abundance) G-->T in the third position of codon 249 (AGG-->AG ($) under bar T), C-->A in the first position of codon 248 (CGG-->($) under bar AGG), and C-->A in the third position of codon 247 (AAC-->AA ($) under bar A. The C-->T transition in the third position of codon 247 (AAC-->AA ($) under bar T) occurred with moderate efficiency. These base-pair changes are compatible with pyrimidine photodimers as premutagenic lesions, but they could also form opposite 8-hydroxyguanine, which is the major oxidation product of guanine. No evidence was obtained for the presence of tandem double CC-->TT transitions in the untranscribed strand at codons 247/248 and and 250. The relative abundance of mutations induced by UVB in the p53 sequence extending from codon 247 to 250 in human fibroblasts does not correlate with mutations observed in the DNA from nonmelanoma skin cancer. This lack of correlation suggests that the mutability of this p53 sequence at the DNA level plays only a minor role in the pathogenesis of non-melanoma skin cancer in humans. (C) 1994 Wiley-Liss, Inc.