CC to TT mutation in the mitochondrial DNA of normal skin: relationship to ultraviolet light exposure.
We have previously reported that ultraviolet (UV)-specific (CC to TT) mutations in p53 gene can be detected in normal skin. This, however, cannot be used as a cumulative marker of UV exposure, since cells with the p53 mutation acquire a clonal growth advantage. Moreover, a large skin biopsy is necessary for each assay. In order to circumvent these problems, we have measured mitochondrial (Mt) DNA mutations; there are more than 1000 copies of the Mt genome per cell, and Mt genes are not directly involved in cell growth. We have established a sensitive allele-specific polymerase chain reaction (AS-PCR) assay capable of detecting one CC to TT mutation in Mt DNA among 10(7) wild-type genes using a mismatch allele-specific primer. With this assay, we found no mutation-positive samples from internal non-exposed tissue (stomach, colon, and blood) (0/50). In contrast, 17 out of 111 skin samples were positive: the mutation frequency in positive samples was around 10(7)-10(-6) (10-100 copies of mutant in 10(8) wild-type Mt DNA). In normal skin tissue, the prevalence of positive samples was higher in those from exposed sites (13/51) than in those from less-exposed sites (1/26) (p<0.05). However, a quantitative correlation between sunlight exposure and the accumulation of mutations was not found. We conclude that the UV exposure-associated CC to TT mutation in Mt DNA can be detected in normal skin, but that further studies are required to develop this as a quantitative marker for UV exposure.
Kawasaki
K
K
Unit of Multistage Carcinogenesis, International Agency for Research on Cancer, Lyon, France.
Suzuki1
T
T
Ueda
M
M
Ichihashi
M
M
Reguer
G
G
Yamasaki
H
H
D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D004272:DNA, Mitochondrial / Q000235:genetics*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000528:radiation effects; D016133:Polymerase Chain Reaction / Q000379:methods; D011740:Pyrimidine Dimers / Q000235:genetics / Q000528:radiation effects*; D012867:Skin / Q000378:metabolism / Q000528:radiation effects*; D012878:Skin Neoplasms / Q000235:genetics; D014466:Ultraviolet Rays
D004272:DNA, Mitochondrial; D011740:Pyrimidine Dimers