The p53 tumor suppressor protein reduces point mutation frequency of a shuttle vector modified by the chemical mutagens (±)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, aflatoxin B1 and meta-chloroperoxybenzoic acid

Abstract

The p53 tumor suppressor protein reduces point mutation frequency of a shuttle vector modi®ed by the chemical mutagens (+)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, a¯atoxin B 1 and meta-chloroperoxybenzoic acid Chantal Courtemanche 1,2 and Alan Anderson* ,1,2 1 Centre de recherche en canceÂrologie de l'Universite Laval, Pavillon L'HoÃtel-Dieu de QueÂbec, Centre hospitalier universitaire de QueÂbec, QueÂbec G1R 2J6 Canada; and 2 DeÂpartement de biologie, Universite Laval, QueÂbec G1K 7P4 Canada p53 has been postulated to be the guardian of the genome. However, results supporting the prediction that point mutation frequencies are elevated in p53-de®cient cells either have not been forthcoming or have been equivocal. To analyse the e ect of p53 on point mutation frequency, we used the supF gene of the pYZ289 shuttle vector as a mutagenic target. pYZ289 was treated in vitro by ultraviolet irradiation, a¯atoxin B 1 , (+)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and meta-chloroperoxybenzoic acid and then transfected into p53-de®cient cells with or without a p53 expression vector. p53 reduced the mutant frequency up to ®vefold when pYZ289 was treated with a¯atoxin B 1 , (+)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene or meta-chloroperoxybenzoic acid but not when it was ultraviolet-irradiated. The p53-dependent mutation frequency reduction was higher at a higher level of premutational lesions for a¯atoxin B 1 and (+)7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene and at a lower level of lesions for meta-chloroperoxybenzoic acid. This suggests that the chemical mutagens produce, in a dose-dependent fashion, two kinds of DNA damage, one subject to p53-dependent mutation frequency reduction and the other not. These results indicate that p53 can reduce the point mutation frequency in a shuttle vector treated by chemical mutagens and suggest that p53 can act as guardian of the genome for at least some kinds of point mutations.

Suppressive activities of OGG1 and MYH proteins against G:C to T:A mutations caused by 8-hydroxyguanine but not by benzo[a]pyrene diol epoxide in human cells in vivo

“…In particular, G:C to T:A transversions were predominant among several types of base substitutions induced (Table II). This result is well consistent with previous studies using shuttle plasmids treated with BPDE (19,20,31,32), and indicates that G:C to T:A transversions were predominantly induced by BPDE-adducts formed on the pMY189 plasmid. Thus, BPDE-treated pMY189 plasmid was subjected to assess the suppression activities of BER proteins against G:C to T:A transversions caused by BPDE.…”

A role for p53 in base excision repair

“…p53‐deficient cells also exhibit a higher tolerance to genetic abnormalities arising from radiation as well as spontaneously (Lee et al ., 1994). Evidence suggesting a role of p53 in DNA repair in vivo is supported by observations that (i) p53 increases global but not transcription‐coupled nucleotide excision repair (Hwang et al ., 1999 and references therein); (ii) p53 reduces point mutation frequency of a shuttle vector modified by several chemical mutagens (Courtemanche and Anderson, 1999); and (iii) p53 inactivation by HPV16 results in increased mutagenesis in human cells (Yu et al ., 1997). So far, most observations of a role of p53 in DNA repair seem to involve nucleotide excision repair (NER) (Ford et al ., 1998; Lloyd and Hanawalt, 2000) and it is believed that p53 plays an indirect role in NER, probably by transactivating the p48 gene (and perhaps some others), which is essential for efficient repair of certain DNA lesions (Hwang et al ., 1999; Tang et al ., 2000).…”