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Critical amino acids in human DNA polymerases eta and kappa involved in erroneous incorporation of oxidized nucleotides.

ABSTRACT: Oxidized DNA precursors can cause mutagenesis and carcinogenesis when they are incorporated into the genome. Some human Y-family DNA polymerases (Pols) can effectively incorporate 8-oxo-dGTP, an oxidized form of dGTP, into a position opposite a template dA. This inappropriate G:A pairing may lead to transversions of A to C. To gain insight into the mechanisms underlying erroneous nucleotide incorporation, we changed amino acids in human Poleta and Polkappa proteins that might modulate their specificity for incorporating 8-oxo-dGTP into DNA. We found that Arg61 in Poleta was crucial for erroneous nucleotide incorporation. When Arg61 was substituted with lysine (R61K), the ratio of pairing of dA to 8-oxo-dGTP compared to pairing of dC was reduced from 660:1 (wild-type Poleta) to 7 : 1 (R61K). Similarly, Tyr112 in Polkappa was crucial for erroneous nucleotide incorporation. When Tyr112 was substituted with alanine (Y112A), the ratio of pairing was reduced from 11: 1 (wild-type Polkappa) to almost 1: 1 (Y112A). Interestingly, substitution at the corresponding position in Poleta, i.e. Phe18 to alanine, did not alter the specificity. These results suggested that amino acids at distinct positions in the active sites of Poleta and Polkappa might enhance 8-oxo-dGTP to favor the syn conformation, and thus direct its misincorporation into DNA.

SUBMITTER: Katafuchi A

PROVIDER: S-EPMC2817480 | biostudies-literature | 2010 Jan

REPOSITORIES: biostudies-literature

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Critical amino acids in human DNA polymerases eta and kappa involved in erroneous incorporation of oxidized nucleotides.

Katafuchi Atsushi A Sassa Akira A Niimi Naoko N Grúz Petr P Fujimoto Hirofumi H Masutani Chikahide C Hanaoka Fumio F Ohta Toshihiro T Nohmi Takehiko T

Nucleic acids research 20091125 3

Oxidized DNA precursors can cause mutagenesis and carcinogenesis when they are incorporated into the genome. Some human Y-family DNA polymerases (Pols) can effectively incorporate 8-oxo-dGTP, an oxidized form of dGTP, into a position opposite a template dA. This inappropriate G:A pairing may lead to transversions of A to C. To gain insight into the mechanisms underlying erroneous nucleotide incorporation, we changed amino acids in human Poleta and Polkappa proteins that might modulate their spec ...[more]

PMID: 19939936

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Project description:Overexpression of human DNA polymerase kappa (hpol ?) in glioblastoma is associated with shorter survival time and resistance to the alkylating agent temozolomide (TMZ), making it an attractive target for the development of small-molecule inhibitors. We previously reported on the development and characterization of indole barbituric acid-derived (IBA) inhibitors of translesion DNA synthesis polymerases (TLS pols). We have now identified a potent and selective inhibitor of hpol ? based on the indole-aminoguanidine (IAG) chemical scaffold. The most promising IAG analogue, IAG-10, exhibited greater inhibitory action against hpol ? than any other human Y-family member, as well as pols from the A-, B-, and X-families. Inhibition of hpol ? by IAG analogues appears to proceed through a mechanism that is distinct from inhibition of hpol ? based on changes in DNA binding affinity and nucleotide insertion kinetics. By way of comparison, both IAG and IBA analogues inhibited binary complex formation by hpol ? and ternary complex formation by hpol ?. Decreasing the concentration of enzyme and DNA in the reaction mixture lowered the IC50 value of IAG-10 to submicromolar values, consistent with inhibition of binary complex formation for hpol ?. Chemical footprinting experiments revealed that IAG-10 binds to a cleft between the finger, little finger, and N-clasp domains on hpol ? and that this likely disrupts the interaction between the N-clasp and the TLS pol core. In cell culture, IAG-10 potentiated the antiproliferative activity and DNA damaging effects of TMZ in hpol ?-proficient cells but not in hpol ?-deficient cells, indicative of a target-dependent effect. Mutagenic replication across alkylation damage increased in hpol ?-proficient cells treated with IAG-10, while no change in mutation frequency was observed for hpol ?-deficient cells. In summary, we developed a potent and selective small-molecule inhibitor of hpol ? that takes advantage of structural features unique to this TLS enzyme to potentiate TMZ, a standard-of-care drug used in the treatment of malignant brain tumors. Furthermore, the IAG scaffold represents a new chemical space for the exploration of TLS pol inhibitors, which could prove useful as a strategy for improving patient response to genotoxic drugs.

Dataset Information

Critical amino acids in human DNA polymerases eta and kappa involved in erroneous incorporation of oxidized nucleotides.

Publications

Critical amino acids in human DNA polymerases eta and kappa involved in erroneous incorporation of oxidized nucleotides.

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