Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
Molecular genetics and structural biology of human MutT homolog, MTH1
Introduction
Endogenous oxidation of DNA and DNA precursors by reactive oxygen species (ROS) appears to induce spontaneous mutations, aging, and various diseases, including cancer and neuronal degeneration [1], [2]. It has been established that 8-oxo-dGTP, an oxidized form of dGTP is highly mutagenic and one of main endogenous sources for spontaneous mutagenesis. During DNA replication, 8-oxo-dGTP can be inserted into the nascent strand opposite adenine and cytosine in the template, with almost equal efficiency, an event which leads to an A:T to C:G transversion mutation [3], [4], [5].
To eliminate such deleterious oxidized nucleotides, organisms come equipped with elaborate mechanisms. In Escherichia coli, the MutT protein hydrolyzes 8-oxo-dGTP to the monophosphate form, thus, eliminating mutagenic substrates from the DNA precursor pool [3]. Lack of the mutT gene increases the spontaneous occurrence of A:T to C:G transversion a 1000-fold over the wild-type level [6], [7], [8]. Moreover, it has been shown that E. coli RNA polymerase misinserts 8-oxo-GTP, an oxidized form of GTP, into mRNA, yielding mutant forms of proteins known as non-genomic mutations in mutT deficient cells. MutT protein also efficiently hydrolyzes 8-oxo-GTP, and, thus, minimizes errors caused by misincorporation of oxidized guanine nucleotides into RNA [9].
Enzymatic activity similar to that of MutT protein has been identified in human cells [10], [11]. Based on partial amino acid sequences obtained from a purified preparation of human 8-oxo-dGTPase, cDNA and the gene for the human enzyme were isolated, and named MTH1 (mutT homolog-1) [11], [12]. Since 30 amino acid residues (23%) are identical between MutT and MTH1 proteins, and expression of the human enzyme in mutT-E. coli cells suppresses the elevated level of spontaneous mutation frequency to an almost normal, the human enzyme appears to have the same antimutagenic capacity as does E. coli MutT protein.
Findings with regard to the human MTH1 protein, the function of which is likely to differ from those in bacteria, are reviewed herein.
Section snippets
Regulation of expression of the MTH1 gene
In human tissues, large amounts of MTH1 mRNA are present in normal thymus, testis and embryonic tissues. In peripheral blood lymphocytes (PBL), the level of MTH1 mRNA was significantly increased after concomitant treatment with phytohemagglutinin (PHA) and interleukin-2 (IL-2), indicating that expression of the MTH1 gene is inducible in human cells during proliferative activation [13].
Cancerous tissues in humans have significantly higher levels of MTH1 transcripts [14], [15], presumably the
MutT family proteins with the phosphohydrolase module
Genes for MutT homolog proteins with dGTPase or 8-oxo-dGTPase activity were identified in Proteus vulgaris and Streptococcus pneumoniae, bacteria distantly related to E. coli (Fig. 3) [7], [20], [21]. All three MutT homolog proteins have a molecular mass ranging from 13 to 18 kDa, and the degree of identity ranges from 19 to 40%. Most of the identical residues are in a region corresponding to the 23 residues from Gly37 to Gly59 of E. coli MutT, known as the MutT signature [22]. Homologs of human
Molecular epidemiology of MTH1 gene
To date, two different SNPs in human MTH1 gene, which affect expression or function of MTH1 protein, were found, as discussed above [13], [17], [32], [43]. We examined the distribution of one of the SNPs, namely Val83/Met83 in the Japanese population, living in Japan, including 400 healthy volunteers and 601 patients with various diseases. Allele frequencies of Val83 and Met83 in the healthy volunteers are 0.91 and 0.09, respectively. There were three homozygotes for Met83/Met83 out of 400
Conclusion
As summarized in Fig. 6, oxidized purine nucleoside triphosphates, such as 2-OH-dATP, 8-oxo-dGTP, 8-oxo-dATP and 8-oxo-GTP are hydrolyzed to the corresponding monophosphates by the action of MTH1 protein. It has been demonstrated that guanylate kinase, which phosphorylates GMP and dGMP to the corresponding nucleoside diphosphates is inactive on 8-oxo-dGMP, thus, preventing re-utilization of the MTH1 cleavage product during DNA replication or transcription [44]. 8-Oxo-dGMP is rapidly
Acknowledgements
I extend special thanks to Drs. M. Furuichi, K. Sakumi, Y. Sakai, T. Tsuzuki, M. Takahashi, M. Shirakawa, and M. Sekiguchi, for helpful discussions, and to M. Ohara for language assistance.
References (44)
- et al.
Endogenous mutagens and the causes of aging and cancer
Mutat. Res.
(1991) - et al.
8-Hydroxyguanine, an abundant form of oxidative DNA damage, causes G→T and A→C substitutions
J. Biol. Chem.
(1992) - et al.
Functional cooperation of MutT, MutM and MutY proteins in preventing mutations caused by spontaneous oxidation of guanine nucleotide in Escherichia coli
Mutat. Res.
(1995) - et al.
Cloning and expression of cDNA for a human enzyme that hydrolyzes 8-oxo-dGTP, a mutagenic substrate for DNA synthesis
J. Biol. Chem.
(1993) - et al.
Genomic structure and chromosome location of the human mutT homologue gene MTH1 encoding 8-oxo-dGTPase for prevention of A:T to C:G transversion
Genomics
(1994) - et al.
Regulation of expression of the human MTH1 gene encoding 8-oxo-dGTPase. Alternative splicing of transcription products
J. Biol. Chem.
(1997) - et al.
Overexpression of hMTH1 mRNA: a molecular marker of oxidative stress in lung cancer cells
FEBS Lett.
(1998) - et al.
Organization and expression of the mouse MTH1 gene for preventing transversion mutation
J. Biol. Chem.
(1997) - et al.
Redox regulation of genes that protect against carcinogens
Comp. Biochem. Physiol. Part B: Biochem. Mol. Biol.
(1997) - et al.
Sequence and characterization of mutT from Proteus vulgaris
Gene (Amsterdum)
(1993)
The MutT proteins or “Nudix” hydrolases, a family of versatile, widely distributed, “Housecleaning” enzymes
J. Biol. Chem.
Mouse MTH1 protein with 8-oxo-7, 8-dihydro-2′-deoxyguanosine 5′-triphosphatase activity that prevents transversion mutation cDNA cloning and tissue distribution
J. Biol. Chem.
Escherichia coli orf17 codes for a nucleoside triphosphate pyrophosphohydrolase member of the MutT family of proteins
J. Biol. Chem.
Orf186 represents a new member of the Nudix hydrolases, active on adenosine(5′) triphospho(5′)adenosine, ADP-ribose, and NADH
J. Biol. Chem.
Identification and characterization of the Nudix hydrolase from the Archaeon, Methanococcus jannaschii, as a highly specific ADP-ribose pyrophosphatase
J. Biol. Chem.
Functional significance of the conserved residues for the 23 residue module among MTH1 and MutT family proteins
J. Biol. Chem.
Biochemical and physicochemical characterization of normal and variant forms of human MTH1 protein with antimutagenic activity
Mutat. Res.
The oxidized forms of dATP are substrates for the human MutT homologue, the hMTH1 protein
J. Biol. Chem.
Intracellular localization of 8-oxo-dGTPase in human cells, with special reference to the role of the enzyme in mitochondria
J. Biol. Chem.
Polymorphisms and probable lack of mutation in a human mutT homolog, hMTH1, in hereditary nonpolyposis colorectal cancer
Biochem. Biophys. Res. Commun.
Oxidants, antioxidants, and the degenerative diseases of aging
Proc. Natl. Acad. Sci. U.S.A.
MutT protein specifically hydrolyses a potent mutagenic substrate for DNA synthesis
Nature
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