Risk factors associated with uterine cervical cancer in Korea: a case-control study with special reference to sexual behavior

OBJECTIVE

A hospital-based case-control study was conducted to identify characteristics of women at high risk of developing cervical cancer with special reference to sexual behavior in Korea.

METHODS

Histologically confirmed cases of invasive cervical cancer were selected from the Department of Gynecology, Seoul National University Hospital between September 1992 to May 1995 (n = 203). Women with normal pap smear tests and women free of past history of any malignancies were regarded as controls (n = 827). Information on risk factors were collected by both a self-administered questionnaire and a direct interview.

RESULTS

Uterine cervical cancer risk was higher in women with a less educated spouse (Ptrend = 0.0003), women with a family history of cervical cancer (adjusted odds ratio [OR] = 2.20., 95% confidence interval [CI] 1.21-4.01), women of shorter height (Ptrend = 0.02), women with early age at first full term pregnancy (Ptrend = 0.0005), and women who have had multiple full term pregnancies (Ptrend = 0.006) by the multiple linear logistic analysis. Particularly noteworthy was a significant decreasing trend in the adjusted OR with the age at first sexual intercourse increasing (Ptrend = 0.002) after adjusting the number of sexual partners. The husband's indecent sexual history showed a borderline significance (Ptrend = 0.07).

CONCLUSIONS

This study confirmed that the risk factors of cervical cancer in Korea are similar with those found in other countries.

Proteolytic cleavage sites of band 3 protein in alkali-treated membranes: fidelity of hydropathy prediction for band 3 protein

To assess the fidelity of hydropathy prediction for band 3 protein, we determined the cleavage sites of the protein and the portions of the protein tightly bound to the membrane lipid bilayer by means of in situ proteolytic digestion. For the removal of all anticipated hydrophilic connector loops from membranes, we had to denature the band 3 protein molecule in situ by alkali treatment. When the alkali-treated membranes were digested with trypsin, chymotrypsin, and pepsin, the majority of the anticipated transmembrane portions remained in the membrane fraction. However, five anticipated transmembrane portions were released into the supernatant fraction. Thus, the first, second, third, sixth and tenth anticipated transmembrane portions, in accordance with the hydropathy prediction, were released into the supernatant with the proteolytic digestion method. This indicates that these anticipated transmembrane portions are not bound with the boundary lipids although the hydrophobicity of these portions is comparable to that of the portions experimentally remaining in the membrane fraction. It is conceivable that the membrane peptide portions of band 3 protein could be classified into at least two categories, i.e. one bound to the boundary lipids and the other free from the boundary lipids. Approximately 90% of the transmembrane domain of the band 3 protein are recovered in either the supernatant fraction or the membrane fraction. The fidelity of hydropathy prediction for polytopic membrane proteins and the nature of the membrane embedded peptide portions are discussed.

Coplanar PCBs and the relative contribution of coplanar PCBs, PCDDs, and PCDFs to the total 2,3,7,8-TCDD toxicity equivalents in human serum

Coplanar PCBs in human serum were measured by high-resolution gas chromatography/isotope-dilution high-resolution mess spectrometry in 46 pulp and paper mill workers and 16 community residents with no specific known source of PCB exposure. The relative contribution of coplanar PCBs, PCDDs, and PCDFs to the total 2,3,7,8-TCDD toxicity equivalents (TEQs) were compared using the toxic equivalency factors proposed by Safe [1] and the factors recently proposed by WHO [2]. The mean concentrations of PCB-126 and PCB-169 were higher in paper mill workers than in community residents. However, these differences were not statistically significant. Serum PCB-126, but not PCB-169, was correlated with body mass index (Spearman's r = 0.40, p = 0.002). Serum PCB-169, but not PCB-126, was correlated with age (Spearman's r = 0.54, p = 0.0001). Multiple linear regression analysis for log-transformed combined PCBs showed that age (p = 0.008), body mass index (p = 0.031), and eating locally caught fish (p = 0.019) were statistically significant predictors. The majority of the total TEQ in serum is due to PCDDs (63%), whereas PCDFs account for 21% and coplanar PCBs account for 15% when calculated using the TEFs proposed by Safe. The percent contributions from PCDDs, PCDFs, and coplanar PCBs were 66%, 24%, and 10% respectively when calculated based on the TEFs proposed by WHO. Age, body mass index, and consumption of locally caught fish are significant predictors for coplanar PCB levels in human serum. Serum PCDDs were the major contributors to the total 2,3,7,8-TCDD equivalent toxicity in this study.

In vivo determination of replication origins of human mitochondrial DNA by ligation-mediated polymerase chain reaction

A large part of replication is aborted in human mitochondria, the result being a D-loop. As few attempts have been made to distinguish free 5' ends of true replicate from those of abortive ones, we examined the 5' ends of true replicate of human mitochondrial DNA at one nucleotide resolution in vivo by making use of ligation-mediated polymerase chain reaction. The distribution and relative amounts of origins of the true replicate are exactly the same as those of total newly synthesized heavy strands, which means that the abortion of replication is independent of 5' ends. Treatment of DNA with RNase H frees 5' ends on both heavy and light strands. This is the first in vivo evidence for covalently attached primer RNA to nascent strand in human mitochondrial DNA.

Interactions between superoxide and nitric oxide: implications in DNA damage and mutagenesis

Chronic inflammation is known to be associated with enhanced production of both nitric oxide (NO) and reactive oxygen species such as superoxide (O2-) and hydrogen peroxide (H2O2). Patients with long-standing ulcerative colitis are also known to be at increased risk of developing colorectal cancer. Although NO and reactive oxygen intermediates alone have been known to damage DNA and to promote a wide array of mutagenic reactions, there is increasing evidence to suggest that the interaction between O2- and NO may dictate the type of mutagenic reactions produced at sites where both these free radicals are produced. In the absence of O2-, NO will engage in nitrosative chemistry to yield stable N-nitrosamine derivatives of secondary amines and promote nitrosative deamination of DNA bases. As the flux of O2- is increased, nitrosation reactions are suppressed and oxidative chemistry is enhanced. Thus, depending upon the fluxes of each radical either nitrosation or oxidation chemistry may predominate. The fundamental understanding between O2- and NO may provide new insight in the mechanisms responsible for inflammation-induced mutagenesis.

The content of intracellular mitochondrial DNA is decreased by 1-methyl-4-phenylpyridinium ion (MPP+)

1-Methyl-4-phenylpyridinium ion (MPP+), an oxidative metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), is considered to be directly responsible for MPTP-induced Parkinson's disease-like symptoms by inhibiting NADH-ubiquinone oxidoreductase (complex I) in the mitochondrial respiratory chain. Here we demonstrate that 25 microM MPP+ decreases the content of mitochondrial DNA to about one-third in HeLa S3 cells. On the contrary, 0.1 microM rotenone, which inhibits complex I to the same extent as 25 microM MPP+ in the cells, increases the content of mitochondrial DNA about 2-fold. Hence, the effect of MPP+ on mitochondrial DNA is not mediated by the inhibition of complex I. To examine the replication state of mitochondrial DNA, we measured the amount of nascent strands of mitochondrial DNA. The amount is decreased by MPP+ but increased by rotenone, suggesting that the replication of mitochondrial DNA is inhibited by MPP+. Because the proper amount of mitochondrial DNA is essential to maintain components of the respiratory chain, the decrease of mitochondrial DNA may play a role in the progression of MPTP-induced Parkinson's disease-like symptoms caused by the mitochondrial respiratory failure.

Genetic evidence for the involvement of tau in progressive supranuclear palsy

A dinucleotide repeat polymorphism in a tau intron was identified and used in a case-control study to analyze the genetic association of tau with several neurodegenerative diseases with tau pathology. Subjects with the homozygous tau AO alleles were excessively represented in the progressive supranuclear palsy (PSP) group, compared with the age-matched healthy control group. Consequently, this allele is more frequently found in PSP than in a group of healthy subjects. This trend was not found in Alzheimer's disease or parkinsonism-dementia complex of Guam, both of which are accompanied by major tau pathology. The result suggests a possible involvement of tau in the pathogenesis of PSP.

Changes of energy metabolism induced by 1-methyl-4-phenylpyridinium (MPP+)-related compounds in rat pheochromocytoma PC12 cells

We examined effects of three structurally related pyridinium compounds, 1-methyl-4-phenylpyridinium (MPP+), paraquat, and 1-methyl-4-(4'-nitrophenyl) pyridinium (analog 1), on the energy metabolism in pheochromocytoma PC12 cells. MPP+ inhibited the intracellular NADH oxidation by the mitochondrial respiratory chain, judging from the decrease of the cytosolic NAD+/NADH ratio. Paraquat enhanced the oxidation of NADH and decreased intracellular ATP more than MPP+. The inhibition of the mitochondrial respiration by MPP+ was partially compensated by enhanced glycolysis, while paraquat inhibited glycolysis at the level of hexokinase probably due to the intracellular production of oxygen radicals. Analog 1 moderately enhanced glycolysis, moderately increased a cytosolic ratio of NAD+/NADH, and caused only a slight decline of intracellular ATP. Paraquat was the most cytotoxic of the three compounds. Thus, the three structurally related compounds, MPP+, paraquat, and analog 1, showed different effects on the mitochondrial respiratory chain and the glycolytic pathway in PC 12 cells. Their properties found in the cells well reflected those obtained by using bovine heart submitochondrial particles.

A dual effect of 1-methyl-4-phenylpyridinium (MPP+)-analogs on the respiratory chain of bovine heart mitochondria

We examined effects of several compounds, structurally related to 1-methyl-4-phenylpyridinium (MPP+), on the NADH-dependent respiration of bovine heart submitochondrial particles. 1-Methyl-4-(3 '-trimethylammoniophenyl)pyridinium (analog 8) as well as MPP+ completely inhibited O2 consumption, reduction of ubiquinone-10, and reduction of cytochrome b in a dose-dependent manner. The production of superoxide (O2-) induced by MPP+ or analog 8 was to the same extent as that by rotenone, an inhibitor of complex I of the mitochondrial respiratory chain. Rotenone had no additive effect on the maximal production of O2- induced by MPP+ or analog 8, suggesting that the production was mediated by the same way as rotenone. 1-Methyl-4-(4'-nitrophenyl) pyridinium (analog 1) induced about 20-fold more production of O2 than MPP+ and the production was additively increased by rotenone. Analog 1 only partially inhibited rotenone-sensitive O2 consumption. Paraquat induced the production of O2- as much as analog 1. Paraquat, however, did not inhibit rotenone-sensitive O2 consumption or reduction of cytochrome b. These results suggest that MPP+ and its analogs interact with the mitochondrial respiratory chain at two sites, the substrate side of the rotenone-binding site and the rotenone-binding site. The analogs may be reduced to produce O2- at the former site and inhibit the respiratory chain at the latter site.

Glial cells in Alzheimer's disease: preferential effect of APOE risk on scattered microglia

Reactive glial cells are consistently found in the brain tissue of Alzheimer's disease (AD) patients. Both clustered and scattered glial cells occur in AD brain. A number of clustered microglial cells, but not astrocytes, had a positive correlation with neurite plaque numbers, suggesting that clustered micro-glial cells are uniquely associated with plaques whereas clustered astrocytes may have functions outside the plaques as well. APOE epsilon 4, the major genetic risk factor for AD, had a dose-dependent effect to increase the numbers of scattered microglial cells whereas the APOE risk showed no correlation with any of the clustered glial cells or scattered astrocytes. These findings raise the possibility that the increased levels of scattered, but not clustered, microglial cells are the immediate response to APOE risk and might be primarily involved in AD pathogenesis.

Analysis of a lysozyme gene from the malaria vector mosquito, Anopheles gambiae

A genomic DNA sequence encoding a basic lysozyme was isolated from the malaria vector mosquito Anopheles gambiae by screening a library with a probe prepared by PCR of reverse transcribed adult RNA. The sequence consists of an upstream region of about 2 kb, a coding region containing three exons and two introns, and a short 3' untranslated region. The coding region indicates that this mosquito lysozyme consists of a signal peptide of 20 residues followed by an 120 aa mature protein which is very similar to other basic lysozymes. The two small introns, 67 and 76 bp, are located at evolutionarily conserved sites. RT-PCR indicated that this gene is expressed abundantly in sugar-fed adults, and at considerably lower levels when females have fed on blood. Although it remains to be seen whether this gene is induced by bacterial infection, the surrounding sequence contains six sequence motifs very similar to the consensus binding sites for a transcription factor similar to NF-kappa B that are found associated with most insect immune response genes. This lysozyme gene maps to division 27 on the left arm of polytene chromosome 2L. An ORF unrelated to any animal protein in current data bases was found at the 5' end of the clone.

Trichoplusia ni attacin A, a differentially displayed insect gene coding for an antibacterial protein

The mRNA differential display method was used to isolate antibacterial defense genes from Trichoplusia ni. The mRNA population in last-instar T. ni larvae injected with bacteria was compared to that of untreated larvae. Using a PCR amplified probe corresponding to an induced mRNA, we were able to clone an attacin homolog from a lambda cDNA library from vaccinated larvae. The corresponding protein showed 63% identity to Hyalophora cecropia acidic attacin. The induction kinetics of T. ni attacin A gave optimal mRNA levels at 20 h post-infection. Genomic analysis showed this to be a single-copy gene with two introns.

Polycyclic aromatic hydrocarbon metabolites in urine as biomarkers of exposure and effect

Humans are exposed to polycyclic aromatic hydrocarbons (PAHs) from various occupational, environmental, medicinal, and dietary sources. PAH metabolites in human urine can be used as biomarkers of internal dose to assess recent exposure to PAHs. PAH metabolites that have been detected in human urine include 1-hydroxypyrene (1-OHP), 1-hydroxypyrene-O-glucuronide (1-OHP-gluc), 3-hydroxybenzo[a]pyrene, 7,8,9,10-tetrahydroxy-7,8,9, 10-tetrahydrobenzo[a]pyrene, and a number of other hydroxylated PAHs. The most widely used of these is 1-OHP-gluc, the major form of 1-OHP in human urine, by virtue of its relatively high concentration and prevalence in urine and its ease of measurement. This metabolite of pyrene can be measured as 1-OHP after deconjugation of the glucuronide with beta-glucuronidase or directly as 1-OHP-gluc without deconjugation. Elevated levels of 1-OHP or 1-OHP-gluc have been demonstrated in smokers (versus nonsmokers), in patients receiving coal tar treatment (versus pretreatment), after workshifts in road pavers (versus before shifts or versus controls), after shifts in coke oven workers (versus before shift), and in subjects ingesting charbroiled meat (versus preingestion). More importantly, this metabolite is found (at low levels) in most human urine, even in persons without apparent occupational or smoking exposure. Although measurement of these metabolites is useful in assessing recent exposure to PAHs, their value as predictive markers of biological effect or health outcomes has not been rigorously tested and at present can only be inferred by association.

PCR differential display of immune gene expression in Trichoplusia ni

The immune state of insects is defined by a set of proteins that is absent in the naive state. To explore the immune system of Trichoplusia ni in more detail we have employed a PCR differential display technique to compare the mRNA population of untreated last instar larvae to that of immunized animals. In the primary display, more than one hundred bands seemed induced upon bacterial challenge. When they were used as probes in Northern blots, 35% of these probes detected inducible mRNA species. Such probes were used to screen a cDNA library from immunized larvae. We isolated clones for T. ni homologs of cecropin A, lysozyme and attacin. One differentially expressed band hybridized to clones for BJHSP1, a hemacy-anin-related protein which is hormonally up-regulated in last instar larvae; this induction is probably not related to the bacterial infection. Still other probes recognized inducible mRNAs of 1.6 and 1.0 kb. The corresponding cDNA clones did not show strong sequence homology to any known proteins. We have demonstrated the potential of this PCR technique to display both known and unknown genes specific for the immune state of whole insects against a background of genes involved in larval development.

A structural study of the carboxyl terminal region of the human erythrocyte band 3 protein

Two peptides derived from the carboxyl terminal region of the human erythrocyte band 3 protein were identified as fragments releasable from cell membranes on trypsin digestion. These peptides, Asn-880-Lys-892 and Ala-893-Val-911-COOH, however, were resistant to trypsin, unless the cell membranes had been treated with high concentrations of NaOH. This suggests that the carboxyl terminal region is located in situ within the native band 3 molecule. Unlike in the cases of other portions of the band 3 protein, such as Gly-647-Arg-656, Ser-731-Lys-743, and Tyr-818-Lys-826, the release of the carboxyl terminal region was not inhibited by pretreatment of erythrocytes with 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), indicating that there is no major structural difference in the carboxyl terminal portion between the outward and inward facing forms. The carboxyl terminal region of the band 3 protein has a negative charge cluster. In the middle of the negative charge cluster, consensus sequences, Val-Asp-X-X-X-Leu-Asp-Ala-Asp-Asp and Thr-Phe-Asp-Glu (TFDE), were found in the carboxyl terminal regions of aquaporin CHIP and glucose transporter 1, respectively. The sequence, TFDE, exists in the highly amphipathic 11-residue sequence of glucose transporter 1, and this amphipathic sequence has been suggested to promote normal membrane insertion of polytopic membrane proteins such as glucose transporter 1 and serine chemoreceptor. The role of the carboxyl terminal region of the band 3 protein is discussed.

Quantitative contribution of the acid production to the intracellular acidification in human neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine

A chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (fMLP), induced an acidification of cytosol by about 0.05 pH units in 30 sec followed by an alkalinization in human neutrophils. The quantitative contribution of acid production to the acidification was studied. The superoxide (O2-) production stimulated by fMLP was not involved in the acidification because the production of acids in neutrophils from patients with chronic granulomatous disease who do not produce O2-, was the same as that in normal neutrophils. The intracellular acidification was completely inhibited by deoxyglucose, suggesting that energy metabolism enhanced upon stimulation by fMLP might be the main source of the acidification. Although enhancement of the lactate formation by fMLP was 0.8 nmol/10(6) cells, which could lower intracellular pH by 0.08 pH units, the lactate production could not explain the initial acidification because the production of lactate started at 1 min after the stimulation while the intracellular acidification began immediately after the stimulation. Mitochondrial respiratory inhibitors such as KCN and rotenone had no effects on the fMLP-induced intracellular acidification. The fMLP-induced production of CO2 in 30 sec through the hexose monophosphate shunt was only 2.6 pmol/10(6) cells, which was calculated to decrease intracellular pH by only 0.0014. Thus, changes of energy metabolism induced by fMLP does not explain the acidification.

Metastatic pleural cancer in radionuclide angiocardiography. A pulmonary time-activity curve mimicking left-to-right cardiac shunt

A 55-year-old man, with a history of nephrectomy for renal cell carcinoma, was evaluated using radionuclide angiocardiography to exclude cardiac shunts as the cause of vascular bruits heard at auscultation. A pulmonary time-activity curve derived from the right lung showed a pattern typical of a large left-to-right shunt, whereas that from the left lung was normal. Increased systemic arterial flow to the lateral right chest was noted in early dynamic images. Subsequent studies revealed that this flow and the abnormal time-activity curve of the right lung were due to systemic arterial supply to metastatic pleural cancer, originating from the kidney. The authors conclude that special caution should be undertaken in the interpretation of the radionuclide angiocardiography for determining left-to-right cardiac shunts, especially in those showing a asymmetric pulmonary time-activity curve.

NACP, the precursor protein of the non-amyloid beta/A4 protein (A beta) component of Alzheimer disease amyloid, binds A beta and stimulates A beta aggregation

NACP, a 140-amino acid presynaptic protein, is the precursor of NAC [the non-amyloid beta/A4 protein (A beta) component of Alzheimer disease (AD) amyloid], a peptide isolated from and immunologically localized to brain amyloid of patients afflicted with AD. NACP produced in Escherichia coli bound to A beta peptides, the major component of AD amyloid. NACP bound to A beta 1-38 and A beta 25-35 immobilized on nitrocellulose but did not bind to A beta 1-28 on the filter under the same conditions. NACP binding to A beta 1-38 was abolished by addition of A beta 25-35 but not by A beta 1-28, suggesting that the hydrophobic region of the A beta peptide is critical to this binding. NACP-112, a shorter splice variant of NACP containing the NAC sequence, bound to A beta, but NACP delta, a deletion mutant of NACP lacking the NAC domain, did not bind A beta 1-38. Furthermore, binding between NACP-112 and A beta 1-38 was decreased by addition of peptide Y, a peptide that covers the last 15 residues of NAC. In an aqueous solution, A beta 1-38 aggregation was observed when NACP was also present in an incubation mixture at a ratio of 1:125 (NACP/A beta), whereas A beta 1-38 alone or NACP alone did not aggregate under the same conditions, suggesting that the formation of a complex between A beta and NACP may promote aggregation of A beta. Thus, NACP can bind A beta peptides through the specific sequence and can promote A beta aggregation, raising the possibility that NACP may play a role in the development of AD amyloid.

Association of exposure to polycyclic aromatic hydrocarbons (estimated from job category) with concentration of 1-hydroxypyrene glucuronide in urine from workers at a steel plant

OBJECTIVES

Increased risk of lung cancer has been associated with employment in the steel industry. This association is thought to be due in part to increased concentrations of polycyclic aromatic hydrocarbons (PAHs) in air found in this work environment. Measurement of PAH metabolites in human urine provides a means of assessing individual internal dose of PAHs. This study examined the relative contribution of occupation and smoking to urinary concentration of 1-hydroxypyrene glucuronide (1-OHPG) among a group of workers at a steel plant.

METHODS

Concentrations of 1-OHPG in urine from 44 workers with jobs associated with increased air concentrations of PAHs and 40 workers with jobs with low or no exposure to PAHs were measured. 20 workers in each group were not current smokers. Urinary 1-OHPG was measured by synchronous fluorescence spectroscopy after immunoaffinity chromatography specific for PAH metabolites.

RESULTS

Mean (SEM) urinary 1-OHPG concentration was 2.16 (0.42) pmol/ml urine among the 44 occupationally exposed workers compared with 0.38 (0.05) among the 40 workers with no or low exposure (P < 0.0001). Mean urinary 1-OHPG concentration was 1.82 (0.41) pmol/ml urine among the 44 current smokers compared with 0.75 (0.20) among the 40 non-smokers (P < 0.005). Mean 1-OHPG concentrations in non-smokers were 0.26 (n = 20), 0.70 (n = 15), and 2.84 pmol/ml urine (n = 5) for strata of exposure to PAHs (no or low, mid, and high) based on job category; the corresponding values in smokers were 0.55 (n = 20), 0.94 (n = 12), and 4.91 pmol/ml (n = 12), respectively. Multiple linear regression showed significant differences between subjects in different PAH exposure with increased concentrations of 1-OHPG in urine. Amounts of foods containing PAHs ingested by this group of workers were relatively low and did not contribute significantly to urinary 1-OHPG concentrations.

CONCLUSIONS

These results indicate that 1-OHPG is a common urinary metabolite in people with recent occupational exposure to PAHs and is associated with both job category and estimated stratum of PAH exposure.

Roles of histidine 752 and glutamate 699 in the pH dependence of mouse band 3 protein-mediated anion transport

In the accompanying paper we have shown that four different histidine residues are involved in the maintenance of mouse band 3 in a state in which it is able to execute its anion transport function. Here we focus on the functional significance of His 752 and demonstrate that this residue, together with Glu 699, plays a key role in the control of pH dependence of Cl- transport. Mouse band 3-encoding cRNA was expressed in Xenopus oocytes, and band 3-mediated Cl- transport was measured at zero membrane potential over the pH range 6.0-9.2. Transport decreased with increasing H+ concentration and was governed by a single pK of 5.8. After correction for temperature differences, this result agrees well with measurements in erythrocyte ghosts of Cl- flux by Funder and Wieth [Funder, J., & Wieth, J. O. (1976) J. Physiol. 262, 679-698] and our own determinations by 35Cl NMR spectroscopy of Cl- exchange between the substrate binding site and the medium. After mutation of either Glu 699 to Asp or of His 752 to Ser, the maximal rate of transport is reduced and the rate of anion exchange is now governed by a single pK of about 6.8-6.9. This suggests that the formation of a hydrogen bond between His 752 and Glu 699 is essential for the decrease of band 3-mediated Cl- transport at low pH. We suggest that in the wild type band 3 both the decrease of the chloride exchange between the medium and the substrate binding site and the inhibition of chloride translocation across the membrane are dominated by a common rate-limiting step and that this step involves hydrogen bond formation between Glu 699 and His 752.

Intracellular localization of 8-oxo-dGTPase in human cells, with special reference to the role of the enzyme in mitochondria

We examined the intracellular distribution of 8-oxo-dGTPase (8-oxo-7,8-dihydrodeoxyguanosine triphosphatase) encoded by the MTH1 gene, a human mutator homologue. The activity of 8-oxo-dGTPase mainly located in cytosolic and mitochondrial soluble fractions of Jurkat cells, a human T-cell leukemia line. Electron microscopic immunocytochemistry, using a specific antibody against MTH1 protein, showed localization of MTH1 protein in the mitochondrial matrix. Activity in the mitochondria accounted for about 4% of the total activity. The specific activity in the mitochondrial soluble fraction (8093 units/mg protein) was as high as that in the cytosolic fraction (8111 unit/mg protein). The 8-oxo-dGTPase activities in cytosolic and mitochondrial soluble fractions co-eluted with MTH1 protein by anion-exchange chromatography, and the molecular mass of the mitochondrial MTH1 protein was much the same as that of the cytosolic MTH1 protein (about 18 kDa). HeLa cells expressing MTH1 cDNA showed an increased cytoplasmic signal together with a weak signal in the nucleus in in situ immunostaining of MTH1 protein, and the overexpressed MTH1 protein was recovered from both cytosolic and mitochondrial fractions. Thus, the 8-oxo-dGTPase encoded by MTH1 gene is localized in mitochondrial and cytosol.