[Primary carcinosarcoma of TE lung--a report of two cases]

Carcinosarcoma is a rare lung tumor and accounts for less than 0.3% of primary lung malignancies. Since the first description by Kika in 1908, only 36 cases with this kind of tumor have been appeared in the Japanese literatures by 1993. This report presents our surgical experiences of two cases with carcinosarcoma of the lung confirmed by pathological examination. Case 1: 64-year-old male underwent left lower lobectomy with lymph node resection. The patient has been well 27 months after the operation without tumor recurrence. Case 2: was a 75-year-old male, who underwent left upper lobectomy, partial resection of left lower lobe (S6) with lymph node resection. This patient died of aspiration pneumonia 90 days after successful resection of the tumor. In both patients, resected lung tumors were diagnosed to be true carcinosarcoma by histopathological examinations. True carcinosarcoma is defined to contain both cancelous and sarcomatous elements. Sarcomatous elements may differentiate into rhabdomyosarcoma, osteosarcoma and so on, or they may have non-epithelial elements demonstrated by electron microscopy or immunohistochemical studies. We reviewed the 36 cases with carcinosarcoma of the lung reported in Japanese literatures with special consideration of their histopathological findings. The prognosis of the patients with this rare tumor is also discussed according to the TMN stages.

Phage specific for Vibrio cholerae O139 Bengal

From the stool of a Vibrio cholerae O139 Bengal-infected patient, a phage that specifically lysed capsulated V. cholerae O139 strains only was isolated. The phage is useful for the confirmatory diagnosis of V. cholerae O139 infection and for the differentiation of variants that lack the capsule.

Activation of chemically diverse procarcinogens by human cytochrome P-450 1B1

A human cytochrome P-450 (P450) 1B1 cDNA was expressed in Saccharomyces cerevisiae and the microsomes containing P450 1B1 were used to examine the selectivity of this enzyme in the activation of a variety of environmental carcinogens and mutagens in Salmonella typhimurium TA1535/pSK1002 or NM2009 tester strains, using the SOS response as an end point of DNA damage. We also determined and compared these activities of P450 1B1 with those catalyzed by recombinant human P450s 1A1 and 1A2, which were purified from membranes of Escherichia coli. The carcinogenic chemicals tested included 27 polycyclic aromatic hydrocarbons and their dihydrodiol derivatives, 17 heterocyclic and aryl amines and aminoazo dyes, three mycotoxins, two nitroaromatic hydrocarbons, N-nitrosodimethylamine, vinyl carbamate, and acrylonitrile. Among the three P450 enzymes examined here, P450 lB1 was found to have the highest catalytic activities for the activation of 11,12-dihydroxy-11,12-dihydrodibenzo[a,l]pyrene, 1,2-dihydroxy-1,2-dihydro-5-methylchrysene, (+)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, 11,12-dihydroxy-11,12-dihydrobenzo[g]chrysene, 3,4-dihydroxy-3,4-dihydrobenzo[c]phenanthrene, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole, 2-aminoanthracene, 3-methoxy-4-aminoazobenzene, and 2-nitropyrene. P450 1B1 also catalyzed the activation of 2-amino-3,5-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3-methylimidazo[4,5-f]quinoline, 2-aminofluorene, 6-aminochrysene and its 1,2-dihydrodiol, (-)-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene, 1,2-dihydroxy-1,2-dihydrochrysene, 1,2-dihydroxy-1,2-dihydro-5,6-dimethylchrysene, 2,3-dihydroxy-2,3-dihydrofluoranthene, 3,4-dihydroxy-3,4-dihydro-7,12-dimethylbenz[a]anthracene, and 6-nitrochrysene to appreciable extents. However, P450 1B1 did not produce genotoxic products from benzo[a]pyrene, trans- 3,4-dihydroxy-3,4-dihydrobenzo[a]anthracene, trans-8,9-dihydroxy-8,9-dihydrobenzo[a]anthracene, 7,12-dimethylbenz[a]anthracene and its cis-5,6-dihydrodiol, 5-methylchrysene, 11,12-dihydroxy-11,12-dihydro-3-methylcholanthrene, 1,2-dihydroxy-1,2-dihydro-6-methylchrysene, benzo[c]phenanthrene, 2-amino-6-methyldipyridol[1,2-a:3',2'-d]imidazole, 2-acetylaminofluorene, benzidine, 2-naphthylamine, aflatoxin B1, aflatoxin G1, sterigmatocystin, N-nitrosodimethylamine, vinyl carbamate, or acrylonitrile in this assay system. P450 1B1 is expressed constitutively in extrahepatic organs, including fetal tissue samples, and is highly inducible in various organs by 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in experimental animal models. Thus, activation of procarcinogens by P450 lB1 may contribute to human tumors of extrahepatic origin.

Stability of p53 tumor suppressor gene mutations during the process of metastasis and during chemotherapy

We analyzed 29 pairs of primary and metastatic lung carcinomas obtained at autopsy for mutations in the p53 gene, using the polymerase chain reaction-single strand conformation polymorphism method (PCR-SSCP). We examined the relationship between p53 gene mutations and the development of metastasis, and the stability of p53 gene mutations during chemotherapy. The tumors consisted of six small cell carcinomas, 13 adenocarcinomas, eight squamous cell carcinomas, one large cell carcinoma, and one adeno-squamous cell carcinoma. PCR-SSCP analysis showed that three small cell carcinomas (50%), three adenocarcinomas (23%), two squamous cell carcinomas (25%), and one large cell carcinoma (100%) had p53 gene mutations. All these abnormalities were found between exon five and exon eight. The mutations in the primary tumors and the metastatic tumors were identical. These results suggest that p53 gene mutations occur before distant metastases develop, and that they may be stable during the process of metastasis. There were nine metastatic tumor samples that existed before the patients received chemotherapy. These samples showed identical p53 mutations as the corresponding primary tumor. This suggests that anticancer drugs rarely induce p53 gene mutations.

Construction of a human cytochrome P450 1A1: rat NADPH-cytochrome P450 reductase fusion protein cDNA and expression in Escherichia coli, purification, and catalytic properties of the enzyme in bacterial cells and after purification

A plasmid (pCW) was modified to code for a fusion protein consisting of the complete sequence of human cytochrome P450 (P450) 1A1 (with only the second amino acid changed) in the N-terminal portion connected by a Ser-Thr linker to the portion of rat NADPH-P450 reductase beginning at amino acid 57. This plasmid was used to express the fusion protein in Escherichia coli DH5alpha cells and the protein was purified from detergent-solubilized bacterial membranes using DEAE and 2',5'-ADP agarose chromatography. The purified fusion protein catalyzed benzo[a]pyrene 3-hydroxylation, 7-ethoxyresorufin O-deethylation, and zoxazolamine 6-hydroxylation. Catalytic activity was not increased in the presence of added NADPH-P450 reductase, cytochrome b5, or phospholipid. The fusion protein could also transfer electrons to cytochromes c and b5 but not P450 lA2. The same oxidation products of benzo[a]pyrene were formed with the purified fusion protein and the fusion protein functioning in bacterial cells. The catalytic activity of the human P450 1A1 fusion protein toward several substrates is markedly less than that of a similar fusion protein constructed with rat P450 1A1, in line with the reported differences in catalytic activities of the rat and human P450 1A1 enzymes. The purified fusion protein also oxidized (+)- and (-)-benzo[a]pyrene 7,8-dihydrodiols and eight aryl and heterocyclic amines to genotoxic products, in the absence of added NADPH-P450 reductase. The demonstration of catalytic activities of the human fusion protein within bacterial cells suggests the prospect of utilizing such cellular systems for production of human P450 metabolites.

Increased serotonin release across the coronary bed during a nonischemic interval in patients with vasospastic angina

BACKGROUND

Platelet activation and coagulation abnormality have been observed during coronary spasm. It is crucial whether platelet activation occurs even during a nonischemic period.

HYPOTHESIS

This study was designed to determine whether platelets might be activated across the coronary bed during a nonischemic interval in patients with vasospastic angina.

METHODS

Plasma levels of serotonin, 6-keto-prostaglandin F1 alpha, and catecholamines in the aorta and the coronary sinus were simultaneously measured in 16 patients with vasospastic angina and 13 control patients with nonischemic heart disease.

RESULTS

None of these patients showed myocardial ischemia during sampling. The difference in transcardiac plasma levels of serotonin in patients with vasospastic angina was significantly higher than that in controls (1.48 +/- 1.08 ng/ml vs. 0.07 +/- 0.12 ng/ml, respectively, p < 0.001). Coronary sinus plasma norepinephrine levels in these two groups were almost the same (204.8 +/- 110.8 pg/ml vs. 190.4 +/- 131.6 pg/ml, respectively). The ratio of 6-keto-prostaglandin F1 alpha in the coronary sinus and the aorta was not different between the two groups (1.17 +/- 0.96 in patients with vasospastic angina vs. 1.15 +/- 0.68 in controls).

CONCLUSIONS

These data suggest that platelet activation across the coronary bed should be ascribed to endothelial dysfunction. Lack of compensatory enhancement of prostacyclin production might be concerned with dysfunction of coronary endothelial cells in these patients.

First-trimester prenatal molecular diagnosis of infantile hypophosphatasia in a Japanese family

We obtained a prenatal molecular diagnosis during the first trimester in a Japanese woman whose first child (the proband) had been a compound heterozygote for infantile hypophosphatasia. We examined chorionic villus DNA samples obtained at 10 weeks of gestation for the base substitutions detected in the proband DNA using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) and PCR-allele-specific oligonucleotide (ASO) analysis. The genotype of the fetus was the same as that of the proband. The same mobility shift patterns of single strand conformation polymorphism (SSCP) bands were observed in the fetus and the proband. This molecular approach to prenatal diagnosis appears to be more accurate than the enzymatic method and also more accurate and more rapid than the conventional RFLP method.

Involvement of cytochrome P450, glutathione S-transferase, and epoxide hydrolase in the metabolism of aflatoxin B1 and relevance to risk of human liver cancer

In recent years there has been considerable interest in the effect of variations in activities of xenobiotic-metabolizing enzymes on cancer incidence. This interest has accelerated with the development of methods for analyzing genetic polymorphisms. However, progress in epidemiology has been slow and the contributions of polymorphisms to risks from individual chemicals and mixtures are often controversial. A series of studies is presented to show the complexities encountered with a single chemical, aflatoxin B1 (AFB1). AFB1 is oxidized by human cytochrome P450 enzymes to several products. Only one of these, the 8,9-exo-epoxide, appears to be mutagenic and the others are detoxication products. P450 3A4, which can both activate and detoxicate AFB1, is found in the liver and the small intestine. In the small intestine, the first contact after oral exposure, epoxidation would not lead to liver cancer. The (nonenzymatic) half-life of the epoxide has been determined to be approximately 1 sec at 23 degrees C and neutral pH. Although the half-life is short, AFB1-8,9-exo-epoxide does react with DNA and glutathione S-transferase. Levels of these conjugates have been measured and combined with the rate of hydrolysis in a kinetic model to predict constants for binding of the epoxide with DNA and glutathione S-transferase. A role for epoxide hydrolase in alteration of AFB1 hepatocarcinogenesis has been proposed, although experimental evidence is lacking. Some inhibition of microsome-generated genotoxicity was observed with rat epoxide hydrolase; further information on the extent of contribution of this enzyme to AFB1 metabolism is not yet available.

[Pulmonary sarcoidosis presenting with many cotton-like unilateral shadows]

A 22-year-old woman came to our hospital for a thorough examination of nodular lesions fund in the right lung field on a chest roentgenogram. A CT scan revealed typical cotton-like infiltrates: fluffy margins and granular interiors. Pulmonary sarcoidosis was diagnosed from examination of biopsy specimens from the lesions. The lesions disappeared in 6 months without therapy. Pulmonary sarcoidosis presenting only with many cotton-like unilateral shadows is rare. A cotton-like infiltrate seen on a CT scan is a valuable finding for the diagnosis of pulmonary sarcoidosis.

Characterization of microsomal cytochrome P450 enzymes involved in the oxidation of xenobiotic chemicals in human fetal liver and adult lungs

Levels and catalytic activities of cytochrome P450 (P450) enzymes involved in the oxidation of drugs and carcinogens were determined in human adult lungs and fetal livers and compared with those in microsomes from adult livers. P450s immunoreactive with anti-human P4501A1 and anti-human P4503A antibodies were detected in fetal liver microsomes by immunoblotting analysis, and P450s related P4501A1, 2A6, 2C9, 2E1, and 3A4 were determined in adult lung microsomes; all of these P450 enzymes were detected in much higher amounts in adult liver microsomes except that P4501A2 was only the 1A subfamily of P450 found in adult livers. Drug oxidation activities with the substrates ethoxyresorufin, coumarin, 7-ethoxycoumarin, bufuralol, and testosterone were determined in these microsomes, and we found that none of the activities were higher in microsomes of adult lungs and fetal livers than in adult livers. Activation of procarcinogens to reactive metabolites that induce umu gene expression in Salmonella typhimurium TA1535/pSK1002 or NM2009 was also examined and it was found that activities with (+)- and (-)-enantiomers of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene were higher in fetal liver microsomes than adult lung or liver microsomes. The adult liver and lung activities for these two procarcinogens were similar on the basis of microsomal protein contents despite the fact that p450 contents are higher in liver than lung microsomes. alpha-Naphthoflavone, a known inhibitor of P4501A-related activities, did not affect these procarcinogen activation in fetal liver microsomes. Fetal liver microsomes catalyzed activation of aflatoxin B1 and sterigmatocystin, two procarcinogens known to be activated by P4503A4/7 in humans, although activation of carcinogenic arylamines that are good substrates for P4501A2 was much lower in microsomes of fetal livers and adult lungs than in adult livers. These results suggest that in human fetal livers at least two P450 enzymes, a form of P450 that is immunoreactive P4501A1 and P4503A7, are actually expressed and these enzymes are suggested as being involved in the activation of the (+)- and (-)-enantiomers of 7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene and the carcinogenic mycotoxins, respectively. The exact nature of the former enzyme in fetal livers is unknown. In adult human lungs, several P450 enzymes are expressed, although the precise roles of these enzymes in the oxidation of xenobiotics were not determined due to the low level of expression of these P450s.

Ethnic-related differences in coumarin 7-hydroxylation activities catalyzed by cytochrome P4502A6 in liver microsomes of Japanese and Caucasian populations

1. Interethnic differences in cytochrome P4502A6 (CYP2A6) levels and coumarin 7-hydroxylation activities were determined in liver microsomes of 30 Japanese and 30 Caucasians. 2. Although CYP2A6 levels and coumarin 7-hydroxylation activities varied very significantly in the 60 human samples examined, both CYP2A6 levels and coumarin 7hydroxylation activities were found to be higher in Caucasian than Japanese population. 3. Interestingly, eight of the 30 Japanese examined showed very low or undetectable levels of coumarin 7-hydroxylation activities as well as of CYP2A6 in liver microsomes. All of the Caucasians, however, had significant CYP2A6 levels and variable 7-hydroxylation activities. 4. Kinetic analvsis of coumarin 7-hydroxylation activities in liver microsomes of various human samples suggested that although there were 260-fold differences in Vmax's in 10 human samples examined, the Km's were very similar (2.1 + or - 107 mu M); a value consistent with that obtained (1.2 mu M) with purified CYP2A6 in reconstituted system. 5. The results suggest that CYP2A6 is actually involved in the 7-hydroxylation of coumarin in human liver microsomes, and that interethnic differences in coumarin 7-hydroxylation activities in Japanese and Caucasian population may be ascribed to the differences in expression of CYP2A6 protein.

Effects of depletion of T cell subpopulations on the course of infection and anti-parasite delayed type hypersensitivity response in mice infected with Babesia microti and Babesia rodhaini

To elucidate the role of T cell subpopulations in the protective cell-mediated immune response at the initial phase of infection with Babesia microti (BM) and B. rodhaini (BR), the changes in the course of infection and anti-parasite delayed type hypersensitivity (DTH) response after BM or BR inoculation were investigated in Lyt-2+ T cell or L3T4+ T cell-depleted mice. Depletion of Lyt-2+ T cells strongly enhanced the resistance to BM infection, whereas it increased the susceptibility to BR infection. In contrast, depletion of L3T4+ T cells increased susceptibility to BM infection, while it enhanced resistance to BR infection. The anti-parasite DTH response in BM-infected mice was significantly enhanced by depletion of Lyt-2+ T cells, while significantly reduced by depletion of L3T4+ T cells. No effects of depletion of either Lyt-2+ or L3T4+ cells on DTH response was observed in BR-infected mice. From these results, it was suggested that the roles of Lyt-2+ and L3T4+ T cells in the protective cell-mediated immune response at the initial phase of infection were different between BM- and BR-infected mice, resulting in the difference in their course of infection.

Current status and future prospects of human gene therapy

Gene therapy is defined as the treatment of diseases by the transfer of genes into patients. Clinical trials of gene therapy became feasible as a result of the development of retroviral mediated gene transfer techniques. The first trial was begun in September 1990 at the National Institutes of Health when a four year old girl was treated for adenosine deaminase deficiency. Currently, more than 500 patients are being treated by this innovative therapeutic strategy. In the present review article, the basic concepts and present status of human gene therapy are summarized.

Characterization of Aeromonas hydrophila: a comparative study of strains isolated from diarrheal feces and the environment

Thirty-five strains of Aeromonas hydrophila isolated from feces of diarrheal patients and from the environments were collected from Thailand and Japan. The physiological, biochemical, and serological characteristics, antibiotic resistance patterns and cell surface-related properties were compared. The diarrheal and environmental isolates of A hydrophila were found to be remarkably consistent in general culture and biochemical characteristics, with the exception of the reaction to D-arabinose in which the diarrheal strains were positive and environmental strains were negative. The plasmid patterns and cell surface-related properties of the environmental and diarrheal isolates were different. All strains produced Vero cell cytotoxin, hemolysin and lecithinase at 37 degrees, 30 degrees and 15 degrees C. In contrast, 83% of the environmental strains produced these virulence factors even at 4 degrees C. All strains indicated almost uniform susceptibility to the 16 antibiotics tested. Variations were found in the plasmid profile, toxin production in relation to the differences of temperature and cell surface-related properties of the strains. These variations between the clinical and environmental isolates could have potential as epidemiological markers for the sources of strains.

Complete sequence analysis of rat transferrin and expression of transferrin but not lactoferrin in the digestive glands

Rat milk and digestive juices contain transferrin but not lactoferrin, which is a major iron-binding protein in these secretions of human and mouse. To compare the structure of rat transferrin to that of transferrins and lactoferrins in other species, we isolated a cDNA clone containing the entire coding region of transferrin from rat liver and determined its sequence. The amino-acid sequence of rat transferrin had 69.8% identity with that of human transferrin and 48.8% identity with that of human lactoferrin. Rat transferrin, like other transferrins, had the potential N-linked glycosylation site only in the C-terminal domain, although lactoferrins characterized so far contained the glycosylation sites in both the N- and C-terminal domains. Southern and Northern analyses showed that there was the gene specifically hybridized with the mouse lactoferrin cDNA in rat genomic DNA, but only the transferrin mRNA was detected in mammary gland, submaxillary gland and pancreas of rat. These results suggest that the rat lactoferrin gene is silent in the mammary gland, and transferrin can serve as a functional substitute for lactoferrin in rat.

A new strategy for large-scale preparation of high-titer recombinant adeno-associated virus vectors by using packaging cell lines and sulfonated cellulose column chromatography

The extensive testing of adeno-associated virus (AAV) as a vector for human gene therapy has been hampered by low efficiency of the current packaging system, which is based on transient transfection with plasmid DNAs and infection with adenovirus in permissive cells. In an effort to resolve this problem, HeLa cell-based packaging cell lines were established. These packaging cells carry multiple copies of the AAV genome lacking the inverted terminal repeat (ITR) sequences. The AAV genes were silent in these cells but inducibly expressed by adenovirus infection. When the AAV vector plasmid containing the neoR gene flanked by the ITRs was also integrated into these cells, efficient production of the recombinant AAV particles occurred after adenovirus infection. AAV vector particles in cell lysates could be concentrated by sulfonated cellulose column chromatography. Using the packaging cells and the column chromatography technique, it is possible to prepare AAV vectors with the titer of higher than 10(8) cfu/ml or 5 x 10(10) particles/ml. This new strategy should be useful for testing AAV vectors in vivo.

7-Ethoxycoumarin O-deethylation catalyzed by cytochromes P450 1A2 and 2E1 in human liver microsomes

7-Ethoxycoumarin O-deethylation has been used widely as a marker activity for assessing substrate specificities of cytochromes P450 (P450) in liver microsomes of mammals, and extensive studies have shown that in rats and mice the major catalysts are P450 1A1, 1A2, and 2B enzymes. In contrast to findings in experimental animal models, P450 2E1 has been reported to be a principal enzyme involved in 7-ethoxy-coumarin O-deethylation in human livers. In this study, we further examined the roles of individual forms of human P450 involved in 7-ethoxycoumarin O-deethylation using microsomes from different human liver samples and from human lymphoblastoid cells expressing human P450 enzymes and purified P450 enzymes isolated from the membrane of Escherichia coli expressing modified P450 proteins. Kinetic analysis showed that there were at least two different enzymes involved in 7-ethoxycoumarin O-deethylation in different human samples. Samples that contained high amounts of P450 2E1 in liver microsomes showed biphasic curves for O-deethylation with relatively high turnover numbers, whereas P450 1A2-rich samples tended to have low Km values with low Vmax values. Anti-human P450 2E1 antibodies inhibited markedly (P < 0.05) the 7-ethoxycoumarin O-deethylation activities catalyzed by human liver microsomes particularly when examined at a high substrate concentration (200 microM). However, we also found that anti-P450 1A2 antibodies suppressed O-deethylation activities only at a low substrate concentration (10 microM). Recombinant human P450 1A2 was found to have a low Km value for 7-ethoxycoumarin O-deethylation, whereas P450 2E1 showed a high Km value. Of the P450 enzymes examined, P450 1A1 gave the highest O-deethylation activities with a low Km value, although this enzyme is reported to be expressed extrahepatically in humans. Other human P450 enzymes, including P450 2A6, 2C10, 2D6, 3A4, and 3A5, did not show significant O-deethylation activities except that P450 2B6, a minor P450 component in human livers, was found to have a Vmax value similar to that of P450 1A2 and a Km value similar to that of P450 2E1. These results suggest that P450 1A2 is a low Km enzyme for 7-ethoxycoumarin O-deethylation in human liver microsome, although it has a low Vmax value than P450 2E1.

Vertebral osteomyelitis presenting with bilateral pleural effusions in a leprous patient

We present a highly rare case of vertebral osteomyelitis due to Salmonella newport that was associated with pleural effusion in a leprous woman. The salmonella infection was considered to be precipitated by her hemolytic anemia resulting from dapsone. The direct spread of infection from the vertebrae led to the pleurisy.

A new Salmonella typhimurium NM5004 strain expressing rat glutathione S-transferase 5-5: use in detection of genotoxicity of dihaloalkanes using an SOS/umu test system

The Escherichia coli mu operon was subcloned into a pKK233-2 vector containing rat glutathione S-transferase (GST) 5-5 cDNA and the plasmid thus obtained was introduced into Salmonella typhimurium TA1535. The newly developed strain S.typhimurium NM5004, was found to have 52-fold greater GST activity than the original umu strain S.typhimurium TA1535/pSK1002. We compared sensitivities of these two tester strains, NM5004 and TA1535/pSK1002, for induction of umuC gene expression with several dihaloalkanes which are activated or inactivated by GST 5-5 activity. The induction of umuC gene expression by these chemicals was monitored by measuring the cellular beta-galactosidase activity produced by umuC"lacZ fusion gene in these two tester strains. Ethylene dibromide, 1-bromo-2-chloroethane, 1,2-dichloroethane, and methylene dichloride induced umuC gene expression more strongly in the NM5004 strain than the original strain. 4-Nitroquinoline 1-oxide and N-methyl-N'-nitro-N-nitrosoguanidine were found to induce umuC gene expression to similar extents in both strains. In the case of 1-nitropyrene and 2-nitrofluorene, however, NM5004 strain showed weaker umuC gene expression responses than the original TA1535/pSK1002 strain. 1,2-Epoxy-3-(4'-nitrophenoxy)propane, a known substrate for GST 5-5, was found to inhibit umuC induction caused by 1-bromo-2-chloroethane. These results indicate that this new tester NM5004 strain expressing a mammalian GST theta class enzyme may be useful for studies of environmental chemicals proposed to be activated or inactivated by GST activity.

Genomic organization and expression of the human MSH3 gene

We have studied the expression and genomic organization of the human MSH3 gene, which encodes a human homologue of the bacterial DNA mismatch repair protein MutS. This gene is located upstream of the dihydrofolate reductase (DHFR) gene. Northern analysis has demonstrated that the hMSH3 gene is expressed in a variety of human tissues at low levels, like the DHFR gene. Characterization of cosmid clones has shown that the hMSH3 gene consists of 24 exons spanning at least 160 kb. All exon-intron junction sequences match the classical GT/AG rule, except that intron 6 has AT and AA at the ends. Two major transcripts of 5.0 and 3.8 kb have been shown to be derived from the differential use of two polyadenylation sites. Elucidation of the complete genomic organization and the nucleotide sequences of the introns of the hMSH3 gene should be useful for studying the function of this gene and the possible involvement of specific mutations of the hMSH3 gene in some diseases.