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Biomedical subjects

N Kamatani

Publications and source records attributed to N Kamatani.

At least 109 records · Page 6Linked to original sources
PubMed1998

Association of HLA class I and class II alleles with myositis in Japanese patients.

OBJECTIVE: To investigate the correlation of HLA class I and class II antigens and alleles with various forms of myositis in Japanese patients. METHODS: Eighty-four Japanese patients with myositis [22 with polymyositis (PM), 46 with dermatomyositis (DM), 16 with myositis overlapping with other collagen vascular diseases] were typed serologically for HLA-A, B, C antigens. HLA-DRB1, DQA1, and DQB1 alleles were determined by polymerase chain reaction dependent DNA typing methods. Fifty-eight Japanese controls were typed serologically while HLA-DRB1, DQA1, and DQB1 allele typing was carried out in 175, 95, and 104 controls, respectively. RESULTS: HLA-B7 was higher in patients than controls [20.2 vs 6.9% in controls: p=0.02, odds ratio (OR)=3.4]. The increase of HLA-B7 was largely dependent on the increase in overlap patients (37.5%; p=0.005, OR=8.1). HLA-A24 and B52 were significantly decreased in PM as compared to DM, while CW3 was significantly increased in PM versus DM. DRB1*08 alleles were significantly increased in patients (36.9 vs 20.5% in controls; p=0.004, OR=2.3), especially in PM and DM. DQA1*0501 and DQB1*0301 were significantly decreased in patients [4.8 vs 13.7% in controls; p=0.04, OR=0.32, and 8.3 vs 20.2% in controls; p=0.02, OR=0.36, respectively]. CONCLUSION: HLA-class I and class II alleles associated with Japanese patients with myositis may be different from those associated with Caucasian patients.

Alleles↗
PubMed1997

Identification of two mutations in human xanthine dehydrogenase gene responsible for classical type I xanthinuria.

Hereditary xanthinuria is classified into three categories. Classical xanthinuria type I lacks only xanthine dehydrogenase activity, while type II and molybdenum cofactor deficiency also lack one or two additional enzyme activities. In the present study, we examined four individuals with classical xanthinuria to discover the cause of the enzyme deficiency at the molecular level. One subject had a C to T base substitution at nucleotide 682 that should cause a CGA (Arg) to TGA (Ter) nonsense substitution at codon 228. The duodenal mucosa from the subject had no xanthine dehydrogenase protein while the mRNA level was not reduced. The two subjects who were siblings with type I xanthinuria were homozygous concerning this mutation, while another subject was found to contain the same mutation in a heterozygous state. The last subject who was also with type I xanthinuria had a deletion of C at nucleotide 2567 in cDNA that should generate a termination codon from nucleotide 2783. This subject was homozygous for the mutation and the level of mRNA in the duodenal mucosa from the subject was not reduced. Thus, in three subjects with type I xanthinuria, the primary genetic defects were confirmed to be in the xanthine dehydrogenase gene.

Adult↗
PubMed1997

An asymptomatic germline missense base substitution in the hypoxanthine phosphoribosyltransferase (HPRT) gene that reduces the amount of enzyme in humans.

A 40-year-old normouricemic (5.5 mg/dl) male showed 46% hemolysate and 37% lymphoblast hypoxanthine phosphoribosyltransferase (HPRT) activities but was otherwise completely free of symptoms. His genomic DNA and cDNA had a missense base substitution (CAT-to-CGT in codon 60) leading to the amino-acid substitution His-to-Arg. Western blot analysis revealed that the amount of HPRT protein in lymphoblasts from this individual was 25%-50% of normal cells, suggesting that the decrease in the amount of enzyme protein was responsible for the partial deficiency. This provides the first clear evidence that a genomic missense mutation at the HPRT locus leads to a decrease in the amount of the enzyme protein but that otherwise it has no evident adverse effects in the hemizygote (asymptomatic mutation).

Adult↗
PubMed1997

Intervention of somatic mutational events in vivo by a germline defect at the adenine phosphoribosyltransferase locus.

Both germline and somatic mutations are known to affect phenotypes of human cells in vivo. In previous studies, we cloned mutant peripheral blood T cells from germline heterozygous humans for adenine phosphoribosyltransferase (APRT) (EC 2.4.2.7) deficiency and found that approximately 1.3 x 10-4 peripheral T cells had undergone in vivo somatic mutations. Loss of heterozygosity (LOH) was the major cause of the mutations at the APRT locus since approximately 80% of the mutant T cell clones exhibited loss of normal alleles. In the present study, we identified three heterozygous individuals for APRT deficiency (representing two separate families), in whom none of the somatic mutant cells exhibited LOH at the APRT locus. The germline mutant APRT alleles of these heterozygotes from two unrelated families had the same gross DNA abnormalities detectable by Southern blotting. None of the germline mutant APRT alleles so far reported had such gross DNA abnormalities. The data suggest that the germline mutation unique to these heterozygous individuals is associated with the abrogation of LOH in somatic cells. The absence of LOH at a different locus has already been reported in vitro in an established cell line but the present study describes the first such event in vivo in human individuals.

Adenine Phosphoribosyltransferase↗
PubMed1997

Generation and molecular characterisation of monoclonal IgG4 rheumatoid factor from a patient with rheumatoid arthritis.

OBJECTIVE: To characterise IgG4 rheumatoid factor (RF) at the molecular level from a patient with rheumatoid arthritis. METHODS: B cells were cloned from the peripheral blood of a patient with rheumatoid arthritis, using EB virus transformation. The supernatants of the clones were screened for IgG RF activity by ELISA. Nucleotide sequences of the expressed immunoglobulin heavy and light chain genes of one IgG RF producing clone were determined by direct sequencing of the products of a polymerase chain reaction. RESULTS: One clone producing monospecific IgG4 RF was obtained. Sequence analysis of the heavy and light chain genes suggested the accumulation of somatic mutations resulting in amino acid replacement in complementarity determining regions. CONCLUSIONS: The results may suggest an antigen driven response in the generation of IgG4 RF in rheumatoid arthritis disease processes.

Amino Acid Sequence↗
PubMed1996

Similarity of in vivo somatic mutations at an autosomal adenine phosphoribosyltransferase locus between T- and B-cells in human peripheral blood.

In vivo somatic mutations have been detected at several human loci by using clonal cultures of peripheral blood T-cells. It has not been fully understood whether or not the somatic mutations in T-cells are similar to those of other cell types. To address this issue, we cloned, from human peripheral blood, T- and B-cells with mutations at an autosomal adenine phosphoribosyltransferase (APRT) locus. For the efficient detection of somatic mutations at the APRT locus, a blood sample from a human individual heterozygous for germline APRT deficiency was used. T- and B-cells deficient in APRT enzyme activity were cloned from peripheral blood mononuclear cells using a selecting agent, 2,6-diaminopurine. The APRT-deficient mutant frequencies were on the order of 10(-4) in both T- and B-cells. The single-strand conformation polymorphism analysis of the APRT DNA of mutant B-cell clones suggested that the molecular mechanisms leading to the APRT deficiency in B-cells were similar to those in T-cells. Our observations suggest that both the frequency and the mode of in vivo somatic mutations occurring spontaneously at general autosomal loci in B-cells are similar to those in T-cells.

Adenine Phosphoribosyltransferase↗
PubMed1996

Differential binding avidities of human IgM for staphylococcal protein A derive from specific germ-line VH3 gene usage.

Human IgM that express the variable region genes of the VH3 family bind staphylococcal protein A (SPA). We previously reported that the SPA-binding IgM can be divided into two groups based on the differential binding avidities for solid-phase SPA. To study the molecular basis for these differences, we cloned B cells from human blood by EBV transformation. The nucleotide sequences of the expressed Ig heavy chain genes were determined on 20 B cell clones that produce SPA-binding IgM. The germ-line VH3 gene usage in IgM with high avidities for SPA were distinct from the germ-line VH3 genes used in IgM with low avidities for SPA. There was no correlation in the usage of D or JH genes or in the usage of light chains in IgM according to the SPA binding avidity. These results suggest that the differential binding avidities for SPA are at least partly due to specific germ-line VH3 gene usage. An investigation of direct binding of SPA to the synthetic peptides corresponding to the portions of the variable regions of SPA-binding and non-SPA-binding IgM showed that the peptides corresponding to the VH3 family specific framework region 3 sequences had significant SPA binding capacities, while the peptides corresponding to the other subdomains and those corresponding to framework region 3 of the reported VH3 sequences from non-SPA-binding IgM showed little or no binding. It is of interest that the Ig-framework region 3 subdomain corresponds to the fourth hypervariable region, which in the TCR-beta chain has been implicated as a critical site for T cell superantigen binding.

Adult↗
PubMed1996

The origin of the most common mutation of adenine phosphoribosyltransferase among Japanese goes back to a prehistoric era.

The incidence of adenine phosphoribosyltransferase (APRT) deficiency is higher among Japanese nationals than among other ethnic groups, and the most common mutation (APRT*J, ATG to ACG mutation at codon 136) accounts for 68% of the disease-causing genes among Japanese. To investigate the origin of these mutations, we studied the geographical distribution of the mutant genes in Japan. The APRT*J mutation is distributed nearly uniformly in the four main islands of Japan and Okinawa, suggesting a very early origin. The products of PCR amplification between positions 2344 and 2750 of the genomic APRT sequence were examined by SSCP analysis in random blood samples from Japanese, Korean, and Taiwanese nationals. Among 955 random Japanese blood samples, 7 (0.73%) were heterozygous for the APRT*J mutation, giving a calculated heterozygote frequency of 1.1% among Japanese for the entire APRT deficiency. None of 231 Taiwanese samples contained heterozygotes for the APRT*J mutation, while 2 (0.53%) of 356 Korean samples were heterozygous. In addition to the APRT*J sequence, a total of five variant sequences was found. Sequencing one variant revealed a base substitution in intron 4, suggesting therefore that they are harmless mutations. Since the APRT*J mutation is present in Koreans and Okinawans who share ancestors only before the Yayoi era (third century BC to third century AD), the origin of the APRT*J mutation predates 300 BC.

Adenine Phosphoribosyltransferase↗
PubMed1996

Divergent effects of methotrexate on the clonal growth of T and B lymphocytes and synovial adherent cells from patients with rheumatoid arthritis.

OBJECTIVE: To define the mechanisms whereby methotrexate (MTX) manifests its effects in patients with rheumatoid arthritis. METHODS: T and B cells from peripheral blood and rheumatoid synovial tissues, synovial adherent cells, and the human fibrosarcoma cell line HT1080 and its mutant (defective in an enzyme in the nucleotide salvage pathway) were tested for clonal growth when cultured with MTX. Normal human fibroblasts and those with a deficiency in a salvage pathway were cultured with MTX in the presence or absence of purine and pyrimidine bases. RESULTS: Clonal growth of T and B cells, but not synovial cells, was inhibited by clinically relevant concentrations of MTX. Slowly proliferating fibroblast lines were resistant to MTX, whereas their rapidly proliferating counterparts were not. However, mutant fibroblast lines deficient in a salvage pathway were sensitive to MTX despite slow proliferation. Similarly, while skin fibroblasts were resistant to MTX, germline mutant fibroblasts deficient in a salvage pathway were sensitive to small concentrations of MTX. CONCLUSION: T and B lymphocytes, but not synovial cells, may be the target of MTX in vivo. Resistance to MTX may be associated with slow proliferation and the ability to synthesise nucleotides via salvage pathways. MTX can inhibit proliferation of even slowly growing cells by restricting the supply of nucleotides obtained via a salvage pathway, by removal of purine and pyrimidine bases, or by inducing a deficiency in a salvage pathway. It may be possible to manipulate the therapeutic effect of MTX by adjusting the amounts of purines and pyrimidines available to the cells in vivo.

Antirheumatic Agents↗
PubMed1996

[Adenine phosphoribosyltransferase (APRT)].

Adenine phosphoribosyltransferase (APRT) is a purine metabolic enzyme that salvages adenine moiety generated via the polyamine synthetic pathway. Adenine is produced by the cleavage of methylthiodenosine (MTA), a by-product of the polyamine synthesis. None of the normal somatic cells but about 23% of human malignant cells lack the enzyme MTA phosphorylase because of the homozygous deletion of 9p21 and are deficient in the salvage route of the adenine molecule. APRT gene is located at 16q24, is about 2200 bp long and is composed of 5 exons. The cDNA codes for 180 amino acids which include a PRPP binding domain. The Met at the N-terminal is removed and the Ala is next acetylated. The protein is cleaved into two peptides at amino acid 136 (Met) by BrCN treatment and the N-terminal peptide includes the PRPP binding domain. Although most of the somatic cells express APRT gene, some cells do not, even in normal subjects. This is because of somatic mutations. APRT locus is one of a few genetic loci where human somatic mutations can be observed. We can observe loss of heterozygosity (LOH) and point mutational events at the somatic cell level at this locus. The mode of the somatic mutations is quite similar to that observed in neoplastic cells at the tumor-suppressor loci.

Adenine↗