摘要:

O6-Alkylguanine-DNA alkyltransferase (AGT, EC 2.1.1.63) is a principle DNA repair protein in repairing O6-alkylguanine in DNA, a major premutagenic lesion produced by environmental and therapeutic alkylating agents. AGT plays a critical role in protecting cells against mutation and cytotoxicity induced by these alkylating agents. The existence of a large interindividual variation in human AGT activity level has been observed and we hypothesize that genetic polymorphism of AGT could be an important determinant for this variation. The present study reports the identification of a novel missense polymorphism in the human AGT gene. The polymorphic alteration occurs at codon 143 in exon 5, converting isoleucine (ATC) to valine (GTC). Because Ile143is adjacent to the alkeyl acceptor Cys145of the AGT active site and is conserved among mammalian AGTs, amino acid substitution at this position may affect the function of AGT. The codon 143 polymorphism appears to be linked to another new polymorphic alteration at codon 178, which converts lysine (AAG) to arginine (AGG). Because it has been reported that human AGT can be truncated at position 176 without loss of activity, the codon 178 polymorphism may not affect AGT activity. The codon 143/178 polymorphism was found in two of 90 (2%) esophageal cancer patients residing in a high incidence area of China, but was not detected in 60 normal individuals residing in the same area. Six of 28 (21%) non-cancer Caucasian individuals, however, were found to carry this polymorphic allele, suggesting a significant ethnic difference in distribution of this codon 143/178 polymorphism between Chinese and Caucasian individuals. In addition, we confirmed the existence of a codon 84 genetic polymorphism previously identified in a Japanese population, which converts leucine (CTT) to phenylalanine (TTT). The distribution of codon 84 polymorphism was 16%, 20% and 36%, respectively, in the Chinese esophageal cancer patients, Chinese and Caucasian non-cancer individuals. Coexistence of codons 84 and 143/178 polymorphic alterations was found in one Caucasian individual. In all the Chinese (n= 150) and Caucasian (n= 28) samples examined, we were unable to detect a previously reported codon 160 polymorphism (Gly to Arg) which occurred in 10–25% of the Japanese individuals and was shown to affect the reaction of AGT with the drug O6-benzylguanine. The functional significance of the codon 143/178 genetic polymorphism of human AGT and its role in determining an Individual's susceptibility to environmental alkylating carcinogens and response to alkylating chemotherapeutic drugs both remain to be studied. Pharmacogenetics 9:81–87 © 1999 Lippincott Williams & Wilkins

ISSN:0960-314X    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Approximately 50% of individuals in most human populations completely lack activity of the detoxifying enzyme glutathione S-transferase M1. The medical consequences of this deficiency have been extensively investigated in molecular epidemiological studies, but possible differences of the highly active homozygous genotype versus the moderately active heterozygous genotype could not be considered because many currently used polymerase chain reaction (PCR) assays cannot distinguish the homozygous genotypesGSTM1*A/AandGSTM1*B/Bfrom the heterozygous genotypesGSTM1*A/0andGSTM1*B/0. Here, we describe that long PCR is suitable for this purpose by specifically producing a signal for theGSTM1*0allele. Based on the published cluster ofGSTMgenes (GSTM1to -M5), a 13-kb segment spanning the site of theGSTM1deletion was amplified using aGSTM2-specific forward primer (5‘-CATCGCTTATGATGTCCTTGAGAGAAACCAAG-3’) and a reverse primer, which is specific for the upstream region of GSTM5 (5‘-GCGTTTCTGAGGACTGGACTGATGATCG-3’). Any failure in the amplification was controlled by co-amplification of a 15-kb human tissue plasminogen activator gene fragment. TheGSTM1*0-specific 13-kb amplicon appears in all carriers of one or two null alleles, but in none of the 14 testedGSTM1*A/Bsamples which served as controls since individuals with this genotype are known to lack anyGSTM1*0allele. While conventional PCR assays for detection of the GSTM1 deletion differentiated homozygously deficient from hetero- or homozygously active individuals, this long PCR assay differentiates homozygously active from hetero- or homozygously deficient individuals. Using both assays, an unambiguous differentiation into carriers of zero, one or two active alleles ofGSTM1is possible. Pharmacogenetics 9:89–94 © 1999 Lippincott Williams & Wilkins

ISSN:0960-314X    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

A substitution of phenylalanine by cysteine in position 124 is the only known naturally occurring variant of the human 5-HT1B(h5-HT1B) receptor. The present study was designed to evaluate the potential influence of the Cys-124 variant on pharmacological properties of the receptor and to test for an involvement of the mutation in the genetic predisposition to schizophrenia or bipolar affective disorder. Binding of [3H]5-carboxamidotryptamine ([3H]5-CT) and its competition with serotonin receptor agonists and antagonists were determined in COS-7 cells transfected with the wild-type or the variant h5-HT1Breceptor cDNA. In saturation experiments with [3H]5-CT, the maximum binding (Bmax) of the variant receptor was approximately 30% of the wild-type receptor. In competition experiments with 1 nM [3H]5-CT, the following serotonin receptor ligands exhibited a two to three times higher affinity for the mutant than for the wild-type receptor: dihydroergotamine, L-694, 247, SB-216641, 5-CT, 5-HT, sumatriptan, RU24969 and methysergide (compounds listed at decreasing order of potency at the wild-type receptor). In contrast, the serotonin receptor antagonist ketanserin exhibited higher binding affinity for the wild-type than for the mutant h5-HT1Breceptor and GR127939, (-)propranolol and BRL-15572 showed equal affinity for both types of receptor. Mutation screening of schizophrenic and bipolar patients revealed no relationship between the variant receptor and development of disease. In conclusion, our data suggest that the Cys-124 variant significantly affects the pharmacological properties of the h5-HT1Breceptor. Carriers of the variant may exhibit differences in response to drugs acting on the h5-HT1Breceptor or may develop side-effects to such agents. Pharmacogenetics 9:95–102 © 1999 Lippincott Williams & Wilkins

ISSN:0960-314X    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Genetically polymorphic xenobiotic metabolizing enzymes are supposed to be host factors for an individual's cancer susceptibility. A total of 255 laryngeal cancer patients was genotyped forNAT1andNAT2and compared with 510 reference individuals, matched by age and gender.NAT1genotypes (NAT1*3, *4, *10, and*11) were found equally distributed between cases and control individuals. However, there was a significant overrepresentation of 20 (7.8%) homozygousNAT2genotypes coding for rapid acetylation (NAT2*4/*4andNAT2*4/*12 A) amongst laryngeal cancer patients versus 19 (3.7%) such individuals in the control group (odds ratio 2.18, 95% confidence limits 1.13, 4.22;P= 0.018). Furthermore, an increasingNAT2*4/*4frequency in cases with strong cigarette consumption was observed, but also in non-smokers. Heterozygous genotypes ofNAT2*4/slowwere not overrepresented. These results correspond with earlier findings in lung cancer. Analysis ofNAT1andNAT2combinations revealed a linkage disequilibrium betweenNAT1*10andNAT2*4; NAT1*10frequency was twofold higher inNAT2*4/*4carriers than in slowNAT2coding genotypes. In conclusion, the distinct genotypeNAT2*4/*4proved to be a rare, but powerful host risk factor for larynx carcinoma. These data support the notion that an individual's specificNAT2genotype may be decisive for the organ of his smoking-initiated cancer. Pharmacogenetics 9:103–111 © 1999 Lippincott Williams & Wilkins

ISSN:0960-314X    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

The NAD(P)H:quinone oxidoreductase 1 (NQO1) genotype-phenotype relationship was examined in individuals with a polymorphism in NQO1. The polymorphism comprises a C to T base change at position 609 of the human NQO1 cDNA (C609T) and codes for a proline to serine substitution in the amino acid structure of the NQO1 protein. Genotyping was performed by polymerase chain reaction-restriction fragment length polymorphism analysis of genomic DNA. Phenotyping was performed using enzyme activity assays and/or immunoblotting of human tumor cell lines and of saliva and bone marrow samples from healthy donors. Phenotyping of uninvolved lung and lung tumors from archived biopsy material was performed by immunohistochemistry. NQO1 activity and protein could be detected in wild-type (C/C) human tumor cells (HT-29) under conditions where NQO1 protein could not be detected in cells (BE) homozygous for the C609T change (T/T). Trace levels of NQO1 protein could be detected in BE cells; however, when immunoblots were subjected to chemiluminescence detection for prolonged periods. In saliva samples from 11 individuals carrying the homozygous C609T change (T/T), no NQO1 protein could be detected even after prolonged chemiluminescence detection. The amount of NQO1 protein present in saliva was quantified and found to be significantly less in heterozygous individuals (C/T) than in wild-type individuals (C/C). In bone marrow stromal cultures, both NQO1 activity and protein could be detected in heterozygotes (C/T) and in wild-type (C/C) samples. In a bone marrow stromal culture from an individual genotyped as T/T at position 609, no NQO1 protein or activity could be detected. NQO1 is elevated in non-small cell lung cancers and could be readily observed as intense immunostaining throughout lung adenocarcinomas genotyped as C/C but no immunostaining could be detected in adenocarcinomas genotyped as T/T at position 609. NQO1 is expressed in normal human lung but is localized to respiratory epithelium and to vascular endothelium. In normal lung tissue from individuals genotyped as T/T, no or faint immunostaining for NQO1 could be detected in either respiratory epithelium or vascular endothelium. These results demonstrate that tissues from individuals homozygous for the C609T change have no detectable or, at best, only trace amounts of NQO1 protein and are devoid of NQO1 activity. Pharmacogenetics 9:113–121 © 1999 Lippincott Williams & Wilkins

ISSN:0960-314X    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

In recent times, an increasing number of different haplotypes of the arylamine N-acetyltransferase 2 gene are reported. Since most of the various alleles are defined by linkages of commonly known hereditary point mutations, some confusion may occur when the mutation pattern revealed by genotyping should be addressed correctly to defined haplotypes. Moreover, problems take place when different nomenclatures are incorrectly transferred. To meet growing concerns regarding exact NAT2 genotyping and correct nomenclature, we summarized typical pitfalls in methodologies and terminologies.NAT2genotypes containing rare alleles, or even combinations of them, should always be checked critically for possible laboratory failures. Novel alleles should be best verified by subcloning or other adequate methodologies. For prediction of the acetylator phenotype it seems generally sufficient to genotypeNAT2mutations C282T and T341C. In African populations, however, it is necessary to check additionally for the frequent G191A mutation, which codes also for a slow acetylator variant. Pharmacogenetics 9:123–127 © 1999 Lippincott Williams & Wilkins

ISSN:0960-314X    

出版商:OVID    

年代:1999

数据来源: OVID