Zhong, Shan; (1994) Molecular genetic analysis of human mu class glutathione s-transferases. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Within human glutathione S-transferases (GSTs; EC 2.5.1.18) multigene family the mu class GSTM1 demonstrates polymorphism. The polymorphism of GSTM1 gene was investigated using DNA-based restriction fragment length polymorphism (RFLP) and polymerase chain reaction (PCR) assays in 225 DNA samples. The results showed that 41.8% of Caucasian population were the GSTM1 null genotype, lacking one polymorphic DNA fragment in both assays due to the homozygous deletion of the GSTM1 gene, as well as the GSTM1 null phenotype. Family studies suggest that this polymorphic DNA fragment is inherited in a autosomal dominant Mendelian fashion. Two mu class GST genes have been isolated. Neither gene has been reported previously. The GSTM1b gene was one of two allelic variants of the GSTM1 gene, the other gene was novel, named GSTM4. The GSTM1b gene was found to be about 5,400 bp in length and the GSTM4 gene was 4,842 bp. The structured of both human mu class GST genes were found to contain eight exons spanned by seven introns. The expression of GSTM4 gene in vivo was confirmed by sequencing the product of selective reverse transcription and PCR. The cDNA of GSTM4 had an open reading frame of 654 bp that encoded a polypeptide of 218 amino acids (including the initial methionine) with a Mr of approximately 25,500. The cloned cDNA of GSTM4 was expressed in E. coli and the product was found to be catalytically active towards 1-chloro-2,4-nitrobenzene (CDNB). Using gene-specific PCR with a panel of somatic hybrids DNA, both of the GSTM1b and GSTM4 genes were assigned unambiguously to chromosome 1p. A PCR assay was developed and utilized to detect the frequency of the GSTM1 null genotype in total of 794 patients with lung, breast, bladder or colorectal cancer. The results comparing healthy controls suggested that the deletion of the GSTM1 gene increases susceptibility to squamous carcinoma of the lung and to colorectal cancer.

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