摘要
Objectives A group of human mismatch repair (MMR) genes, hMSH2, GTBP, hMLH1, hPMS1, and hPMS2 has been found to be responsible for the inherited susceptibility to colorectal and related cancers. Among the genes, hMSH2, the human homologue of bacterial MutS, may account for about 45% of the tumors. hMSH2 is located on chromosome 2p 16 and has been cloned and shown to cover about 73 kb of genomic DNA. Its 16 exons encode components of a mismatch repair system. The purpose of the work was to study somatic and germline mutations of hMSH2 in sporadic ovarian cancers, and to examine the microsatellite instability (MIN) in the patients. Methods Genomic DNA was purified from the peripheral lymphocytes and tumor tissues in 15 patients with sporadic ovarian cancers. PCR was used to detect MIN in 3 DNA microsatellite markers. PCR single strand conformation polymorphism (SSCP) labeled with α 32 PdCTP was used to examine hMSH2 gene (exon 7, 8, 12, 14 and 15) mutations. DNA sequence analysis was performed using cycle sequencing kit (Promega Corp., Madison, WI), end labeled primers and the protocols supplied by the manufacturer. Results 3/15 (20%) ovarian cancers exhibited MIN. hMSH2 germline mutations (exon 7, 15) were detected in 2 patients, one of whom showed MIN of D2S123 marker. Two somatic mutations (exon 7, 8) were found in a patient. Of the two sequenced, a 1 bp deletion at nucleotide 2518 created a stop codon in patient 6. Patient 30 exhibited the same sense mutation at codon 444 (CGT CGA). Conclusions Cells have evolved a number of mechanisms to ensure the high fidelity transmission of genetic material from one generation to the next because mutations can lead to genotypes that may be deleterious to the cell. The DNA lesions that lead to mutations are most frequently modified, missing, or mismatched nucleotides, and multiple enzymatic pathways (including MMR system) specifically repair these lesions. MMR system genes play roles in maintaining the genetic stability of DNA. Mutants of MMR genes exhibit increased rates of expansion and contraction of dinucleotide repeat sequences. Our results suggest that the carcinogenesis of ovarian cancer is related to the mutation of MMR genes. Mutations in MMR genes are postulated to cause microsatellite instabilities and other gene mutations that eventually induce cell transformation.
Objectives A group of human mismatch repair (MMR) genes, hMSH2, GTBP, hMLH1, hPMS1, and hPMS2 has been found to be responsible for the inherited susceptibility to colorectal and related cancers. Among the genes, hMSH2, the human homologue of bacterial MutS, may account for about 45% of the tumors. hMSH2 is located on chromosome 2p 16 and has been cloned and shown to cover about 73 kb of genomic DNA. Its 16 exons encode components of a mismatch repair system. The purpose of the work was to study somatic and germline mutations of hMSH2 in sporadic ovarian cancers, and to examine the microsatellite instability (MIN) in the patients. Methods Genomic DNA was purified from the peripheral lymphocytes and tumor tissues in 15 patients with sporadic ovarian cancers. PCR was used to detect MIN in 3 DNA microsatellite markers. PCR single strand conformation polymorphism (SSCP) labeled with α 32 PdCTP was used to examine hMSH2 gene (exon 7, 8, 12, 14 and 15) mutations. DNA sequence analysis was performed using cycle sequencing kit (Promega Corp., Madison, WI), end labeled primers and the protocols supplied by the manufacturer. Results 3/15 (20%) ovarian cancers exhibited MIN. hMSH2 germline mutations (exon 7, 15) were detected in 2 patients, one of whom showed MIN of D2S123 marker. Two somatic mutations (exon 7, 8) were found in a patient. Of the two sequenced, a 1 bp deletion at nucleotide 2518 created a stop codon in patient 6. Patient 30 exhibited the same sense mutation at codon 444 (CGT CGA). Conclusions Cells have evolved a number of mechanisms to ensure the high fidelity transmission of genetic material from one generation to the next because mutations can lead to genotypes that may be deleterious to the cell. The DNA lesions that lead to mutations are most frequently modified, missing, or mismatched nucleotides, and multiple enzymatic pathways (including MMR system) specifically repair these lesions. MMR system genes play roles in maintaining the genetic stability of DNA. Mutants of MMR genes exhibit increased rates of expansion and contraction of dinucleotide repeat sequences. Our results suggest that the carcinogenesis of ovarian cancer is related to the mutation of MMR genes. Mutations in MMR genes are postulated to cause microsatellite instabilities and other gene mutations that eventually induce cell transformation.
