RESUMO
AIM: To clarify possible contributions of DNA mismatch repair (MMR) system in carcinogenesis of liver fluke infection-associated intrahepatic cholangiocarcinoma (ICC) by using immunohistochemical assay. METHODS: A total of 29 ICC samples, which had been assessed for genomic instability by a PCR-based method, were used for study. They were examined immunohistochemically to demonstrate protein expression of two MMR genes, hMSH2 and hMLH1. Results obtained were compared with their mutator phenotype assessed previously. RESULTS: Either hMSH2 or hMLH1 protein was obviously expressed in 28 of 29 (96.6%) ICC samples. Positive nuclear localization of hMSH2 or hMLH1 protein was observed in 86.2% (25/29) or 93.1% (27/29) ICC cases, respectively, while their negative nuclear reactivity was only detected in 13.8% (4/29) or 6.9% (2/29) ICC cases analyzed, respectively. CONCLUSION: Our study, probably for the first time, showed through immunohistochemical detection of hMSH2 and hMLH1 gene that DNA MMR system does not play a prominent role in liver fluke infection-associated cholangiocarcinogenesis. These results confirm previous findings on mutational status of these genes assessed through a PCR-based method. The immunohistochemical analysis has proven to be an effective and sensitive approach for screening MMR deficiency regardless of somatic inactivation or promoter hypermethylation of hMSH2 and/or hMLH1 gene. Furthermore, immunohistochemistry is more advantageous compared to mutator phenotyping assay in terms of simplicity, less time consuming and cost effectiveness for screening possible involvements of target MMR genes in tumorigenesis.
Assuntos
Neoplasias dos Ductos Biliares/etiologia , Neoplasias dos Ductos Biliares/genética , Ductos Biliares Intra-Hepáticos/química , Proteínas de Transporte/genética , Colangiocarcinoma/etiologia , Colangiocarcinoma/genética , Fasciolíase/complicações , Proteína 2 Homóloga a MutS/genética , Proteínas Nucleares/genética , Proteínas Adaptadoras de Transdução de Sinal , Adulto , Idoso , Ductos Biliares Intra-Hepáticos/parasitologia , Ductos Biliares Intra-Hepáticos/patologia , Proteínas de Transporte/fisiologia , DNA de Neoplasias/genética , Feminino , Regulação Neoplásica da Expressão Gênica , Genes Neoplásicos/genética , Predisposição Genética para Doença , Humanos , Imuno-Histoquímica , Masculino , Programas de Rastreamento , Pessoa de Meia-Idade , Proteína 1 Homóloga a MutL , Proteína 2 Homóloga a MutS/fisiologia , Mutação/genética , Proteínas Nucleares/fisiologia , FenótipoRESUMO
The liver fluke infection-associated intrahepatic cholangiocarcinoma (ICC) is a major liver cancer in Northeast Thailand. The molecular basis of this ICC is poorly understood. To address possible roles of the DNA mismatch repair (MMR) system in ICC carcinogenesis, a fluorescence-labeling PCR/laser scanning technique with high sensitivity was employed to analyze genomic instability in the nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) in 24 fresh and 13 formalin-fixed, paraffin-embedded tissues of ICC and their corresponding normal parts. Microsatellite instability (MSI) was assessed in nDNA, using 12 highly polymorphic loci including 5 Bethesda markers. These loci were mainly related to major MMR genes, hMSH2 and hMLH1. Also 3 (C)n and/or (C)n(A)n repeat instability at 1 noncoding region in the displacement-loop (D-loop) and 2 coding sequences in NADH dehydrogenase subunit 1 and subunit 5 gene in mtDNA were analyzed. MSI was only detected in 1 (2.7%), 6 (16.7%), 1 (2.9%), 1 (2.9%) or 2 (6.3%) out of 37, 36, 35, 35 or 32 cases at BAT-25, D2S123, D3S1611, D11S904 or D17S250, respectively. LOH was found at D3S1298, D3S1561, D5S346 and TP53 in 4 (18.2%) out of 22, 2 (18.2%) out of 11, 6 (33.3%) out of 18 and 3 (12.5%) out of 24 informative cases, respectively. In mtDNA, none except a single case out of the 37 (2.7%) exhibited repeat sequence instability in the D-loop. We conclude that the liver fluke infection-associated ICC in Thailand is classified as low frequency MSI or microsatellite stable type and that DNA MMR system, through hMSH2 and hMLH1 gene mutations, does not play a major role in its carcinogenesis.