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Activity (transcription) of the genes for MLH1, MSH2 and p53 in sporadic colorectal tumours with micro-satellite instability.

ABSTRACT: Micro-satellite instability (MSI) is relevant in the management of colorectal cancers (CRC) and relies on analysis of gene mutations, or production of the proteins involved in DNA mismatch repair (e.g. MLH1, MSH2). p53 mutation is also relevant in MSI, but high-level CRC (MSI-H) demonstrate fewer mutations than low-level (MSI-L) or stable (MSS) cancers. Recently, the importance of gene activity (transcription) in MSI has been identified, where rather than being mutated genes have been downregulated. In this study, 67 sporadic CRC and eight samples of normal bowel were analysed for MSI status (by SSCP) and levels of MLH1, MSH2 and p53 gene transcription (by RT-PCR and scanning densitometry). Micro-satellite instability correlated with gender and site, with more MSI-H CRC in females (P<0.02) and in the right colon (P<0.04). In MSI-H, p53 transcription was markedly reduced (P<0.003). Compared to normal bowel, MLH1 transcription was elevated in all cancers (P<0.01), while MSH2 transcription was elevated only in MSI-H (P<0.04). There was a direct correlation between MLH1 and MSH2 transcription (P<0.001). Although fewer mutations are reported in MSI-H than MSI-L/MSS, these results suggest that reduced p53 transcription might account for decreased tumour suppression in MSI-H. The direct correlation between MLH1 and MSH2 transcription suggests that control of these genes might be coordinated.

SUBMITTER: Tou SI

PROVIDER: S-EPMC2409469 | biostudies-other | 2004 May

REPOSITORIES: biostudies-other

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Project description:BACKGROUND:The development of colorectal cancer (CRC) is a complicated multistep process that involves an accumulation of mutations in tumor suppressor genes and oncogenes. In the process of DNA replication, base mismatch often occurs due to various factors leading to abnormal expression of mismatch repair genes (MMR), among which MLH1 and MSH2 are the most important. Recently, numerous studies indicated that MLH1/MSH2 phenotype is associated with CRC. We wanted to elucidate the role of MLH1/MSH2 in the prediction and prognosis of CRC through long-term clinical observation. AIM:To evaluate the prognostic and predictive significance of MLH1/MSH2 in patients with stage II-III CRC using immunohistochemical analysis and GeneScan. METHODS:Specimens from 681 patients with CRC (395 stage II and 286 stage III, 387 males and 294 females) who underwent curative surgical resection from 2013 to 2016 were tested. Immunohistochemistry was used to analyze MMR status and the microsatellite status of 133 patients was determined by GeneScan analysis. RESULTS:Five hundred and fifty (80.76%) patients were MLH1/MSH2 positive and 131 (19.24%) were negative by immunohistochemistry. MLH1/MSH2-positive tumors were significantly more frequent in the colon than in the rectum, and had poor differentiation and less mucin production (P < 0.05). Patients of different groups did not differ in terms of age, gender, tumor size, tumor stage, lymphocytic infiltration, or circumscribed margin. MLH1/MSH2-negative patients had a more favorable OS than MLH1/MSH2-positive patients (P < 0.001). Univariate and multivariate analyses demonstrated MLH1/MSH2 expression as an independent prognostic and predictive factor for stage II/III CRC. MLH1/MSH2 expression was a strong prognostic factor in all patients [P < 0.001, hazard ratio (HR) = 4.064, 95%CI: 2.241-7.369]. Adjuvant chemotherapy had a greater correlation with survival advantage in MLH1/MSH2-negative patients with stage III disease (P < 0.001, HR = 7.660, 95%CI: 2.974-15.883). However, patients with stage II disease or MLH1/MSH2-positive patients with stage III disease did not benefit from adjuvant chemotherapy. GeneScan analysis demonstrated that among 133 patients, 105 (78.95%) were microsatellite stable, and 28 (21.05%) had microsatellite instability (MSI), including 18 (13.53%) with high MSI and 10 (7.52%) with low MSI. This is consistent with the immunohistochemical results. CONCLUSION:MLH1/MSH2 phenotype constitutes a pathologically and clinically distinct subtype of sporadic CRC. MLH1/MSH2 is an independent prognostic and predictive factor for outcome of stage II-III CRC.

Project description:Methylation of the MLH1 promoter region has been suggested to be a major mechanism of gene inactivation in sporadic microsatellite instability-positive (MSI-H) colorectal cancers (CRCs). Recently, single-nucleotide polymorphism (SNP) in the MLH1 promoter region (MLH1-93G/A; rs1800734) has been proposed to be associated with MLH1 promoter methylation, loss of MLH1 protein expression and MSI-H tumors. We examined the association of MLH1-93G/A and six other SNPs surrounding MLH1-93G/A with the methylation status in 210 consecutive sporadic CRCs in Japanese patients.Methylation of the MLH1 promoter region was evaluated by Na-bisulfite polymerase chain reaction (PCR)/single-strand conformation polymorphism (SSCP) analysis. The genotype frequencies of SNPs located in the 54-kb region surrounding the MLH1-93G/A SNP were examined by SSCP analysis.Methylation of the MLH1 promoter region was observed in 28.6% (60/210) of sporadic CRCs. The proportions of MLH1-93G/A genotypes A/A, A/G and G/G were 26% (n=54), 51% (n=108) and 23% (n=48), respectively, and they were significantly associated with the methylation status (p=0.01). There were no significant associations between genotype frequency of the six other SNPs and methylation status. The A-allele of MLH1-93G/A was more common in cases with methylation than the G-allele (p=0.0094), especially in females (p=0.0067). In logistic regression, the A/A genotype of the MLH1-93G/A SNP was shown to be the most significant risk factor for methylation of the MLH1 promoter region (odds ratio 2.82, p=0.003). Furthermore, a haplotype of the A-allele of rs2276807 located -47 kb upstream from the MLH1-93G/A SNP and the A-allele of MLH1-93G/A SNP was significantly associated with MLH1 promoter methylation.These results indicate that individuals, and particularly females, carrying the A-allele at the MLH1-93G/A SNP, especially in association with the A-allele of rs2276807, may harbor an increased risk of methylation of the MLH1 promoter region.

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Activity (transcription) of the genes for MLH1, MSH2 and p53 in sporadic colorectal tumours with micro-satellite instability.

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