Reduced mRNA expression in paraffin-embedded tissue identifies MLH1- and MSH2-deficient colorectal tumours and potential mutation carriers
Müller A et al. - In a trial to identify MLH1 or MSH2-deficient colorectal tumours, it was found that RT-PCR allows relative quantification of MMR gene mRNA expression in formalin-fixed and paraffin-embedded tissue, and this approach enables quantification of haploinsufficiency due to nonsense-mediated mRNA decay in normal tissue and B-lymphocytes from pts carrying MSH2 germline mutations and may be useful for identification of asymptomatic carriers of pathogenic germline mutations Methods- Based on the principle of nonsense-mediated mRNA decay, MLH1 or MSH2-deficient colorectal tumours were identified through relative quantification of mRNA expression with real-time PCR (RT-PCR) analysis
Results- MLH1 and MSH2 mRNAs were almost equally expressed as defined by MLH1 to MSH2 transcript ratio in 16 microsatellite stable, mismatch repair (MMR) proficient tumours
- A close correlation between loss of protein expression and MMR–mRNA levels was found in highly microsatellite instable (MSI-H) tumours deficient of MLH1 or MSH2
- MLH1/MSH2 ratio was low in 11 sporadic and 9 hereditary MLH1-deficient carcinomas, whereas the ratio was high in 17 MSH2-deficient hereditary non-polyposis colorectal cancer (HNPCC) associated carcinomas
- In the normal tissues of HNPCC pts with MSH2 mutations, the MLH1/MSH2 transcript ratios were significantly elevated as compared with the ratios of normal mucosa in pts with MMR-proficient tumours
- Analysis of B-lymphocytes of HNPCC pts with proven MMR gene mutation confirmed these findings
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