Implications of mismatch repair genes hMLH1 and hMSH2 in patients with sporadic renal cell carcinoma.

Abstract

To analyse the implications of DNA mismatch repair genes hMLH1 and hMSH2 in sporadic renal cell carcinoma (RCC). Specimens of tumour and healthy renal tissue were collected from 89 patients treated for sporadic RCC. Another 95 blood samples taken from individuals with no history of cancer were also analysed. After DNA extraction and PCR amplification, microsatellite instability (MSI) was determined using the Bethesda microsatellite panel, two exonic microsatellites of the TGFbRII and BAX genes, and the microsatellite D3S1611. The promoter methylation status of hMLH1 was investigated using the HpaII and MspI restriction enzymes. In addition, a sequencing analysis of complete coding region of hMLH1 and hMSH2 genes was performed. MSI and promoter hypermethylation of hMLH1 were not detected. Interestingly, loss of heterozygosity (LOH) was common among patients with RCC, particularly in microsatellite D3S1611 (34.9%). Mutations were identified in eight patients: K618A and V716M in gene hMLH1; and I145V, G322D, and the novel mutation P349A, in gene hMSH2. The mutations also appeared in healthy renal tissue and therefore, were considered as germline DNA sequence variations. There were G322D and K618A changes in >1% of the healthy control subjects, suggesting that they are DNA polymorphisms. Our data show that loss of function of both hMLH1 and hMSH2 is not involved in sporadic RCC, either by promoter methylation or mutation in their exons. However, LOH indicated that chromosomal instability affecting large fragments of DNA was the main genetic alteration we detected associated with RCC.