Promoter methylation and expression of DNA repair genes hMLH1 and MGMT in acute myeloid leukemia.

Gene silencing of DNA repair genes hMLH1 and MGMT caused by aberrant promoter methylation has been detected in various solid tumors. However, in acute myeloid leukemia (AML) the frequency of hMLH1 and MGMT promoter methylation is not yet fully elucidated. To determine the methylation status and expression of hMLH1 and MGMT, we investigated 22 AML cases by methylation-specific polymerase chain reaction (MS-PCR) and reverse transcription PCR (RT-PCR). To exclude unspecific PCR amplifications DNA sequencing was performed. hMLH1 promoter methylation was detectable in 4 of 20 AML cases. However, DNA sequencing could only confirm a methylated hMLH1 promoter in one case. mRNA expression was absent in one case and reduced in another. However, these cases did not display aberrant promoter methylation. In contrast, MGMT promoter methylation was not detectable in the investigated AML patient samples. Accordingly, MGMT mRNA expression was found to be normal in all but one case. Aberrant promoter methylation of hMLH1 was detectable only in a small number of AML cases. Additionally, in two cases the promoter methylation detected by MS-PCR could not be confirmed by sequencing, clearly indicating the importance of controlling MS-PCR results by the more specific sequence analysis. Surprisingly, hMLH1 promoter methylation was not associated with gene silencing, suggesting monoallelic methylation or promoter methylation only in a small subpopulation of malignant cells. The reduced mRNA expression in additional samples may indicate an involvement of hMLH1 in the malignant transformation in a small subset of cases. In contrast, MGMT does not seem to be involved in the pathogenesis of AML.