Methylation of the hMLH1 promoter and its association with microsatellite instability in acute myeloid leukemia

Abstract

The hMLH1 and hMSH2 genes are involved in the DNA mismatch repair (MMR) pathway. Defects in either of these genes have been associated with genetic instability in a wide variety of malignancies. A molecular mechanism involved in aberrant MMR gene expression is the epigenetic silencing of transcription by promoter methylation. The importance of MMR promoter methylation in leukemia is presently unclear and we have therefore undertaken a detailed analysis of the promoter regions of hMLH1 and hMSH2 using the technique of bisulfite genomic sequencing. DNA from 55 patients with acute myeloid leukemia (AML) including 23 patients with therapy-related AML (t-AML) have been analyzed. Two patients with de novo AML demonstrated extensive methylation throughout the whole hMLH1 region sequenced, one of whom had previously shown widespread genetic instability, measured as microsatellite instability (MSI). However methylation of hMLH1 was not found in t-AML which has previously been associated with MSI. In addition, methylation was seen at a restricted region of the hMLH1 promoter in both AML patients and healthy controls. The significance of this methylated region of the hMLH1 promoter is uncertain, however, our results confirm that in some patients with AML extensive methylation of hMLH1, but not of hMSH2 may occur, and as is the case in solid tumors this can be associated with the presence of a defective DNA mismatch repair pathway resulting in MSI.

National Institutes of Health Hematopoietic Cell Transplantation Late Effects Initiative: The Subsequent Neoplasms Working Group Report

“…Associations have been observed for glutathione S-transferase genes ( GSTM1 , GSTT1 and GSTP1 ), particularly among those with prior exposure to chemotherapeutic agents that are known GSTP1 substrates, 144 and for P-glycoprotein (encoded by MDR1 ), a cell membrane protein that impacts response to numerous chemotherapeutic agents. 145 A number of studies also have evaluated key DNA repair genes, including mismatch repair family members MLH1 146,147 and MSH2 , 148,149 RAD51 , 150 and XRCC3 . 151–153 Other polymorphisms in candidate genes from DNA repair pathways include ERCC2 of the nucleotide excision repair pathway 154 and two common functional p53-pathway variants.…”

Subsequent Malignant Neoplasms After Hematopoietic Cell Transplantation

“…Defects in the MMR pathway result in genetic instability or a mutator phenotype, manifested by an elevated rate of spontaneous mutations characterized as multiple replication errors in simple repetitive DNA sequences (microsatellites) -functionally identified as microsatellite instability (MSI). Approximately 50% of t-MDS/ AML patients have MSI, associated with methylation of the MMR family member MLH1 (61,62), low expression of MSH2 (63), or polymorphisms in MSH2 (64)(65)(66). The appearance of MMR-deficient, drug-resistant clones during genotoxic treatment for a primary cancer could be a vital factor in SMN susceptibility, particularly because the mutator phenotype (inherent of MMR-deficient cells) would be expected to accelerate the accumulation of further mutations and eventually SMN initiation.…”

DNA Repair in Acute Myeloid Leukemia and Myelodysplastic Syndromes

“…Multiple replication errors occur in repetitive DNA sequences leading to microsatellite instability. Inadequate MMR may increase the risk of solid tumors and myeloid neoplasms (Ben-Yehuda, Krichevsky et al 1996;Seedhouse, Das-Gupta et al 2003). Microsatellite instability was observed in secondary leukemia and in elderly patients with AML (Das-Gupta, Seedhouse et al 2001), but not in de-novo young AML patients.…”