Differential MSH2 promoter methylation in blood cells of Neurofibromatosis type 1 (NF1) patients.
Neurofibromatosis type 1 (NF1) is caused by NF1 gene mutations. The phenotype is highly variable, with 'modifiers' being discussed as potential determinants. Mismatch repair deficiency was shown to cause NF1 mutations, but constitutional mutation of mismatch repair genes was identified only once in a NF1 patient. We aimed to analyze whether DNA methylation of mismatch repair gene promoters, known to lead to transcriptional silencing, is associated with increased tumor load in NF1 defined by the number of cutaneous neurofibromas. Leukocyte DNA of 79 controls and 79 NF1 patients was investigated for methylation of mismatch repair genes MLH1, MSH2, MSH6, and PMS2 by methylation-specific PCR and pyrosequencing. MLH1, MSH6, and PMS2 promoters were not methylated. By contrast, we found promoter methylation of MSH2 with a higher rate of methylation in NF1 patients compared with controls. Furthermore, when comparing NF1 patients with a low vs those with a high number of cutaneous neurofibromas, MSH2 promoter methylation was significantly different. In patients with a high tumor burden, methylation of two (out of six) CpGs was enhanced. This finding was not confounded by age. In conclusion, enhanced methylation involving transcription start points of mismatch repair genes, such as MSH2 in NF1, has not been described so far. Methylation-induced variability of MSH2 gene expression may lead to variable mismatch repair capacity. Our results may point toward a role of MSH2 as a modifier for NF1, although the amount of DNA methylation and subsequent gene expression in other cell types of NF1 patients needs to be elucidated.
Titze
Sabrina
S
Department of Neuropathology, Charité - Universitätsmedizin Berlin, Berlin 10117, Germany.
Peters
Hartmut
H
Währisch
Sandra
S
Harder
Thomas
T
Guse
Katrin
K
Buske
Annegret
A
Tinschert
Sigrid
S
Harder
Anja
A
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D000251:Adenosine Triphosphatases / Q000235:genetics; D001773:Blood Cells / Q000378:metabolism*; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics*; D045643:DNA Repair Enzymes / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000235:genetics*; D009456:Neurofibromatosis 1 / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000251:Adenosine Triphosphatases; C094934:PMS2 protein, human; C497172:MSH2 protein, human; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D045643:DNA Repair Enzymes