title: Microsatellite instability is associated with hypermethylation of the hMLH1 gene and reduced gene expression in mycosis fungoides.
abstract: Fifty-one mycosis fungoides samples were analyzed for microsatellite instability (MSI) using the panel of markers recommended for hereditary nonpolyposis colorectal cancer kindred and a panel we designed for cutaneous T cell lymphoma in order to compare detection rates and determine if MSI is a genome-wide phenomenon. Samples demonstrating MSI were analyzed for abnormalities of the hMLH1 gene including loss of heterozygosity, mutations, and promoter hypermethylation. MSI was detected in 16% using the hereditary nonpolyposis colorectal cancer panel and 22% with the cutaneous T cell lymphoma panel. Overall, 27% demonstrated MSI and 73% had a stable phenotype. hMLH1 gene studies did not detect loss of heterozygosity or reveal any mutations. Promoter hypermethylation was detected in nine of 14 patients with MSI, however (64%). In addition hMLH1 and hMSH2 protein expression was studied using immunohistochemical techniques. Five of nine patients with MSI and hMLH1 promoter methylation showed abnormal hMLH1 protein expression with normal hMSH2 gene expression. All other patients tested demonstrated normal hMLH1 and hMSH2 protein expression. MSI was found to be more prevalent in tumor stage mycosis fungoides (47%) than early stage disease (20%) and was associated with an older age of onset of mycosis fungoides. MSI may be a consequence of hMLH1 promoter hypermethylation in mycosis fungoides patients and may prevent transcription in a subset of patients. This suggests that the development of a mutator phenotype may contribute to disease progression in mycosis fungoides.
authors: Skin Tumour Unit, St John's Institute Dermatology, St Thomas' Hospital, London, UK. juliascarisbrick@doctors.org.uk
authors: Julia J
authors: JJ
authors: Scarisbrick
authors: Tracey J
authors: TJ
authors: Mitchell
authors: Eduardo
authors: E
authors: Calonje
authors: Guy
authors: G
authors: Orchard
authors: Robin
authors: R
authors: Russell-Jones
authors: Sean J
authors: SJ
authors: Whittaker
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D019175:DNA Methylation; D004268:DNA-Binding Proteins; D005260:Female; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D019656:Loss of Heterozygosity; D008297:Male; D018895:Microsatellite Repeats / Q000502:physiology*; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009182:Mycosis Fungoides / Q000378:metabolism / Q000401:mortality / Q000503:physiopathology*; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins; D010641:Phenotype; D011401:Promoter Regions, Genetic / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics; D012878:Skin Neoplasms / Q000378:metabolism / Q000401:mortality / Q000503:physiopathology*; D015996:Survival Rate
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein