Inactivation of the tissue inhibitor of metalloproteinases-2 gene by promoter hypermethylation in lymphoid malignancies

The tissue inhibitor of metalloproteinases-2 (TIMP-2) is known to antagonize matrix metalloproteinase activity and to suppress tumor growth, angiogenesis, invasion and metastasis. We analysed the methylation status of the CpG island in the TIMP-2 promoter region by methylation-specific polymerase chain reaction (MSP) in hematopoietic cell lines. TIMP-2 promoter hypermethylation in the lymphoma cell line Raji and the leukemia cell line KG1a was associated with transcriptional repression. Treatment with the demethylating agent 5-aza-2'-deoxycytidine resulted in TIMP-2 upregulation in both cell lines. TIMP-2 was expressed in the cell lines HL60, U266 and XG1, which carry an unmethylated promoter region. MSP analysis of primary patient samples revealed aberrant methylation of TIMP-2 in 33/90 (36.7%) cases of non-Hodgkin's lymphoma (NHL), but not in normal peripheral blood lymphocytes as well as in nonmalignant bone marrow and lymph nodes. The frequency of TIMP-2 methylation was slightly higher in aggressive NHL subtypes compared to those with an indolent subtype (38.6 versus 33.3%). In contrast, TIMP-2 was not hypermethylated in any of the 40 cases of acute myelogenous leukemia examined. We conclude that promoter hypermethylation of TIMP-2 is a novel epigenetic event in the pathogenesis of lymphoid malignancies and may contribute to a more aggressive NHL phenotype.