Epigenetic Dysregulation of the Tissue Inhibitor of Metalloproteinases-2 Gene in Multiple Myeloma

Multiple myeloma (MM) is a B-cell neoplasm characterized by the accumulation of malignant plasma cells in the bone marrow (BM) as well as abundant BM angiogenesis. Aberrant methylation of CpG islands near gene promoter regions is the most widely studied epigenetic abnormality in human malignancies and is associated with loss of gene expression. There is increasing evidence for a role of the tissue inhibitor of metalloproteinases 2 (TIMP2) gene as a tumor suppressor. Overexpression of TIMP2 may result in decreased invasive potential, suppression of tumor growth and vascularization as well as inhibition of angiogenesis. We could previously show that TIMP2 may become hypermethylated in association with transcriptional silencing in indolent and aggressive non-Hodgkin's lymphomas. Recently, downregulation of TIMP2 was also reported in MM, and this is thought to contribute to increased BM angiogenesis. In this study, we determined the methylation status of the promoter-associated CpG island of TIMP2 in primary MM samples and investigated correlations between TIMP2 methylation and clinical parameters.

Methylation of the promoter-associated CpG island of TIMP2 was analyzed by methylation-specific polymerase chain reaction (MSP) in samples from 76 MM patients (median age 65 years [range 40–94]; 44 males, 32 females; 71 BM samples, 5 peripheral blood samples). Overall survival curves were plotted according to the method of Kaplan and Meier and compared using the log-rank test. Correlations between variables were analyzed using the Fisher's exact two-sided test and independent t-test, respectively.

MSP analysis revealed that there was aberrant methylation of the TIMP2 promoter region in 4/76 MM patient samples. We found an association of TIMP2 hypermethylation with plasma cell leukemia (p<0.0001) and decreased platelet counts (257.1 G/l vs. 111.5 G/l; p=0.04). There was a trend towards an inferior overall survival in MM cases with a hypermethylated TIMP2 gene, but this difference was not statistically significant (p=0.11).

Our study shows that promoter hypermethylation of TIMP2 is a novel epigenetic event in MM that may contribute to disease progression and could serve as a prognostic biomarker. Further studies are warranted to elucidate the functional consequences of epigenetic dysregulation of TIMP2 in the pathogenesis of MM. Additionally, the increasing evidence for the role of DNA methylation changes in MM may serve as a basis for the use of epigenetically targeted therapeutic approaches in malignant plasma cell disorders.

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