Effects of 5-aza-2′-deoxycytidine on matrix metalloproteinase expression and pancreatic cancer cell invasiveness

To investigate whether DNA methylation and the invasive phenotype of pancreatic adenocarcinoma are associated, we studied the role of methylation in the transcriptional regulation of several matrix metalloproteinases (MMPs) and the effect of 5-aza-2'-deoxycytidine (5Aza-dC), an inhibitor of DNA methylation, on the invasive behavior of pancreatic cancer cells. Using the Boyden chamber in vitro invasion assay, we found a statistically significant increase in invasive potential in four of five pancreatic cancer cell lines after treatment with 5Aza-dC. This enhanced invasiveness was associated with the induction of mRNAs for one or more MMPs critical for tumor invasion, including MMP-1, -2, -3, -7, -9, and -14. Addition of an MW inhibitor (GM6001, GM1489, doxycycline, or tissue inhibitor of metalloproteinase 2) blocked the 5Aza-dC-induced increase in the number of invading cells. As shown by a methylation-specific polymerase chain reaction, 5' CpG sites in MMP-2, -7, and -9 genes were partially or completely methylated in cell lines that expressed little or no corresponding mRNAs. Thus, DNA methylation influences the expression of MMP genes, and use of methylation inhibitors may stimulate the invasion of pancreatic cancer by reactivating invasion-promoting genes.