Epigenetic Up-regulation of Gene Expression in KAS 6/1 Human Multiple Myeloma Cells

Cytosine methylation, an epigenetic form of regulating gene transcription, has gained importance upon the discovery that genes involved in the carcinogenic process may be regulated by this mechanism and, moreover, that certain cancers respond to treatment with demethylation-promoting drugs. Typically, the use of DNA methyltransferase inhibitor drugs results in the up-regulation of important tumor suppressor genes, previously down-regulated by the existence of abnormal cytosine methylation within their promoters. Here, we show microarray and RT-PCR results indicating that many genes are down-regulated upon treatment of KAS 6/1 multiple myeloma cells with Zebularine, a demethylating agent. Our findings suggest that, in addition to the typical methylation inhibitor-induced up-regulation of genes, removal of methylation in some genes may have a profound down-regulating effect upon their expression. The analysis of gene function showed that, of the down-regulated genes, 38 are associated with cell proliferation and/or cancer. Our analysis of the promoters of the subset of selected genes containing CpG islands showed that the distribution of cis elements differs between genes up- and down-regulated by methylation. Finally, we propose a model which shows how genes containing methylation sites within their basic promoters and/or enhancer sequences are susceptible to down-regulation, whereas genes methylated within silencer regions are up-regulated, thus providing a model as to how DNA methylation could induce such opposing effects on transcription.