However some inhibitors might be doing more and their anti-90365-57-4 cancer properties could be much more complicated. For instance, many non-histone cellular proteins such as transcription factors are also substrates of HDAC, and their transcriptional activities could be affected by the HDAC inhibitor TSA as well. Most tumor suppressor genes are epigenetically silenced by either DNA methylation and/or histone deacetylation in their promoters. To our knowledge, there is no report showing that the expression of such genes can be differentially regulated by inhibitors of methylation or histone deacetylation in a cancerspecific fashion without having epigenetic modifications in the promoter. The regulation of MIG-6 by these inhibitors, as we show here, unveils a novel mechanism by which a tumor suppressor gene can be epigenetically silenced in an indirect and tissuespecific manner. Our luciferase reporter assay results indicated that the regulation of MIG-6 expression in melanoma and in lung cancer was most likely mediated by different factors. We have identified a minimal TSA response element in exon 1 of MIG-6 proximal to its promoter, while location of the 5- aza-dC response element is still uncertain. We speculate that the TSA response element in the MIG-6 gene is most likely regulated by a factor whose expression is affected by histone deacetylation in its promoter or whose protein activity is directly regulated by acetylation/deacetylation. This factor would be activated in lung cancer cells upon TSA treatment, but not in melanoma cells. Within the minimal TSAresponse element that we identified in MIG-6 gene exon 1, there are putative DNA binding sequences for the transcription factor activator protein-2, which has five family members and binds to the consensus sequence 59- GCCNNNGGC-39. When the putative TFAP2 binding sites were mutated, we observed a significant drop in TSAresponsiveness, indicating that those sequences are crucial for TSA-mediated regulation. It will be interesting to see if TFAP2 or other factor binds to those sequences and regulates MIG-6 gene expression. As for 5-aza-dC, its response element is likely outside the tested 1.605-65-2 383-kb MIG-6 promoter regulatory region ; that is, it is either directly affected by methylatio
