Cyclooxygenase-2 regulation in colon cancer cells: modulation of RNA polymerase II elongation by histone deacetylase inhibitors.

We are interested in the mechanism of cyclooxygenase-2 (Cox-2) regulation in colon cancer cells because this knowledge could provide insight into colon carcinogenesis and suggest ways to suppress Cox-2 expression in colon tumors. Studying the HT-29 colon cancer cell line as a model, we found that Cox-2 mRNA and protein levels were activated over 10-fold by the inflammatory cytokine tumor necrosis factor (TNF)-alpha. Moreover, we found that the histone deacetylase inhibitors butyrate and trichostatin A could block Cox-2 activation in a gene-specific manner. TNF-alpha and butyrate did not significantly affect Cox-2 promoter activity, mRNA stability, or negative regulation by the Cox-2 3'-untranslated RNA region. A nuclear run-on assay showed that TNF-alpha increased Cox-2 transcription, whereas butyrate was suppressive. Because butyrate has been reported to suppress polymerase elongation on the c-myc gene, we employed the chromatin immunoprecipitation assay to determine the influence of butyrate and trichostatin A on polymerase distribution on the Cox-2 gene. These data indicated that butyrate restricted polymerase elongation from exon 1 to 2 on both the c-myc and Cox-2 genes. We propose that histone deacetylases regulate a transcriptional block on the Cox-2 and c-myc genes and that this block may be a potential target for pharmacological intervention.