Transcriptional regulation of human osteopontin promoter by histone deacetylase inhibitor, trichostatin A in cervical cancer cells

Background: Trichostatin A (TSA), a potent inhibitor of histone deacetylases exhibits strong anti-tumor and growth inhibitory activities, but its mechanism(s) of action is not completely understood. Osteopontin (OPN) is a secreted glycoprotein which has long been associated with tumor metastasis. Elevated OPN expression in various metastatic cancer cells and the surrounding stromal cells often correlates with enhanced tumor formation and metastasis. To investigate the effects of TSA on OPN transcription, we analyzed a proximal segment of OPN promoter in cervical carcinoma cells. Results: In this paper, we for the first time report that TSA suppresses PMA-induced OPN gene expression in human cervical carcinoma cells and previously unidentified AP-1 transcription factor is involved in this event. Deletion and mutagenesis analyses of OPN promoter led to the characterization of a proximal sequence (-127 to -70) that contain AP-1 binding site. This was further confirmed by gel shift and chromatin immunoprecipitation (ChIP) assays. Western blot and reverse transcription-PCR analyses revealed that TSA suppresses c-jun recruitment to the OPN promoter by inhibiting c-jun levels while c-fos expression was unaffected. Silencing HDAC1 followed by stimulation with PMA resulted in significant decrease in OPN promoter activity suggesting that HDAC1 but not HDAC3 or HDAC4 was required for AP-1-mediated OPN transcription. TSA reduces the PMA-induced hyperacetylation of histones H3 and H4 and recruitment of RNA pol II and TFIIB, components of preinitiation complex to the OPN promoter. The PMA-induced expression of other AP-1 regulated genes like cyclin D1 and uPA was also altered by TSA. Interestingly, PMA promoted cervical tumor growth in mice xenograft model was significantly suppressed by TSA. Conclusions: In conclusion, these findings provide new insights into mechanisms underlying anticancer activity of TSA and blocking OPN expression at transcriptional level by TSA may act as novel therapeutic strategy for the management of cervical cancer.