The Effect And Epigenetic Mechanism Of ATRA Activated HOXB13Gene Expression In Prostate Cancer Cells

Prostate cancer is the most common malignancy in men in Europe, North America and ina number of African countries. The incidence of prostate cancer has increased following theaging of population worldwide. At present, conventional therapies such as surgery andhormone treatment frequently fail to achieve the satisfactory effect. Moreover, cancer cellsmay acquire the hormone and drug resistant features under these treatment stresses. So far,efforts to conquer this malignant disease have achieved limited success. Thus, researchesaimed at the development of new and more effective therapeutic strategies for prostate cancerremain an open opportunity.ATRA (All-trans Retinoic acid), the vitamin A metabolite, plays an essential role in thedevelopment by regulating cellular processes such as proliferation, differentiation andmigration. Since ATRA can rectify aberrant cell growth and induce apoptosis, it has beenwidely investigated in preclinical and clinical trials for the treatment of many cancer types,including early gastric cancer and prostate cancer. Homeobox B13(HOXB13) gene belongs toa large homeobox superfamily, limited expression of HOXB13was observed at the caudalextent of the spinal cord, urogenital sinus, and colon and rectum cells in anandrogen-independent manner. HOXB13, silenced in androgen receptor-negative (AR-)prostate cancer cells, plays a role in AR-prostate cancer cell growth arrest.In this study, we discussed the roles of HOXB13in the progress that ATRA induced AR-prostate cancer cells growth arrest. In addition we investigated the changing of epigeneticmodifications and possible mechanisms of HOXB13in DU145cells treetment of ATRA. Wedemonstrated that ATRA is able to induce cell growth arrest and increase HOXB13expression.MTT assays suggested that the ATRA-induced DU145cell growth arrest was associated, atleast in part, with the expression of HOXB13. Luciferase assays showed that ATRA couldenhance the activity of the HOXB13promoter. BSP assays revealed that ATRA could reducethe methylation level of CpG islands on HOXB13promoter, meanwile, the expressions ofDNMT3b was downregulated upon ATRA treatment. The chromatin immunoprecipitation(ChIP) and co-immunoprecipitation (CoIP) assays have verified that EZH2not just inducesH3K27me3, but also recruites DNMT3b to HOXB13promoter to affect the promotermethylation status and further repress the gene transcription. Results from this study validatedthat the expressions of EZH2was decreased after ATRA treatment in prostate cancer cells.Also, the binding of EZH2and the H3K27me3level on the HOXB13promoter were reduced.In addition, the binding of DNMT3b was also reduced. Additionally, we discovered thattreatment of both ATRA and5-aza-dC exhibited a much stronger inhibitory effects to DU145 cells than each of the two drugs alone. Meanwhile, the expression of HOXB13wasupregulated, but both EZH2and DNMT3b were downregulated markedly upon the treatmentof the two drugs.Perspectively, data arising from this study may provide useful clues for the developmentof new therapeutic strategies for AR-prostate cancer that involve the use of ATRA andepigenetic modifiers.