The Experimental Study Of The Relationship Between Retinoic Acid Receptor Beta And Prostate Cancer

Prostate cancer is the most common gentitourlogic malignancy. Apart from lung cancer, prostate cancer is the first leading cause of death in American men. The incidence of prostate cancer increase in our country, and it has become the third cancer of gentitourlogic malignancy. A reduction in tumor suppressor gene expression is one of the key mechanisms involved in prostate cancer. Modifications of chromatin structure by acetylation/deacetylation of the histone proteins play a central role in the regulation of gene expression. Histone acetylation contributes to expression of gene, while histone deacetylation leads to repression of gene expression. The levels of acetylation/deacetylation of histone proteins are determined by 2 opposing enzymes, histone acetyltransferases and histone deacetylases. These alterations of gene expression by histone acetyltransferases and histone deacetylases have been implicated in the process of prostate cancer.The growth of most prostate tumors depends on androgens during the initial stages of tumor development. In early stage disease, surgery can be curative and anti-androgen therapy can be of significant benefit. In the final stages, it becomes androgen independent and is unresponsive to androgyne ablation therapy. At this stage, induction of apoptosis is considered as a better strategy to control cancer. Histone deacetylases inhibitors induced apoptosis and histone acetylation which can be correlated with the expression of antiproliferative genes. This study includes two parts as follows:Part IExpression of the RARβand its relationship to acetylated histone H3 inprostate cancerPurpose: To study expression of RARP and acetylated histone H3 in benign prostatic hyperplasia and prostate cancer, and their clinical significances, analyzing the relationship of RARp and acetylated histone H3.Methods: The expression levels of RARβprotein and the acetylation levels of histone H3 in 41 prostate cancer and 10 benign prostatic hyperplasia were examined, using immunohistochemistry.Results: The expression levels of RARβprotein and the acetylation levels of histone H3 in prostate cancer were lower than which were in the benign prostatic hyperplasia (p<0.05 ) . The expression levels of RARβprotein were higher in the well differentiated group than the poorly differentiated group (p<0.01) , lower in the final stages group than the early stages group (p<0.01) and lower in the hormone refractory ones than hormone dependent ones (p<0.05). The acetylation levels of histone H3 inversely correlated to pathological grade and stage(p<0.05). Immunostaining patterns of RARβand acetylated histone H3 were positively correlated (p<0.01) .Conclusion: The expression levels of RARβprotein are inversely related to the development of prostate cancer, which are closely concerned with the acetylation levels of histone H3.Part IIEffect of the trichostatin A in combination with all-trans retinoic acid onexpression of RARβin DU-145Purpose: We tested whether combining histone deacetylase inhibitor trichostatin A with all-trans retinoic acid would restore RARβreceptor expression, leading to increased growth inhibition in retinoic acid resistant androgen independent prostate cancer cell DU-145.Methods: ATRA, TSA or the combination of ATRA and TSA was added to the culture media respectively for 8 to 24 hours. The growth of each group was evaluated by MTT. Western blotting was used to detect the expression levels of acetylated histone H3 protein. RARβmRNA was determined using RT-PCR.Results: Enhanced inhibition of the proliferation of DU-145 was observed with the combination of ATRA plus TSA. Western blotting analyses showed increased acetylation of histone H3 on treatment with increasing doses of TSA in the presence or absence of ATRA. Reactivation of RARβmRNA expression was observed in DU-145 treated with TSA alone or TSA in combination with ATRA.Conclusion: The combination of ATRA and the histone deacetylase inhibitor TSA elicits an additive inhibition of cell proliferation in the retinoic acid resistant androgen independent prostate cancer cell DU-145. Enhanced inhitition of the proliferation of DU-145 treated with TSA in combination with ATRA in part is concerned with re-expression of RARβ.