Curcumin Down-Regulates Human Homeobox Gene NKX3.1 In Prostate Cancer Cell LNCaP

Curcumin is a natural, phenolic compound in the rhizomes of plant Curcuma longa Linn, which has been traditionally used as a seasoning spice and coloring agent in food, and endowed with beneficial biological activities, including anti-inflammatory and antioxidant effect as well as chemopreventive and anticarcinogenic properties. Prostate cancer is the most common male cancer and the second leading cause of male cancer deaths in the developed countries. Prostate cancer has intimate relation to the Prostate-specific homeobox gene NKX3. 1. Homeobox gene NKX3.1 is discoveried recendly, which plays central role in prostate organogenesis and carcinogenesis. Human's NKX3.1gene is located at 8P21, containing 2 extrons and 1 intron. NKX3.1 mainly expresses in epidermic cells of prostate specifically, which is regulated by androgen. AR is a ligand -mediated transcriptional factor that belongs to the superfamily of nuclear receptors. Activated by androgen binding, AR can recognize and bind androgen responsive element(ARE).Androgen is essential for the development, differentiation and normal function of prostate gland. Androgen exerts its function via the intracellular androgen receptor (AR). AR moves into the nucleus, binds to the specific DNA sequences— ARE and regulates the transcriptional activity of target genes.To better understand the function of curcumin, the androgen-sensitive prostate cancer cell line LNCaP was treated with different concentrationof curcumin, and the expression of prostate specific homeobox gene NKX3. 1 and AR were investigated by RT-PCR and Western blotting. EMSA was used to demonstrate the influence of curcumin on the binding of AR-ARE. To detect the influence of Curcumin on NKX3.1 promoter, prostate cancer cell line LNCaP was cotransfected with pGL3~1040(which is a luciferase reporter plasmid containing NKX3.1 5'-1040bp promoter)and pRL-TK using lipofectaminTM 2000 in different concentration of Curcumin for 24 hours, and then the expression of luciferase reporter driven by 1040bp-promoter of NKX3. 1 was tested by assay of luciferase activity. To observe whether or not 1040bp-promoter is regulated by androgen and identify the mechanism of curcumin on NKX3. 1, the transfected LNCaP was treated with 10-6 mol/L of R1881 and 30μmol/L curcumin respectively or altogether , then investigated the luciferase activity.The results show that (1)Curcumin inhibits the expression of NKX3. land AR in LNCap, which depends on Curcumin concentration and 40μmol/L Curcumin has the most obvious effect. (2)There is no interference on the specific binding of AR-ARE in LNCap when treated by curcumin. (3) The influence of Curcumin on NKX3.1 promoter also has the same tendency as(1)to some extent. (4)The activity of 1040bp-promoter is increased by 31% at 12 hours after LNCaP cells are transfected with pGL3-1040bp promoter and treated with 10-6 mol/L R1881 comparing with those transfected with pGL3-1040bp promoter only. The results indicated that 1040bp promoter was regulated by androgen to some extent.Conclusion: To sum up, the results indicate that Curcumin inhibits the expression of NKX3. land AR. The influence of Curcumin on NKX3.1 is mediate by AR. These findings in the present study provide a new explore about the anti-tumor mechanism of Curcumin on prostate cancer and a valuable inspiration on NKX3.1 function study.