Aim: To explore whether the anti-tumor action of 17-estradiol is enhanced by re-expression of the homeodomain transcription factor Nkx3.1 in PC3 human prostate cancer cells.

Methods: PC3 cells were stably transfected with pcDNA3.1-Nkx3.1-His vector, which carries a full-length cDNA of human Nkx3.1. The PC3 cells stably transfected with vector pcDNA3.1 were set as a control. The expression of Nkx3.1 protein in the cells was confirmed by Western blot analysis. The effect of Nkx3.1 on cell proliferation of PC3 cells was examined with MTT assay. The antiproliferative and apoptotic effects of 17-estradiol alone or in combination with Nkx3.1 were estimated on PC3 cells by using MTT growth tests and flow cytometric analyses. The expression of apoptosis-related proteins was analyzed using Western blotting.

Results: The plasmid carrying Nkx3.1 gene induced high expression of Nkx3.1 protein in PC3 cells. The re-expression of exogenous Nkx3.1 did not cause a significant reduction in cellular proliferation, whereas the expression of Nkx3.1 enhanced the 17-estradiol anti-proliferative effect in PC3 cells. Nkx3.1 expression promoted 17-estradiol-induced apoptosis of PC3 cells, as shown by analysis of Bcl-2, Bax, Caspase-3 and poly (ADP-ribose) polymerase expression.

Conclusion: The present study demonstrates that re-expression of Nkx3.1 enhances 17-estradiol anti-tumor action in PC3 human prostate cancer cells. The in vitro study suggests that re-expression of Nkx3.1 is worthy of further consideration as an adjuvant treatment of androgen independent prostate cancer with estrogen anti-tumor therapies.

Keywords: apoptosis, estrogen, Nkx3.1, prostate cancer cell, 17-estradiol, androgen independent prostate cancer

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