Possner Maria, Heuser Markus, Kaulfuss Silke, Scharf Jens-Gerd, Schulz Wolfgang, Hermann-Ringert Rolf, Thelen Paul
Department of Urology, Georg-August-University, D-37099 Göttingen, Germany.
Int J Oncol. 2008 Apr;32(4):877-84.
The function of the androgen-regulated homeobox protein NKX3.1 in prostate cancer is controversial. NKX3.1 is necessary for correct prostate development and undergoes frequent allelic loss in prostate cancer. However, no mutations occur in the coding region and some particularly aggressive cancers over-express the protein. Nevertheless NKX3.1 is often referred to as candidate tumor suppressor gene. Recent findings suggest a function in protection against oxidative damage involved in prostate carcinogenesis. Thus NKX3.1 may act differently at various stages of prostate cancer. Unlike a classical tumor suppressor NKX3.1 is up-regulated by androgens and down-regulated by phytoestrogens. In this study we performed RNAi based functional analysis by knocking down NKX3.1 expression in LNCaP prostate cancer cells and analyzing the impact of NKX3.1 on gene expression and cell proliferation. Knock-down of NKX3.1 evoked a massive down-regulation of NKX3.1 expression, followed by reduction in mRNA expression of the androdrogen receptor (AR) and the insulin-like growth factor receptor (IGF-1R). Western blot analysis showed strong decreases of NKX3.1, AR, and IGF-1R protein expression. Concomitantly, cell proliferation decreased and expression of prostate-specific antigen (PSA) mRNA and its secretion were diminished, whereas expression of IGF binding protein 3 (IGFBP-3) and MMP tissue inhibitor 3 (TIMP-3) was up-regulated. In tumor cells not deprived of NKX3.1 expression this gene still has a function which might differ from its role in prostate development and carcinogenesis. NKX3.1 knock-down altered the expression of genes highly relevant in prostate cancer cell proliferation and apoptosis. In LNCaP NKX3.1 most probably plays the role of an androgen-regulated transcription factor whose down-regulation is paralleled by anti-proliferative and pro-apoptotic effects. Since NKX3.1 can regulate AR expression it may become a target for interference in hormone refractory prostate carcinoma.
雄激素调节的同源盒蛋白NKX3.1在前列腺癌中的作用存在争议。NKX3.1对于前列腺的正常发育是必需的，且在前列腺癌中经常发生等位基因缺失。然而，其编码区未发生突变，一些侵袭性特别强的癌症反而过度表达该蛋白。尽管如此，NKX3.1仍常被视为候选肿瘤抑制基因。最近的研究结果表明，它在预防前列腺癌发生过程中涉及的氧化损伤方面发挥作用。因此，NKX3.1在前列腺癌的不同阶段可能发挥不同作用。与经典的肿瘤抑制基因不同，NKX3.1受雄激素上调，受植物雌激素下调。在本研究中，我们通过敲低LNCaP前列腺癌细胞中NKX3.1的表达，并分析NKX3.1对基因表达和细胞增殖的影响，进行了基于RNA干扰的功能分析。敲低NKX3.1可引起NKX3.1表达的大量下调，随后雄激素受体（AR）和胰岛素样生长因子受体（IGF-1R）的mRNA表达降低。蛋白质印迹分析显示NKX3.1、AR和IGF-1R蛋白表达显著下降。与此同时，细胞增殖减少，前列腺特异性抗原（PSA）mRNA的表达及其分泌减少，而胰岛素样生长因子结合蛋白3（IGFBP-3）和基质金属蛋白酶组织抑制剂3（TIMP-3）的表达上调。在未缺失NKX3.1表达的肿瘤细胞中，该基因仍具有一种功能，这一功能可能与其在前列腺发育和致癌过程中的作用不同。敲低NKX3.1改变了与前列腺癌细胞增殖和凋亡高度相关的基因表达。在LNCaP细胞中，NKX3.1很可能发挥雄激素调节转录因子的作用，其下调与抗增殖和促凋亡作用同时出现。由于NKX3.1可以调节AR的表达，它可能成为激素难治性前列腺癌干预的靶点。
