Department of Medical Microbiology, Southern Illinois University School of Medicine, Springfield, Illinois 62794-9626, USA.
J Biol Chem. 2011 May 27;286(21):18949-59. doi: 10.1074/jbc.M111.232637. Epub 2011 Mar 21.
NDRG1 and KAI1 belong to metastasis suppressor genes, which impede the dissemination of tumor cells from primary tumors to distant organs. Previously, we identified the metastasis promoting transcription factor, ATF3, as a downstream target of NDRG1. Further analysis revealed that the KAI1 promoter contained a consensus binding motif of ATF3, suggesting a possibility that NDRG1 suppresses metastasis through inhibition of ATF3 expression followed by activation of the KAI1 gene. In this report, we found that ectopic expression of NDRG1 was able to augment endogenous KAI1 gene expression in prostate cancer cell lines, whereas silencing NDRG1 was accompanied with significant decrease in KAI1 expression in vitro and in vivo. In addition, our results of ChIP analysis indicate that ATF3 indeed bound to the promoter of the KAI1 gene. Importantly, our promoter-based analysis revealed that ATF3 modulated KAI1 transcription through cooperation with other endogenous transcription factor as co-activator (ATF3-JunB) or co-repressor (ATF3-NFκB). Moreover, loss of KAI1 expression significantly abrogated NDRG1-mediated metastatic suppression in vitro as well as in a spontaneous metastasis animal model, indicating that KA11 is a functional downstream target of the NDRG1 pathway. Our result of immunohistochemical analysis showed that loss of NDRG1 and KAI1 occurs in parallel as prostate cancer progresses. We also found that a combined expression status of these two genes serves as a strong independent prognostic marker to predict metastasis-free survival of prostate cancer patients. Taken together, our result revealed a novel regulatory network of two metastasis suppressor genes, NDRG1 and KAI1, which together concerted metastasis-suppressive activities through an intrinsic transcriptional cascade.
NDRG1 和 KAI1 属于转移抑制基因，可阻碍肿瘤细胞从原发性肿瘤向远处器官的扩散。之前，我们鉴定了转移促进转录因子 ATF3 是 NDRG1 的下游靶标。进一步分析表明，KAI1 启动子含有 ATF3 的一个保守结合基序，提示 NDRG1 可能通过抑制 ATF3 表达，从而激活 KAI1 基因，来抑制转移。在本报告中，我们发现 NDRG1 的异位表达能够增强前列腺癌细胞系中内源性 KAI1 基因的表达，而沉默 NDRG1 则伴随着 KAI1 表达在体外和体内的显著下降。此外，我们的 ChIP 分析结果表明，ATF3 确实与 KAI1 基因的启动子结合。重要的是，我们的启动子分析表明，ATF3 通过与其他内源性转录因子（作为共激活因子（ATF3-JunB）或共抑制因子（ATF3-NFκB））合作，调节 KAI1 转录。此外，KAI1 表达的缺失显著削弱了 NDRG1 在体外以及自发转移动物模型中的转移抑制作用，表明 KAI1 是 NDRG1 途径的功能性下游靶标。我们的免疫组织化学分析结果表明，随着前列腺癌的进展，NDRG1 和 KAI1 的缺失同时发生。我们还发现，这两个基因的联合表达状态可作为预测前列腺癌患者无转移生存的强有力的独立预后标志物。总之，我们的结果揭示了两个转移抑制基因 NDRG1 和 KAI1 的一个新的调控网络，它们通过内在的转录级联协同发挥转移抑制活性。
