Institute of Biomedical Sciences, National Sun Yat-Sen University, Taiwan.
Clin Cancer Res. 2012 Dec 1;18(23):6416-25. doi: 10.1158/1078-0432.CCR-12-0832. Epub 2012 Oct 8.
Prospero homeobox 1 (PROX1) has been shown to function as a tumor suppressor in various types of cancer. However, it promotes colon cancer progression. The aim of this study is to clarify the underlying mechanism by which PROX1 regulates tumorigenicity of colon cancer.
Association of PROX1 and clinicopathological features was studied by immunohistochemical staining. Pri-miR-9-2 and miR-9 were detected by quantitative real-time PCR. Assays of cell invasion, adhesion, and matrix metalloproteinase activity were used to study PROX1-mediated epithelial-mesenchymal transition (EMT).
PROX1 was overexpressed in 43% (59/136) of colon cancer tissues and its expression was correlated with E-cadherin downregulation (P = 0.00005), advanced tumor staging (P = 0.005), and lymph node metastasis (P = 0.000009). Enforced expression of PROX1 in DLD-1 cells caused downregulation of E-cadherin and integrins and attenuated cell adhesion. These cells showed increase of matrix metalloproteinase activity and invasive ability. Conversely, knockdown of PROX1 in SW620 cells restored E-cadherin protein expression and reduced invasiveness. Unexpectedly, repression of E-cadherin by PROX1 was not mediated by transcriptional inhibition. We found that PROX1 bound to miR-9-2 promoter and triggered its expression to suppress E-cadherin 3'UTR reporter activity and protein expression. Anti-miR-9 restored E-cadherin in SW620 cells, whereas precursor miR-9 inhibited E-cadherin in PROX1-knockdown cells. The miR-9 level was higher in tumor tissues with high PROX1/low E-cadherin than that of tumor tissues with low PROX1/high E-cadherin.
Our results provide mechanistic insights by which PROX1 promotes EMT and colon cancer progression. Targeting of PROX1-mediated oncogenic activity may be helpful for the treatment of colon cancer.
Prospero 同源盒 1（PROX1）已被证明在多种类型的癌症中作为肿瘤抑制因子发挥作用。然而，它促进了结肠癌的进展。本研究旨在阐明 PROX1 调节结肠癌致瘤性的潜在机制。
通过免疫组织化学染色研究 PROX1 与临床病理特征的关联。通过定量实时 PCR 检测 pri-miR-9-2 和 miR-9。细胞侵袭、黏附和基质金属蛋白酶活性测定用于研究 PROX1 介导的上皮-间充质转化（EMT）。
PROX1 在 43%（59/136）的结肠癌组织中过表达，其表达与 E-钙黏蛋白下调（P=0.00005）、肿瘤分期进展（P=0.005）和淋巴结转移（P=0.000009）相关。在 DLD-1 细胞中过表达 PROX1 导致 E-钙黏蛋白和整合素下调，并减弱细胞黏附。这些细胞表现出基质金属蛋白酶活性和侵袭能力的增加。相反，在 SW620 细胞中敲低 PROX1 恢复了 E-钙黏蛋白蛋白表达并降低了侵袭性。出乎意料的是，PROX1 对 E-钙黏蛋白的抑制不是通过转录抑制介导的。我们发现 PROX1 结合 miR-9-2 启动子并触发其表达，从而抑制 E-钙黏蛋白 3'UTR 报告基因活性和蛋白表达。抗 miR-9 在 SW620 细胞中恢复了 E-钙黏蛋白，而前体 miR-9 抑制了 PROX1 敲低细胞中的 E-钙黏蛋白。在 PROX1 高/低 E-钙黏蛋白表达的肿瘤组织中，miR-9 水平高于 PROX1 低/高 E-钙黏蛋白表达的肿瘤组织。
我们的研究结果提供了 PROX1 促进 EMT 和结肠癌进展的机制见解。靶向 PROX1 介导的致癌活性可能有助于结肠癌的治疗。
