BACKGROUND Recent studies have shown that selenium-binding protein 1 (SELENBP1) is significantly down-regulated in a variety of solid tumors. Nevertheless, the clinical relevance of SELENBP1 in human bladder cancer has not been described in any detail, and the molecular mechanism underlying its inhibitory role in cancer cell growth is largely unknown. METHODS SELENBP1 expression levels in tumor tissues and adjacent normal tissues were evaluated using immunoblotting assay. The association of SELENBP1 expression, clinicopathological features, and clinical outcome was determined using publicly available dataset from The Cancer Genome Atlas bladder cancer (TCGA-BLCA) cohort. DNA methylation in SELENBP1 gene was assessed using online MEXPRESS tool. We generated stable SELENBP1-overexpression and their corresponding control cell lines to determine its potential effect on cell cycle and transcriptional activity of p21 by using flow cytometry and luciferase reporter assay, respectively. The dominant-negative mutant constructs, TAM67 and STAT1 Y701F, were employed to define the roles of c-Jun and STAT1 in the regulation of p21 protein. RESULTS Here, we report that the reduction of SELENBP1 is a frequent event and significantly correlates with tumor progression as well as unfavorable prognosis in human bladder cancer. By utilizing TCGA-BLCA cohort, DNA hypermethylation, especially in gene body, is shown to be likely to account for the reduction of SELENBP1 expression. However, an apparent paradox is observed in its 3'-UTR region, in which DNA methylation is positively related to SELENBP1 expression. More importantly, we verify the growth inhibitory role for SELENBP1 in human bladder cancer, and further report a novel function for SELENBP1 in transcriptionally modulating p21 expression through a p53-independent mechanism. Instead, ectopic expression of SELENBP1 pronouncedly attenuates the phosphorylation of c-Jun and STAT1, both of which are indispensable for SELENBP1-mediated transcriptional induction of p21, thereby resulting in the G0/G1 phase cell cycle arrest in bladder cancer cell. CONCLUSIONS Taken together, our findings provide clinical and molecular insights into improved understanding of the tumor suppressive role for SELENBP1 in human bladder cancer, suggesting that SELENBP1 could potentially be utilized as a prognostic biomarker as well as a therapeutic target in future cancer therapy.

中文翻译：

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硒结合蛋白1通过独立于p53的机制转录激活p21表达，其频繁减少与膀胱癌的不良预后相关。

背景技术最近的研究表明，硒结合蛋白1（SELENBP1）在各种实体瘤中均显着下调。然而，尚未详细描述SELENBP1在人膀胱癌中的临床相关性，并且其在癌细胞生长中抑制作用的分子机制在很大程度上尚不清楚。方法采用免疫印迹法检测肿瘤组织和癌旁正常组织中SELENBP1的表达水平。使用来自癌症基因组图谱膀胱癌（TCGA-BLCA）队列的公开可用数据集确定SELENBP1表达，临床病理特征和临床结果之间的关联。使用在线MEXPRESS工具评估SELENBP1基因中的DNA甲基化。我们生成了稳定的SELENBP1过表达及其相应的对照细胞系，分别通过流式细胞术和荧光素酶报告基因测定法确定其对p21细胞周期和转录活性的潜在影响。使用显性负突变体构建体TAM67和STAT1 Y701F来定义c-Jun和STAT1在调节p21蛋白中的作用。结果在这里，我们报道SELENBP1的减少是一个经常发生的事件，并且与人膀胱癌的肿瘤进展以及不良的预后显着相关。通过利用TCGA-BLCA队列，DNA高甲基化，尤其是在基因体内的DNA高甲基化，很可能解释了SELENBP1表达的降低。但是，在其3'-UTR区域发现了明显的悖论，其中DNA甲基化与SELENBP1表达呈正相关。更重要的是，我们验证了SELENBP1在人膀胱癌中的生长抑制作用，并进一步报道了SELENBP1在通过p53独立机制转录调节p21表达中的新功能。相反，异位表达SELENBP1明显减弱了c-Jun和STAT1的磷酸化，这两者对于SELENBP1介导的p21转录诱导都是必不可少的，从而导致膀胱癌细胞中G0 / G1期细胞周期停滞。结论综上所述，我们的发现为更好地了解SELENBP1在人类膀胱癌中的抑癌作用提供了临床和分子方面的见解，