Luu Van-Duc, Boysen Gunther, Struckmann Kirsten, Casagrande Silvia, von Teichman Adriana, Wild Peter J, Sulser Tullio, Schraml Peter, Moch Holger
Department of Pathology, Institute of Surgical Pathology, University Hospital Zurich, Zurich, Switzerland.
Clin Cancer Res. 2009 May 15;15(10):3297-304. doi: 10.1158/1078-0432.CCR-08-2779. Epub 2009 Apr 28.
The paired box gene 2, PAX2, encodes for a transcription factor that is up-regulated during nephrogenesis and becomes silenced in mature epithelium of the glomeruli, the proximal, and distal tubules. Reactivation of PAX2 has been frequently observed in clear cell renal cell carcinoma (ccRCC), a tumor type characterized by loss of von Hippel-Lindau (VHL) tumor suppressor function. The regulation of PAX2 expression in ccRCC is unknown.
We applied reporter gene assays to investigate PAX2 promoter regulation. Furthermore, PAX2 expression was determined in ccRCC cell lines under normoxic and hypoxic condition in a VHL wild-type and mutated background. PAX2 expression was also assessed in 831 human ccRCC and correlated with hypoxia-inducible factor alpha (HIFalpha) and clinical parameters.
Here, we show that both loss of VHL protein (pVHL) function and hypoxia leads to strong PAX2 reexpression. Using luciferase reporter gene assays, no induction was obtained in spite of six hypoxia response element motifs identified in the promoter of PAX2. Comprehensive immunohistochemical analyses showed significant correlations between PAX2, HIF1alpha, and HIF2alpha-target CCND1 expression patterns in ccRCC patients. Notably, PAX2 expression was highly associated with early-stage, well-differentiated ccRCC and, consequently, better clinical outcome (P < 0.0001 each). Additional analyses indicated that PAX2 repressor WT1 and cancer-linked hypomethylation are not important for transcriptional regulation of PAX2 in ccRCC.
We conclude that in ccRCC, PAX2 reactivation is driven by HIF-dependent mechanisms following pVHL loss.
配对盒基因2（PAX2）编码一种转录因子，该转录因子在肾发生过程中上调，并在肾小球、近端和远端小管的成熟上皮细胞中沉默。PAX2的重新激活在透明细胞肾细胞癌（ccRCC）中经常被观察到，ccRCC是一种以冯·希佩尔-林道（VHL）肿瘤抑制功能丧失为特征的肿瘤类型。ccRCC中PAX2表达的调控尚不清楚。
我们应用报告基因检测来研究PAX2启动子调控。此外，在VHL野生型和突变背景下，在常氧和低氧条件下测定ccRCC细胞系中的PAX2表达。还评估了831例人类ccRCC中的PAX2表达，并将其与缺氧诱导因子α（HIFα）和临床参数相关联。
在此，我们表明VHL蛋白（pVHL）功能丧失和缺氧均导致PAX2强烈重新表达。使用荧光素酶报告基因检测，尽管在PAX2启动子中鉴定出六个缺氧反应元件基序，但未获得诱导。全面的免疫组织化学分析显示，ccRCC患者中PAX2、HIF1α和HIF2α靶标CCND1表达模式之间存在显著相关性。值得注意的是，PAX2表达与早期、高分化的ccRCC高度相关，因此临床结果更好（每项P<0.0001）。进一步分析表明，PAX2阻遏物WT1和癌症相关的低甲基化对ccRCC中PAX2的转录调控并不重要。
我们得出结论，在ccRCC中，PAX2的重新激活是由pVHL缺失后HIF依赖性机制驱动的。
