Jokilehto Terhi, Rantanen Krista, Luukkaa Marjaana, Heikkinen Pekka, Grenman Reidar, Minn Heikki, Kronqvist Pauliina, Jaakkola Panu M
Turku Centre for Biotechnology, Turku University, Finland.
Clin Cancer Res. 2006 Feb 15;12(4):1080-7. doi: 10.1158/1078-0432.CCR-05-2022.
Hypoxia in tumors is associated with poor prognosis and resistance to treatment. The outcome of hypoxia is largely regulated by the hypoxia-inducible factors (HIF-1alpha and HIF-2alpha). HIFs in turn are negatively regulated by a family of prolyl hydroxylases (PHD1-3). The PHD2 isoform is the main down-regulator of HIFs in normoxia and mild hypoxia. This study was designed to analyze the correlation of the expression and subcellular localization of PHD2 with the pathologic features of human carcinomas and HIF-1alpha expression.
The expression of PHD2 was studied from paraffin-embedded normal tissue (n = 21) and head and neck squamous cell carcinoma (HNSCC; n = 44) by immunohistochemistry. Further studies included PHD2 mRNA detection and HIF-1alpha immunohistochemistry from HNSCC specimens as well as PHD2 immunocytochemistry from HNSCC-derived cell lines.
In noncancerous tissue, PHD2 is robustly expressed by endothelial cells. In epithelium, the basal proliferating layer also shows strong expression, whereas the more differentiated epithelium shows little or no PHD2 expression. In HNSCC, PHD2 shows strongly elevated expression both at the mRNA and protein level. Moreover, PHD2 expression increases in less differentiated phenotypes and partially relocalizes from the cytoplasm into the nucleus. Endogenously high nuclear PHD2 is seen in a subset of HNSCC-derived cell lines. Finally, although most of the tumor regions with high PHD2 expression show down-regulated HIF-1alpha, regions with simultaneous HIF-1alpha and PHD2 expression could be detected.
Our results show that increased levels and nuclear translocation of the cellular oxygen sensor, PHD2, are associated with less differentiated and strongly proliferating tumors. Furthermore, they imply that even the elevated PHD2 levels are not sufficient to down-regulate HIF-1alpha in some tumors.
肿瘤中的缺氧与预后不良及治疗抵抗相关。缺氧的结果在很大程度上由缺氧诱导因子（HIF - 1α和HIF - 2α）调控。而HIF又受到脯氨酰羟化酶家族（PHD1 - 3）的负调控。PHD2亚型是常氧和轻度缺氧条件下HIF的主要下调因子。本研究旨在分析PHD2的表达及亚细胞定位与人类癌组织病理特征及HIF - 1α表达之间的相关性。
通过免疫组织化学研究石蜡包埋的正常组织（n = 21）和头颈部鳞状细胞癌（HNSCC；n = 44）中PHD2的表达。进一步研究包括对HNSCC标本进行PHD2 mRNA检测和HIF - 1α免疫组织化学，以及对HNSCC来源的细胞系进行PHD2免疫细胞化学。
在非癌组织中，PHD2在内皮细胞中强烈表达。在上皮组织中，基底增殖层也显示出强表达，而分化程度较高的上皮组织中PHD2表达很少或无表达。在HNSCC中，PHD2在mRNA和蛋白质水平均显示出强烈升高的表达。此外，PHD2表达在分化程度较低的表型中增加，并部分从细胞质重新定位到细胞核。在一部分HNSCC来源的细胞系中可观察到内源性高核PHD2。最后，尽管大多数PHD2高表达的肿瘤区域显示HIF - 1α下调，但仍可检测到同时存在HIF - 1α和PHD2表达的区域。
我们的结果表明，细胞氧传感器PHD2水平的升高和核转位与分化程度较低且增殖强烈的肿瘤相关。此外，这意味着即使PHD2水平升高，在某些肿瘤中也不足以下调HIF - 1α。
