Institute of Virology, Centre of Molecular Medicine, Slovak Academy of Sciences, 845 05 Bratislava, Slovak Republic.
Oncol Rep. 2010 Mar;23(3):869-74.
Carbonic anhydrase IX (CA IX) belongs to the physiologically important enzymes which contribute to tumor physiology. Tumor-associated expression of CA IX is induced mainly due to its strong transcriptional activation via hypoxia-inducible factor 1 (HIF-1). Therefore, CA IX can serve as a surrogate marker of hypoxia and a prognostic indicator. HIF-1 is a master transcription factor that mediates essential homeostatic responses to cellular and systemic hypoxia by activating transcription of multiple genes including those encoding glycolytic enzymes and vascular endothelial growth factor. In addition to hypoxia, HIF-1alpha expression can be up-regulated by growth factors and oncogenic signals (e.g. Src oncogene). Consequently, induction of the HIF-1alpha transcription factor up-regulates target gene expression. The results from the present study suggest that Src oncogene induces CA IX expression under normoxic, as well as hypoxic conditions. Moreover, we demonstrate that Src-mediated induction of CA IX expression is critically dependent on HIF-1alpha activity. Transcriptional activity of the CA9 promoter was significantly increased by expression of v-Src or c-Src. The effect was more prominent in normoxia, most likely because of already high level of HIF-1alpha expression in hypoxia. By co-transfection with dominant-negative HIF-1alpha we confirmed that Src-induced stimulation of CA9 transcription is mediated via HIF-1alpha. Consistent with this, Src-expressing HeLa cells displayed higher levels of HIF-1alpha protein. Finally, these results indicate a novel regulatory pathway responsible for increased CA IX expression in tumor cells and define CA IX as a new down-stream target for Src oncogene.
碳酸酐酶 IX（CA IX）属于对肿瘤生理学有重要贡献的生理酶。CA IX 的肿瘤相关性表达主要是由于其通过缺氧诱导因子 1（HIF-1）的强烈转录激活而诱导的。因此，CA IX 可以作为缺氧的替代标志物和预后指标。HIF-1 是一种主要的转录因子，通过激活包括糖酵解酶和血管内皮生长因子在内的多种基因的转录，介导细胞和全身缺氧的基本稳态反应。除了缺氧之外，HIF-1alpha 的表达还可以通过生长因子和致癌信号（例如 Src 癌基因）而上调。因此，HIF-1alpha 转录因子的诱导上调靶基因的表达。本研究的结果表明，Src 癌基因在常氧和缺氧条件下诱导 CA IX 的表达。此外，我们证明 Src 介导的 CA IX 表达诱导严重依赖于 HIF-1alpha 的活性。表达 v-Src 或 c-Src 显著增加了 CA9 启动子的转录活性。在常氧条件下，效果更为明显，这很可能是由于缺氧时 HIF-1alpha 的表达水平已经很高。通过与显性负性 HIF-1alpha 共转染，我们证实 Src 诱导的 CA9 转录刺激是通过 HIF-1alpha 介导的。与此一致的是，表达 Src 的 HeLa 细胞显示出更高水平的 HIF-1alpha 蛋白。最后，这些结果表明了一种新的调节途径，负责肿瘤细胞中 CA IX 表达的增加，并将 CA IX 定义为 Src 癌基因的新下游靶标。
