Department of Molecular Embryology, Faculty of Medicine, Institute of Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany.
Institute of Neurobiology, Heinrich Heine University, D-40225 Düsseldorf, Germany.
Int J Mol Sci. 2022 Aug 11;23(16):8975. doi: 10.3390/ijms23168975.
Glioblastoma multiforme (GBM) is the most common and malignant brain tumour. It is characterised by transcriptionally distinct cell populations. In tumour cells, physiological pH gradients between the intracellular and extracellular compartments are reversed, compared to non-cancer cells. Intracellular pH in tumour cells is alkaline, whereas extracellular pH is acidic. Consequently, the function and/or expression of pH regulating transporters might be altered. Here, we investigated protein expression and regulation of the electrogenic sodium/bicarbonate cotransporter 1 (NBCe1) in mesenchymal (MES)-like hypoxia-dependent and -independent cells, as well as in astrocyte-like glioblastoma cells following chemical hypoxia, acidosis and elucidated putative underlying molecular pathways. Immunoblotting, immunocytochemistry, and intracellular pH recording with the H-sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein were applied. The results show NBCe1 protein abundance and active NBCe1 transport. Hypoxia upregulated NBCe1 protein and activity in MES-like hypoxia-dependent GBM cells. This effect was positively correlated with HIF-1α protein levels, was mediated by TGF-β signalling, and was prevented by extracellular acidosis. In MES-like hypoxia-dependent GBM cells, acidosis (but not hypoxia) regulated NBCe1 activity in an HIF-1α-independent manner. These results demonstrate a cell-specific adaptation of NBCe1 expression and activity to the microenvironment challenge of hypoxia and acidosis that depends on their transcriptional signature in GBM.
多形性胶质母细胞瘤（GBM）是最常见和恶性的脑肿瘤。它的特征是转录上不同的细胞群体。与非癌细胞相比，肿瘤细胞的细胞内和细胞外隔室之间的生理 pH 梯度发生逆转。肿瘤细胞内的 pH 值呈碱性，而细胞外 pH 值呈酸性。因此，pH 调节转运体的功能和/或表达可能会发生改变。在这里，我们研究了电中性钠/碳酸氢盐共转运蛋白 1（NBCe1）在间充质（MES）样缺氧依赖性和非依赖性细胞中的蛋白表达和调节，以及在化学缺氧、酸中毒后星形细胞瘤样胶质母细胞瘤细胞中的表达和调节，并阐明了潜在的分子途径。应用免疫印迹、免疫细胞化学和用 H 敏感染料 2'，7'-双（羧乙基）-5-（和-6）-羧基荧光素进行细胞内 pH 记录。结果表明 NBCe1 蛋白丰度和活性 NBCe1 转运。缺氧上调 MES 样缺氧依赖性 GBM 细胞中 NBCe1 蛋白和活性。这种效应与 HIF-1α 蛋白水平呈正相关，由 TGF-β 信号介导，并被细胞外酸中毒所阻止。在 MES 样缺氧依赖性 GBM 细胞中，酸中毒（而非缺氧）以 HIF-1α 非依赖性方式调节 NBCe1 活性。这些结果表明 NBCe1 表达和活性对缺氧和酸中毒的微环境挑战具有细胞特异性的适应性，这取决于 GBM 中的转录特征。
