Department of Biological Sciences, Oakland University, Rochester, MI, 48309, USA.
Department of Medical Laboratory and Biotechnology, Chung Shan Medical University, Taichung, Taiwan.
Biometals. 2017 Oct;30(5):747-755. doi: 10.1007/s10534-017-0042-x. Epub 2017 Aug 10.
AQP9 is an aquaglyceroporin with a very broad substrate spectrum. In addition to its orthodox nutrient substrates, AQP9 also transports multiple neutral and ionic arsenic species including arsenic trioxide, monomethylarsenous acid (MAs) and dimethylarsenic acid (DMA). Here we discovered a new group of AQP9 substrates which includes two clinical relevant selenium species. We showed that AQP9 efficiently transports monomethylselenic acid (MSeA) with a preference for acidic pH, which has been demonstrated in Xenopus laevis oocyte following the overexpression of human AQP9. Specific inhibitors that dissipate transmembrane proton potential or change the transmembrane pH gradient, such as FCCP, valinomycin and nigericin did not significantly inhibit MSeA uptake, suggesting MSeA transport is not proton coupled. AQP9 was also found to transport ionic selenite and lactate, with much less efficiency compared with MSeA uptake. Selenite and lactate uptake via AQP9 is pH dependent and inhibited by FCCP and nigericin, but not valinomycin. The selenite and lactate uptake via AQP9 can be inhibited by different lactate analogs, indicating that their translocation share similar mechanisms. AQP9 transport of MSeA, selenite and lactate is all inhibited by a previously identified AQP9 inhibitor, phloretin, and the AQP9 substrate arsenite (As). These newly identified AQP9 selenium substrates imply that AQP9 play a significant role in MSeA uptake and possibly selenite uptake involved in cancer therapy under specific microenvironments.
水通道蛋白 9（AQP9）是一种具有非常广泛底物谱的水甘油通道蛋白。除了其正统的营养底物外，AQP9 还转运多种中性和离子砷物种，包括三氧化二砷、一甲基砷酸（MMA）和二甲基砷酸（DMA）。在这里，我们发现了一组新的 AQP9 底物，其中包括两种临床相关的硒物种。我们表明，AQP9 能够有效地转运一甲基硒酸（MSeA），并偏爱酸性 pH 值，这在人 AQP9 过表达的非洲爪蟾卵母细胞中得到了证明。消耗跨膜质子势或改变跨膜 pH 梯度的特定抑制剂，如 FCCP、缬氨霉素和尼可霉素，并没有显著抑制 MSeA 的摄取，这表明 MSeA 转运不是质子偶联的。AQP9 也被发现转运离子亚硒酸盐和乳酸盐，但与 MSeA 摄取相比效率要低得多。亚硒酸盐和乳酸盐通过 AQP9 的摄取依赖于 pH 值，并被 FCCP 和尼可霉素抑制，但不受缬氨霉素抑制。通过 AQP9 摄取的亚硒酸盐和乳酸盐可被不同的乳酸类似物抑制，表明它们的转运机制相似。先前鉴定的 AQP9 抑制剂根皮苷以及 AQP9 底物亚砷酸盐（As）均能抑制 MSeA、亚硒酸盐和乳酸盐的 AQP9 转运。这些新鉴定的 AQP9 硒底物表明，AQP9 在特定的微环境中可能在 MSeA 的摄取和可能的亚硒酸盐摄取中发挥重要作用。
