br Acknowledgements br Introduction Water and electrolytes c
Introduction Water and electrolytes constitute an integral part of all living things, and Azithromycin governing their movements play important roles in a wide variety of physiological and/or pathophysiological processes. Given the importance of channel proteins in cancer cell proliferation, apoptosis, migration and/or invasion, these channels have been considered to be potential targets for cancer diagnosis, prognosis and therapy (Hong et al., 2015, Lang and Stournaras, 2014, Verkman et al., 2014). The channel proteins do not always operate in isolation. Evidence has suggested that some channels are not functional without an accessory subunit, such as ClC-K and barttin, Kv and its auxiliary α/β-subunit, and sodium or calcium channels and their accessory subunit (Chapman, 2005, Dolphin, 2012, Stolting et al., 2014, Tseng et al., 2007). Some studies demonstrated that aquaporins (AQPs) can regulate potassium channel activity and potassium channels show active regulatory effects on the AQPs through formation of complexes (Abu-Hamdah et al., 2004, Connors and Kofuji, 2006, Goodyear et al., 2010, Illarionova et al., 2010, Kelly et al., 2005, Soe et al., 2009), but this was not supported by all reports (Ruiz-Ederra et al., 2007, Zhang and Verkman, 2008). Lithium salts are used to treat bipolar disorders and they possess side effect such as polyuria, which appears to be associated with severe AQP-2 and AQP-3 down-regulation (Kishore and Ecelbarger, 2013, Kwon et al., 2000). Lithium could inhibit the swelling-induced chloride current (ICl,swell) reported by us (Bai et al., 2010), suggesting there may be a relationship between aquaporins and chloride channels. The molecular entity for the native volume-regulated anion channel (VRAC) is hardly confirmed. ClC-3, a member of the voltage-gated chloride channel family, shows the properties of cell cycle-dependent expression and subcellular distribution, and plays an important role in the regulation of cell proliferation, migration and apoptosis, especially in cancerous cells (Hong et al., 2015, Liu et al., 2013, Mao et al., 2012, Mao et al., 2013, Xu et al., 2014, Zhang et al., 2013a). The inducible ClC-3 gene deletion eliminating native VRAC in adult mice overwhelmingly suggested that ClC-3 is a key component of native VRAC in mammalian heart, not in the brain (Xiong et al., 2010). The controversial idea was mainly based on the finding of normal VRAC currents existing in Clcn3−/− mice (Stobrawa et al., 2001). It may be ignored that major compensatory changes in other proteins may occur in the development of survivable Clcn3−/− animals. Lastly recent evidence supported that the leucine-rich repeat-containing 8A (LRRC8A) is a main molecular determinant of VRAC currents (Qiu et al., 2014, Voss et al., 2014). However, in human retinal pigment epithelium cells, bestrophin 1 but not LRRC8A is indispensable for volume regulation (Milenkovic et al., 2015). All data show that the molecular identity of VRAC is more complex and VRAC could be formed by cell type- or tissue-specific subunit component. Nasopharyngeal carcinoma is a leading form of cancer in a few well-defined populations, including natives of southern China, Southeast Asia, the Arctic, and Middle East/North Africa (Chang and Adami, 2006). AQP-3 and ClC-3 are functionally-related integral membrane channel proteins, which could form complexes to regulate cell volume in nasopharyngeal carcinoma cells (Zhang et al., 2014). However, the mechanism is still unknown. The rapid entry of glycerol via aquaglyceroporin leads to intracellular hypertonicity, cell swelling and activation of VRAC (Best et al., 2009). In this study, the mechanism of AQP-3 influence on chloride channels was investigated by testing the effects of glycerol on chloride channels in nasopharyngeal carcinoma CNE-2Z cells.
Materials and methods