AQP1 Is Up-Regulated by Hypoxia and Leads to Increased Cell Water Permeability, Motility, and Migration in Neuroblastoma

Abstract

The water channel aquaporin 1 (AQP1) has been implicated in tumor progression and metastasis. It is hypothesized that AQP1 expression can facilitate the transmembrane water transport leading to changes in cell structure that promote migration. Its impact in neuroblastoma has not been addressed so far. The objectives of this study have been to determine whether AQP1 expression in neuroblastoma is dependent on hypoxia, to demonstrate whether AQP1 is functionally relevant for migration, and to further define AQP1-dependent properties of the migrating cells. This was determined by investigating the reaction of neuroblastoma cell lines, particularly SH-SY5Y, Kelly, SH-EP Tet-21/N and SK-N-BE(2)-M17 to hypoxia, quantitating the AQP1-related water permeability by stopped-flow spectroscopy, and studying the migration-related properties of the cells in a modified transwell assay. We find that AQP1 expression in neuroblastoma cells is up-regulated by hypoxic conditions, and that increased AQP1 expression enabled the cells to form a phenotype which is associated with migratory properties and increased cell agility. This suggests that the hypoxic tumor microenvironment is the trigger for some tumor cells to transition to a migratory phenotype. We demonstrate that migrating tumor cell express elevated AQP1 levels and a hypoxic biochemical phenotype. Our experiments strongly suggest that elevated AQP1 might be a key driver in transitioning stable tumor cells to migrating tumor cells in a hypoxic microenvironment.

Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease

“…The exact mechanisms by which AQPs influence the expression of MMPs to enhance ECM degradation remain elusive, but could involve interactions with integrins. AQP1 enhanced the migration of neuroblastoma cells under hypoxic conditions [412]. AQP1 but not AQP4 accelerated migration in glioma cell lines [411], suggesting that more than water permeability alone was needed for AQP1-facilitated migration.…”

“…Various classes, including AQP1, AQP4, AQP5, and AQP9, have been found to polarize at the leading edges of migrating cells depending on cell type [67,336,[408][409][410], and might contribute to all stages of movement, with roles in polarization, protrusion, adhesion, and retraction. A single class of AQPs can support migration across diverse cell types; AQP1 for example is linked to motility in glia, epithelia, microvascular endothelia, and other cells [406][407][408]411,412].…”

“…AQP1 expression and activation in vascular endothelial cells is sensitive to multiple angiogenic factors [294,300,443,485]. For example, the aqp1 gene promoter contains a consensus HIF-1α binding motif [486]; AQP1 mRNA and protein levels are elevated under conditions of low oxygen [322,412,487,488], supporting the presumption that AQP1 activity can be regulated by the interplay of growth factors within the tumor microenvironment [489,490]. Secondly, it has been shown that AQP1 knockdown in breast adenoma mice models resulted in decreased tumor formation and microvascular density within the tumor as well as reduced lung metastasis [447].…”

“…Inhibition of AQP1 using the bumetanide-derived small molecule AqB013, shown to block AQP1 and AQP4 water channel function in Xenopus laevis oocytes, impaired angiogenesis in in vitro model systems [492]. Finally, upregulated AQP1 levels have been found in various vascularizing and metastasizing cancer types, including brain [485], breast [493], lung [494], and colorectal [495] cancers, and are associated with a poor prognosis, especially in tumor stages with increased hypoxic conditions [398,412,496,497].…”

Metastatic Esophageal Carcinoma Cells Exhibit Reduced Adhesion Strength and Enhanced Thermogenesis

“…Our own investigations in migrating neuroblastoma cells have revealed an increased expression of the water channel AQP1 that furthers migration by promoting water in- and efflux through the tumor cell membrane and facilitating restructuring of the cytoskeleton [ 38 ]. On the other hand, the inhibition of the polymerization of actin led to a reduced heat release [ 12 ].…”