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Development of cytosolic hypoxia and hypoxia-inducible factor stabilization are facilitated by aquaporin-1 expression

Laboratorio de Investigaciones Biomédicas, Departamento de Fisiología Médica y Biofísica, Hospital Universitario Virgen del Rocío, Universidad de Sevilla, Sevilla, 41013 Spain.
Journal of Biological Chemistry (Impact Factor: 4.57). 11/2007; 282(41):30207-15. DOI: 10.1074/jbc.M702639200
Source: PubMed

ABSTRACT O(2) is essential for aerobic life, and the classic view is that it diffuses freely across the plasma membrane. However, measurements of O(2) permeability of lipid bilayers have indicated that it is much lower than previously thought, and therefore, the existence of membrane O(2) channels has been suggested. We hypothesized that, besides its role as a water channel, aquaporin-1 (AQP-1) could also work as an O(2) transporter, because this transmembrane protein appears to be CO(2)-permeable and is highly expressed in cells with rapid O(2) turnover (erythrocytes and microvessel endothelium). Here we show that in mammalian cells overexpressing AQP-1 and exposed to hypoxia, the loss of cytosolic O(2), as well as stabilization of the O(2)-dependent hypoxia-inducible transcription factor and expression of its target genes, is accelerated. In normoxic endothelial cells, knocking down AQP-1 produces induction of hypoxia-inducible genes. Moreover, lung AQP-1 is markedly up-regulated in animals exposed to hypoxia. These data suggest that AQP-1 has O(2) permeability and thus could facilitate O(2) diffusion across the cell membrane.

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    • "The resuspended pellet was left on ice 5 min, vortex, and then centrifuged at 16,000g for 15 min at 4°C, and extracted proteins remain in the supernatant. Protein concentration was analyzed with the Bradford method (BioRad Protein Assay, BioRad, Berkeley, CA) and kept at –20°C until Western blot assay (Echevarría et al., 2007). Afterwards, 20–40 mg of whole-cell extracts were resolved by SDS–PAGE (10%) for AQP3 and Cyclin A, B1, D1, and E. After electrophoresis, proteins were transferred into PVDF membranes (Hybond-P, Amersham Biosciences, Pittsburgh, PA) using a Novex apparatus (Novel Experimental Technology, San Diego, CA). "
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    • "The aquaporins that have been identified demonstrate tissue-specific localization and membranes that express aquaporins are more water permeable than membranes lacking aquaporins (King and Agre 1996; Saadoun et al. 2005; Yang et al. 2001). AQP1 is highly expressed in microvascular endothelia and has been shown to accelerate cytosolic hypoxia and to regulate hypoxiainducible genes (Echevarria et al. 2007). Although mice lacking AQP1 show decreased pulmonary vascular permeability and are not able to create a hypertonic renal medullary interstitium to regulate urine concentration, no clinical symptoms have yet been identified as a consequence of AQP1 deficiency (King and Agre 1996; Ma et al. 1998; Umenishi and Schrier 2003; Verkman 2008). "
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