Aquaporin (AQP) water channels are expressed in high-grade tumor cells of different tissue origins. Based on the involvement of AQPs in angiogenesis and cell migration, we tested whether AQP expression in tumor cells might enhance their migration and metastatic potential. Transfection of B16F10 and 4T1 tumor cells with AQP1 did not affect their appearance, size, growth, or substrate adherence but increased their plasma membrane osmotic water permeability by 5- to 10-fold. In vitro analysis of cell migration by transwell assay, wound healing and video microscopy showed a 2- to 3-fold accelerated migration of the AQP1-expressing tumor cells compared to control cells. In mice, AQP1 expression increased tumor cell extravasation by >1.5-fold as quantified by counting tumor cells in lung at 6 h after tail vein injection of a mixture of fluorescently tagged AQP1-expressing and control tumor cells. AQP1 expression also increased by 3-fold the number of lung metastases 14 days after tail vein injection of tumor cells, with alveolar wall infiltration seen with AQP1-expressing tumor cells. Our results provide evidence for AQP-facilitated tumor cell migration and spread, suggesting a novel function for AQP expression in high-grade tumors. AQP inhibition may thus reduce the metastatic potential of some tumors.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel cause cystic fibrosis. The ⌬F508 mutation produces defects in channel gating and cellular processing, whereas the G551D mutation produces primarily a gating defect. To identify correctors of gating, 50,000 diverse small molecules were screened at 2.5 M (with forskolin, 20 M) by an iodide uptake assay in epithelial cells coexpressing ⌬F508-CFTR and a fluorescent halide indicator (yellow fluorescent protein-H148Q/I152L) after ⌬F508-CFTR rescue by 24-h culture at 27°C. Secondary analysis and testing of Ͼ1000 structural analogs yielded two novel classes of correctors of defective ⌬F508-CFTR gating ("potentiators") with nanomolar potency that were active in human ⌬F508 and G551D cells. The most potent compound of the phenylglycine class, 2-[(2-1H-indol-3-yl-acetyl)-methylamino]-N-(4-isopropylphenyl)-2-phenylacetamide, reversibly activated ⌬F508-

Water channel aquaporin 5 (AQP5) is highly expressed at the apical membrane of alveolar type I epithelial cells and confers high osmotic water permeability. AQP5 is also expressed in lung cancer tissue. Previous studies showed there was an up-regulation of AQP5 expression in cancer tissue compared to surrounding normal tissue. In addition, expression of AQP5 in lung cancer tissue was associated with poor prognosis. Herein, we tested the role of AQP5 in lung cancer oncogenesis and development. Lung cancer cells with different expression of AQP5 were used to study cell proliferation and migration, two important parameters for tumour cell biology. We found enhanced proliferation and migration potential in cancer cells with high AQP5 expression, while reduced proliferation and metastasis potential in cancer cells with low AQP5 expression. Oncogene analysis showed significantly increased PCNA and c-myc expression in AQP5 transfected cells. AQP5 transfected cells also showed significant increased MUC5AC mucin expression, which might contribute to the enhanced metastasis potential of lung cancer. AQP5 overexpression resulted in enhanced activation of the epidermal growth factor receptor (EGFR), extracellular receptor kinase (ERK1/2), and p38 mitogen-activated protein kinase (p38 MAPK) pathway in cancer cells. Moreover, deletion of AQP5 demonstrated decreased activation of the EGFR/ERK/p38 MAPK pathway in AQP5 knockout mice lungs, while deletion of AQP1 or AQP3 did not exhibit significant changes on activation of the EGFR/ERK/p38 MAPK pathway in lung tissue. In conclusion, our results provide evidence for AQP5-facilitated lung cancer cell proliferation and migration, possibly through activation of the EGFR/ERK/p38 MAPK signalling pathway, but why AQP5 but not other aquaporin expression affects the EGFR/ERK/p38 MAPK pathway still needs further exploration.