Aquaporin-1 (AQP1) is a water channel protein expressed widely in vascular endothelia, where it increases cell membrane water permeability. The role of AQP1 in endothelial cell function is unknown. Here we show remarkably impaired tumour growth in AQP1-null mice after subcutaneous or intracranial tumour cell implantation, with reduced tumour vascularity and extensive necrosis. A new mechanism for the impaired angiogenesis was established from cell culture studies. Although adhesion and proliferation were similar in primary cultures of aortic endothelia from wild-type and from AQP1-null mice, cell migration was greatly impaired in AQP1-deficient cells, with abnormal vessel formation in vitro. Stable transfection of non-endothelial cells with AQP1 or with a structurally different water-selective transporter (AQP4) accelerated cell migration and wound healing in vitro. Motile AQP1-expressing cells had prominent membrane ruffles at the leading edge with polarization of AQP1 protein to lamellipodia, where rapid water fluxes occur. Our findings support a fundamental role of water channels in cell migration, which is central to diverse biological phenomena including angiogenesis, wound healing, tumour spread and organ regeneration.

Aquaporin-11 (AQP11) has been identified with unusual pore-forming NPA (asparagine-proline-alanine) boxes, but its function is unknown. We investigated its potential contribution to the kidney. Immunohistochemistry revealed that AQP11 was localized intracellularly in the proximal tubule. When AQP11 was transfected in CHO-K1 cells, it was localized in intracellular organelles. AQP11-null mice were generated; these mice exhibited vacuolization and cyst formation of the proximal tubule. AQP11-null mice were born normally but died before weaning due to advanced renal failure with polycystic kidneys, in which cysts occupied the whole cortex. Remarkably, cyst epithelia contained vacuoles. These vacuoles were present in the proximal tubules of newborn mice. In 3-week-old mice, these tubules contained multiple cysts. Primary cultured cells of the proximal tubule revealed an endosomal acidification defect in AQP11-null mice. These data demonstrate that AQP11 is essential for the proximal tubular function. AQP11-null mice are a novel model for polycystic kidney diseases and will provide a new mechanism for cystogenesis.Aquaporins (AQPs) are a family of membrane proteins that facilitate the transport of water and small solutes (8,15,21). They are distributed widely in nature from bacteria to animals. Eleven aquaporins (AQP0 to AQP10) have been identified and functionally characterized in humans. We reported the most recent AQP, AQP10 (11, 13). Their physiological importance is documented by the targeted disruption in mice (knockout mice) and by the discovery of humans and mice with nonfunctioning mutations. Of nine AQPs disrupted in mice and humans (AQP0 to AQP7 and AQP10), only AQP2-null mice die due to massive polyuria from nephrogenic diabetes insipidus (23). The milder phenotypes in AQP disruptions in general are surprising, since water is vital for organisms. Therefore, AQPs seem to be not critically essential for the survival of mammals but seem to be involved in the quality of their lives.The completion of human genome projects has revealed two more aquaporin-like genes, which we have deposited in GenBank under the names of AQPX1 and AQPX2 (9). They are renamed AQP11 and AQP12 with the approval of the Human Gene Nomenclature Committee. Rat AQP11 (AQPX1) is highly expressed in the testis and moderately expressed in the kidney, liver, and brain. On the other hand, rat AQP12 (AQPX2) is selectively expressed in the pancreas. They share similar genome structures with three exons, which are distinct from other AQPs: AQP0, AQP1, AQP2, AQP4, AQP5, and AQP6 have four exons; AQP3, AQP7, AQP8, AQP9, and AQP10 have six exons. In humans, AQP11 is mapped to chromosome 11q14 and AQP12 to chromosome 2q34-37, to which no diseases have been mapped. Moreover, we were not able to express them functionally in Xenopus oocytes. Therefore, their functions and physiological significance remain to be clarified.Previous AQPs have two highly conserved, short sequences named NPA (asparagine-proline-alanine) boxes. Each one of the NPA boxes has ...

Healing of skin wounds is a multi-step process involving the migration and proliferation of basal keratinocytes in epidermis, which strongly express the water/glycerol-transporting protein aquaporin-3 (AQP3). In this study, we show impaired skin wound healing in AQP3-deficient mice, which results from distinct defects in epidermal cell migration and proliferation. In vivo wound healing was approximately 80% complete in wild-type mice at 5 days vs approximately 50% complete in AQP3 null mice, with remarkably fewer proliferating, BrdU-positive keratinocytes. After AQP3 knock-down in keratinocyte cell cultures, which reduced cell membrane water and glycerol permeabilities, cell migration was slowed by more than twofold, with reduced lamellipodia formation at the leading edge of migrating cells. Proliferation of AQP3 knock-down keratinocytes was significantly impaired during wound repair. Mitogen-induced cell proliferation was also impaired in AQP3 deficient keratinocytes, with greatly reduced p38 MAPK activity. In mice, oral glycerol supplementation largely corrected defective wound healing and epidermal cell proliferation. Our results provide evidence for involvement of AQP3-facilitated water transport in epidermal cell migration and for AQP3-facilitated glycerol transport in epidermal cell proliferation.

The aquaporins (AQPs) are small, integralmembrane proteins that selectively transport water across cell plasma membranes. A subset of AQPs, the aquaglyceroporins, also transport glycerol. AQPs are strongly expressed in tumor cells of different origins, particularly aggressive tumors. Recent discoveries of AQP involvement in cell migration and proliferation suggest that AQPs play key roles in tumor biology. AQP1 is ubiquitously expressed in tumor vascular endothelium, and AQP1-null mice show defective tumor angiogenesis resulting from impaired endothelial cell migration. AQP-expressing cancer cells show enhanced migration in vitro and greater local tumor invasion, tumor cell extravasation, and metastases in vivo. AQP-dependent cell migration may involve AQP-facilitated water influx into lamellipodia at the front edge of migrating cells. The aquaglyceroporin AQP3, which is found in normal epidermis and becomes upregulated in basal cell carcinoma, facilitates cell proliferation in different cell types. Remarkably, AQP3-null mice are resistant to skin tumorigenesis by a mechanism that may involve reduced tumor cell glycerol metabolism and ATP generation. Together, the data suggest that AQP expression in tumor cells and tumor vessels facilitates tumor growth and spread, suggesting AQP inhibition as a novel antitumor therapy.