Role of cytoplasmic termini in sorting and shuttling of the aquaporin-2 water channel

Abstract

of cytoplasmic termini in sorting and shuttling of the aquaporin-2 water channel. Am J Physiol Cell Physiol 286: C372-C379, 2004. First published October 15, 2003 10.1152/ajpcell.00271.2003.-In mammals, the regulation of water homeostasis is mediated by the aquaporin-1 (AQP1) water channel, which localizes to the basolateral and apical membranes of the early nephron segment, and AQP2, which is translocated from intracellular vesicles to the apical membrane of collecting duct cells after vasopressin stimulation. Because a similar localization and regulation are observed in transfected Madin-Darby Canine Kidney (MDCK) cells, we investigated which segments of AQP2 are important for its routing to forskolin-sensitive vesicles and the apical membrane through analysis of AQP1-AQP2 chimeras. AQP1 with the entire COOH tail of AQP2 was constitutively localized in the apical membrane, whereas chimeras with shorter COOH tail segments of AQP2 were localized in the apical and basolateral membrane. AQP1 with the NH2 tail of AQP2 was constitutively localized in both plasma membranes, whereas AQP1 with the NH2 and COOH tail of AQP2 was sorted to intracellular vesicles and translocated to the apical membrane with forskolin. These data indicate that region N220-S229 is essential for localization of AQP2 in the apical membrane and that the NH2 and COOH tail of AQP2 are essential for trafficking of AQP2 to intracellular vesicles and its shuttling to and from the apical membrane. routing signals; chimera; Madin-Darby canine kidney cells; regulated trafficking TO MAINTAIN WATER AND OSMOLYTE BALANCE, the human kidney daily forms 180 l of pro-urine. The main portion of the water from the pro-urine is reabsorbed, which occurs mainly through aquaporin-1 (AQP1) and AQP2 (9, 10, 35). AQP1, responsible for 90% of the water reabsorption, is constitutively present in the apical and basolateral membrane of proximal tubules and the descending limbs of Henle (40). The fine-tuning of water reabsorption takes place in the renal collecting duct and is regulated by the antidiuretic hormone arginine vasopressin (AVP). After release of AVP by the pituitary gland and binding to its type-2 receptor (V2R) in the basolateral membrane of collecting duct principal cells, an intracellular cAMP signaling cascade is initiated, resulting in the phosphorylation of AQP2 and its redistribution from vesicles to the apical membrane. Then, driven by an osmotic gradient, collecting duct water uptake and urine concentration is initiated via AQP2 in the apical and AQP3/AQP4 in the basolateral membranes (11, 37). Removal of AVP reverses this translocation process, restoring the water-impermeable state of the apical membrane (7,23,26). A proper regulation of AQP2 sorting and translocation to the apical membrane is thus of critical importance for human water homeostasis. At present, however, it is unclear which protein segments of AQP2 are critical for this regulation.All AQPs are homotetrameric integral membrane proteins, consisting of subunits of about 30 kDa, which pas...

The phosphorylation state of serine 256 is dominant over that of serine 261 in the regulation of AQP2 trafficking in renal epithelial cells

“…Experiments using simultaneous mutations of S256 and S261 showed that the phosphorylation or dephosphorylation state of S261 does not alter the dominant effect driven by the phosphorylation and dephosphorylation state of S256 in VP-induced AQP2 trafficking. It remains possible that the effects that we have observed in our transfected cell model may not exactly mimic AQP2 trafficking in principal cells in vivo in this instance, although LLC-PK cells have proven to be a reliable predictor of the in vivo AQP2 signaling machinery in many previous studies (1,2,7,12,(21)(22)(23)(24)(25). Also, it is possible that more subtle kinetic differences in the intracellular trafficking pathway of AQP2 occur that were not detectable using the present techniques.…”

“…vasopressin; cAMP AQUAPORIN-2 (AQP2) is expressed in kidney collecting duct principal cells and has a critical role in the urinary concentrating mechanism (4,11,19,20). It is well known that phosphorylation of the serine 256 residue (S256) on the cytoplasmic COOH terminus by PKA is required for the functionally important vasopressin (VP)-induced membrane accumulation of AQP2 in VP target cells (6,14,16,18,25,26). In addition to S256, other potential phosphorylation sites in the AQP2 COOH terminus, including serine 261 (S261), were identified recently (10).…”

Noncanonical Control of Vasopressin Receptor Type 2 Signaling by Retromer and Arrestin

“…Cells were grown on filters for 5 days to be fully polarized and treated with 50 mM indomethacin overnight to lower endogenous cAMP levels (26). Culture medium was replaced with serum-and antibiotic-free DMEM for 2 h before stimulation.…”

Aquaporin 2 Promotes Cell Migration and Epithelial Morphogenesis

“…Under physiologic conditions, the trafficking of AQP2 is regulated mainly by vasopressin via a well established signaling pathway that results in the elevation of cAMP, activation of protein kinase A (PKA) and phosphorylation of AQP2. [1][2][3] In addition to regulated trafficking, AQP2 also constitutively recycles between intracellular vesicles and the cell membrane. 4,5 Critical protein/protein interactions that orchestrate the regulated and constitutive trafficking of AQP2 have been extensively investigated and include actin and microtubules, SNAREs, Rab proteins, heat shock protein 70, clathrin, and others.…”