Counteracting vasopressin-mediated water reabsorption by ATP, dopamine, and phorbol esters: mechanisms of action

Abstract

Water homeostasis is regulated by a wide variety of hormones. When in need for water conservation, vasopressin, released from the brain, binds renal principal cells and initiates a signaling cascade resulting in the insertion of aquaporin-2 (AQP2) water channels in the apical membrane and water reabsorption. Conversely, hormones, including extracellular purines and dopamine, antagonize AVP-induced water permeability, but their mechanism of action is largely unknown, which was investigated here. Addition of these hormones to mpkCCD cells decreased total and plasma membrane abundance of AVP-induced AQP2, partly by increasing its internalization to vesicles and lysosomal degradation. This internalization was ubiquitin dependent, because the hormones increased AQP2 ubiquitination, and the plasma membrane localization of AQP2-K270R, which cannot be monoubiquitinated, was unaffected by these hormones. Both hormones also increased AQP2 phosphorylation at S261, which followed ubiquitination, but was not essential for hormone-induced AQP2 degradation. A similar process occurs in vivo, as incubation of dDAVP-treated kidney slices with both hormones also resulted in the internalization and S261 phosphorylation of AQP2. Both hormones also reduced cAMP and AQP2 mRNA levels, suggesting an additional effect on AQP2 gene transcription. Interestingly, phorbol esters only reduced AQP2 through the first pathway. Together, our results indicate that ATP and dopamine counteract AVP-induced water permeability by increasing AQP2 degradation in lysosomes, preceded by ubiquitin-dependent internalization, and by decreasing AQP2 gene transcription by reducing the AVP-induced cAMP levels.water transport; mpkCCD cells; aquaporin-2 water channel VASOPRESSIN (AVP)-regulated maintenance of water balance in the renal collecting duct occurs via alternating cell surface expression of the water channel aquaporin-2 (AQP2) and depends on the body's need for water conservation. In states of hypernatremia and hypovolemia, vasopressin (AVP) is released into the bloodstream, interacts with its renal type 2 receptors, and initiates a signal transduction cascade (32). This includes activation of adenylate cyclase, a rise in intracellular cAMP and calcium levels, activation of PKA and its recruitment to AQP2-containing vesicles, and subsequent phosphorylation of AQP2 at Ser256 (10, 20, 35). This phosphorylation is essential for the redistribution of tetrameric AQP2 from intracellular storage vesicles to the apical plasma membrane (18). In addition, cAMP also increases AQP2 expression via phosphorylation of the cAMP-responsive element binding protein (CREB), which activates the AQP2 promoter (27, 43). Due to the increased plasma membrane expression of AQP2, water is able to pass the apical membrane passively along an osmotic gradient and enters the blood via AQP3 and AQP4 water channels, which are constitutively expressed in the basolateral membrane. Once water balance is restored, AVP levels drop and AQP2 is internalized via ubiquitination at Lys270 (19).Bes...

A Protein Kinase A–Independent Pathway Controlling Aquaporin 2 Trafficking as a Possible Cause for the Syndrome of Inappropriate Antidiuresis Associated with Polycystic Kidney Disease 1 Haploinsufficiency

“…35 Briefly, male SpragueDawley rats were anesthetized and euthanized by decapitation. Kidneys were quickly removed, and sections of approximately 0.5 mm were made and divided in four groups.…”

Cell biology of vasopressin-regulated aquaporin-2 trafficking

“…Although AVP is the major regulator of AQP2 trafficking and is the focus of this review, it must be emphasized that a variety of other molecules/hormones can influence AQP2 membrane accumulation and cellular expression, e.g., prostaglandins [87,115,130], bradykinin [107], dopamine [3], arginine/NO [4], ANP [47], oxytocin [9], and angiotensin II [56].…”

Integrin Signaling Modulates AQP2 Trafficking via Arg-Gly-Asp (RGD) Motif

“…Although membrane abundance of AQP2 is mainly under vasopressin control, it has also been shown that the cell surface expression of AQP2 might be tightly modulated by the synergic activity of various small molecules and hormones such as PGE2 [8,9], bradykinin [10], dopamine, ATP [11] and ANP [12]. Importantly, signal pathways controlled by these agonists are often associated with a profound reorganization of the actin cytoskeleton.…”