| Aquaporin 2 (AQP2), a member of the major intrinsic protein family of water channels, predominantly resides in the principal cells of the kidney collecting duct, where it governs transepithelial water reabsorption to maintain systemic fluid and electrolyte homeostasis. It forms homotetramers with each monomer featuring six transmembrane helices and two extracellular loops that create a narrow, hourglass-shaped pore selective for water and occasionally small solutes like urea. The dominant mechanism hinges on vasopressin (AVP) binding to basolateral V2 receptors, which activates adenylyl cyclase to elevate cAMP levels, thereby stimulating protein kinase A (PKA) to phosphorylate AQP2 at Ser256 within its C-terminal tail; this triggers a cascade of actin depolymerization via RhoA inhibition and trafficking events involving Rab11-positive recycling endosomes, rapidly translocating AQP2 vesicles to the apical membrane to boost water permeability by over 100-fold. Phosphorylation at Ser261 by p90RSK counteracts this under hyperosmotic stress, while dephosphorylation by calcineurin recycles AQP2 intracellularly upon AVP withdrawal, ensuring dynamic regulation within the cAMP-PKA-AQP2 trafficking axis that integrates with prostaglandin E2 and calcium signaling for fine-tuned response to hydration status. This pathway enables antidiuresis during dehydration, concentrating urine to preserve plasma osmolality, and positions AQP2 as a prime target for researchers studying membrane protein trafficking, vasopressin signaling fidelity, or high-throughput screens for water channel modulators in renal physiology models. Dysregulation through mutations disrupting trafficking or phosphorylation impairs water conservation, leading to nephrogenic diabetes insipidus with polyuria, while upregulation contributes to hyponatremia in SIADH. |
Lane 1: Mouse kidney
