Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P41181 (collecting duct)
 5,183 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Before the identification of aquaporin (AQP) proteins, vasopressin-regulated "water channels" were identified by freeze-fracture electron microscopy as aggregates or clusters of intramembraneous particles (IMPs) on hormonally stimulated target cell membranes. In the kidney collecting duct, these IMP clusters were subsequently identified as possible sites of clathrin-coated pit formation on the plasma membrane, and a clathrin-mediated mechanism for internalization of vasopressin-sensitive water channels was suggested. Using an antibody raised against the extracellular C loop of AQP2, we now provide direct evidence that AQP2 is concentrated in clathrin-coated pits on the apical surface of collecting duct principal cells. Furthermore, by using a fracture-label technique applied to LLC-PK(1) cells expressing an AQP2-c-myc construct, we show that AQP2 is located in IMP aggregates and is concentrated in shallow membrane invaginations on the surface of forskolin-stimulated cells. We also studied the functional role of clathrin-coated pits in AQP2 trafficking by using a GTPase-deficient dynamin mutation (K44A) to inhibit clathrin-mediated endocytosis. Immunofluorescence labeling and freeze-fracture electron microscopy showed that dominant-negative dynamin 1 and dynamin 2 mutants prevent the release of clathrin-coated pits from the plasma membrane and induce an accumulation of AQP2 on the plasma membrane of AQP2-transfected cells. These data provide the first direct evidence that AQP2 is located in clathrin-coated pits and show that AQP2 recycles between the plasma membrane and intracellular vesicles via a dynamin-dependent endocytotic pathway. We propose that the IMP clusters previously associated with vasopressin action represent sites of dynamin-dependent, clathrin-mediated endocytosis in which AQP2 is concentrated before internalization.
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PMID:Aquaporin-2 localization in clathrin-coated pits: inhibition of endocytosis by dominant-negative dynamin. 1199 16

Biallelic mutations in MAPKBP1 were recently associated with late-onset cilia-independent nephronophthisis. MAPKBP1 was found at mitotic spindle poles but could not be detected at primary cilia or centrosomes. Here, by identification and characterization of novel MAPKBP1 variants, we aimed at further investigating its role in health and disease. Genetic analysis was done by exome sequencing, homozygosity mapping, and a targeted kidney gene panel while coimmunoprecipitation was used to explore wild-type and mutant protein-protein interactions. Expression of MAPKBP1 in non-ciliated HeLa and ciliated inner medullary collecting duct cells enabled co-localization studies by fluorescence microscopy. By next generation sequencing, we identified two novel homozygous MAPKBP1 splice-site variants in patients with nephronophthisis-related chronic kidney disease. Splice-site analyses revealed truncation of C-terminal coiled-coil domains and patient-derived deletion constructs lost their ability to homodimerize and heterodimerize with paralogous WDR62. While wild-type MAPKBP1 exhibited centrosomal, basal body, and microtubule association, mutant proteins lost the latter and showed reduced recruitment to cell cycle dependent centriolar structures. Wild-type and mutant proteins had no reciprocal influence upon co-expression excluding dominant negative effects. Thus, MAPKBP1 appears to be a novel microtubule-binding protein with cell cycle dependent centriolar localization. Truncation of its coiled-coil domain is enough to abrogate its dimerization and results in severely disturbed intracellular localizations. Delineating the impact of impaired dimerization on cell cycle regulation and intracellular kidney signaling may provide new insights into common mechanisms of kidney degeneration. Thus, due to milder clinical presentation, MAPKBP1-associated nephronophthisis should be considered in adult patients with otherwise unexplained chronic kidney disease.
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PMID:Novel nephronophthisis-associated variants reveal functional importance of MAPKBP1 dimerization for centriolar recruitment. 3250 65