(c, f, g) Merged color illustrations from the images shown ina-b, d-eandg-h, respectively. expressing AQP2 variant proteins exposed disabled phosphorylation, impaired trafficking and intracellular accumulation of AQP2-R254W protein. Notably, blocking of the endocytic pathway exhibited impairment of AQP2-R254W to achieve the cell surface. == TC21 Conclusions == Partial CNDI in the Pioglitazone hydrochloride Swedish family is caused by anAQP2variation that seems to disable the encoded AQP2-R254W protein to reach the subapical vesicle population as well as impairing its phosphorylation at S256. The AQP2-R254W protein is thus unable to reach the plasma membrane to facilitate AVP mediated urine concentration. == Electronic supplementary material == The online edition of this article (doi: 10. 1186/s12882-015-0213-3) contains supplementary material, which is available to certified users. Keywords: Aquaporin 2, Diabetes insipidus, Congenital nephrogenic diabetes insipidus, Lentivirus, Cellular trafficking, Intracellular localization == Background == Congenital nephrogenic diabetes insipidus (CNDI) is a disorder characterized by polyuria and polydipsia due to renal resistance to the antidiuretic hormone, arginine vasopressin (AVP). The majority of cases are caused by variations in theAVPR2gene encoding the renal V2 receptor or by autosomal recessively inherited variations in theAQP2gene encoding the collecting duct water channel aquaporin-2 (AQP2) [1]. AQP2 forms tetramers that are localized to sub-apical vesicles and the apical plasma membrane in kidney collecting duct principal cells [2, 3]. Upon AVP stimulation, AQP2 is phosphorylated at the C-terminal S256 by Protein Kinase A (PKA) [4], where after AQP2-containing subapical vesicles are inserted into the apical plasma membrane, facilitating AQP2 build up and thus, urine concentration. Evidence suggests that AQP2 constitutively shuttles between the plasma membrane and subapical vesicles Pioglitazone hydrochloride [5], and that the life-time in the plasma membrane is determined by phosphorylation at S256 [6, 7]. It has been shown that AQP2-S256A, which mimics constitutively non-phosphorylated AQP2, accumulates in the plasma membrane in the event that endocytosis is blocked by expressing dominant-negative dynamin-2 [8]. Thus, it seems that S256 phosphorylation shifts the balance of AQP2 recycling, facilitating AQP2 accumulation in the plasma membrane. In addition , phosphorylation at S256 on at least three out of Pioglitazone hydrochloride four monomers in the AQP2 tetramer seems to be necessary for accumulation of AQP2 in the apical membrane [911]. Defective trafficking of AQP2 in response to AVP activation is suggested because the cause of the rare cases of dominantly inherited CNDI [12, 13] and dominating inherited variations affecting the PKA consensus site are suggested to disable phosphorylation at S256 [14, 15] and consequently, disrupt the kidneys urinary concentration ability. Variant AQP2 monomers are further believed to possess a dominating negative effect on wildtype (WT) monomers resulting in altered trafficking, missorting or retention in the Golgi apparatus [13, 1618]. Of special note, the majority of variations causing dominantly inherited CNDI are associated with partial diabetes insipidus (DI), where affected subjects maintain an ability to concentrate urine in response to high levels of AVP or desamino-8-D-arginine vasopressin (dDAVP). This has led to the suggestion that functional AQP2 tetramers either in the form of WT homo-tetramers or WT-variant hetero-tetramers are created and reaches the apical plasma membrane [1, 12, 14, 15, 18]. In the present study, we determined a book g. 4807C > T variant in theAQP2gene in a Swedish family with dominant inheritance of CNDI. This variant causes substitution of arginine-254 to tryptophan (AQP2-R254W) in the C-terminal of AQP2. In order to substantiate the variation determined is causal to CNDI in the family and investigate the underlying mechanism responsible, we further investigated the cellular handling from the AQP2 protein in Madin-Darby canine kidney (MDCK) cells stably expressing AQP2-R254W. == Methods == == Clinical tests == The family history was recorded in order to determine the presence of symptoms of DI in a.