Ketchem CJ, Khundmiri SJ, Gaweda AE, Murray R, Clark BJ, Weinman EJ, Lederer ED. Role of Na ϩ /H ϩ exchanger regulatory factor 1 in forward trafficking of the type IIa Na ϩ -Pi cotransporter. Am J Physiol Renal Physiol 309: F109 -F119, 2015. First published May 20, 2015 doi:10.1152 doi:10. /ajprenal.00133.2015 ϩ /H ϩ exchanger regulatory factor (NHERF1) plays a critical role in the renal transport of phosphate by binding to Na ϩ -Pi cotransporter (NpT2a) in the proximal tubule. While the association between NpT2a and NHERF1 in the apical membrane is known, the role of NHERF1 to regulate the trafficking of NpT2a has not been studied. To address this question, we performed cell fractionation by sucrose gradient centrifugation in opossum kidney (OK) cells placed in low-P i medium to stimulate forward trafficking of NpT2a. Immunoblot analysis demonstrated expression of NpT2a and NHERF1 in the endoplasmic reticulum (ER)/Golgi. Coimmunoprecipitation demonstrated a NpT2a-NHERF1 interaction in the ER/Golgi. Low-P i medium for 4 and 8 h triggered a decrease in NHERF1 in the plasma membrane with a corresponding increase in the ER/Golgi. Time-lapse total internal reflection fluorescence imaging of OK cells placed in low-P i medium, paired with particle tracking and mean square displacement analysis, indicated active directed movement of NHERF1 at early and late time points, whereas NpT2a showed active movement only at later times. Silence of NHERF1 in OK cells expressing green fluorescent protein (GFP)-NpT2a resulted in an intracellular accumulation of GFPNpT2a. Transfection with GFP-labeled COOH-terminal (TRL) PDZbinding motif deleted or wild-type NpT2a in OK cells followed by cell fractionation and immunoprecipitation confirmed that the interaction between NpT2a and NHERF1 was dependent on the TRL motif of NpT2a. We conclude that appropriate trafficking of NpT2a to the plasma membrane is dependent on the initial association between NpT2a and NHERF1 through the COOH-terminal TRL motif of NpT2a in the ER/Golgi and requires redistribution of NHERF1 to the ER/Golgi. endoplasmic reticulum/Golgi; Na ϩ /H ϩ exchanger regulatory factor 1; sodium phosphate cotransporter 2a; plasma membrane; trafficking DESPITE THE IMPORTANCE of Na ϩ -P i cotransporter (NpT2a) in the regulation of total body phosphate homeostasis, our understanding of the factors regulating the apical membrane expression of this transporter remains incomplete. Major physiological regulators of NpT2a expression include parathyroid hormone (PTH), dopamine, fibroblast growth factor-23, and high-phosphate diet, which decrease apical membrane expression by stimulation of endocytosis and degradation of NpT2a as well as decreased mRNA expression (40). A low-phosphate diet has the opposite effect, stimulating insertion of NpT2a into the apical membrane and inhibiting endocytosis (22, 31). Thus, the regulation of the protein is dynamic and responsive to multiple physiological regulatory mechanisms. NpT2a is an intrinsic membrane protein for which hydropathy analysis predi...

Our laboratory has recently demonstrated that low concentrations of ouabain increase blood pressure in rats associated with stimulation of Na-K ATPase activity and activation of the Src signaling cascade in NHE1-dependent manner. Proteomic analysis of human kidney proximal tubule cells (HKC11) suggested that the Angiotensin II type 1 receptor (AT1R) as an ouabain-associating protein. We hypothesize that ouabain-induced stimulation of Na-K ATPase activity is mediated through AT1R. To test this hypothesis, we examined the effect of ouabain on renal cell angiotensin II production, the effect of AT1R inhibition on ouabain-stimulated NKA activity, and the effect of ouabain on NKA-AT1R association. Ouabain increased plasma angiotensin II levels in rats treated with ouabain (1 μg/kg body wt./day) for 9 days and increased angiotensin II levels in cell culture media after 24 h treatment with ouabain in human (HKC11), mouse (MRPT), canine (MDCK) kidney cells, and human adrenal cells. Ouabain 10 pM stimulated NKA-mediated 86Rb uptake and phosphorylation of EGFR, Src, and ERK1/2. These effects were prevented by the AT1R receptor blocker candesartan. FRET and TIRF microscopy using Bodipy-labeled ouabain and mCherry-NKA or mCherry-AT1R demonstrated association of ouabain with AT1R and NKA. Further our FRET and TIRF studies demonstrated increased association between AT1R and NKA upon treatment with low dose ouabain. We conclude that ouabain stimulates NKA in renal proximal tubule cells through an angiotensin/AT1R-dependent mechanism and that this pathway contributes to cardiac glycoside associated hypertension.

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Summary No approved medication exists for the treatment of eosinophilic esophagitis (EoE) in the United States, which forces patients to utilize off-label drugs and/or create their own formulations. We assessed the efficacy of a standardized compounded fluticasone suspension. To do this, we performed a retrospective cohort study identifying all EoE patients treated with compounded fluticasone. Compounded fluticasone was prescribed during routine clinical care and dispensed by a specialty compounding pharmacy. Clinical data were extracted from medical records. Outcomes (symptomatic, endoscopic, and histologic) were assessed after the initial and last compounded fluticasone treatment in our system. There were 27 included patients (mean age 34.2; 67% male; 96% white) treated for a mean length of 5.4 ± 4.4 months. The majority (89%) previously utilized dietary elimination or topical corticosteroids, and many (75%) had primary non-response or secondary loss of response to these treatments. After starting compounded fluticasone, symptoms and endoscopic findings improved [dysphagia (89 vs. 56%, P = 0.005), food impaction (59 vs. 4%, P = 0.003), heartburn (26 vs. 4%, P = 0.01), chest pain (26 vs. 8%, P = 0.05), white plaques (63 vs. 32%; P = 0.005), furrows (81 vs. 60%; P = 0.06), and edema (15 vs. 4%; P = 0.16)]. The median of the peak eosinophil counts decreased from 52 to 37 eos/hpf (P = 0.10) and 35% of patients achieved <15 eos/hpf. In conclusion, compounded fluticasone provided a significant improvement in symptoms and endoscopic findings, with more than a third achieving histologic response in a treatment refractory EoE population. Compounded fluticasone should be considered as an EoE management option.