Conformational changes in the Niemann-Pick type C1 protein NCR1 drive sterol translocation.

The membrane protein Niemann-Pick type C1 (NPC1, named NCR1 in yeast) is central to sterol homeostasis in eukaryotes. NCR1 is localized to the vacuolar membrane, where it is suggested to carry sterols across the protective glycocalyx and deposit them into the vacuolar membrane. However, documentation of a vacuolar glycocalyx in fungi is lacking, and the mechanism for sterol translocation has remained unclear.

Diabetic Foot Assessment using Skin Impedance in a Custom Made Sensor-sock.

Diabetic peripheral neuropathy (DPN) may lead to several changes in the skin, and some of these may influence the skin impedance spectrum. In the present study we have developed a prototype solution for skin impedance spectroscopy at selected skin sites (big toe pulp, heel and toe ball) that was tested in a pilot study on five patients with DPN and five healthy controls. At the big toe, most of the controls had markedly lower impedance than the DPN group, especially in the range of 1-100 kHz.

A Vasopressin-Induced Change in Prostaglandin Receptor Subtype Expression Explains the Differential Effect of PGE on AQP2 Expression.

Arginine vasopressin (AVP) stimulates the concentration of renal urine by increasing the principal cell expression of aquaporin-2 (AQP2) water channels. Prostaglandin E (PGE) and prostaglandin (PGF) increase the water absorption of the principal cell without AVP, but PGE decreases it in the presence of AVP. The underlying mechanism of this paradoxical response was investigated here.

Sterol uptake by the NPC system in eukaryotes: a Saccharomyces cerevisiae perspective.

Sterols are an essential component of membranes in all eukaryotic cells and the precursor of multiple indispensable cellular metabolites. After endocytotic uptake, sterols are integrated into the lysosomal membrane by the Niemann-Pick type C (NPC) system before redistribution to other membranes. The process is driven by two proteins that, together, compose the NPC system: the lysosomal sterol shuttle protein NPC2 and the membrane protein NPC1 (named NCR1 in fungi), which integrates sterols into the lysosomal membrane.

Aquaporin 2 regulation: implications for water balance and polycystic kidney diseases.

Targeting the collecting duct water channel aquaporin 2 (AQP2) to the plasma membrane is essential for the maintenance of mammalian water homeostasis. The vasopressin V2 receptor (V2R), which is a G protein-coupled receptor that increases intracellular cAMP levels, has a major role in this targeting process. Although a rise in cAMP levels and activation of protein kinase A are involved in facilitating the actions of V2R, studies in knockout mice and cell models have suggested that cAMP signalling pathways are not an absolute requirement for V2R-mediated AQP2 trafficking to the plasma membrane.

Bioimpedance and NIR for Non-invasive Assessment of Blood Glucose.

Sixteen volunteers each drank 700 ml sugar-containing soft drink during two successive periods and the blood sugar was measured at 10 min intervals together with electrical impedance spectroscopy and near infrared spectroscopy (NIR). A maximum correlation of 0.46 was found for the electrical measurements but no clear separation between low and high blood glucose levels were found in the NIR measurements.

Rapid Aldosterone-Mediated Signaling in the DCT Increases Activity of the Thiazide-Sensitive NaCl Cotransporter.

Background: The NaCl cotransporter NCC in the kidney distal convoluted tubule (DCT) regulates urinary NaCl excretion and BP. Aldosterone increases NaCl reabsorption NCC over the long-term by altering gene expression. But the acute effects of aldosterone in the DCT are less well understood.

Distinct Roles of Extracellular Domains in the Epstein-Barr Virus-Encoded BILF1 Receptor for Signaling and Major Histocompatibility Complex Class I Downregulation.

The Epstein-Barr virus (EBV) BILF1 gene encodes a constitutively active G protein-coupled receptor (GPCR) that downregulates major histocompatibility complex (MHC) class I and induces signaling-dependent tumorigenesis. Different BILF1 homologs display highly conserved extracellular loops (ECLs) including the conserved cysteine residues involved in disulfide bridges present in class A GPCRs (GPCR bridge between transmembrane helix 3 [TM-3] and ECL-2) and in chemokine receptors (CKR bridge between the N terminus and ECL-3). In order to investigate the roles of the conserved residues in the receptor functions, 25 mutations were created in the extracellular domains.

Aquaporin-2 membrane targeting: still a conundrum.

The targeting of the water channel aquaporin-2 (AQP2) to the apical plasma membrane of kidney collecting duct principal cells is regulated mainly by the antidiuretic peptide hormone arginine vasopressin (AVP). This process is of crucial importance for the maintenance of body water homeostasis. In this brief review we assess the role of cyclic adenosine monophosphate (cAMP) and discuss the emerging concept that type 2 AVP receptor (V2R)-mediated AQP2 trafficking is cAMP-independent.

The vasopressin type 2 receptor and prostaglandin receptors EP2 and EP4 can increase aquaporin-2 plasma membrane targeting through a cAMP-independent pathway.

Apical membrane targeting of the collecting duct water channel aquaporin-2 (AQP2) is essential for body water balance. As this event is regulated by Gs coupled 7-transmembrane receptors such as the vasopressin type 2 receptor (V2R) and the prostanoid receptors EP2 and EP4, it is believed to be cAMP dependent. However, on the basis of recent reports, it was hypothesized in the current study that increased cAMP levels are not necessary for AQP2 membrane targeting.

AQP4 plasma membrane trafficking or channel gating is not significantly modulated by phosphorylation at COOH-terminal serine residues.

Aquaporin 4 (AQP4) is the predominant water channel in the mammalian brain and is mainly expressed in the perivascular glial endfeet at the brain-blood interface. AQP4 serves as a water entry site during brain edema formation, and regulation of AQP4 may therefore be of therapeutic interest. Phosphorylation of aquaporins can regulate plasma membrane localization and, possibly, the unit water permeability via gating of the AQP channel itself.

Is there a role for PGE2 in urinary concentration?

Prostanoids are prominent, yet complex, components in the maintenance of body water homeostasis. Recent functional and molecular studies have revealed that the local lipid mediator PGE2 is involved both in water excretion and absorption. The biologic actions of PGE2 are exerted through four different G-protein-coupled receptors; designated EP1-4, which couple to separate intracellular signaling pathways.

Vasopressin-independent targeting of aquaporin-2 by selective E-prostanoid receptor agonists alleviates nephrogenic diabetes insipidus.

In the kidney, the actions of vasopressin on its type-2 receptor (V2R) induce increased water reabsorption alongside polyphosphorylation and membrane targeting of the water channel aquaporin-2 (AQP2). Loss-of-function mutations in the V2R cause X-linked nephrogenic diabetes insipidus. Treatment of this condition would require bypassing the V2R to increase AQP2 membrane targeting, but currently no specific pharmacological therapy is available.

Regulation of the water channel aquaporin-2 by posttranslational modification.

The cellular functions of many eukaryotic membrane proteins, including the vasopressin-regulated water channel aquaporin-2 (AQP2), are regulated by posttranslational modifications. In this article, we discuss the experimental discoveries that have advanced our understanding of how posttranslational modifications affect AQP2 function, especially as they relate to the role of AQP2 in the kidney. We review the most recent data demonstrating that glycosylation and, in particular, phosphorylation and ubiquitination are mechanisms that regulate AQP2 activity, subcellular sorting and distribution, degradation, and protein interactions.

Rapid and segmental specific dysregulation of AQP2, S256-pAQP2 and renal sodium transporters in rats with LPS-induced endotoxaemia.

Background: Acute renal failure (ARF) is a frequent complication of sepsis. Characteristics of ARF in sepsis are impaired urinary concentration, increased natriuresis and decreased glomerular filtration rate (GFR), in which inducible nitric oxide synthase (iNOS) has been revealed to play a role. Aims.

Long-term aldosterone treatment induces decreased apical but increased basolateral expression of AQP2 in CCD of rat kidney.

The purpose of the present studies was to determine the effects of high-dose aldosterone and dDAVP treatment on renal aquaporin-2 (AQP2) regulation and urinary concentration. Rats were treated for 6 days with either vehicle (CON; n = 8), dDAVP (0.5 ng/h, dDAVP, n = 10), aldosterone (Aldo, 150 microg/day, n = 10) or combined dDAVP and aldosterone treatment (dDAVP+Aldo, n = 10) and had free access to water with a fixed food intake.

The requirement of localized, CR2-mediated, alternative pathway activation of complement for covalent deposition of C3 fragments on normal B cells.

We have shown previously that normal B cells share, with Epstein-Barr virus-transformed and malignant B cells, the ability to activate the alternative pathway (AP) of complement in vitro, resulting in the deposition of C3 fragments on the cell surface. Complement receptor type 2 (CR2, CD21) has been implicated directly as the site for formation of an AP convertase, which provides nascent C3b for deposition at secondary sites on the B-cell surface. In the present study, we have examined C3 fragment deposition in vitro in more detail by (1) assessing the importance of locally generated C3b for the deposition process, (2) investigating whether CR2 is the sole requirement for conferring AP activation capacity on a cell, and (3) determining whether CR2's function, as an AP activator, has different structural requirements from ligand binding.

A comparative study of normal B cells and the EBV-positive Burkitt's lymphoma cell line, Raji, as activators of the complement system.

Contradictory reports regarding the ability of complement receptor type 2 (CR2,CD21) on normal B cells to activate complement (C') via the alternative pathway (AP), prompted us to compare the performance of human peripheral blood B cells and the Epstein-Barr virus-positive Burkitt's lymphoma cell line, Raji (a well characterized AP activator) by using flow cytometry. Measured in terms of the membrane deposition of C3 fragments per cell, Raji cells were significantly (6- to 26-fold) more effective as complement activators than were normal B cells. Raji cells were also found to express approximately four to five times as many CR2 as normal B cells.

Stripping of the distal ureter in association with nephroureterectomy. Evaluation of the method.

Nephroureterectomy is the standard treatment for transitional cell tumours of the renal pelvis. A single-incision surgical technique with use of a vein stripper to remove the distal ureter is evaluated. The method proved to be safe.