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PubMed1997

The endoplasmic reticulum can act as a functional Ca2+ store in all subcellular regions of the pancreatic acinar cell.

Stimulation of pancreatic acinar cells raises [Ca2+]i via Ca2+ release from inositol-1,4,5-trisphosphate (InsP3)-sensitive intracellular Ca2+ stores, generally considered to reside within the endoplasmic reticulum (ER). However, with physiological doses of cholinergic agonists, the [Ca2+]i increase is localized to the apical (secretory) pole of the cell, leading to suggestions that zymogen (secretory) granules themselves may constitute an InsP3-sensitive Ca2+ store responsible for localized Ca2+ release. We have therefore re-investigated whether the ER in pancreatic acinar cells is capable of acting as a functional Ca2+ store in all, or only some, cellular regions. In streptolysin O-permeabilized cells, the ER accumulated up to 25 mmol of 45Ca2+ per liter ER volume by an ATP-dependent, thapsigargin-sensitive, process. This tracer Ca2+ uptake was dependent on ambient (loading) [Ca2+], as was the intra-ER free [Ca2+], assessed by imaging the fluorescence of Magfura-2 within the Ca2+ stores. Comparison of free and total intra-ER [Ca2+] indicated that 200-300 Ca2+ ions are bound within the ER lumen for every Ca2+ ion remaining free. Subcellular analysis showed that ER stores in all regions of the permeabilized cell took up Ca2+ at loading [Ca2+] between 60 nM and 1 microM. Thapsigargin released Ca2+ from stores in all cellular regions, as did InsP3. Immunofluorescence with antibodies against sarco(endo)plasmic reticulum-2b type Ca2+,Mg2+-ATPase or calreticulin confirmed that ER Ca2+ stores were present throughout the cytoplasm. In summary, these results clearly show that the endoplasmic reticulum can act as a functional Ca2+ store in all regions of the acinar cell, including the apical pole.

Animals↗
PubMed1998

Sarcolipin regulates the activity of SERCA1, the fast-twitch skeletal muscle sarcoplasmic reticulum Ca2+-ATPase.

The 31-amino acid proteolipid, sarcolipin (SLN), is associated with the fast-twitch skeletal muscle sarcoplasmic reticulum Ca2+-ATPase (SERCA1). Constructs of human and rabbit SLN and of rabbit SLN with the FLAG epitope at its N terminus (NF-SLN) or its C terminus (SLN-FC) were coexpressed with SERCA1 in HEK-293 T-cells. Immunohistochemistry was used to demonstrate colocalization of NF-SLN and SERCA1 in the endoplasmic reticulum membrane and to demonstrate the cytosolic orientation of the N terminus of SLN. Coexpression of native rabbit SLN or NF-SLN with SERCA1 decreased the apparent affinity of SERCA1 for Ca2+ but stimulated maximal Ca2+ uptake rates (Vmax). The N terminus of SLN is not well conserved among species, and the addition of an N-terminal FLAG epitope did not alter SLN function. Anti-FLAG antibody reversed both the inhibition of Ca2+ uptake by NF-SLN at low Ca2+ concentrations and the stimulatory effect of NF-SLN on Vmax. Addition of the FLAG epitope to the highly conserved C terminus decreased the apparent affinity of SERCA1 for Ca2+ relative to native SLN and decreased Vmax significantly. Mutations in the C-terminal domain showed that this sequence is critical for SLN function. Mutational analysis of the transmembrane helix, together with the additive regulatory effects of coexpression of both SLN and phospholamban (PLN) with SERCA1, provided evidence for different mechanisms of interaction of SLN and PLN with SERCA molecules. Ca2+ uptake rates in sarcoplasmic reticulum vesicles, isolated from rabbit fast-twitch muscle (tibialis anterior) subjected to chronic low frequency stimulation, were reduced by approximately 40% in 3- and 4-day stimulated muscle, with a marginal increase in apparent affinity of SERCA1 for Ca2+. SERCA1 mRNA and protein levels were unaltered after stimulation. In contrast, SLN mRNA was decreased by 15%, and SLN protein was reduced by 40%. Reduced SLN expression could explain the decrease in SERCA1 activity observed in these muscles and might represent an early functional adaptation to chronic low frequency stimulation.

Amino Acid Sequence↗
PubMed1998

Dimerization of the human MUC2 mucin in the endoplasmic reticulum is followed by a N-glycosylation-dependent transfer of the mono- and dimers to the Golgi apparatus.

Pulse-chase experiments in the colon cell line LS 174T combined with subcellular fractionation by sucrose density gradient centrifugation showed that the initial dimerization of the MUC2 apomucin started directly after translocation of the apomucin into the rough endoplasmic reticulum as detected by calnexin reactivity. As the mono- and dimers were chased, O-glycosylated MUC2 mono- and dimers were precipitated using an O-glycosylation-insensitive antiserum against the N-terminal domain of the MUC2 mucin. These O-glycosylated species were precipitated from the fractions that comigrated with the galactosyltransferase activity during the subcellular fractionation, indicating that not only MUC2 dimers but also a significant amount of monomers are transferred into the Golgi apparatus. Inhibition of N-glycosylation with tunicamycin treatment slowed down the rate of dimerization and introduced further oligomerization of the MUC2 apomucin in the endoplasmic reticulum. Results of two-dimensional gel electrophoresis demonstrated that these oligomers (putative tri- and tetramers) were stabilized by disulfide bonds. The non-N-glycosylated species of the MUC2 mucin were retained in the endoplasmic reticulum because no O-glycosylated species were precipitated after inhibition by tunicamycin. This suggests that N-glycans of MUC2 are necessary for the correct folding and dimerization of the MUC2 mucin.

Anti-Bacterial Agents↗
PubMed1998

Proteasome-mediated degradation of apolipoprotein B targets both nascent peptides cotranslationally before translocation and full-length apolipoprotein B after translocation into the endoplasmic reticulum.

A major portion of newly synthesized apolipoprotein B (apoB) is degraded intracellularly. This degradation has been demonstrated to be mediated largely by the ubiquitin-proteasome pathway. We examined whether nascent apoB polypeptides or full-length apoB is selectively retrotranslocated from the endoplasmic reticulum into the cytosol for degradation. Herein, we found that full-length apoB as well as partial-length apoB peptides are ubiquitinated in HepG2 cells, and ubiquitination is an exclusively cytosolic process. Calnexin, which binds specifically to glycoproteins, has been postulated to promote apoB folding and complete translocation; we found that ubiquitinated apoB is bound to calnexin, suggesting that ubiquitinated apoB is glycosylated. In addition to calnexin binding, we have other pieces of evidence that the full-length intracellular ubiquitinated apoB is glycosylated, because (i) it binds to concanavalin A, and (ii) glycan can be demonstrated in the full-length ubiquitinated apoB by a chemical detection method involving oxidation of adjacent hydroxyl groups in the glycan moiety. Because glycosylation occurs inside the endoplasmic reticulum, the full-length glycosylated apoB must have been retrotranslocated into the cytosol for ubiquitination and proteasome-mediated degradation. Next we synchronized translation in HepG2 cells by puromycin treatment. A pulse-chase experiment using [35S]methionine labeling of intracellular apoB in these synchronized cells demonstrated that nascent partial-length apoB peptides are also ubiquitinated cotranslationally. We conclude that the ubiquitin proteasome-mediated degradation of apoB targets both nascent peptides cotranslationally before translocation as well as full-length apoB after its translocation into the endoplasmic reticulum.

Acetylcysteine↗
PubMed1998

Evidence for a cholesterol transport pathway from lysosomes to endoplasmic reticulum that is independent of the plasma membrane.

We have studied the movement of low density lipoprotein (LDL)-derived cholesterol in cultured Chinese hamster ovary cells. Our hypothesis is that when LDL cholesterol is effluxed from lysosomes, the bulk of LDL cholesterol is mobilized to the plasma membrane, while another pathway delivers LDL cholesterol from lysosomes to acyl-CoA/cholesterol acyltransferase (ACAT) in the endoplasmic reticulum. Three lines of evidence support this model. First, LDL cholesterol transport to ACAT can be blocked without inhibiting the movement of cholesterol from lysosomes to plasma membrane or from plasma membrane to endoplasmic reticulum. Second, LDL cholesterol transport to ACAT is normal in a Chinese hamster ovary mutant with defective plasma membrane-to-ACAT movement. Third, LDL cholesterol is not diluted by the plasma membrane cholesterol pool before reaching ACAT. Our evidence supports a vesicular model of cholesterol transport from lysosomes to the endoplasmic reticulum that is independent of the plasma membrane.

Amphotericin B↗
PubMed1999

Elevation of intracellular glucosylceramide levels results in an increase in endoplasmic reticulum density and in functional calcium stores in cultured neurons.

Gaucher disease is a glycosphingolipid storage disease caused by defects in the activity of the lysosomal hydrolase, glucocerebrosidase (GlcCerase), resulting in accumulation of glucocerebroside (glucosylceramide, GlcCer) in lysosomes. The acute neuronopathic type of the disease is characterized by severe loss of neurons in the central nervous system, suggesting that a neurotoxic agent might be responsible for cellular disruption and neuronal death. We now demonstrate that upon incubation with a chemical inhibitor of GlcCerase, conduritol-B-epoxide (CBE), cultured hippocampal neurons accumulate GlcCer. Surprisingly, increased levels of tubular endoplasmic reticulum elements, an increase in [Ca(2+)](i) response to glutamate, and a large increase in [Ca(2+)](i) release from the endoplasmic reticulum in response to caffeine were detected in these cells. There was a direct relationship between these effects and GlcCer accumulation since co-incubation with CBE and an inhibitor of glycosphingolipid synthesis, fumonisin B(1), completely antagonized the effects of CBE. Similar effects on endoplasmic reticulum morphology and [Ca(2+)](i) stores were observed upon incubation with a short-acyl chain, nonhydrolyzable analogue of GlcCer, C(8)-glucosylthioceramide. Finally, neurons with elevated GlcCer levels were much more sensitive to the neurotoxic effects of high concentrations of glutamate than control cells; moreover, this enhanced toxicity was blocked by pre-incubation with ryanodine, suggesting that [Ca(2+)](i) release from ryanodine-sensitive intracellular stores can induce neuronal cell death, at least in neurons with elevated GlcCer levels. These results may provide a molecular mechanism to explain neuronal dysfunction and cell death in neuronopathic forms of Gaucher disease.

Animals↗
PubMed1999

Impaired cardiac performance in heterozygous mice with a null mutation in the sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2) gene.

The sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2) gene encodes both SERCA2a, the cardiac sarcoplasmic reticulum Ca2+ pump, and SERCA2b, which is expressed in all tissues. To gain a better understanding of the physiological functions of SERCA2, we used gene targeting to develop a mouse in which the promoter and 5' end of the gene were eliminated. Mating of heterozygous mutant mice yielded wild-type and heterozygous offspring; homozygous mutants were not observed. RNase protection, Western blotting, and biochemical analysis of heart samples showed that SERCA2 mRNA was reduced by approximately 45% in heterozygous mutant hearts and that SERCA2 protein and maximal velocity of Ca2+ uptake into the sarcoplasmic reticulum were reduced by approximately 35%. Measurements of cardiovascular performance via transducers in the left ventricle and right femoral artery of the anesthetized mouse revealed reductions in mean arterial pressure, systolic ventricular pressure, and the absolute values of both positive and negative dP/dt in heterozygous mutants. These results demonstrate that two functional copies of the SERCA2 gene are required to maintain normal levels of SERCA2 mRNA, protein, and Ca2+ sequestering activity, and that the deficit in Ca2+ sequestering activity due to the loss of one copy of the SERCA2 gene impairs cardiac contractility and relaxation.

Animals↗
PubMed2003

Deubiquitination, a new player in Golgi to endoplasmic reticulum retrograde transport.

Modification by ubiquitin plays a major role in a broad array of cellular functions. Although reversal of this process, deubiquitination, likely represents an important regulatory step contributing to cellular homeostasis, functions of deubiquitination enzymes still remain poorly characterized. We have previously shown that the ubiquitin protease Ubp3p requires a co-factor, Bre5p, to specifically deubiquitinate the coat protein complex II (COPII) subunit Sec23p, which is involved in anterograde transport between endoplasmic reticulum and Golgi compartments. In the present report, we show that disruption of BRE5 gene also led to a defect in the retrograde transport from the Golgi to the endoplasmic reticulum. Further analysis indicate that the COPI subunit beta'-COP represents another substrate of the Ubp3p.Bre5p complex. All together, our results indicate that the Ubp3p.Bre5p deubiquitination complex co-regulates anterograde and retrograde transports between endoplasmic reticulum and Golgi compartments.

Amino Acid Sequence↗
PubMed2000

Low temperature molecular adaptation of the skeletal muscle sarco(endo)plasmic reticulum Ca2+-ATPase 1 (SERCA 1) in the wood frog (Rana sylvatica).

We have compared the primary sequence and enzymatic properties of the sarcoplasmic reticulum Ca(2+)-ATPases from a cold-tolerant frog Rana sylvatica with those of a closely related cold-intolerant frog, Rana clamitans. Sarcoplasmic reticulum isolated from leg muscles of both species contains a major protein ( approximately 100 kDa) that reacts with a monoclonal antibody against sarco(endo)plasmic reticulum Ca(2+)-ATPase type 1 (SERCA1). The apparent molecular mass of R. sylvatica SERCA1 is 115 kDa, whereas that of R. clamitans is 105 kDa. However, the deduced amino acid sequences obtained from cDNAs do not indicate a difference in molecular weight, thus suggesting post-translational protein modification of R. sylvatica SERCA1. Comparison of the temperature dependence of both ATP hydrolysis and Ca(2+) transport indicates that R. sylvatica SERCA1 exhibits significantly lower activation energy below 20 degrees C and an approximately 2-fold greater Ca(2+)-ATPase activity near 0 degrees C. Furthermore, R. sylvatica SERCA1 exhibits simple Michaelis-Menten kinetics with ATP and Ca(2+) as opposed to the two-site ATP kinetics and positive cooperativity with Ca(2+) observed for R. clamitans and mammalian SERCA1s. Cooperativity has been linked to protein-protein interaction in SERCA1, and this property may be altered in R. sylvatica SERCA1. Primary sequence comparison shows that R. sylvatica SERCA1 exhibits seven unique amino acid substitutions, three of which are in the ATP binding domain. We also report for the first time the presence of alternative splicing in the frog, resulting in isoforms SERCA1a and SERCA1b. Thus, it appears that the low temperature muscle contractility of R. sylvatica can be explained partially by significant functional and structural differences in SERCA1.

Adaptation, Physiological↗
PubMed2001

Interaction of HRC (histidine-rich Ca(2+)-binding protein) and triadin in the lumen of sarcoplasmic reticulum.

HRC (histidine-rich Ca(2+) binding protein) has been identified from skeletal and cardiac muscle and shown to bind Ca(2+) with high capacity and low affinity. While HRC resides in the lumen of the sarcoplasmic reticulum, the physiological function of HRC is largely unknown. In the present study, we have performed co-immunoprecipitation experiments and show that HRC binds directly to triadin, which is an integral membrane protein of the sarcoplasmic reticulum. Using a fusion protein binding assay, we further identified the histidine-rich acidic repeats of HRC as responsible for the binding of HRC to triadin. These motifs may represent a novel protein-protein interaction domain. The HRC binding domain of triadin was also localized by fusion protein binding assay to the lumenal region containing the KEKE motif that was previously shown to be involved in the binding of triadin to calsequestrin. Notably, the interaction of HRC and triadin is Ca(2+)-sensitive. Our data suggest that HRC may play a role in the regulation of Ca(2+) release from the sarcoplasmic reticulum by interaction with triadin.

Amino Acid Sequence↗
PubMed2001

An endoplasmic reticulum protein implicated in chaperoning peptides to major histocompatibility of class I is an aminopeptidase.

gp96, an abundant peptide-binding chaperone of the lumen of the endoplasmic reticulum and an acceptor of peptides transported into the endoplasmic reticulum through transporter associated with antigen processing, is shown to be an aminopeptidase. gp96 can trim an amino-terminal extended 19-mer precursor of the K(b)-binding VSV8 epitope for recognition by the cognate cytotoxic T lymphocyte clone. These observations support a role for gp96 in the amino-terminal trimming of extended peptides in the endoplasmic reticulum.

Aminopeptidases↗
PubMed2002

Ultraviolet light inhibits translation through activation of the unfolded protein response kinase PERK in the lumen of the endoplasmic reticulum.

Exposure to ultraviolet light can cause inflammation, premature skin aging, and cancer. UV irradiation alters the expression of multiple genes that encode functions to repair DNA damage, arrest cell growth, and induce apoptosis. In addition, UV irradiation inhibits protein synthesis, although the mechanism is not known. In this report, we show that UV irradiation induces phosphorylation of eukaryotic translation initiation factor 2 on the alpha-subunit (eIF2alpha) and inhibits protein synthesis in a dosage- and time-dependent manner. The UV-induced phosphorylation of eIF2alpha was prevented by the overexpression of a non-phosphorylatable mutant of eIF2alpha (S51A). PERK is an eIF2alpha protein kinase localized to the endoplasmic reticulum that is activated by the accumulation of unfolded proteins in the endoplasmic reticulum. Expression of trans-dominant-negative mutants of PERK also prevented eIF2alpha phosphorylation upon UV treatment and protected from the associated translation attenuation. The luminal domain of dominant-negative mutant PERK formed heterodimers with endogenous PERK to inhibit the PERK signaling pathway. In contrast, eIF2alpha phosphorylation was not inhibited by overexpression of a trans-dominant-negative mutant kinase, PKR, supporting the theory that UV-induced eIF2alpha phosphorylation is specifically mediated by PERK. These results support a novel mechanism by which UV irradiation regulates translation via an endoplasmic reticulum-stress signaling pathway.

Animals↗
PubMed2002

The signal peptide of the G protein-coupled human endothelin B receptor is necessary for translocation of the N-terminal tail across the endoplasmic reticulum membrane.

The initial step of the intracellular transport of G protein-coupled receptors, their insertion into the membrane of the endoplasmic reticulum, follows one of two different pathways. Whereas one group uses the first transmembrane domain of the mature receptor as an uncleaved signal anchor sequence for this process, a second group possesses additional cleavable signal peptides. The reason this second subset requires the additional signal peptide is not known. Here we have assessed the functional significance of the signal peptide of the endothelin B (ET(B)) receptor in transiently transfected COS.M6 cells. A green fluorescent protein-tagged ET(B) receptor mutant lacking the signal peptide was nonfunctional and retained in the endoplasmic reticulum, suggesting that it has a folding defect. To determine the defect in more detail, ET(B) receptor fragments containing the N-terminal tail, first transmembrane domain, and first cytoplasmic loop were constructed. We assessed N tail translocation across the endoplasmic reticulum membrane in the presence and absence of a signal peptide and show that the signal peptide is necessary for N tail translocation. We postulate that signal peptides are necessary for those G protein-coupled receptors for which post-translational translocation of the N terminus is impaired or blocked by the presence of stably folded domains.

Amino Acid Sequence↗
PubMed2003

Kinectin anchors the translation elongation factor-1 delta to the endoplasmic reticulum.

Kinectin has been proposed to be a membrane anchor for kinesin on intracellular organelles. A kinectin isoform that lacks a major portion of the kinesin-binding domain does not bind kinesin but interacts with another resident of the endoplasmic reticulum, the translation elongation factor-1 delta (EF-1 delta). This was shown by yeast two-hybrid analysis and a number of in vitro and in vivo assays. EF-1 delta provides the guanine nucleotide exchange activities on EF-1 alpha during elongation step of protein synthesis. The minimal EF-1 delta-binding domain on kinectin resides within a conserved region present in all the kinectin isoforms. Overexpression of the kinectin fragments in vivo disrupted the intracellular localization of EF-1 delta proteins. This report provides evidence of an alternative kinectin function as the membrane anchor for EF-1 delta on the endoplasmic reticulum and provides clues to the EF-1 complex assembly and anchorage on the endoplasmic reticulum.

Endoplasmic Reticulum↗
PubMed2003

Initiation of the decorin glycosaminoglycan chain in the endoplasmic reticulum-Golgi intermediate compartment.

We have transiently expressed decorin with a C-terminal KDEL endoplasmic reticulum retention signal peptide in COS-7 cells to study initiation of galactosaminoglycan synthesis in the endoplasmic reticulum-Golgi intermediate compartment. All decorin-KDEL molecules were substituted with N-linked oligosaccharides sensitive to endoglycosidase H, indicating that the core protein was located proximal to the medial-Golgi. O-Linked glycosylation was only initiated in a minor fraction of the molecules. The O-linked saccharides were characterized by gel filtration after stepwise degradations using chondroitin ABC/AC-I lyases, beta1-3-glycuronidase, beta-galactosidase, and alkaline phosphatase. The major O-linked saccharide was the linkage region pentasaccharide GalNAcbeta1-4GlcUAbeta1-3Galbeta1-3Galbeta1-4Xyl-2-phosphate, demonstrating initiation of chondroitin synthesis in the endoplasmic reticulum-Golgi intermediate compartment. In the presence of brefeldin A, partial elongation of a chondroitin chain took place, indicating retrieval of polymerases but not of sulfotransferases.

Alkaline Phosphatase↗
PubMed2003

A major fraction of endoplasmic reticulum-located glutathione is present as mixed disulfides with protein.

The tripeptide glutathione is the most abundant thiol/disulfide component of the eukaryotic cell and is known to be present in the endoplasmic reticulum lumen. Accordingly, the thiol/disulfide redox status of the endoplasmic reticulum lumen is defined by the status of glutathione, and it has been assumed that reduced and oxidized glutathione form the principal redox buffer. We have determined the distribution of glutathione between different chemical states in rat liver microsomes by labeling with the thiol-specific label monobromobimane and subsequent separation by reversed phase high performance liquid chromatography. More than half of the microsomal glutathione was found to be present in mixed disulfides with protein, the remainder being distributed between the reduced and oxidized forms of glutathione in the ratio of 3:1. The high proportion of the total population of glutathione that was found to be in mixed disulfides with protein has significant implications for the redox state and buffering capacity of the endoplasmic reticulum and, hence, for the formation of disulfide bonds in vivo.

Animals↗
PubMed2003

The novel skeletal muscle sarcoplasmic reticulum JP-45 protein. Molecular cloning, tissue distribution, developmental expression, and interaction with alpha 1.1 subunit of the voltage-gated calcium channel.

JP-45 is a novel integral protein constituent of the skeletal muscle sarcoplasmic reticulum junctional face membrane. We identified its primary structure from a cDNA clone isolated from a mouse skeletal muscle cDNA library. Mouse skeletal muscle JP-45 displays over 86 and 50% identity with two hypothetical NCBI data base protein sequences from mouse tongue and human muscle, respectively. JP-45 is predicted to have a cytoplasmic domain, a single transmembrane segment followed by an intralumenal domain enriched in positively charged amino acids. Northern and Western blot analyses reveal that the protein is mainly expressed in skeletal muscle. The mRNA encoding JP-45 appears in 17-day-old mouse embryos; expression of the protein peaks during the second month of postnatal development and then decreases approximately 3-fold during aging. Double immunofluorescence of adult skeletal muscle fibers demonstrates that JP-45 co-localizes with the sarcoplasmic reticulum calcium release channel. Co-immunoprecipitation experiments with a monoclonal antibody against JP-45 show that JP-45 interacts with the alpha1.1 subunit voltage-gated calcium channel and calsequestrin. These results are consistent with the localization of JP-45 in the junctional sarcoplasmic reticulum and with its involvement in the molecular mechanism underlying skeletal muscle excitation-contraction coupling.

Amino Acid Sequence↗
PubMed2003

Glycosylation is important for cell surface expression of the water channel aquaporin-2 but is not essential for tetramerization in the endoplasmic reticulum.

Aquaporin-2 (AQP2) is a pore-forming protein that is required for regulated reabsorption of water from urine. Mutations in AQP2 lead to nephrogenic diabetes insipidus, a disorder in which functional AQP2 is not expressed on the apical cell surface of kidney collecting duct principal cells. The mechanisms and pathways directing AQP2 from the endoplasmic reticulum to the Golgi complex and beyond have not been defined. We found that approximately 25% of newly synthesized AQP2 is glycosylated. Nonglycosylated and complex-glycosylated wild-type AQP2 are stable proteins with a half-life of 6-12 h and are both detectable on the cell surface. We show that AQP2 forms tetramers in the endoplasmic reticulum during or very early after synthesis and reaches the Golgi complex in 1-1.5 h. We also report that glycosylation is neither essential for tetramerization nor for transport from the endoplasmic reticulum to the Golgi complex. Instead, the N-linked glycan is important for exit from the Golgi complex and sorting of AQP2 to the plasma membrane. These results are important for understanding the molecular mechanisms responsible for the intracellular retention of AQP2 in nephrogenic diabetes insipidus.

Animals↗