Liver X Receptor β regulates bile volume and the expression of Aquaporins and Cystic Fibrosis Transmembrane Conductance Regulator in the gallbladder

The gallbladder is considered an important organ in maintaining digestive and metabolic homeostasis. Given that therapeutic options for gallbladder diseases are often limited to cholecystectomy, understanding gallbladder pathophysiology is essential in developing novel therapeutic strategies.Since Liver X Receptor β (LXRβ), an oxysterol-activated transcription factor, is strongly expressed in gallbladder cholangiocytes, the aim was to investigate LXRβ physiological function in the gallbladder. Thus, we studied the gallbladders of WT and LXRβ-/- male mice using immunohistochemistry, electron-microscopy, qRT-PCR, bile duct cannulation, bile and blood biochemistry and duodenal pH measurements.LXRβ-/- mice presented a large gallbladder bile volume with high duodenal mRNA levels of the Vasoactive Intestinal Polypeptide (Vip), a strong mediator of gallbladder relaxation. LXRβ-/- gallbladders, showed lower mRNA and protein expression of Aquaporin-1, Aquaporin-8 and Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). A cystic fibrosis-resembling phenotype was evident in the liver showing higher serum cholestatic markers and the presence of reactive cholangiocytes. For LXRβ being a transcription factor, we identified 8 putative binding sites of LXR on the promoter and enhancer of the Cftr gene, suggesting Cftr as a novel LXRβ regulated gene. In conclusion LXRβ was recognized as a regulator of gallbladder bile volume through multiple mechanisms involving CFTR and Aquaporins.

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Endoplasmic reticulum stress and the unfolded protein response regulate genomic cystic fibrosis transmembrane conductance regulator expression

AJP Cell Physiology ◽

10.1152/ajpcell.00391.2006 ◽

2007 ◽

Vol 292 (2) ◽

pp. C756-C766 ◽

Cited By ~ 49

Author(s):

András Rab ◽

Rafal Bartoszewski ◽

Asta Jurkuvenaite ◽

John Wakefield ◽

James F. Collawn ◽

...

Keyword(s):

Cystic Fibrosis ◽

Er Stress ◽

Mrna Levels ◽

Transmembrane Conductance Regulator ◽

Wild Type ◽

Transmembrane Conductance ◽

Unfolded Protein ◽

The Unfolded Protein Response ◽

Protein Response ◽

Cystic Fibrosis Transmembrane

The unfolded protein response (UPR) is a cellular recovery mechanism activated by endoplasmic reticulum (ER) stress. The UPR is coordinated with the ER-associated degradation (ERAD) to regulate the protein load at the ER. In the present study, we tested how membrane protein biogenesis is regulated through the UPR in epithelia, using the cystic fibrosis transmembrane conductance regulator (CFTR) as a model. Pharmacological methods such as proteasome inhibition and treatment with brefeldin A and tunicamycin were used to induce ER stress and activate the UPR as monitored by increased levels of spliced XBP1 and BiP mRNA. The results indicate that activation of the UPR is followed by a significant decrease in genomic CFTR mRNA levels without significant changes in the mRNA levels of another membrane protein, the transferrin receptor. We also tested whether overexpression of a wild-type CFTR transgene in epithelia expressing endogenous wild-type CFTR activated the UPR. Although CFTR maturation is inefficient in this setting, the UPR was not activated. However, pharmacological induction of ER stress in these cells also led to decreased endogenous CFTR mRNA levels without affecting recombinant CFTR message levels. These results demonstrate that under ER stress conditions, endogenous CFTR biogenesis is regulated by the UPR through alterations in mRNA levels and posttranslationally by ERAD, whereas recombinant CFTR expression is regulated only by ERAD.

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Murine colonic mucosa hyperproliferation. II. PKC-β activation and cPKC-mediated cellular CFTR overexpression

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.2000.278.5.g765 ◽

2000 ◽

Vol 278 (5) ◽

pp. G765-G774 ◽

Cited By ~ 12

Author(s):

Shahid Umar ◽

Joseph H. Sellin ◽

Andrew P. Morris

Keyword(s):

Cellular Proliferation ◽

Mrna Levels ◽

Transmembrane Conductance Regulator ◽

Transmembrane Conductance ◽

Subcellular Membrane ◽

Physiol Gastrointest Liver ◽

Mrna And Protein Expression ◽

Membrane Bound ◽

Cystic Fibrosis Transmembrane ◽

New Hypothesis

In the companion article (Umar S, Scott J, Sellin JH, Dubinsky WP, and Morris AP, Am J Physiol Gastrointest Liver Physiol 278: 753–764, 2000), we have shown that transmissible murine colonic hyperplasia (TMCH) increased cellular cystic fibrosis transmembrane conductance regulator (CFTR) mRNA and protein expression, relocalized CFTR within colonocytes, and enhanced mucosal cAMP-dependent Cl−secretion. We show here that these changes were dependent on elevated cellular levels of membrane-bound Ca2+- and diacylglycerol-sensitive protein kinase C (PKC) activity (12-fold), induced by selective (3- to 4-fold) rises in conventional PKC (cPKC) isoform expression and membrane translocation. Three cPKC isoforms were detected in isolated crypts: α, β1, and β2. cPKC-β1 rises preceded and those of cPKC-α and cPKC-β2 paralleled cellular hyperproliferation and its effects on CFTR expression and cAMP-dependent Cl−current secretion. Only cPKC-β1 and cPKC-β2 were membrane translocated during TMCH. Furthermore, only cPKC-β1 trafficked to the nucleus, whereas cPKC-β2 remained partitioned among cytosolic, membrane, and cytoskeletal subcellular fractions. Modest increases in novel PKC-ε (nPKC-ε) expression and subcellular membrane partitioning were recorded during TMCH, but no changes were seen for PKC-δ or -η. No nPKC isoform nuclear partitioning was detected. The orally bioactive cPKC inhibitor Ro-32–0432 reversed both TMCH and elevated cellular CFTR mRNA levels, whereas a pharmacologically inert analog (Ro-31–6045) failed to inhibit either response. On the basis of these facts, we present a new hypothesis whereby PKC-dependent cellular proliferation promotes endogenous cellular CFTR levels. PKC-β1 was identified as a candidate regulatory PKC isoform.

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Differential regulation of cystic fibrosis transmembrane conductance regulator and Na+,K+-ATPase in gills of striped bass, Morone saxatilis: effect of salinity and hormones

Journal of Endocrinology ◽

10.1677/joe-06-0016 ◽

2007 ◽

Vol 192 (1) ◽

pp. 249-260 ◽

Cited By ~ 19

Author(s):

Steffen Søndergaard Madsen ◽

Lars Nørholm Jensen ◽

Christian Kølbæk Tipsmark ◽

Pia Kiilerich ◽

Russell John Borski

Keyword(s):

Cystic Fibrosis ◽

Atpase Activity ◽

Striped Bass ◽

Mrna Level ◽

Mrna Levels ◽

Transmembrane Conductance Regulator ◽

Transmembrane Conductance ◽

Α Subunit ◽

Igf I ◽

Cystic Fibrosis Transmembrane

Effects of salinity and hormones on cystic fibrosis transmembrane conductance regulator (CFTR) and α-subunit Na+,K+-ATPase (α-NKA) mRNA (analysed by semi-quantitative PCR) and protein expression (analysed by western blotting and immunocytochemistry) were investigated in gills of striped bass. Freshwater (FW) to seawater (SW) transfer induced a disturbance in serum [Na+]. Gill CFTR protein, mRNA level and Na+,K+-ATPase activity were unaffected by SW transfer, whereas α-NKA mRNA increased after transfer. CFTR immunoreactivity was observed in large cells in FW and SW gill filaments at equal intensity. Cortisol decreased serum [Na+] in FW fish, but had no effect on gill Na+,K+-ATPase activity, α-NKA and CFTR mRNA levels. Incubation of gill tissue with cortisol (24 h, >0.01 μg/ml) and epidermal growth factor (EGF 10 μg/ml) decreased CFTR mRNA levels relative to pre-incubation and control levels. CFTR expression was unaffected by IGF-I (10 μg/ml). α-NKA mRNA levels decreased by 50% after 24 h control incubation; it was slightly stimulated by cortisol and unaffected by IGF-I and EGF. In isolated gill cells, phosphorylation of extracellular-regulated kinase (ERK) 1/2 was stimulated by EGF but not affected by IGF-I. This study is the first to report a branchial EGF response and to demonstrate a functional ERK 1/2 pathway in the teleost gill. In conclusion, CFTR and Na+,K+-ATPase are differentially regulated by salinity and hormones in gills of striped bass, despite the putative involvement of both in salt excretion.

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