The membrane protein ATPase class I type 8B member 1 signals through protein kinase C zeta to activate the farnesoid X receptor.

UNLABELLED: Prior loss-of-function analyses revealed that ATPase class I type 8B member 1 [familial intrahepatic cholestasis 1 (FIC1)] posttranslationally activated the farnesoid X receptor (FXR). Mechanisms underlying this regulation were examined by gain-of-function studies in UPS cells, which lack endogenous FIC1 expression. FXR function was assayed in response to wild-type and mutated FIC1 expression constructs with a human bile salt export pump (BSEP) promoter and a variety of cellular localization techniques. FIC1 overexpression led to enhanced phosphorylation and nuclear localization of FXR that was associated with FXR-dependent activation of the BSEP promoter. The FIC1 effect was lost after mutation of the FXR response element in the BSEP promoter. Despite similar levels of FIC1 protein expression, Byler disease FIC1 mutants did not activate BSEP, whereas benign recurrent intrahepatic cholestasis mutants partially activated BSEP. The FIC1 effect was dependent on the presence of the FXR ligand, chenodeoxycholic acid. The effect of FIC1 on FXR phosphorylation and nuclear localization and its effects on BSEP promoter activity could be blocked with protein kinase C zeta (PKC zeta) inhibitors (pseudosubstrate or small interfering RNA silencing). Recombinant PKC zeta directly phosphorylated immunoprecipitated FXR. The mutation of threonine 442 of FXR to alanine yielded a dominant negative protein, whereas the phosphomimetic conversion to glutamate resulted in FXR with enhanced activity and nuclear localization. Inhibition of PKC zeta in Caco-2 cells resulted in activation of the human apical sodium-dependent bile acid transporter promoter. CONCLUSION: These results demonstrate that FIC1 signals to FXR via PKC zeta. FIC1-related liver disease is likely related to downstream effects of FXR on bile acid homeostasis. Benign recurrent intrahepatic cholestasis emanates from a partially functional FIC1 protein. Phosphorylation of FXR is an important mechanism for regulating its activity.

Surgical portosystemic shunts and the Rex bypass in children: a single-centre experience.

OBJECTIVES: This study aimed to illustrate the indications for, and types and outcomes of surgical portosystemic shunt (PSS) and/or Rex bypass in a single centre. METHODS: Data were collected from children with a PSS and/or Rex bypass between 1992 and 2006 at Mount Sinai Medical Center, New York. RESULTS: Median age at surgery was 10.7 years (range 0.3-22.0 years). Indications included: (i) refractory gastrointestinal bleeding in portal hypertension associated with (a) compensated cirrhosis (n= 12), (b) portal vein thrombosis (n= 10), (c) hepatoportal sclerosis (n= 3); (ii) refractory ascites secondary to Budd-Chiari syndrome (n= 3), and (iii) familial hypercholesterolaemia (n= 4). There were 20 distal splenorenal, four portacaval, three Rex bypass, two mesocaval, two mesoatrial and one proximal splenorenal shunts. At the last follow-up (median 2.9 years, range 0.1-14.1 years), one shunt (Rex bypass) was thrombosed. Two patients had died and two had required a liver transplant. These had a patent shunt at last imaging prior to death or transplant. CONCLUSIONS: Portosystemic shunts and Rex bypass have been used to manage portal hypertension with excellent outcomes. In selected children with compensated liver disease, PSS may act as a bridge to liver transplantation or represent an attractive alternative.

Regulation of the mouse organic solute transporter alpha-beta, Ostalpha-Ostbeta, by bile acids.

The mechanisms responsible for bile acid regulation of mouse intestinal organic solute transporter alpha-beta (Ostalpha-Ostbeta) expression were investigated. Expression of Ostalpha-Ostbeta mRNA was increased in cecum and proximal colon of cholic acid-fed mice and in chenodeoxycholate-treated mouse CT26 colon adenocarcinoma cells. Sequence analysis revealed potential cis-acting elements for farnesoid X receptor (FXR) and liver receptor homolog-1 (LRH-1) in the mouse Ostalpha and Ostbeta promoters and reporter constructs containing Ostalpha and Ostbeta 5'-flanking sequences were positively regulated by bile acids. Expression of a dominant-negative FXR, reduction of FXR with interfering small RNA (siRNA), or mutation of the potential FXR elements decreased Ostalpha and Ostbeta promoter activity and abolished the induction by chenodeoxycolic acid. Negative regulation of the Ostalpha and Ostbeta promoters by bile acids was mediated through LRH-1 elements. Ostalpha and Ostbeta promoter activities were increased by coexpression of LRH-1 and decreased by coexpression of SHP. Mutation of the potential LRH-1 elements and siRNA-mediated reduction of LRH-1 expression decreased basal promoter activity. As predicted from the promoter analyses, ileal Ostalpha and Ostbeta mRNA expressions were increased in wild-type mice administered the FXR agonist GW4064 and decreased in FXR-null mice. Immunoblotting analysis revealed that Ostalpha and Ostbeta intestinal protein expressions correlated with mRNA expression. The mouse Ostalpha and Ostbeta promoters are unusual in that they contain functional FXR and LRH elements, which mediate, respectively, positive and negative feedback regulation by bile acids. Although the positive regulatory pathway appears to be dominant, this arrangement provides a mechanism to finely titrate Ostalpha-Ostbeta expression to the bile acid flux.

c-Fos is a critical mediator of inflammatory-mediated repression of the apical sodium-dependent bile acid transporter.

BACKGROUND & AIMS: Ileal bile acid malabsorption is present in Crohn's ileitis. The molecular mechanisms of regulation of the apical sodium-dependent bile acid transporter (ASBT) by inflammatory cytokines in vitro and in vivo are investigated. METHODS: Transient transfection studies of the human, mouse, and rat ASBT promoters and Northern analyses were performed in cells treated with the inflammatory cytokines and/or various activator protein-1 constructs. Rat ASBT promoter transgenic, wild-type, and c-fos-null mice were treated with indomethacin to assess the response to acute inflammation of the ileal mucosa. RESULTS: In Caco-2 cells, ASBT messenger RNA expression was reduced 65% after interleukin-1beta treatment, while c-fos and c-jun were up-regulated 2-fold. Human ASBT promoter activity was enhanced by c-jun and repressed by a dominant negative c-jun, c-fos, or a dominant negative c-fos. Meanwhile, c-fos antisense treatment activated the human ASBT promoter 5-fold and not only abrogated interleukin-1beta-mediated repression but led to a paradoxical increase in ASBT promoter activity. Indomethacin-induced acute ileitis led to repression of ASBT in wild-type mice and in the transgenic rat ASBT promoter reporter, while paradoxical activation of ASBT was seen in c-fos-null mice. Indomethacin-induced ileal injury was greater in the c-fos-null mice compared with the wild-type littermates. CONCLUSIONS: Human, rat, and mouse ASBT is inhibited by inflammatory cytokines via direct interactions of c-fos with the ASBT promoter.

Critical analysis of the pediatric end-stage liver disease scoring system: a single center experience.

The Pediatric End-Stage Liver Disease (PELD) scoring system is a new nationally utilized formula developed to provide a continuous numerical assessment of the risk of death in order to allocate livers to children for transplantation. A retrospective review of the clinical course of children undergoing liver transplantation at the Mount Sinai Medical Center was performed in order to assess the effectiveness of this scoring system in the first 24 months of its utilization. Forty-eight patients underwent liver transplantation with overall patient and graft survival rates of 98% and 96%, respectively. In 23 cases the PELD scoring system determined waiting time for transplantation. Of these 23 patients, 7 moved to the intensive care unit (ICU). Only 2 of 23 patients underwent transplantation with their actual PELD score. The rest required petition for exception (17) or status 1 listing (4). Significant morbidity occurred while awaiting transplantation: failure to thrive (78%), ascites (73%), hemorrhage (49%), infectious complications (39%), encephalopathy (30%), peritonitis (17%), pathologic bone fractures (13%), and hepatopulmonary syndrome (9%). In patients with PELD scores granted by exception the average score that did not yield a liver offer was 38 with an average waiting time of 55 days. At the time of transplantation actual PELD score averaged 22, while the petitioned score was 40. Based upon our center's initial experience, the current PELD scoring system is not adequate. Actual PELD scores did not lead to timely allocation of livers to children. It appears that this scoring system underestimates the near-term risk of death. Urgent reassessment is required to prevent potential morbidity and mortality in children. In conclusion the United Network for Organ Sharing policy that permits granting of exceptions has circumvented these problems with the PELD scoring system.