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Primary biliary cirrhosis (PBC) is a chronic and progressive cholestatic liver disease of unknown etiopathogenesis that mainly affects middle-aged women. Patients show non-suppurative cholangitis with damage and destruction of the small- and medium-sized intrahepatic bile ducts. Characteristically, the disease is strongly associated with autoimmune phenomena such as the appearance of serum antimitochondrial autoantibodies (AMA) and portal infiltrating T cells against the inner lipoyl domain in the E2 component of the pyruvate dehydrogenase complex (PDC-E2). Here we review the major characteristics of a series of inducible and genetically modified animal models of PBC and analyze the similarities and differences to PBC features in humans.

Background: Chloride-bicarbonate anion exchangers (AE) are thought to be essential to the generation of ion fluxes into biliary, salivary, pancreatic, and other secretions. In primary biliary cirrhosis (PBC), chronic cholestasis is frequently associated with pluriglandular exocrine failure. The present study examined the expression of AE genes in PBC at the messenger RNA (mRNA) level. Methods: Two AE messages, i.e., AE1 and AE2 mRNAs, were analyzed by a polymerase chain reaction-based procedure in liver specimens and peripheral mononuclear cells of patients with PBC and control subjects (with normal livers or with miscellaneous liver diseases). Results: AE1 mRNA was detected in only a few liver biopsy specimens of patients with PBC and control subjects, whereas AE2 mRNA was found in all liver specimens tested. In lymphoid cells, however, both transcripts were consistently detected. AE2 mRNA levels in liver as well as in lymphoid cells were significantly lower in PBC patients than in controls. In contrast to AE2 mRNA, AE1 mRNA levels were increased in lymphoid cells from patients with PBC. Interestingly, the levels of liver AE2 mRNA in a few PBC patients treated with ursodeoxycholic acid were within the range of the controls. Conclusions: The expression of AE genes is altered in patients with PBC. It is suggested that this disturbance may have a role in the cholestasis, exocrine failure, and immunodysfunction of PBC.

A cDNA encoding an arachidonate 12-lipoxygenase from rat brain was obtained by polymerase chain reaction cloning. Primers specific for porcine leukocyte 12-lipoxygenase cDNA were used to isolate the initial polymerase-chain-reaction product (395 bp). The final sequence of the rat 12-lipoxygenase cDNA coding region (1989 bp) was verified by analysis of several separate polymerase-chain-reaction products. The open reading frame corresponded to a protein of 662 amino acid residues, with a calculated molecular mass of 75,305 Da. Also the rat 12-lipoxygenase contained the six conserved histidines, characteristic for all cloned lipoxygenases. It displayed the highest degree of identity to porcine leukocyte 12-lipoxygenase (71%) and to human 15-lipoxygenase (75%), with less resemblance to human platelet 12-lipoxygenase (59%) or rat leukocyte 5-lipoxygenase (41%). The recombinant enzyme was expressed in Escherichia coli and incubated with arachidonic acid. Primarily 12-lipoxygenase (but also some 15-lipoxygenase) enzyme activity was obtained. A part of the brain 12-lipoxygenase cDNA was used as probe in Northern blots. A 2.7-kb mRNA was more abundant in RNA from rat leukocytes, lung, and aorta, than in RNA from rat brain. Sequencing of parts of the corresponding cDNAs (from leukocytes and lung), and comparison to the brain 12-lipoxygenase sequence, indicated that these mRNAs from the different rat tissues were identical.

Ursodeoxycholic acid (UDCA) induces bicarbonate-rich hypercholeresis by incompletely defined mechanisms that involve the stimulation of adenosine triphosphate (ATP) release from cholangiocytes. As nitric oxide (NO) at a low concentration can stimulate a variety of secretory processes, we investigated whether this mediator could be implicated in the choleretic response to UDCA. Our in vivo experiments with the in situ perfused rat liver model in anesthetized rats, showed that UDCA infusion increased the biliary secretion of NO derivatives, hepatic inducible NO synthase expression, and NO synthase activity in liver tissue. UDCA also stimulated NO release by isolated rat hepatocytes. In contrast to UDCA, cholic acid was a poor inducer of NO secretion, and tauroursodeoxycholic acid showed no effect on NO secretion. Upon UDCA administration, NO was found in bile as low-molecular-weight nitrosothiols, of which S-nitrosoglutathione (GSNO) was the predominant species. UDCA-stimulated biliary NO secretion was abolished by the inhibition of inducible NO synthase with Nω-nitro-L-arginine methyl ester in isolated perfused livers and also in rats whose livers were depleted of glutathione with buthionine sulfoximine. Moreover, the biliary secretion of NO species was significantly diminished in UDCA-infused transport mutant [ATP–binding cassette C2 (ABCC2)/multidrug resistance–associated protein 2 (Mrp2)–deficient] rats, and this finding was consistent with the involvement of the glutathione carrier ABCC2/Mrp2 in the canalicular transport of GSNO. It was particularly noteworthy that in cultured normal rat cholangiocytes, GSNO activated protein kinase B, protected against apoptosis, and enhanced UDCA-induced ATP release to the medium; this effect was blocked by phosphoinositide 3-kinase inhibition. Finally, retrograde GSNO infusion into the common bile duct increased bile flow and biliary bicarbonate secretion. Conclusion: UDCA induces biliary secretion of GSNO, which contributes to stimulating ductal secretion. (HEPATOLOGY 2010;)

The metal-binding motif in the sequence of leukotriene A4 (LTA4) (EC 3.3.2.6), a bifunctional zinc metalloenzyme, contains a glutamic acid that is conserved in several zinc hydrolases. To study its role for the two catalytic activities, Glu-296 in mouse leukotriene A4 hydrolase was replaced by a glutamine or alanine residue by site-directed mutagenesis. Wild-type and mutated cDNAs were expressed four or five times in Escherichia coli, and the resulting proteins were purified to apparent homogeneity. With respect to their epoxide hydrolase activities--i.e., the conversion of LTA4 into leukotriene B4--the mutated enzymes [Gln296]LTA4 hydrolase and [Ala296]LTA4 hydrolase exhibited specific activities of 1070 +/- 160 and 90 +/- 30 nmol of LTB4 per mg of protein per min (mean +/- SD; n = 4 or 5), respectively, corresponding to 150% and 15% of unmutated enzyme. In contrast, when the mutated proteins were assayed for peptidase activity toward alanine-4-nitroanilide, they were found to be virtually inactive (less than or equal to 0.2% of unmutated enzyme). To serve as a positive control, we also replaced Ser-298 with an alanine residue, which resulted in a protein ([Ala298]LTA4 hydrolase) with catalytic properties almost indistinguishable from the wild-type enzyme. Substitution of Glu-296 by glutamine or alanine was also carried out with human LTA4 hydrolase, and the mutated human enzymes displayed specific activities similar to the corresponding mouse proteins. Zinc analyses of the purified mouse and human proteins confirmed that the mutations did not significantly influence their zinc content. In conclusion, the results of the present study indicate a direct catalytic role for Glu-296 in the peptidase reaction of LTA4 hydrolase, where it presumably acts as a base to polarize water, whereas its function, if any, is apparently not essential in the epoxide hydrolase reaction.

Extracellular acidification by osteoclasts is essential to bone resorption. During proton pumping, intracellular pH (pH(i)) is thought to be kept at a near-neutral level by chloride/bicarbonate exchange. Here we show that the Na+-independent chloride/bicarbonate anion exchanger 2 (Ae2) is relevant for this process in the osteoclasts from the long bones of Ae2(a,b)(-/-) mice ( deficient in the main isoforms Ae2a, Ae2b(1), and Ae2b(2)). Although the long bones of these mice had normal numbers of multinucleated osteoclasts, these cells lacked a ruffled border and displayed impaired bone resorption activity, resulting in an osteopetrotic phenotype of long bones. Moreover, in vitro osteoclastogenesis assays using long-bone marrow cells from Ae2(a,b)(-/-) mice suggested a role for Ae2 in osteoclast formation, as fusion of preosteoclasts for the generation of active multinucleated osteoclasts was found to be slightly delayed. In contrast to the abnormalities observed in the long bones, the skull of Ae2(a,b)(-/-) mice showed no alterations, indicating that calvaria osteoclasts may display normal resorptive activity. Microfluorimetric analysis of osteoclasts from normal mice showed that, in addition to Ae2 activity, calvaria osteoclasts-but not long-bone osteoclasts-possess a sodium-dependent bicarbonate transporting activity. Possibly, this might compensate for the absence of Ae2 in calvaria osteoclasts of Ae2(a,b)(-/-) mice.-Jansen, I. D. C., Mardones, P., Lecanda, F., de Vries, T. J., Recalde, S., Hoeben, K. A., Schoenmaker, T., Ravesloot, J.-H., van Borren, M. M. G. J., van Eijden, T. M., Bronckers, A. L. J. J., Kellokumpu, S., Medina, J. F., Everts, V., Oude Elferink, R. P. J. Ae2(a,b)-deficient mice exhibit osteopetrosis of long bones but not of calvaria. FASEB J. 23, 3470-3481 ( 2009). www.fasebj.org

Autosomal recessive polycystic kidney disease (ARPKD) is a genetic disorder in which affected infants often die at birth or shortly thereafter, primarily as the result of markedly enlarged kidney cysts and impaired lung function. In surviving patients, hepatic fibrosis, bile duct dilatation (Caroli’s disease) and/or cyst development becomes progressively more severe and may be the major cause of morbidity and mortality.1 ARPKD is linked to mutations in the PKHD1 gene which encodes fibrocystin, a large trans-membrane protein with unknown function,2, 3 located on cholangiocyte primary cilia;4 these non-motile long tubular organelles extend from the cholangiocyte apical membrane and function as mechano-,5 chemo-6 and osmo-sensors,7 detecting and transmitting luminal stimuli into intracellular signals. Although the pathophysiology of hepatic cystogenesis in ARPKD is unclear, abnormalities in cholangiocyte fluid secretion and proliferation likely contribute.1, 8 Indeed, in the PCK rat, a well-characterized animal model of ARPKD,9 liver cysts originate from intrahepatic bile ducts and their growth is associated with increased proliferative activity of cystic cholangiocytes.10 However, the mechanism underlying this benign hyperproliferative process is not fully understood. Accumulated evidence suggests that two intracellular signaling mediators, cAMP and Ca2+, regulate proliferation in different cell types,11, 12 including cholangiocytes.13 We recently demonstrated that cAMP levels are increased in cholangiocytes of the PCK rat and that octreotide, a somatostatin analog known to inhibit cAMP, decreases hepatic cyst volume, hepatic fibrotic scores and mitotic indices.10 cAMP has two downstream targets, cAMP-GEF/Epac (Epac) and protein kinase A (PKA).14 Epac proteins, a family of Rap guanine nucleotide exchange factors, regulate many cellular processes via PKA-independent mechanisms.15 There are two different Epac isoforms (Epac1 and Epac2, also known as RapGEF3 and RapGEF4, respectively) which are expressed from different genes in a variety of tissues.15–17 PKA is a heterotetrameric holoenzyme with two regulatory and two catalytic subunits, that responds to intracellular changes of cAMP regulating a wide range of intracellular processes.14 There exist several members of PKA regulatory (RIα, RIβ, RIIα and RIIβ) and catalytic (Cα, Cβ, Cγ and PrKX) subunits. The biochemical and functional features of PKA are largely determined by the structure and properties of the regulatory subunits, which are differentially expressed depending on the tissue and the cellular state.14 cAMP binds to the PKA regulatory subunits, leading to dissociation and activation of the catalytic subunits that may regulate the phosphorylation of a number of proteins and the expression of different genes.14 Both cAMP downstream effectors, Epac and PKA, may be involved in regulation of proliferation in different cell types. In polycystic diseases, however, only PKA has been shown to be responsible for hyperproliferation of epithelial cells lining renal cysts from patients with autosomal dominant polycystic kidney disease (ADPKD).18 But no data exist regarding the expression, intracellular localization and function of PKA regulatory subunits and Epac isoforms in cholangiocytes, and the involvement of these effectors in cystic cholangiocyte proliferation remains unknown. Intracellular Ca2+ [Ca2+]i may also participate in the control of cell growth.11, 12 In fact, renal cystic cells of patients with ARPKD have low calcium levels,11 and silencing of Pkhd1 in cultured normal kidney cells results in decreased intracellular calcium and hyperproliferation.19 The interconnection between cAMP and [Ca2+]i signaling pathways under normal and pathological conditions is currently attracting considerable attention. In particular, it has been shown that in renal cells from ADPKD patients, intracellular calcium modulates cAMP-dependent proliferation. Moreover, these cells were characterized by decreased [Ca2+]i and exhibited higher rates of cell proliferation in response to cAMP, while experimental restoration of [Ca2+]i inhibited their cAMP-stimulated growth.11 We recently demonstrated in normal rat cholangiocytes that elevated [Ca2+]i is able to terminate cAMP signaling (i.e., turn off regulation) initially activated by choleretic stimuli.5 However, it is unclear whether intracellular Ca2+ levels are altered in cystic cholangiocytes and what role, if any, intracellular Ca2+ plays in hepatic cystogenesis. Thus, we examined the: i) expression and intracellular localization of two cAMP downstream effectors, PKA and Epac, in cultured cholangiocytes from normal and PCK rats; ii) role of PKA and Epac activation in proliferation of normal and PCK cholangiocytes; iii) intracellular calcium levels in PCK cholangiocytes; and iv) relationships between cAMP-stimulated proliferation and calcium levels in PCK cholangiocytes.

Polycystic kidney (PCK) rats are a spontaneous model of autosomal recessive polycystic kidney disease that exhibit cholangiocyte-derived liver cysts. We have previously reported that in normal cholangiocytes a subset of vesicles contain three proteins (ie, the water channel AQP1, the chloride channel CFTR, and the anion exchanger AE2) that account for ion-driven water transport. Thus, we hypothesized that altered expression and location of these functionally related proteins contribute to hepatic cystogenesis. We show here that under basal conditions and in response to secretin and hypotonicity, cysts from PCK rats expanded to a greater degree than cysts formed by normal bile ducts. Quantitative reverse transcriptase-polymerase chain reaction, immunoblot analysis, and confocal and immunoelectron microscopy all indicated increased expression of these three proteins in PCK cholangiocytes versus normal cholangiocytes. AQP1, CFTR, and AE2 were localized preferentially to the apical membrane in normal rats while overexpressed at the basolateral membrane in PCK rats. Exposure of the cholangiocyte basolateral membrane to CFTR inhibitors [5-nitro-2-(3-phenylpropylamino)-benzoic acid and CFTRinh172], or Cl − /HCO 3 − exchange inhibitors (4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid disodium salt hydrate and 4-acetamido-4′-isothiocyanato-2,2′-stilbenedisulfonic acid disodium salt hydrate) blocked secretin-stimulated fluid accumulation in PCK but not in normal cysts. Our data suggest that hepatic cystogenesis in autosomal recessive polycystic kidney disease may involve increased fluid accumulation because of overexpression and abnormal location of AQP1, CFTR, and AE2 in cystic cholangiocytes. Therapeutic interventions that block the activation of these proteins might inhibit cyst expansion in polycystic liver disease.

Background & Aims: Cl − /HCO 3 − anion exchanger 2 (AE2) is involved in intracellular pH (pH i ) regulation and transepithelial acid-base transport, including secretin-stimulated biliary bicarbonate excretion. AE2 gene expression was found to be reduced in liver biopsy specimens and blood mononuclear cells from patients with primary biliary cirrhosis (PBC), a disease characterized by chronic nonsuppurative cholangitis associated with antimitochondrial antibodies (AMA) and other autoimmune phenomena. In mice with widespread Ae2 gene disruption, we previously reported altered spermiogenesis and reduced gastric acid secretion. We now describe the hepatobiliary and immunologic changes observed in these Ae2 a.b -deficient mice. Methods: In this murine model, splenocyte pH i and T-cell populations were studied by flow cytometry. CD3-stimulated cytokine secretion was estimated using cytokine arrays. AMA were evaluated by immunoblotting and proteomics. Hepatobiliary changes were assessed by immunohistopathology, flow cytometry, and serum biochemistry. Cholangiocyte gene expression was analyzed by real-time polymerase chain reaction. Results: Ae2 a,b −/− mice exhibit splenomegaly, elevated pH i in splenocytes, increased production of interleukin-12p70 and interferon gamma, expanded CD8 + T-cell population, and under represented CD4 + FoxP3 + /regulatory T cells. Most Ae2 a,b −/− mice tested positively for AMA, showing increased serum levels of immunoglobulin M and G, and liver-specific alkaline phosphatase. About one third of Ae2 a,b −/− mice had extensive portal inflammation with CD8 + and CD4 + T lymphocytes surrounding damaged bile ducts. Cholangiocytes isolated from Ae2 a,b −/− mice showed gene expression changes compatible with oxidative stress and increased antigen presentation. Conclusions: Ae2 deficiency alters pH i homeostasis in immunocytes and gene expression profile in cholangiocytes, leading to immunologic and hepatobiliary changes that resemble PBC.

Anion exchanger 2 (AE2, SLC4A2) is a ubiquitously expressed membrane solute carrier that regulates intracellular pH (pH(i)) by exchanging cytosolic bicarbonate for extracellular chloride. We used fibroblasts from Ae2-deficient (Ae2(a,b)(-/-)) mice to study the effects of an alkaline shift in resting intracellular pH (pH(i)) on the activation of cAMP signaling and gene expression. Ae2(a,b)(-/-) fibroblasts show increased pH(i) (by 0.22 +/- 0.03 unit) compared with wild type cells at extracellular pH (pH(o)) 7.4 and 37 degrees C. This shift in resting pH(i) is associated with an up-regulation of bicarbonate-activated soluble adenylyl cyclase expression, increased cAMP production, Creb phosphorylation, inducible cAMP early repressor 1 mRNA expression, and impaired activation of c-Fos transcription by forskolin. These results highlight the importance of bicarbonate transport via Ae2 in maintaining pH(i) homeostasis in cultured mouse fibroblasts and unveil the role of cAMP in the cellular response to chronic alkalization, which putatively includes an inducible cAMP early repressor 1-mediated attenuation of phosphorylated Creb activity.

Primary biliary cirrhosis (PBC) is a cholestatic disease associated with autoimmune phenomena and alterations in both biliary bicarbonate excretion and expression of the bicarbonate carrier AE2. The bile acid ursodeoxycholic acid (UCDA) is currently used in treatment of cholestatic liver diseases and is the treatment of choice in PBC; however, a subset of PBC patients respond poorly to UDCA monotherapy. In these patients, a combination of UDCA and glucocorticoid therapy appears to be beneficial. To address the mechanism of this benefit, we analyzed the effects of UDCA and dexamethasone on AE2 gene expression in human liver cells from hepatocyte and cholangiocyte lineages. The combination of UDCA and dexamethasone, but not UDCA or dexamethasone alone, increased the expression of liver-enriched alternative mRNA isoforms AE2b1 and AE2b2 and enhanced AE2 activity. Similar effects were obtained after replacing UDCA with UDCA conjugates. In in vitro and in vivo reporter assays, we found that a UDCA/dexamethasone combination upregulated human AE2 alternate overlapping promoter sequences from which AE2b1 and AE2b2 are expressed. In chromatin immunoprecipitation assays, we demonstrated that combination UCDA/dexamethasone treatment induced p300-related interactions between HNF1 and glucocorticoid receptor on the AE2 alternate promoter. Our data provide a potential molecular explanation for the beneficial effects of the combination of UDCA and glucocorticoids in PBC patients with inadequate response to UDCA monotherapy.

Human fibroblasts in cell culture converted the epoxide intermediate leukotriene A4 into the potent chemotaxin leukotriene B4. The identity of leukotriene B4 was ascertained by its mobility in reverse-phase high performance liquid chromatography, ultraviolet spectroscopy and gas chromatography/mass spectrometry. The presence of the enzyme responsible for the conversion (i.e. leukotriene A4 hydrolase), as well as the corresponding mRNA, were demonstrated by Western and Northern blot analyses. Leukotriene-A4-hydrolase enzyme activity, protein and mRNA were all enhanced (approximately threefold) in human fibroblasts that had been transformed by simian virus 40.

One of the mechanisms by which epithelial cells regulate intracellular pH is exchanging bicarbonate for Cl(-). We tested the hypothesis that in ameloblasts the anion exchanger-2 (Ae2) is involved in pH regulation during maturation stage amelogenesis. Quantitative X-ray microprobe mineral content analysis, scanning electron microscopy, histology, micro-computed tomography and Ae2 immuno-localisation analyses were applied to Ae2-deficient and wild-type mouse mandibles. Immuno-localisation of Ae2 in wild-type mouse incisors showed a very strong expression of Ae2 in the basolateral membranes of the maturation stage ameloblasts. Strikingly, zones of contiguous ameloblasts were found within the maturation stage in which Ae2 expression was extremely low as opposed to neighbouring cells. Maturation stage ameloblasts of the Ae2(a,b)(-/-) mice failed to stain for Ae2 and showed progressive disorganisation as enamel development advanced. Maturation stage enamel of the Ae2(a,b)(-/-) mice contained substantially less mineral and more protein than wild-type enamel as determined by quantitative X-ray microanalysis. Incisor enamel was more severely affected than molar enamel. Scanning electron microscopy revealed that the rod-inter-rod structures of the Ae2(a,b)(-/-) mice incisor enamel were absent. Mineral content of dentine and bone of Ae2(a,b)(-/-) mice was not significantly different from wild-type mice. The enamel from knockout mouse teeth wore down much faster than that from wild-type litter mates. Basolateral bicarbonate secretion via the anionic exchanger Ae2 is essential for mineral growth in the maturation stage enamel. The observed zonal expression of Ae2 in the maturation stage ameloblasts is in line with a model for cyclic proton secretion during maturation stage amelogenesis.

Canalicular bile is modified along bile ducts through reabsorptive and secretory processes regulated by nerves, bile salts, and hormones such as secretin. Secretin stimulates ductular cystic fibrosis transmembrane conductance regulator (CFTR)-dependent Cl- efflux and subsequent biliary HCO3- secretion, possibly via Cl-/HCO3- anion exchange (AE). However, the contribution of secretin to bile regulation in the normal rat, the significance of choleretic bile salts in secretin effects, and the role of Cl-/HCO3- exchange in secretin-stimulated HCO3- secretion all remain unclear. Here, secretin was administered to normal rats with maintained bile acid pool via continuous taurocholate infusion. Bile flow and biliary HCO3- and Cl- excretion were monitored following intrabiliary retrograde fluxes of saline solutions with and without the Cl- channel inhibitor 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) or the Cl-/HCO3- exchange inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). Secretin increased bile flow and biliary excretion of HCO3- and Cl-. Interestingly, secretin effects were not observed in the absence of taurocholate. Whereas secretin effects were all blocked by intrabiliary NPPB, DIDS only inhibited secretin-induced increases in bile flow and HCO3- excretion but not the increased Cl- excretion, revealing a role of biliary Cl-/HCO3- exchange in secretin-induced, bicarbonate-rich choleresis in normal rats. Finally, small hairpin RNA adenoviral constructs were used to demonstrate the involvement of the Na+-independent anion exchanger 2 (AE2) through gene silencing in normal rat cholangiocytes. AE2 gene silencing caused a marked inhibition of unstimulated and secretin-stimulated Cl-/HCO3- exchange. In conclusion, maintenance of the bile acid pool is crucial for secretin to induce bicarbonate-rich choleresis in the normal rat and that this occurs via a chloride-bicarbonate exchange process consistent with AE2 function.

AE2 (SLC4A2) is the member of the Na + -independent anion exchanger (AE) family putatively involved in the secretion of bicarbonate to bile. In humans, three variants of AE2 mRNA have been described: the full-length transcript AE2a (expressed from the upstream promoter in most tissues), and alternative transcripts AE2b 1 and AE2b 2 (driven from alternate promoter sequences in a tissue-restricted manner, mainly in liver and kidney). These transcripts would result in AE protein isoforms with short N-terminal differences. To ascertain their translation, functionality, and membrane sorting, we constructed expression vectors encoding each AE2 isoform fused to GFP at the C-terminus. Transfected HEK293 cells showed expression of functional GFP-tagged AE2 proteins, all three isoforms displaying comparable AE activities. Primary rat hepatocytes transfected with expression vectors and repolarized in a collagen-sandwich configuration showed a microtubule-dependent apical sorting of each AE2 isoform. This shared apical sorting is liver-cell specific, as sorting of AE2 isoforms was basolateral in control experiments on polarized kidney MDCK cells. Hepatocytic apical targeting of AE2 isoforms suggests that they all may participate in the canalicular secretion of bicarbonate to bile.

Complementary DNA expression of mature human serum albumin was engineered into potato plants under the transcriptional control of patatin B33 promoter and potato proteinase inhibitor II terminator. Protein secretion was achieved by using the signal sequence from potato proteinase inhibitor II. Recombinant albumin accumulated up to 0.2% of total soluble tuber protein in single transformant lines, regardless of the potato cultivar used. Electrophoretic mobility and N-terminal amino acid sequence analysis of partially purified recombinant albumin confirmed proper processing of an immune responsive recombinant albumin, and revealed that the proteinase inhibitor II signal sequence was correctly removed. No further optimisation of these yields was obtained by HSA expression in patatin antisense plants (line Pas58). Subcellular localisation showed that recombinant protein was successfully targeted to the apoplast. Potato tubers may be used, by applying this technology, to produce other heterologous proteins of interest in the biopharmaceutical industry.

Primary biliary cirrhosis (PBC) is a disorder of unknown origin with autoimmune features. Recently, impaired biliary secretion of bicarbonate has been shown in patients with PBC. Here we have investigated whether bile duct epithelial cells isolated from PBC patients exhibit defects in transepithelial bicarbonate transport by analyzing the activities of 2 ion exchangers, Cl(-)/HCO3(-) anion exchanger 2 (AE2) and Na(+)/H(+) exchanger (NHE) in isolated cholangiocytes. AE2 and NHE activities were studied in basal conditions and after stimulation with cyclic adenosine monophosphate (cAMP) and extracellular adenosine triphosphate (ATP), respectively. Cholangiocytes were grown from needle liver biopsies from 12 PBC patients, 8 normal controls, and 9 patients with other liver diseases. Also, intrahepatic cholangiocytes were cultured after immunomagnetic isolation from normal liver tissue (n = 6), and from recipients undergoing liver transplantation for end-stage PBC (n = 9) and other forms of liver disease (n = 8). In needle-biopsy cholangiocytes, basal AE2 activity was significantly decreased in PBC as compared with normal livers and disease controls. In addition, we observed that though cAMP increased AE2 activity in cholangiocytes from both normal and non-PBC livers, this effect was absent in PBC cholangiocytes. Similarly, though in cholangiocytes from normal and disease control livers extracellular ATP induced a marked enhancement of NHE activity, cholangiocytes from PBC patients failed to respond to purinergic stimulation. In conclusion, our findings provide functional evidence that PBC cholangiocytes exhibit a widespread failure in the regulation of carriers involved in transepithelial H(+)/HCO3(-) transport, thus, providing a molecular basis for the impaired bicarbonate secretion in this cholestatic syndrome.

We investigated the expression of glucocorticoid receptors (GcRs) in the intrahepatic biliary epithelium and the role of corticosteroids in the regulation of cholangiocyte secretion.GcR was studied by immunohistochemistry, reverse-transcription polymerase chain reaction, and Western blots. The effects of dexamethasone and budesonide on biliary bicarbonate excretion and H+/HCO3- transport processes were investigated in bile fistula rats, isolated intrahepatic bile duct units (IBDUs), and purified cholangiocytes.GcRs were expressed by rat cholangiocytes. Although acute administration of corticosteroids showed no effect, treatment for 2 days with dexamethasone or budesonide increased (P0.05) biliary bicarbonate concentration and secretion, which were blocked by the specific GcR antagonist, RU-486. IBDUs isolated from rats treated with dexamethasone or budesonide showed an increased (P0.05) activity of the Na+/H+ exchanger (NHE1 isoform) and Cl-/HCO3- exchanger (AE2 member), which was blocked by RU-486. Protein expression of NHE1 and AE2 and messenger RNA for NH1 but not AE2 were increased (P0.05) in isolated cholangiocytes by dexamethasone treatment.The intrahepatic biliary epithelium expresses GcR and responds to corticosteroids by increasing bicarbonate excretion in bile. This is caused by corticosteroid-induced enhanced activities and protein expression of transport processes driving bicarbonate excretion in the biliary epithelium.

Background/Aims : The understanding of the physiology and function of human biliary epithelial cells (hBEC) has been improved by studies in monolayer culture systems. The aim was to develop a polarized model to elucidate the mechanisms of ductular morphogenesis and functional differentiation of hBEC. Methods : The morphological, phenotypic and functional properties of hBEC cultured as three-dimensional aggregates in collagen gel were assessed in medium supplemented with (or without) human hepatocyte growth factor (hHGF) and foetal bovine serum. Results : In the absence of added mitogens and serum, cells maintained as morphologically polarized aggregates, organized around a central lumen, were positive for phenotypic markers of biliary epithelium and negative for markers of other cell types. Functional markers, gamma-glutamyl-transferase, anion exchanger-2, responses to gamma interferon and forskolin induced secretion, were preserved. hHGF increased both the size and number of aggregates and induced hBEC to invade the gel and lumena forming anastomosing networks of cells. Conclusions : Collagen gel culture in the absence of added growth factors and serum provides a model for analysis of the polarized functions of hBEC. The formation of poorly organized cords of cells in response to hHGF suggests that collagen gel culture may provide a model for the investigation of atypical ductular morphogenesis of the human biliary tract.

The molecular organization of the AE2 (SLC4A2) gene, a member of the multigene family encoding sodium-independent chloride/bicarbonate anion exchangers, has previously been described in both humans and rats. In these two species, AE2 shows alternate promoter usages and tissue-specific expression of isoforms in a similar, but not identical, fashion. Here we report the molecular cloning and organization of the entire mouse AE2 gene. The gene consists of 23 exons and 22 introns and spans about 17 kb. Moreover, it drives transcription of N-terminal truncated isoforms from alternate promoter sequences in a way analogous to that described for rat and/or human orthologs. Thus, sequences within intron 2 function as overlapping alternate promoters for truncated isoforms AE2b1 and AE2b2, and sequences of intron 5 drive transcription of isoforms AE2c1 and AE2c2. Each of these variants has a specific alternative first exon, while remaining exons are common to the complete form of the message AE2a, the diversity at 5′ leading to different N-termini in corresponding encoded proteins. As expected, mouse AE2 promoter sequences and the patterns of tissue expression of AE2 isoforms resemble rat counterparts more closely than human ones.

Failure of distal nephrons to excrete excess acid results in the “distal renal tubular acidoses” (dRTA). Early childhood features of autosomal recessive dRTA include severe metabolic acidosis with inappropriately alkaline urine, poor growth, rickets, and renal calcification. Progressive bilateral sensorineural hearing loss (SNHL) is evident in approximately one-third of patients. We have recently identified mutations in ATP6B1, encoding the B-subunit of the collecting-duct apical proton pump, as a cause of recessive dRTA with SNHL. We now report the results of genetic analysis of 13 kindreds with recessive dRTA and normal hearing. Analysis of linkage and molecular examination of ATP6B1 indicated that mutation in ATP6B1 rarely, if ever, accounts for this phenotype, prompting a genomewide linkage search for loci underlying this trait. The results strongly supported linkage with locus heterogeneity to a segment of 7q33-34, yielding a maximum multipoint LOD score of 8.84 with 68% of kindreds linked. The LOD-3 support interval defines a 14-cM region flanked by D7S500 and D7S688. That 4 of these 13 kindreds do not support linkage to rdRTA2 and ATP6B1 implies the existence of at least one additional dRTA locus. These findings establish that genes causing recessive dRTA with normal and impaired hearing are different, and they identify, at 7q33-34, a new locus, rdRTA2, for recessive dRTA with normal hearing.

Na+-independent anion exchangers, a family of membrane proteins that mediate electroneutral exchanges of chloride and bicarbonate ions across the cell membrane, are considered to be involved in intracellular pH regulation as well as in transepithelial acid/base transport. Previous immunohistochemical data have shown that anion-exchanger-2 (AE2) protein is expressed in the liver parenchyma, localizing at both the canaliculi and the luminal surfaces of intrahepatic bile ducts, where it may have a role in the biliary secretion of bicarbonate. In the present study, we have carried out in situ hybridization experiments on biopsies of human liver using three overlapping antisense anion-exchanger-2 riboprobes. Anion-exchanger-2 mRNA signals were localized mainly in the cytoplasm of terminal and interlobular bile-duct cells, whereas weaker signals were observed in bile-duct cells of larger intrahepatic ducts. Furthermore, some hepatocytes, mostly periportal, contained detectable anion-exchanger-2 mRNA signals in their cytoplasm. No hybridization signals were observed in controls with sense riboprobes, with omission of the antisense probe, or with treatment of the sections with RNase before hybridizations. Finally, intense anion-exchanger-2 hybridization signals were observed in lymphomononuclear cells in sinusoids and in portal infiltrates. Immunocytochemical data from reverse-phase sections suggest that these cells correspond to some of the CD45R+ (UCHL1+) T lymphocytes resident in the liver.

Background/Aims: In transporting epithelia, like the biliary epithelium, most plasma membrane proteins present a polarized distribution, essential for the maintenance of the structural and functional properties of the epithelium. We therefore analyzed the expression of polarized plasma membrane proteins by human biliary epithelial cells in order to compare them with other transporting epithelial cells and to search for differences in plasma membrane protein expression between their different anatomical subsets. Methods: We designed an in situ immunohistochemical study of the various anatomical compartments of the human biliary tract in order to assess the pattern of expression of selected polarized plasma membrane proteins, including integrin receptors, ectopeptidases, membrane transporters and GPI-linked proteins. Results: All biliary epithelial cells expressed the same repertoire of integrins, except for integrin chain α5, restricted to the intra-hepatic compartments. All biliary epithelial cells expressed the following apical ectopeptidases: aminopeptidase-N, neutral-endopeptidase, dipeptidyl-peptidase IV. All biliary epithelial cells epxressed the mebrane transporter Na + K + -ATPase, restricted to the basolateral domain, and the apical transporters CFTR and MDR-1. The apical AE2 anion exchanger was restricted to the small intra-hepatic bile ducts and the gallbladder. The GPI-linked protein protectin was basolateral in the intrahepatic bile ducts and apical in the gallbladder. Conclusions: The structural organization of the plasma membrane of biliary epithelial cells is very similar to that of other simple epithelia and exhibits a limited degree of heterogeneity.

BACKGROUND/AIMS: Cysteinyl-containing leukotrienes seem to exert a cholestatic effect. However, leukotriene inhibitors were found to reduce bile salt efflux in isolated rat hepatocytes, suggesting a role for leukotrienes in bile flow formation. METHODS: In the isolated rat liver, the effects of two different concentrations of leukotriene C4 on bile flow and bile salt excretion are analyzed, as well as the possible effect of taurocholate on the hepatic production of cysteinyl-containing leukotrienes. RESULTS: Leukotriene C4 (0.25 fmol) increased bile salt excretion (+22.2%; P < 0.05), whereas a much higher dose (0.25 x 10(6) fmol) showed the known cholestatic effect, reducing bile salt excretion (-25.9%; P < 0.01). These dose-dependent biphasic effects were specific because they could be prevented by the simultaneous administration of cysteinyl-containing leukotriene antagonists. On the other hand, taurocholate administration induced a dose-dependent increase in biliary excretion of cysteinyl-containing leukotrienes. Furthermore, taurocholate increased messenger RNA levels of 5-lipoxygenase, a key enzyme in leukotriene biosynthesis. Taurocholate increase of hepatocyte intracellular calcium was not significant, suggesting that taurocholate effects are not mediated by stimulation of calcium metabolism. CONCLUSIONS: These results constitute evidence for the existence of a positive feedback mechanism by which bile salts stimulate the synthesis of leukotrienes that, in turn, stimulate bile salt excretion.

Corrigendum to “Murine ameloblasts are immunonegative for Tcirg1, the v-H-ATPase subunit essential for the osteoclast plasma membrane pump” [Bone 50/4 (2012) 901–908] Antonius L.J.J. Bronckers⁎, Donacian M. Lyaruu, Theodore J. Bervoets , Juan F. Medina, Pamela DenBesten, Johan Richter, Vincent Everts a a Dept of Oral Cell Biology, ACTA, University of Amsterdam and VU University Amsterdam, Research Institute MOVE, Gustav Mahlerlaan 3004, Amsterdam, The Netherlands b Division of Gene Therapy and Hepatology, University Hospital/School of Medicine/CIMA, University of Navarra, and Ciberehd, Pamplona, Spain c Dept of Orofacial Sciences, School of Dentistry, University of California at San Francisco, CA, USA d Molecular Medicine and Gene Therapy, Lund Stem Cell Centre, University of Lund, Lund, Sweden

Purpose BMS-936558 is a monoclonal antibody that blocks the PD-1 co-inhibitory receptor expressed by activated T cells. This study describes its activity and safety in pts with previously treated advanced MEL. Methods BMS-936558 was administered IV q2wk to pts with various tumors at 0.1 - 10 mg/kg during dose-escalation and/or cohort expansion. Pts received up to 12 cycles (4 doses/cycle) of treatment or until unacceptable toxicity, confirmed progressive disease, or complete response. Clinical activity was assessed by RECIST v1.0. Results As of Feb 24, 2012, 104 MEL pts had received BMS-936558 at 0.1 (n = 17), 0.3 (n = 19), 1 (n = 31), 3 (n = 17), or 10 mg/kg (n = 20). ECOG performance status was 0/1/2 in 63/38/3 pts, respectively. Most pts (67/104) had received prior immunotherapy (IT); prior anti-CTLA-4, -PD-1, or -PD-L1 was not permitted. The number of prior therapies was 1 (39%), 2 (35%), or ≥3 (26%). Median therapy duration was 20 wks (range 2.0 - 121.7 wks). The incidence of grade 3 - 4 related AEs was 20% and included gastrointestinal (4%), endocrine (2%), and hepatobiliary disorders (1%). There were no drug-related deaths in MEL pts. Clinical activity (responses or prolonged stable disease) was observed at all doses (Table). Of the 26/94 (28%) evaluable responders, 19 (73%) are ongoing ranging from 1.9+ to 24.9+ months. For the 23 responders followed ≥6 months from first dose on study, 16 (70%) are progression free. ORs occurred in pts with visceral or bone metastases. Six pts (6%; 95% CI 2 - 13%) had prolonged SD (≥24 wk); 3 pts had a persistent decrease in target lesion tumor burden in the presence of new lesions and were not categorized as responders. Conclusions BMS-936558 had durable clinical benefit in pts with advanced MEL, including those who had received prior IT. Additional long-term follow-up data will be reported. Dose, (mg/kg) No. ptsa ORR, No. pts (%) [95% CI] PFSR at 24 wk (%) [95% CI] 0.1 14 4 (29) [8 - 58] 40 [13 - 66] 0.3 16 3 (19) [4 - 46] 31 [9 - 54] 1 27 8 (30) [14 - 50] 45 [26 - 65] 3 17 7 (41) [18 - 67] * 55 [30 - 80] 10 20 4 (20) [6 - 44] 30 [9 - 51] * 1 CR aResponse-evaluable pts dosed by 7/01/2011 ORR = objective response rate ([{CR + PR} ÷ n] × 100); PFSR = progression-free survival rate. Disclosure J. Sosman: Research Funding: Bristol-Myers Squibb (myself). M. Sznol: Consultant or Advisory Role: Bristol-Myers Squibb (myself, compensated). Research Funding: Bristol-Myers Squibb (myself, clinical trials funding). D.F. McDermott: Advisory Board Role: Bristol-Myers Squibb (myself). R. Carvajal: Research Funding: Bristol-Myers Squibb (myself). S.L. Topalian: Consultant or Advisory Role: Bristol-Myers Squibb (myself, immediate family member, uncompensated). Research Funding: Bristol-Myers Squibb (myself). J.M. Wigginton: Employment or Leadership Position: Bristol-Myers Squibb (myself, employment, compensated). Stock Ownership: Bristol-Myers Squibb (myself). G. Kollia: Employment or Leadership Role: Bristol-Myers Squibb (employment, myself, compensated). Stock Ownership: Bristol-Myers Squibb/BMY stocks (myself). A. Gupta: Employment or Leadership Role: Bristol-Myers Squibb (employment, myself, compensated). Stock Ownership: Bristol-Myers Squibb (myself). F.S. Hodi: Consultant or Advisory Role: Bristol-Myers Squibb (myself, uncompensated). Research Funding: Bristol-Myers Squibb (myself). All other authors have declared no conflicts of interest.

X-ray crystallographic analysis and sequence comparisons of zinc enzymes have identified onsensus sequences for catalytic and structural zinc binding sites (1). Such reference structures have served to predict zinc binding ligands among members of related zinc enzyme families and also, more noticeable, in apparently unrelated proteins. Thus, comparison of the amino acid sequence of LTA4 hydrolase with the corresponding primary structures of certain aminopeptidases and neutral proteases, typified by thermolysin, revealed the presence of a putative catalytic zinc site (1, 2). Consequently, LTA4 hydrolase was found, not only to contain one zinc atom per molecule, essential for the catalytic activity, but also to possess a zinc-dependent peptidase activity towards synthetic amides (3–5).

Exposure of human peripheral blood mononuclear cells (PBMC) to the stilbene derivative DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) (60 microM and above) significantly increased the release of tumor necrosis factor-alpha (TNF-alpha), as determined by TNF-alpha activity in the incubation media. When the TNF-alpha message was analyzed in PBMC by a reverse transcription/polymerase chain reaction (RT/PCR)-based procedure, it was found that incubation with DIDS (60 microM) was followed by a time-dependent accumulation of TNF-alpha mRNA. Measurements of intracellular pH showed that the presence of increasing concentrations of DIDS resulted in a progressive intracellular alkalinization of PBMC. It is suggested that the known DIDS effect of inhibiting transmembrane anion exchange, i.e., chloride/bicarbonate exchange, might play a role in the stimulation of TNF-alpha production by PBMC exposed to DIDS.

Recombinant mouse leukotriene A 4 hydrolase was expressed in Escherichia coli as a fusion protein with ten additional amino acids at the amino terminus and was purified to apparent homogeneity by means of precipitation, anion exchange, hydrophobic interaction and chromatofocusing chromatographies. By atomic absorption spectrometry, the enzyme was shown to contain one mol of zinc/mol of enzyme. Apparent kinetic constants ( K m and V max ) for the conversion of leukotriene A 4 to leukotriene B 4 (at 0°C, pH 8) were 5 μM and 900 nmol/mg per min, respectively. The purified enzyme also exhibited significant peptidase activity towards the synthetic amide alanine-4-nitroanilide. K m and V max for this reaction (at 37°C, pH 8) were 680 μM and 365 nmol/mg per min, respectively. Apo-leukotriene A 4 hydrolase, prepared by treating the enzyme with 1,10-phenanthroline, was virtually inactive with respect to both enzymatic activities, but could be reactivated by addition of stoichiometric amounts of zinc or cobalt. Exposure of the enzyme to leukotriene A 4 resulted in a dose-dependent inactivation of both enzyme activities.

Three mutants of recombinant mouse leukotriene A4 (LTA4) hydrolase (3.3.2.6) were produced by site-directed mutagenesis on cDNA. The codons corresponding to His-295, His-299, or Glu-318 were replaced by codons encoding tyrosine, tyrosine, and glutamine, respectively. The mutated cDNAs were expressed in Escherichia coli, and the three mutated proteins were purified to apparent homogeneity. None of these mutants contained significant amounts of zinc, as determined by atomic absorption spectrometry, and all of them were practically devoid of both LTA4 hydrolase and peptidase enzyme activities. Nevertheless, the mutated proteins could be positively identified by their immunoreactivities with an antiserum for human LTA4 hydrolase in immunoblot analysis. Site-directed mutagenesis was also carried out on human LTA4 hydrolase cDNA. Codons encoding His-295, His-299, and Glu-318 were replaced by ones encoding tyrosine, leucine, and alanine, respectively, and the three mutants were expressed in E. coli. The LTA4 hydrolase activities of the total soluble proteins produced in these expressions were less than 10% of that obtained for bacteria harboring nonmutated cDNA. In agreement with earlier predictions, our experimental data demonstrate that His-295, His-299, and Glu-318 constitute the three ligands of the intrinsic zinc atom in LTA4 hydrolase. Additionally, the combined loss of enzyme activities and zinc content in the purified mutated mouse proteins, emphasizes the critical role of the zinc atom for catalysis, whereas the virtually identical chromatographic behaviors of the mutated and nonmutated mouse LTA4 hydrolase proteins suggest that the metal is of limited importance for the maintenance of the enzyme tertiary structure.

A cDNA clone for mouse leukotriene A4 hydrolase encoding the full sequence of the enzyme was isolated from a mouse spleen λ ZAP-II library. The identification was ascertained by expression of enzyme activity in Escherichia coli. The encoded protein has 610 amino acids and exhibits an extensive identity (93%) with the human leukotriene A4 hydrolase. A region spanning between residues 233 and 340, where the zinc binding site is located, was found to be perfectly conserved between the two species. We found six sites of polymorphism in the cDNA sequence of mouse LTA4 hydrolase, one of which leads to a difference in the encoded amino acid. The polymorphism of cDNA was confirmed by reverse transcription-PCR sequencing of mouse spleen total RNA, prepared as a mixture from ten different strains.

Leukotriene (LT) A4 hydrolase converts the unstable epoxide intermediate LTA4 into the potent proinflammatory compound LTB4. The formation of LTA4 is catalyzed by the enzyme 5-lipoxygenase and involves the dioxygenation of arachidonic acid with subsequent epoxide formation (1).

Canalicular bile is modified along bile ducts through reabsorptive and secretory processes regulated by nerves, bile salts, and hormones such as secretin. Secretin stimulates ductular cystic fibrosis transmembrane conductance regulator (CFTR)–dependent Cl efflux and subsequent biliary HCO3 secretion, possibly via Cl /HCO3 anion exchange (AE). However, the contribution of secretin to bile regulation in the normal rat, the significance of choleretic bile salts in secretin effects, and the role of Cl /HCO3 exchange in secretin-stimulatedHCO3 secretion all remainunclear.Here, secretinwas administered tonormal ratswithmaintainedbile acidpool via continuous taurocholate infusion. Bile flow and biliary HCO3 and Cl excretion were monitored following intrabiliary retrograde fluxes of saline solutions with and without the Cl channel inhibitor 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) or the Cl /HCO3 exchange inhibitor 4,4 -diisothiocyanatostilbene-2,2 -disulfonic acid (DIDS). Secretin increased bile flow and biliary excretion ofHCO3 andCl . Interestingly, secretin effects were not observed in the absence of taurocholate.Whereas secretin effects were all blocked by intrabiliary NPPB, DIDS only inhibited secretin-induced increases in bile flow and HCO3 excretion but not the increased Cl excretion, revealing a role of biliary Cl /HCO3 exchange in secretininduced, bicarbonate-rich choleresis in normal rats. Finally, small hairpin RNA adenoviral constructs were used to demonstrate the involvement of the Na -independent anion exchanger 2 (AE2) through gene silencing in normal rat cholangiocytes. AE2 gene silencing caused amarked inhibition of unstimulated and secretin-stimulated Cl /HCO3 exchange. In conclusion, maintenance of the bile acid pool is crucial for secretin to induce bicarbonate-rich choleresis in the normal rat and that this occurs via a chloride–bicarbonate exchange process consistent with AE2 function. (HEPATOLOGY 2006;43:266-275.)

Primary canalicular bile undergoes a process of fluidization and alkalinization along the biliary tract that is influenced by several factors including hormones, innervation/neuropeptides, and biliary constituents. The excretion of bicarbonate at both the canaliculi and the bile ducts is an important contributor to the generation of the so-called bile-salt independent flow. Bicarbonate is secreted from hepatocytes and cholangiocytes through parallel mechanisms which involve chloride efflux through activation of Cl- channels, and further bicarbonate secretion via AE2/SLC4A2-mediated Cl-/HCO3- exchange. Glucagon and secretin are two relevant hormones which seem to act very similarly in their target cells (hepatocytes for the former and cholangiocytes for the latter). These hormones interact with their specific G protein-coupled receptors, causing increases in intracellular levels of cAMP and activation of cAMP-dependent Cl- and HCO3- secretory mechanisms. Both hepatocytes and cholangiocytes appear to have cAMP-responsive intracellular vesicles in which AE2/SLC4A2 colocalizes with cell specific Cl- channels (CFTR in cholangiocytes and not yet determined in hepatocytes) and aquaporins (AQP8 in hepatocytes and AQP1 in cholangiocytes). cAMP-induced coordinated trafficking of these vesicles to either canalicular or cholangiocyte lumenal membranes and further exocytosis results in increased osmotic forces and passive movement of water with net bicarbonate-rich hydrocholeresis.