S100A9 is a biliary protein marker of disease activity in primary sclerosing cholangitis.

BACKGROUND AND AIMS: Bile analysis has the potential to serve as a surrogate marker for inflammatory and neoplastic disorders of the biliary epithelium and may provide insight into biliary pathophysiology and possible diagnostic markers. We aimed to identify biliary protein markers of patients with primary sclerosing cholangitis (PSC) by a proteomic approach. METHODS: Bile duct-derived bile samples were collected from PSC patients (n = 45) or patients with choledocholithiasis (n = 24, the control group). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to analyse the proteins, 2-D-gel patterns were compared by densitometry, and brush cytology specimens were analysed by RT-PCR. RESULTS: A reference bile-duct bile proteome was established in the control group without signs of inflammation or maligancy comprising a total of 379 non-redundant biliary proteins; 21% were of unknown function and 24% had been previously described in serum. In PSC patients, the biliary S100A9 expression was elevated 95-fold (p<0.005), serum protein expression was decreased, and pancreatic enzyme expression was unchanged compared to controls. The S100A9 expression was 2-fold higher in PSC patients with high disease activity than in those with low activity (p<0.05). The brush cytology specimens from the PSC patients with high disease activity showed marked inflammatory activity and leukocyte infiltration compared to the patients with low activity, which correlated with S100A9 mRNA expression (p<0.05). CONCLUSIONS: The bile-duct bile proteome is complex and its analysis might enhance the understanding of cholestatic liver disease. Biliary S100A9 levels may be a useful marker for PSC activity, and its implication in inflammation and carcinogenesis warrants further investigation.

Sustained hydrogen peroxide induces iron uptake by transferrin receptor-1 independent of the iron regulatory protein/iron-responsive element network.

Local and systemic inflammatory conditions are characterized by the intracellular deposition of excess iron, which may promote tissue damage via Fenton chemistry. Because the Fenton reactant H(2)O(2) is continuously released by inflammatory cells, a tight regulation of iron homeostasis is required. Here, we show that exposure of cultured cells to sustained low levels of H(2)O(2) that mimic its release by inflammatory cells leads to up-regulation of transferrin receptor 1 (TfR1), the major iron uptake protein. The increase in TfR1 results in increased transferrin-mediated iron uptake and cellular accumulation of the metal. Although iron regulatory protein 1 is transiently activated by H(2)O(2), this response is not sufficient to stabilize TfR1 mRNA and to repress the synthesis of the iron storage protein ferritin. The induction of TfR1 is also independent of transcriptional activation via hypoxia-inducible factor 1alpha or significant protein stabilization. In contrast, pulse experiments with (35)S-labeled methionine/cysteine revealed an increased rate of TfR1 synthesis in cells exposed to sustained low H(2)O(2) levels. Our results suggest a novel mechanism of iron accumulation by sustained H(2)O(2), based on the translational activation of TfR1, which could provide an important (patho) physiological link between iron metabolism and inflammation.

Nox1 induces differentiation resistance in immortalized human keratinocytes generating cells that express simple epithelial keratins.

We have shown that superoxide radical-generating NADPH oxidase 1 (Nox1) is increased in intermediate human transformed cells. It was unknown whether Nox1 overexpression could accelerate early transformation steps. We demonstrated that Nox1 rendered human immortalized (GM16) keratinocytes resistant against Ca(2+)/serum-induced differentiation. Nox1-transfected cells produced fast dividing resistant cells within 7-10 days after DMEM exposure. Progenitor lines (or Nox1 lines) were reproducibly generated from Nox1-transfected cells, while no lines were obtained from control transfections. From several attempts to generate control cells, one resistant population was obtained from untransfected GM16 cells after a 6-week DMEM exposure. Prolonged passaging of the control line could induce Nox1. Compared with the control line, Nox1 lines showed greater expression of Nox1, Rac1, p47phox, p67phox, NOXO1, and NOXA1 with concomitant increased superoxide generation. All five Nox1 lines contained varying amounts of E-cadherin, involucrin, vimentin, and K8/K18, while the control line did not. Since vimentin and K8/K18 are associated with malignant progression in different types of human epithelial tumors, our data demonstrate that Nox1 accelerated neoplastic-like progression by inducing generation of progenitor cells. Our data also emphasize the importance of Nox1 in inducing resistance against differentiation-induced cell death, suggesting a contribution of Nox1 and its oxidants during early stage of cell transformation.

Localization of the iron-regulatory proteins hemojuvelin and transferrin receptor 2 to the basolateral membrane domain of hepatocytes.

The newly discovered proteins hemojuvelin (Hjv) and transferrin receptor type 2 (TfR2) are involved in iron metabolism. Mutations in the Hjv and TfR2 gene cause hemochromatosis. We investigated the expression and cellular localization of Hjv and TfR2 in rat and human liver. The expression of Hjv and TfR2 was shown on mRNA and protein level by RT-PCR and immunoblot experiments. Their cellular localization was studied by immunofluorescence with antibodies raised against Hjv and TfR2. Hjv and TfR2 are present in human and rat liver and in primary human hepatocytes. Antisera raised against Hjv identified immunoreactive proteins with an apparent size of 44 and 46 kDa in immunoblot experiments of rat and human liver extracts, which are in accordance with the putative membrane-bound and cleaved soluble forms of this protein, respectively. TfR2 was detected as a 105 kDa protein corresponding to the predicted size of glycosylated TfR2 monomers. In immunofluorescence experiments, Hjv and TfR2 were found in rat liver only in hepatocytes. At the subcellular level, both proteins were predominantly localized to the basolateral membrane domain of hepatocytes. The localization of Hjv and TfR2 at the same membrane domain renders a functional interaction of these two proteins in iron homeostasis possible.

Iron stores modulate hepatic hepcidin expression by an HFE-independent pathway.

BACKGROUND/AIMS: In HFE-related hereditary hemochromatosis an inappropriately low hepatic expression of the iron-regulatory peptide hepcidin (encoded by HAMP) has been suggested to cause iron overload. The aim of the present study was to evaluate whether the hepatic expression of HAMP in relation to iron stores requires HFE or might involve other important iron-related genes including HJV (encoding hemojuvelin) and TFR2 (encoding transferrin receptor-2). METHODS: Using quantitative RT-PCR, the iron-dependent hepatic expression patterns of HAMP, HJV, and TFR2 were evaluated in human and murine HFE-related hemochromatosis. RESULTS: The overall level of hepatic HAMP expression in human and murine HFE-related hemochromatosis is impaired but can still be modulated by iron stores. Moreover, we demonstrate an HFE-independent correlation between the expression of HAMP and TFR2 in mouse and human livers. On the other hand, a strong correlation between the hepatic expression of HAMP and HJV was only found in hemochromatosis patients and Hfe-deficient mice. CONCLUSION: The central pathogenetic step in HFE-related hemochromatosis is an impaired basal expression of HAMP rather than a lack of HAMP upregulation in response to iron stores. An HFE-independent pathway that seems to involve TFR2 and HJV can regulate HAMP expression under conditions of iron overload.

Iron overload in adult Hfe-deficient mice independent of changes in the steady-state expression of the duodenal iron transporters DMT1 and Ireg1/ferroportin.

Patients suffering from hereditary hemochromatosis (HH) show progressive iron overload as a consequence of increased duodenal iron absorption. It has been hypothesized that mutations in the HH gene HFE cause misprogramming of the duodenal enterocytes towards a paradoxical iron-deficient state, resulting in increased iron transporter expression. Previous reports concerning gene expression levels of the duodenal iron transporters DMT1 and IREG1 in HH patients and animal models are controversial, however, and in many cases only mRNA expression levels were investigated. To analyze the duodenal expression of DMT1, Ireg1, Dcytb, and hephaestin and the association with iron overload in adult Hfe(-/-) mice, an Hfe(-/-) mouse line was generated. Duodenal DMT1 and Ireg1 protein levels, duodenal DMT1, Ireg1, Dcytb, hephaestin, and TfR1 mRNA levels, and hepatic hepcidin mRNA levels were quantified and the correlation to liver iron contents was calculated. We report that duodenal DMT1 and Ireg1 mRNA levels and DMT1 and Ireg1 protein levels remained unaffected by the Hfe deletion. Furthermore, duodenal hephaestin and TfR1 mRNA expression and hepatic hepcidin mRNA expression remained unaltered, while the duodenal mRNA expression of the brush border ferric reductase Dcytb was significantly increased in Hfe(-/-) mice. We found no correlation between the expression level of any of the analyzed transcripts and the liver iron content. In conclusion, the lack of correlation between DMT1 and Ireg1 protein expression and the liver iron content suggests that elevated duodenal iron transporter expression is not required for high liver iron overload. Hfe(-/-) mice do not necessarily display features of iron deficiency in the duodenum, indicated by an increase in mRNA and protein levels of DMT1 and Ireg1. Rather, the duodenal ferric reductase Dcytb may act as a possible mediator of iron overload in Hfe deficiency.

Hemochromatosis and transferrin receptor gene polymorphisms in chronic hepatitis C: impact on iron status, liver injury and HCV genotype.

Mild iron overload in chronic hepatitis C is associated with liver fibrosis, hepatitis C virus (HCV) genotype 1b infection, and an impaired response to interferon therapy. In this study we evaluated whether polymorphisms in the hemochromatosis gene HFE and the transferrin receptor gene TFR1 are associated with these typical findings. The study considered 246 HCV-infected patients and 200 blood donors as controls, in which C282Y, H63D, and S65C mutations ( HFE) and the S142G polymorphism ( TFR1) were detected. HCV genotype, serum ferritin levels, stainable intrahepatic iron, and grade of fibrosis according to the METAVIR score (F0-F4) were determined. In HCV-infected patients, heterozygosity for the C282Y mutation in HFE was significantly associated with elevated serum ferritin levels, stainable liver iron, and advanced fibrosis or cirrhosis (F2-F4). By multivariate logistic regression analysis the odds ratio for the development of advanced fibrosis or cirrhosis (F2-F4) was 2.5 for HCV-infected patients carrying a heterozygous C282Y mutation and 4.8 for HCV-infected patients with C282Y/H63D and C282Y/S65C compound heterozygosity. Heterozygosity for the C282Y mutation in HFE contributes to iron accumulation and fibrosis progression in chronic hepatitis C.

Expression of hepcidin in hereditary hemochromatosis: evidence for a regulation in response to the serum transferrin saturation and to non-transferrin-bound iron.

Experimental data suggest the antimicrobial peptide hepcidin as a central regulator in iron homeostasis. In this study, we characterized the expression of human hepcidin in experimental and clinical iron overload conditions, including hereditary hemochromatosis. Using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), we determined expression of hepcidin and the most relevant iron-related genes in liver biopsies from patients with hemochromatosis and iron-stain-negative control subjects. Regulation of hepcidin mRNA expression in response to transferrin-bound iron, non-transferrin-bound iron, and deferoxamine was analyzed in HepG2 cells. Hepcidin expression correlated significantly with serum ferritin levels in controls, whereas no significant up-regulation was observed in patients with hemochromatosis despite iron-overload conditions and high serum ferritin levels. However, patients with hemochromatosis showed an inverse correlation between hepcidin transcript levels and the serum transferrin saturation. Moreover, we found a significant correlation between hepatic transcript levels of hepcidin and transferrin receptor-2 irrespective of the iron status. In vitro data indicated that hepcidin expression is down-regulated in response to non-transferrin-bound iron. In conclusion, the presented data suggest a close relationship between the transferrin saturation and hepatic hepcidin expression in hereditary hemochromatosis. Although the causality is not yet clear, this interaction might result from a down-regulation of hepcidin expression in response to significant levels of non-transferrin-bound iron.

UbcH5A, a member of human E2 ubiquitin-conjugating enzymes, is closely related to SFT, a stimulator of iron transport, and is up-regulated in hereditary hemochromatosis.

SFT, a stimulator of iron (Fe) transport, has been described as a transmembrane protein that facilitates the uptake of ferrous and ferric iron in mammalian cells. This study was initiated to investigate the 5' regulatory region of SFT and its role in the etiology of hereditary hemochromatosis. Sequence analyses of the putative 5' regulatory region revealed that the SFT cDNA sequence corresponds to intron 6/exon 7 of UbcH5A, a member of E2 ubiquitin-conjugating enzymes, which is involved in the iron-dependent ubiquitination of the hypoxia-inducible factor (HIF) by the von Hippel-Lindau tumor suppressor (pVHL) E3 ligase complex. Further mRNA expression studies using a sequence-specific reverse transcriptase-polymerase chain reaction (RT-PCR) assay showed that UbcH5A is significantly up-regulated in the liver of iron-overloaded patients with hereditary hemochromatosis, as previously published for SFT. However, in vitro studies on HepG2 cells failed to demonstrate any significant UbcH5A regulation in response to iron loading or iron chelation. In conclusion, in vivo mRNA expression data previously obtained for SFT might be attributed to UbcH5A. The role of UbcH5A and the ubiquitination pathway in the etiology of hereditary hemochromatosis remains to be elucidated further.