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The secretion of bilirubin conjugates from hepatocytes into bile represents a decisive step in the prevention of hyperbilirubinemia. The bilirubin conjugates, monoglucuronosyl bilirubin (MGB) and bisglucuronosyl bilirubin (BGB), were previously suggested to be endogenous substrates for the apical multidrug resistance protein (

Regulation of bilirubin glucuronide transporters during hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the bilirubin glucuronide transporters, multidrug resistance-associated proteins (MRP)2 and 3, in rats with obstructive jaundice. Bile duct ligation (BDL) or sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL (n = 4, in each group). Serum and urine were collected to measure bilirubin levels just before animal killing. MRP2 And MRP3 mRNA expressions were determined by real-time RT-PCR. Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated bilirubin, unconjugated bilirubin, human bile, and sulfate-conjugated bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum bilirubin and urinary bilirubin excretion increased significantly after BDL. In the liver, the mRNA expression of MRP2 decreased 59, 86, and 82%, and its protein expression decreased 25, 74, and 93% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3 mRNA increased 138, 2,137, and 3,295%, and its protein expression increased 560, 634, and 612% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the mRNA expression of MRP2 increased 162, 73, and 21%, and its protein expression increased 387, 558, and 472% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The mRNA expression of MRP2 increased in renal proximal tubular epithelial cells after treatment with conjugated bilirubin, sulfate-conjugated bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve bilirubin clearance during obstructive jaundice.

Bilirubin is taken up from blood into hepatocytes by sinosuidal membrane transporters and then excreted into bile through the bile canalicular membrane mainly as bilirubin glucuronides. (1) Mechanism of bilirubin uptake into hepatocytes: many organic anions are incorporated into hepatocytes by organic anion transporting polypeptides (rat, oatp1, oatp2, oatp3; human, OATP), liver-specific transporter (rlst/HLST), and/or by organic anion transporters (OAT2, OAT3). Oatp1 and HLST transport bilirubin monoglucuronide. However, a transporter of unconjugated bilirubin in the sinusoidal membrane has not as yet been identified. Unconjugated bilirubin may also go across the hepatocyte sinusoidal membrane by a diffusion process. (2) Intrahepatic transport and conjugation of bilirubin: ligandin carries bilirubin to the endoplasmic reticulum (ER) of hepatocytes. In the ER, bilirubin is conjugated by bilirubin uridine diphosphate (UDP)-glycosyltransferase (bilirubin UGT; UGT1A1) to form mono- and diglucuronides of bilirubin. (3) Transport mechanism of bilirubin glucuronides across the hepatocyte canalicular membrane: at the canalicular membrane, bilirubin glucuronides are excreted into bile by multidrug resistance-associated protein 2 (MRP2), a member of the ATP-binding cassette transporter family. (4) Regurgitation of bilirubin glucuronides into blood: MRP3, which is located in the lateral membrane, transports bilirubin glucuronides into blood under conditions of impaired biliary bilirubin excretion.

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The innate immunity to viral infections induces a potent antiviral response mediated by interferons (IFN). Although IFN-c is detected during the acute stages of illness in the upper respiratory tract secretions and in the serum of influenza A virus-infected individuals, control of influenza A virus is not dependent upon IFN-c as evidenced by studies using anti-IFN-c Ab and IFN-c -/-mice. Thus, we hypothesized that IFN-c is not critical in host survival because influenza A virus has mechanisms to evade the antiviral activity of IFN-c. To test this, A549 cells, an epithelial cell line derived from lung adenocarcinoma, were infected with influenza virus strain A/Aichi/2/68 (H3N2) (Aichi) and/or stimulated with IFN-c to detect IFN-c-stimulated MHC class II expression. Influenza A virus infection inhibited IFN-c-induced up-regulation of HLA-DRa mRNA and the IFN-c induction of class II transactivator (CIITA), an obligate mediator of MHC class II expression. Nuclear translocation of Stat1a upon IFN-c stimulation was significantly inhibited in influenza A virus-infected cells and this was associated with a decrease in Tyr701 and Ser727 phosphorylation of Stat1a. Thus, influenza A virus subverts antiviral host defense mediated by IFN-c through effects on the intracellular signaling pathways. IntroductionInfluenza A viruses are negative-strand RNA viruses that have a segmented genome with a coding capacity for 11 polypeptides. The virus genome is composed of eight different RNA segments, which are tightly associated with the viral nucleoprotein and polymerases in ribonucleoprotein complexes [1]. Influenza A viruses, causing acute infections, continuously escape from recognition by virus neutralizing Ab as a result of accumulation of mutations in their surface glycoproteins hemagglutinin and neuraminidase (antigenic drift) or by introduction of new subtypes of these glycoproteins (antigenic shift) [2,3]. Recent outbreaks of highly pathogenic avian influenza A virus infections in poultry and in humans have raised concerns that a new influenza pandemic will occur in the near future [4]. Thus, prediction of the severity of continuously emerging human influenza virus strains remains a high public health priority, but it is limited by our incomplete understanding of the molecular determinants of pathogenicity in this disease. Although factors dictating the severity of virus disease are complex, interaction between inherent viral properties and host cellular response ultimately determines disease outcome. The first site of viral contact with the host and main target of infection and inflammation is the airway mucosal epithelium. Epithelial cells at the airway mucosal surface have a variety of inflammatory and immune defense mechanisms to deal with virus, including Eur. J. Immunol. 2008. 38: 1559-1573 Immunity to infection expression of cytokines with chemoattractant and proinflammatory functions [5], intercellular adhesion molecule-1 (ICAM-1) [6], IFN regulatory factor 1 (IRF-1) [7], nitric oxide synthase 2 (NOS2) [8], and MHC ...

Crigler-Najjar syndrome type II (CN-II) is caused by a severely reduced hepatic activity of bilirubin UDP-glucuronosyltransferase (UGT). Recently, by the analysis of the genetic background of CN-II patients, it has been clarified that the patients carry homozygous missense mutations or nonsense plus missense mutations on the gene for UGT, and CN-II was inherited as an autosomal recessive trait. We encountered a new case which had a nonsense mutation caused by a single nucleotide substitution on one allele. This indicates that CN-II is also inherited as a dominant trait as well as a recessive trait. Expression study in vitro strongly suggests that the disease in this case is caused by a dominant negative mutation by forming a heterologous subunit structure.