Infection with Helicobacter pylori (H. pylori) is a risk factor for the development of gastric cancer. Here we show that infection of gastric epithelial cells with 'cag' pathogenicity island (cagPAI)-positive H. pylori induced aberrant expression of activation-induced cytidine deaminase (AID), a member of the cytidine-deaminase family that acts as a DNA- and RNA-editing enzyme, via the IkappaB kinase-dependent nuclear factor-kappaB activation pathway. H. pylori-mediated upregulation of AID resulted in the accumulation of nucleotide alterations in the TP53 tumor suppressor gene in gastric cells in vitro. Our findings provide evidence that aberrant AID expression caused by H. pylori infection might be a mechanism of mutation accumulation in the gastric mucosa during H. pylori-associated gastric carcinogenesis.

Sterol regulatory element-binding protein 2 (SREBP-2) transcription factor has been identified as a key protein in cholesterol metabolism through the transactivation of the LDL receptor and cholesterol biosynthesis genes. Here, we generated mice lacking microRNA (miR)-33, encoded by an intron of the Srebp2, and showed that miR-33 repressed the expression of ATP-binding cassette transporter A1 (ABCA1) protein, a key regulator of HDL synthesis by mediating cholesterol efflux from cells to apolipoprotein A (apoA)-I. In fact, peritoneal macrophages derived from miR-33-deficient mice showed a marked increase in ABCA1 levels and higher apoA-I-dependent cholesterol efflux than those from WT mice. ABCA1 protein levels in liver were also higher in miR-33-deficient mice than in WT mice. Moreover, miR-33-deficient mice had significantly higher serum HDL cholesterol levels than WT mice. These data establish a critical role for miR-33 in the regulation of ABCA1 expression and HDL biogenesis in vivo.A TP-binding cassette transporter A1 (ABCA1), a 254-kDa cytoplasmic membrane protein, is a pivotal regulator of lipid efflux from cells to apolipoproteins (1). ABCA1 mediates the ratecontrolling step in HDL particle formation and plays an important role in reverse cholesterol transfer (2, 3). Mutations in the ABCA1 gene cause Tangier disease, which is characterized by the near absence of plasma HDL cholesterol associated with storage of cholesterol esters in reticuloendothelial tissues (4-7). Abca1 mRNA and protein are very unstable, with a half life of 1-2 h in murine macrophages (8), which indicates that new transcription and translation are major factors in ensuring constant and inducible ABCA1 expression.Sterol regulatory element-binding proteins (SREBPs), including SREBP-1a, -1c, and -2, modulate the transcription of a number of genes involved in the synthesis and receptor-mediated uptake of cholesterol and fatty acids (9-11). In sterol-depleted cells, SREBPs are cleaved by proteases in the Golgi, releasing the N-termini, which translocate into the nucleus and bind to SREs in the enhancers of multiple genes encoding enzymes and proteins involved in cholesterol biosynthesis and lipid uptake (11-13). Results to date support the notion that SREBP-1 primarily activates the fatty acid triglyceride and phospholipid pathways, whereas SREBP-2 is the prominent isoform for cholesterol synthesis and uptake (9,10,12).MicroRNAs (miRs) are small, non-protein-coding RNAs that base pair with specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports have indicated that miR-33 controls cholesterol homeostasis based on knockdown experiments using antisense technology (14-16). Antisense inhibition of miRNA function has been an important tool for elucidating miRNA biology. However, to determine the potential developmental function of specific miRNAs and to perform longer-term studies, it is necessary to generate mice lacking each miRNA. We generated miR-33-deficient mice, which were born at the expected Mendelian ratio, a...

Survivin is an anti-apoptotic protein that is overexpressed in most human cancers. We show that survivin forms complexes with a cellular protein, hepatitis B X-interacting protein (HBXIP), which was originally recognized for its association with the X protein of hepatitis B virus (HBX). Survivin±HBXIP complexes, but neither survivin nor HBXIP individually, bind pro-caspase-9, preventing its recruitment to Apaf1, and thereby selectively suppressing apoptosis initiated via the mitochondria/cytochrome c pathway. Viral HBX protein also interacts with the survivin± HBXIP complex and suppresses caspase activation in a survivin-dependent manner. Thus, HBXIP functions as a cofactor for survivin, and serves as a link between the cellular apoptosis machinery and a viral pathogen involved in hepatocellular carcinogenesis.

Regulators of apoptosis are thought to work in concert, but the molecular interactions of this process are not understood. Here, we show that in response to cell death stimulation, survivin, a member of the inhibitor of apoptosis (IAP) gene family, associates with another IAP protein, XIAP, via conserved baculovirus IAP repeats. Formation of a survivin-XIAP complex promotes increased XIAP stability against ubiquitination/proteasomal destruction and synergistic inhibition of apoptosis, which is abolished in XIAP ؊/؊ cells. Therefore, orchestration of an IAP-IAP complex regulates apoptosis.Among the regulators of programmed cell death, or apoptosis (1), Bcl-2 proteins (2) control the release of apoptogenic proteins from mitochondria, notably cytochrome c (3), whereas members of the inhibitor of apoptosis (IAP) 1 gene family act as endogenous inhibitors of caspases (4), the enzymatic effectors of apoptosis (1). The structural requirements of IAP-caspase(s) complexes have been defined in considerable detail (5).Survivin is a structurally unique IAP protein that has been implicated in protection from apoptosis and regulation of mitosis (6). A role of survivin in cell division has been linked to assembly/stability of metaphase and anaphase microtubules (7) and spindle checkpoint function (8). In contrast, despite its ability to counteract apoptosis in vitro, and in transgenic animals (6), the mechanism(s) by which survivin inhibits apoptosis has remained elusive. This is important because IAPs, especially XIAP (9) and survivin (6), have emerged as critical regulators of cell survival in tumors and promising targets for rational anti-cancer therapy (10,11).In this study, we investigated the mechanism(s) of survivin cytoprotection. We found that in response to cell death stimulation, survivin physically associates with XIAP, and this complex promotes enhanced XIAP stability and synergistic inhibition of caspase-9 activation. MATERIALS AND METHODSCell Culture-Breast carcinoma MCF-7, lymphoblastoid Raji, and kidney embryonic HEK293T cells were from the American Type Culture Collection (ATCC, Manassas, VA). Wild type (WT) or XIAP Ϫ/Ϫ mouse embryonic fibroblasts (MEF) (12) were the gift of Dr. C. Duckett (University of Michigan).Protein-Protein Interactions-Affinity fractionation and immunoprecipitation experiments were carried out as described (10, 13). Fulllength survivin, truncated survivin BIR-(1-87), full-length XIAP, cIAP1, cIAP2, or the three isolated XIAP, BIR1-(1-123), BIR2-(123-259) and BIR3-(260 -336) were expressed as GST fusion proteins (14). Replication-deficient adenoviruses encoding GFP (pAd-GFP) or survivin (pAd-survivin) were described (15). Pull-down experiments with recombinant survivin (0.1-0.4 g) and GST, GST-XIAP, GST-cIAP1, GST-cIAP2 (8 g), or the individual GST-BIR1, -BIR2, or -BIR3 of XIAP (10 g) bound to glutathione beads (100 l) were as described (13). Alternatively, XIAP was translated in vitro in the presence of [ 35 S]methionine (Amersham Sciences), mixed with 5 g of GST or GST-survivin, and u...

HBV exists in the liver of healthy HBcAb(+) individuals, but not in the blood. Therefore, HBV is thought to be transmitted to recipients by liver grafts from the HBcAb(+) donors at a significantly high rate. The prevention of viral activation and clinical disease development by means of passive immunization with HBIG seems promising, although the follow-up period in our study may be too short for any definitive conclusions.