Biomedical subjects

Jack Wands

Publications and source records attributed to Jack Wands.

9 recordsLinked to original sources

PubMed2006

cAMP-response element-binding protein mediates acid-induced NADPH oxidase NOX5-S expression in Barrett esophageal adenocarcinoma cells.

Gastroesophageal reflux disease complicated by Barrett esophagus (BE) is a major risk factor for esophageal adenocarcinoma (EA). The mechanisms whereby acid reflux may accelerate the progression from BE to EA are not known. We found that NOX1 and NOX5-S were the major isoforms of NADPH oxidase in SEG1-EA cells. The expression of NOX5-S mRNA was significantly higher in these cells than in esophageal squamous epithelial cells. NOX5 mRNA was also significantly higher in Barrett tissues with high grade dysplasia than without dysplasia. Pulsed acid treatment significantly increased H(2)O(2) production in both SEG1-EA cells and BE mucosa, which was blocked by the NADPH oxidase inhibitor apocynin. In SEG1 cells, acid treatment increased mRNA expression of NOX5-S, but not NOX1, and knockdown of NOX5 by NOX5 small interfering RNA abolished acid-induced H(2)O(2) production. In addition, acid treatment increased intracellular Ca(2+) and phosphorylation of cAMP-response element-binding protein (CREB). Acid-induced NOX5-S expression and H(2)O(2) production were significantly inhibited by removal of extracellular Ca(2+) and by knockdown of CREB using CREB small interfering RNA. Two novel CREB-binding elements TGACGAGA and TGACGCTG were identified in the NOX5-S gene promoter. Overexpression of CREB significantly increased NOX5-S promoter activity. Knockdown of NOX5 significantly decreased [(3)H]thymidine incorporation, which was restored by 10(-13) M H(2)O(2). Knockdown of NOX5 also significantly decreased retinoblastoma protein phosphorylation and increased cell apoptosis and caspase-9 expression. In conclusion, in SEG1 EA cells NOX5-S is overexpressed and mediates acid-induced H(2)O(2) production. Acid-induced NOX5-S expression depends on an increase in intracellular Ca(2+) and activation of CREB. NOX5-S contributes to increased cell proliferation and decreased apoptosis.

Adenocarcinoma↗

PubMed2006

Hepatitis C infection and alcohol use: A dangerous mix for the liver and antiviral immunity.

This article presents the proceedings of a symposium presented at the meeting of the Research Society on Alcoholism, held in Santa Barbara, California, in June 2005. The organizers and chairs were Sam Zakhari and Gyongyi Szabo. The presentations included (1) Mitochondrial Abnormalities Induced by Hepatitis C -Alcohol Interaction by Steven Weinman; (2) Effects of Acute and Chronic Ethanol on Innate Antiviral Signaling Pathways, Hepatitis C Replication, and Human Liver Cell Transcription by Stephen Polyak; (3) Ethanol Alters Dendritic Cell Function In Vivo and Impairs the Subsequent Cellular Immune Responses to Hepatitis C Proteins by Costica Aloman; and (4) Pathogenic Interactions Between Hepatitis C Virus and Alcohol Use in Humans: Dendritic Cells as Common Targets by Gyongyi Szabo. This symposium summarizes the state of knowledge of cellular and molecular pathways by which alcohol and HCV have pathogenic interactions resulting in depression of the immune response and liver damage in chronic HCV infection.

Alcoholism↗

PubMed2006

Point mutations upstream of hepatitis B virus core gene affect DNA replication at the step of core protein expression.

The pregenomic RNA directs replication of the hepatitis B virus (HBV) genome by serving both as the messenger for core protein and polymerase and as the genome precursor following its packaging into the core particle. RNA packaging is mediated by a stem-loop structure present at its 5' end designated the epsilon signal, which includes the core gene initiator AUG. The precore RNA has a slightly extended 5' end to cover the entire precore region and, consequently, directs the translation of a precore/core protein, which is secreted as e antigen (HBeAg) following removal of precore-derived signal peptide and the carboxyl terminus. A naturally occurring G1862T mutation upstream of the core AUG affects the bulge of the epsilon signal and generates a "forbidden" residue at the -3 position of the signal peptide cleavage site. Transfection of this and other mutants into human hepatoma cells failed to prove their inhibition of HBeAg secretion but rather revealed great impairment of genome replication. This replication defect was associated with reduced expression of core protein and could be overcome by a G1899A covariation, or by nonsense or frameshift mutation in the precore region. All these mutations antagonized the G1862T mutation on core protein expression. Cotransfection of the G1862T mutant with a replication-deficient HBV genome that provides core protein in trans also restored genome replication. Consistent with our findings in cell culture, HBV genotype A found in African/Asian patients has T1862 and is associated with much lower viremia titers than the European subgroup of genotype A.

Amino Acid Sequence↗

PubMed2005

Effect of mutating the two cysteines required for HBe antigenicity on hepatitis B virus DNA replication and virion secretion.

Hepatitis B virus (HBV) variants with impaired expression of e antigen (HBeAg) frequently arise at the chronic stage of infection, as exemplified by precore and core promoter mutants. Since an intramolecular disulfide bond maintains the secondary structure of HBeAg, we explored effect of missense mutations of either cysteine codon. Consistent with earlier reports, substitution of each cysteine rendered HBeAg nearly undetectable. With underlying nucleotide changes at the loop of pregenome encapsidation signal, the C-7 mutants were severely impaired in pregenomic RNA packaging and hence DNA replication. Although none of the missense mutations at C61 reduced DNA replication, replacement with arginine, but not alanine, aspartic acid, phenylalanine, or serine, blocked virion secretion. Consistent with the detection of C61R genome from a patient serum, secretion block of the C61R mutant could be overcome by co-expression of wild-type core protein. In conclusion, point mutations of the C61 codon may generate viable HBeAg-negative variants.

Codon↗

PubMed2005

Hepatitis B Virus e Antigen Variants.

More than 300 million people worldwide are chronically infected with hepatitis B virus (HBV). Considering the very short generation time for a virus, and the high error rate associated with the reverse transcription step of HBV replication, decades of HBV infection are probably equivalent to million years of human evolution. The most important selective force during the natural course of HBV infection appears to be the immune response. The development of anti-HBe antibody in hepatitis B patients usually correlates with reduction of HBV viremia. As a consequence, escape mutants of anti-HBe are selected. The core promoter mutants express less HBe antigen (HBeAg) through transcriptional down regulation, while precore mutants express truncated products. We recently identified additional mutations that modulate HBeAg translation initiation, proteolytic cleavage, and secondary structure maintenance through a disulfide bond. The core promoter mutants have been associated with the development of fulminant hepatitis during acute infection and liver cancer during chronic infection. Consistent with their enhanced pathogenicity, core promoter mutants were found to replicate at up to 10-fold higher levels in transfected human hepatoma cells than the wild-type virus. Moreover, some core promoter mutants are impaired in virion secretion due to missense mutations in the envelope gene. These virological properties may help explain enhanced pathogenicity of core promoter mutants in vivo.

Journal Article↗

PubMed2004

The molecular pathogenesis of cholangiocarcinoma.

Cholangiocarcinoma is rising in clinical importance because of increasing incidence, poor prognosis, and suboptimal response to therapy. Recent investigations into the underlying molecular mechanisms involved in cholangiocarcinogenesis and tumor growth have contributed greatly to our understanding of this disease. To review this topic, we discuss the molecular mechanisms in sections reflecting the unique features that allow cancer cells to develop and maintain a growth advantage. Through a better understanding of these mechanisms, improved and more specific diagnostic, therapeutic, and preventative strategies may be developed and hopefully improve the outcome of this devastating disease.

Animals↗

PubMed2003

Ethanol impairs insulin-stimulated neuronal survival in the developing brain: role of PTEN phosphatase.

Gestational exposure to ethanol causes fetal alcohol syndrome, which is associated with cerebellar hypoplasia. Previous in vitro studies demonstrated ethanol-impaired neuronal survival with reduced signaling through the insulin receptor (IRbeta). We examined insulin signaling in an experimental rat model of chronic gestational exposure to ethanol in which the pups exhibited striking cerebellar hypoplasia with increased apoptosis. Immunoprecipitation and Western blot analyses detected reduced levels of tyrosyl-phosphorylated IRbeta, tyrosyl-phosphorylated insulin receptor substrate-1 (IRS-1), and p85-associated IRS-1 but no alterations in IRbeta, IRS-1, or p85 protein expression in cerebellar tissue from ethanol-exposed pups. In addition, ethanol exposure significantly reduced the levels of total phosphoinositol 3-kinase, Akt kinase, phospho-BAD (inactive), and glyceraldehyde-3-phosphate dehydrogenase and increased the levels of glycogen synthase kinase-3 activity, activated BAD, phosphatase and tensin homolog deleted in chromosome 10 (PTEN) protein, and PTEN phosphatase activity in cerebellar tissue. Cerebellar neurons isolated from ethanol-exposed pups had reduced levels of insulin-stimulated phosphoinositol 3-kinase and Akt kinase activities and reduced insulin inhibition of PTEN and glycogen synthase kinase-3 activity. The results demonstrate that cerebellar hypoplasia produced by chronic gestational exposure to ethanol is associated with impaired survival signaling through insulin-regulated pathways, including failure to suppress PTEN function.

Alcoholism↗

PubMed2003

Sequence variation upstream of precore translation initiation codon reduces hepatitis B virus e antigen production.

BACKGROUND & AIMS: Most South African hepatitis B virus strains harbor point mutations immediately upstream of the precore AUG codon. The aim of this study was to determine their effect on hepatitis B e antigen expression. METHODS: The hepatitis B virus DNA sequence around the precore region was determined from sera of 45 black South Africans. The South African mutations were introduced into hepatitis B virus dimers of the same genotype, and hepatitis B e antigen was quantified from culture medium of transfected HepG2 or Huh7 cells. RESULTS: The South African sequence changes were easily detectable in the acute, hepatitis B e antigen-positive phase of infection, suggesting that they were stable traits and were not selected by immune pressure. Triple mutations at the -5, -3, and -2 positions of the AUG codon severely impaired hepatitis B e antigen expression (P < 0.001). The frequent double mutation at the -5 and -2 positions moderately reduced hepatitis B e antigen levels (P < 0.001) to an extent comparable to that of the common core promoter mutations (1762(T)1764(A)). The presence of both South African and core promoter mutations diminished hepatitis B e antigen expression in an additive manner. It is interesting to note that the triple South African mutations enabled core protein translation from precore messenger RNA, which could rescue the replication defect of a hepatitis B virus genome with an ablated core gene. CONCLUSIONS: We have identified a novel class of hepatitis B e antigen variants with reduced hepatitis B e antigen translation by a ribosomal leaky scanning mechanism. Reduction in hepatitis B e antigen expression may contribute to accelerated seroconversion from hepatitis B e antigen to its antibody in black South Africans infected with hepatitis B virus very early in life.

Adolescent↗

PubMed2003

Genome replication, virion secretion, and e antigen expression of naturally occurring hepatitis B virus core promoter mutants.

The core promoter mutants of hepatitis B virus (HBV) emerge as the dominant viral population at the late HBeAg and the anti-HBe stages of HBV infection, with the A1762T/G1764A substitutions as the hotspot mutations. The double core promoter mutations were found by many investigators to moderately enhance viral genome replication and reduce hepatitis B e antigen (HBeAg) expression. A much higher replication capacity was reported for a naturally occurring core promoter mutant implicated in the outbreak of fulminant hepatitis, which was caused by the neighboring C1766T/T1768A mutations instead. To systemically study the biological properties of naturally occurring core promoter mutants, we amplified full-length HBV genomes by PCR from sera of HBeAg(+) individuals infected with genotype A. All 12 HBV genomes derived from highly viremic sera (5 x 10(9) to 5.7 x 10(9) copies of viral genome/ml) harbored wild-type core promoter sequence, whereas 37 of 43 clones from low-viremia samples (0.2 x 10(7) to 4.6 x 10(7) copies/ml) were core promoter mutants. Of the 11 wild-type genomes and 14 core promoter mutants analyzed by transfection experiments in human hepatoma cell lines, 6 core promoter mutants but none of the wild-type genomes replicated at high levels. All had 1762/1764 mutations and an additional substitution at position 1753 (T to C), at position 1766 (C to T), or both. Moreover, these HBV clones varied greatly in their ability to secrete enveloped viral particles irrespective of the presence of core promoter mutations. High-replication clones with 1762/1764/1766 or 1753/1762/1764/1766 mutations expressed very low levels of HBeAg, whereas high-replication clones with 1753/1762/1764 triple mutations expressed high levels of HBeAg. Experiments with site-directed mutants revealed that both 1762/1764/1766 and 1753/1762/1764/1766 mutations conferred significantly higher viral replication and lower HBeAg expression than 1762/1764 mutations alone, whereas the 1753/1762/1764 triple mutant displayed only mild reduction in HBeAg expression similar to the 1762/1764 mutant. Thus, core promoter mutations other than those at positions 1762 and 1764 can have major impact on viral DNA replication and HBeAg expression.

Base Sequence↗