Induction of human methionine adenosyltransferase 2A expression by tumor necrosis factor alpha. Role of NF-kappa B and AP-1

Two genes (MAT1A and MAT2A) encode for methionine adenosyltransferase (MAT), an essential cellular enzyme responsible for S-adenosylmethionine biosynthesis. MAT1A is expressed mostly in the liver, whereas MAT2A is widely distributed. We showed a switch from MAT1A to MAT2A expression in human hepatocellular carcinoma (HCC), which facilitates cancer cell growth. Using DNase I footprinting analysis, we previously identified a region in the MAT2A promoter protected from DNase I digestion in HCC. This region contains NF-kappa B and AP-1 elements, and the present study examined whether they regulate MAT2A promoter activity. We found nuclear binding of NF-kappa B and AP-1 to the MAT2A promoter increased in HCC. Tumor necrosis factor alpha (TNFalpha), which activates both NF-kappa B and AP-1, increased MAT2A expression in a dose- and time-dependent manner, binding of both NF-kappa B and AP-1 to the MAT2A promoter and MAT2A promoter activity, with the latter effect blocked by site-directed mutagenesis of the NF-kappa B and AP-1 binding sites. Blocking NF-kappa B with I kappa B super-repressor or AP-1 with dominant-negative c-Jun led to decreased basal MAT2A expression and prevented the TNF alpha-induced increase in MAT2A expression. Although blocking NF-kappa B had no influence on the ability of TNF alpha to increase AP-1 nuclear binding, blocking AP-1 with dominant-negative c-Jun prevented the TNF alpha-mediated increase in NF-kappa B binding. In conclusion, both NF-kappa B and AP-1 are required for basal MAT2A expression in HepG2 cells and mediate the increase in MAT2A expression in response to TNF alpha treatment. Increased trans-activation of these two sites also contributes to MAT2A up-regulation in HCC.     

Induction of colony stimulating factor in vivo by recombinant interleukin 1 alpha and recombinant tumor necrosis factor alpha 1

In response to a potent inflammatory challenge, such as Gram-negative endotoxin, a number of cytokines are induced that, in turn, mediate many of the pathophysiologic alterations associated with endotoxicity. In this study, we have observed two endotoxin-associated monokines, recombinant interleukin-1 alpha (rIL 1 alpha) and recombinant tumor necrosis factor alpha (rTNF alpha), to induce colony stimulating factor (CSF) in vivo. The CSF activities produced in response to rIL 1 alpha or rTNF alpha gave rise to a mixture of granulocyte-macrophage colonies and were induced in a dose- and time-dependent fashion, peaking within 3 hr of cytokine injection (preceding peak CSF induction by endotoxin by several hours). Combined injection of suboptimal concentrations of rIL 1 alpha and rTNF alpha were additive, and simultaneous injection of optimal concentrations of each failed to increase CSF levels over that observed with either cytokine alone. Unlike endotoxin, neither cytokine induced interferon in vivo. These findings extend our understanding of the cytokine cascade that is operative in an inflammatory response and may account for many of the observed hematopoietic alterations that accompany inflammation.     

Up-regulation of microRNA-155 in macrophages contributes to increased tumor necrosis factor {alpha} (TNF{alpha}) production via increased mRNA half-life in alcoholic liver disease

Activation of Kupffer cells (KCs) by gut-derived lipopolysaccharide (LPS) and Toll-Like Receptors 4 (TLR4)-LPS-mediated increase in TNFα production has a central role in the pathogenesis of alcoholic liver disease. Micro-RNA (miR)-125b, miR-146a, and miR-155 can regulate inflammatory responses to LPS. Here we evaluated the involvement of miRs in alcohol-induced macrophage activation. Chronic alcohol treatment in vitro resulted in a time-dependent increase in miR-155 but not miR-125b or miR-146a levels in RAW 264.7 macrophages. Furthermore, alcohol pretreatment augmented LPS-induced miR-155 expression in macrophages. We found a linear correlation between alcohol-induced increase in miR-155 and TNFα induction. In a mouse model of alcoholic liver disease, we found a significant increase in both miR-155 levels and TNFα production in isolated KCs when compared with pair-fed controls. The mechanistic role of miR-155 in TNFα regulation was indicated by decreased TNFα levels in alcohol-treated macrophages after inhibition of miR-155 and by increased TNFα production after miR-155 overexpression, respectively. We found that miR-155 affected TNFα mRNA stability because miR-155 inhibition decreased whereas miR-155 overexpression increased TNFα mRNA half-life. Using the NF-κB inhibitors, MG-132 or Bay11-7082, we demonstrated that NF-κB activation mediated the up-regulation of miR-155 by alcohol in KCs. In conclusion, our novel data demonstrate that chronic alcohol consumption increases miR-155 in macrophages via NF-κB and the increased miR-155 contributes to alcohol-induced elevation in TNFα production via increased mRNA stability.     

TFF3 modulates NF-{kappa}B and a novel negative regulatory molecule of NF-{kappa}B in intestinal epithelial cells via a mechanism distinct from TNF-{alpha}

Trefoil factor 3 (intestinal trefoil factor) is a cytoprotective factor in the gut. Herein we compared the effect of trefoil factor 3 with tumor necrosis factor- on 1) activation of NF-B in intestinal epithelial cells; 2) expression of Twist protein (a molecule essential for downregulation of nuclear factor-B activity in vivo); and 3) production of interleukin-8. We showed that Twist protein is constitutively expressed in intestinal epithelial cells. Tumor necrosis factor- induced persistent degradation of Twist protein in intestinal epithelial cells via a signaling pathway linked to proteasome, which was associated with prolonged activation of NF-B. In contrast to tumor necrosis factor, trefoil factor 3 triggered transient activation of NF-B and prolonged upregulation of Twist protein in intestinal epithelial cells via an ERK kinase-mediated pathway. Unlike tumor necrosis factor-, transient activation of NF-B by trefoil factor 3 is not associated with induction of IL-8 in cells. To examine the role of Twist protein in intestinal epithelial cells, we silenced the Twist expression by siRNA. Our data showed that trefoil factor 3 induced interleukin-8 production after silencing Twist in intestinal epithelial cells. Together, these observations indicated that 1) trefoil factor 3 triggers a diverse signal from tumor necrosis factor- on the activation of NF-B and its associated molecules in intestinal epithelial cells; and 2) trefoil factor 3-induced Twist protein plays an important role in the modulation of inflammatory cytokine production in intestinal epithelial cells. trefoil factor 3; signal transduction     

Transcription of the {beta}-galactoside {alpha}2,6-sialyltransferase gene in B lymphocytes is directed by a separate and distinct promoter{dagger}

A single human gene, SIAT1, encodes the ß-galactoside