ABSTRACT
The mRNA coding for FGF-2 (fibroblast growth factor 2), a major angiogenic factor, is translated by an IRES (internal ribosome entry site)-dependent mechanism. We have studied the role of the IRES in the regulation of FGF-2 expression in vivo, under pathophysiological conditions, by creating transgenic mice lines expressing bioluminescent bicistronic transgenes. Analysis of FGF-2 IRES activity indicates strong tissue specificity in adult brain and testis, suggesting a role of the IRES in the activation of FGF-2 expression in testis maturation and brain function. We have explored translational control of FGF-2 mRNA under diabetic hyperglycaemic conditions, as FGF-2 is implied in diabetes-related vascular complications. FGF-2 IRES is specifically activated in the aorta wall in streptozotocin-induced diabetic mice, in correlation with increased expression of endogenous FGF-2. Thus, under hyperglycaemic conditions, where cap-dependent translation is blocked, IRES activation participates in FGF-2 overexpression, which is one of the keys of diabetes-linked atherosclerosis aggravation. IRES activation under such pathophysiological conditions may involve ITAFs (IRES trans-acting factors), such as p53 or hnRNP AI (heterogeneous nuclear ribonucleoprotein AI), recently identified as inhibitory or activatory ITAFs respectively for FGF-2 IRES.
Subject(s)
Fibroblast Growth Factor 2/genetics , Gene Expression Regulation , Peptide Chain Initiation, Translational , Protein Biosynthesis , Animals , Blood Vessels/metabolism , Blood Vessels/pathology , Codon, Initiator , Diabetes Mellitus/genetics , Diabetes Mellitus/metabolism , Fibroblast Growth Factor 2/metabolism , Mice , Mice, Transgenic , Ribosomes/metabolismABSTRACT
The cag pathogenicity island (cag PAI) genes are a major determinant of virulence of Helicobacter pylori (Hp). Lipopolysaccharide (LPS) purified from the cag PAI-positive (type I) strains induced apoptosis of primary cultures of guinea pig gastric mucosal cells. Lipid A catalyzed this apoptosis. These cells expressed the Toll-like receptor 4 (TLR4) mRNA and its protein, and type I Hp LPS phosphorylated transforming growth factor beta-activated kinase 1 (TAK1) and TAK1-binding protein 1 (TAB1) in association with up-regulation of the TLR4 expressions, suggesting that type I Hp LPS evoked distinct TLR4 signaling. In contrast, Hp LPS from type II strains with complete or partial deletion of the cag PAI genes did not phosphorylate TAK1 and TAB1 and failed to induce apoptosis. Accelerated apoptosis of gastric epithelial cells is one of the important events relevant to chronic, atrophic gastritis caused by Hp infection. The difference in proapoptotic action of LPS between the type I and II strains may support an important role of the cag PAI genes in the pathogenesis of gastric lesions caused by Hp infection.
Subject(s)
Adaptor Proteins, Signal Transducing , Antigens, Bacterial , Apoptosis/drug effects , Drosophila Proteins , Gastric Mucosa/drug effects , Helicobacter pylori/chemistry , Intracellular Signaling Peptides and Proteins , Lipopolysaccharides/pharmacology , Animals , Atrophy , Bacterial Proteins/genetics , Carrier Proteins/metabolism , Epithelial Cells/cytology , Epithelial Cells/drug effects , Epithelial Cells/metabolism , Gastric Mucosa/pathology , Gastritis/microbiology , Gastritis/pathology , Genotype , Guinea Pigs , Helicobacter Infections/microbiology , Helicobacter Infections/pathology , Helicobacter pylori/classification , Helicobacter pylori/genetics , Helicobacter pylori/isolation & purification , Humans , Lipid A/isolation & purification , Lipid A/pharmacology , Lipopolysaccharides/isolation & purification , MAP Kinase Kinase Kinases/metabolism , Membrane Glycoproteins/biosynthesis , Membrane Glycoproteins/genetics , Phosphorylation/drug effects , Protein Processing, Post-Translational/drug effects , Receptors, Cell Surface/biosynthesis , Receptors, Cell Surface/genetics , Signal Transduction , Stimulation, Chemical , Toll-Like Receptor 4 , Toll-Like ReceptorsABSTRACT
Gastric pit cells express mitogen oxidase1 (Mox1) and essential components for the phagocyte NADPH oxidase (p67-, p47-, p40-, and p22-phoxes). Helicobacter pylori (Hp) lipopolysaccharide (LPS) is a potent up-regulator of the Mox 1 oxidase. In this study, we examined the expression levels of several key members of the Toll-like receptor (TLR) family in primary cultures of guinea pig gastric pit cells. These cells expressed the TLR4 mRNA. Immunoblot analysis and immunofluorescence histochemistry with an anti-TLR4 antibody showed that gastric pit cells possessed significant amounts of TLR4 protein preferentially on the plasma membrane. In contrast, the cells did not express the TLR2 and TLR9 transcripts and did not contain detectable amounts of TLR2 protein. Neither peptidoglycan from Staphylococcus aureus nor Hp DNA with the CpG motif up-regulated Mox1 oxidase activity. Hp LPS activated nuclear factor-kappa B in association with the expression of cyclooxygenase II and tumor necrosis factor alpha transcripts. These findings suggest that TLR4 may play a crucial role in the initiation of inflammatory responses of gastric pit cells against Hp infection.
