ABSTRACT
In hepatocytes, the amount of the Spot 14 (S14) protein is closely related to the full expression of enzymes involved in the glycolytic and lipogenic pathways. In the present study we address the role played by this protein in the control of transcription of the L-type pyruvate kinase (L-PK) gene in primary hepatocytes. We show that human S14, which by itself does not bind to the L-PK promoter, physically interacts with the human chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1) and induces the switch of this factor from a repressor to an activator. However, the enhancing activity of S14 and COUP-TF1 depends on the presence of a proximal GC-rich box (the L0 element) that specifically binds nuclear proteins from the livers of rats fed a glucose-rich diet. Moreover, the L0 element, which strongly binds dephosphorylated specificity protein 1 (Sp1), loses all affinity when this factor is phosphorylated by cAMP-dependent protein kinase. Mutations that affect binding of Sp1 and nuclear proteins to the L0 box also decrease basal transcription and impair glucose responsiveness of the promoter. These results therefore shed light on the mechanism by which the S14 protein, whose concentration rapidly rises after glucose intake, contributes to the full activity of the L-PK promoter.
Subject(s)
DNA-Binding Proteins/chemistry , DNA-Binding Proteins/metabolism , Proteins/chemistry , Proteins/metabolism , Pyruvate Kinase/genetics , Sp1 Transcription Factor/chemistry , Transcription Factors/chemistry , Transcription Factors/metabolism , Transcription, Genetic , Animals , Binding Sites , COUP Transcription Factor I , Cell Nucleus/metabolism , Cells, Cultured , Chickens , Cyclic AMP/metabolism , Glucose/metabolism , Glutathione Transferase/metabolism , Hepatocytes/metabolism , Humans , Male , Mutation , Nuclear Proteins , Phosphorylation , Plasmids/metabolism , Precipitin Tests , Promoter Regions, Genetic , Protein Binding , Rats , Rats, Sprague-Dawley , Recombinant Fusion Proteins/metabolism , TransfectionABSTRACT
The activation of peroxisome proliferator-activated receptor gamma (PPARgamma) has been shown to inhibit the production and the effects of proinflammatory cytokines. Since interleukin-1beta (IL-1beta) directly mediates cartilage degradation in osteoarthritis, we investigated the capability of PPARgamma ligands to modulate IL-1beta effects on human chondrocytes. RT-PCR and Western blot analysis revealed that PPARgamma expression was decreased by IL-1beta. 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), in contrast to troglitazone, was highly potent to counteract IL-1beta-induced cyclooxygenase-2 and inductible nitric oxide synthase expression, NO production and the decrease in proteoglycan synthesis. Western blot and gel-shift analyses demonstrated that 15d-PGJ2 inhibited NF-kappaB activation, while troglitazone was ineffective. Although 15d-PGJ2 attenuated activator protein-1 binding on the DNA, it potentiated c-jun migration in the nucleus. The absence or the low effect of troglitazone suggests that 15d-PGJ2 action in human chondrocytes is mainly PPARgamma-independent.
Subject(s)
Chondrocytes/drug effects , Chromans/pharmacology , Gene Expression Regulation/drug effects , Interleukin-1/pharmacology , NF-kappa B/metabolism , Prostaglandin D2/pharmacology , Thiazoles/pharmacology , Thiazolidinediones , Transcription Factor AP-1/metabolism , Active Transport, Cell Nucleus/drug effects , Blotting, Western , Cell Nucleus/drug effects , Cell Nucleus/metabolism , Cells, Cultured , Chondrocytes/cytology , Chondrocytes/metabolism , Cyclooxygenase 2 , DNA/genetics , DNA/metabolism , Enzyme Induction/drug effects , Humans , Interleukin-1/antagonists & inhibitors , Isoenzymes/genetics , Ligands , Membrane Proteins , Nitric Oxide/metabolism , Nitric Oxide Synthase/genetics , Nitric Oxide Synthase Type II , Prostaglandin D2/analogs & derivatives , Prostaglandin-Endoperoxide Synthases/genetics , Prostaglandins/biosynthesis , Protein Binding/drug effects , Proteoglycans/biosynthesis , Proto-Oncogene Proteins c-jun/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptors, Cytoplasmic and Nuclear/genetics , Receptors, Cytoplasmic and Nuclear/metabolism , Signal Transduction/drug effects , Transcription Factors/genetics , Transcription Factors/metabolism , TroglitazoneABSTRACT
The endothelial Na,K-ATPase is an active component in maintaining a variety of normal vascular functions. The enzyme is characterized by a complex molecular heterogeneity that results from differential expression and association of multiple isoforms of both its alpha- and beta-subunits. The aim of the present study was to determine which isoforms of the Na,K-ATPase are expressed in human endothelial cells. HUVEC (human umbilical vein endothelial cells) were used as a model of well known human endothelial cells. The high sensitive method RT-PCR was used with primers specific for the various isoforms of the alpha- and beta-subunits of the Na,K-ATPase. The results show that HUVEC express alpha1-, but not alpha2-, alpha3- or alpha4-isoforms of the catalytic subunit and that beta3- but not beta2- or beta1-isoforms is present in these cells. These findings are in contradiction with our previous detection of Na,K-ATPase isoforms in HUVEC using antibodies (14). Such results raise the technical problem of the specificity of the available antibodies directed against the different isoforms as well as the question of the physiological relevance of the diversity of the Na,K-ATPase isoforms.
Subject(s)
Endothelium, Vascular/enzymology , Sodium-Potassium-Exchanging ATPase/chemistry , Sodium-Potassium-Exchanging ATPase/metabolism , Endothelium, Vascular/chemistry , Endothelium, Vascular/cytology , Humans , Isoenzymes/chemistry , Isoenzymes/genetics , Isoenzymes/metabolism , Protein Subunits , Reverse Transcriptase Polymerase Chain Reaction , Sodium-Potassium-Exchanging ATPase/geneticsABSTRACT
Mutations in the XNP/ATR-X gene, located in Xq13.3, are associated with several X linked mental retardation syndromes, the best known being alpha thalassaemia with mental retardation (ATR-X). The XNP/ATR-X protein belongs to the family of SWI/SNF DNA helicases and contains three C2-C2 type zinc fingers of unknown function. Previous studies have shown that 65% of mutations of XNP have been found within the zinc finger domain (encoded by exons 7, 8, and the beginning of exon 9) while 35% of the mutations have been found in the helicase domain extending over 3 kb at the C-terminus of the protein. Although different types of mutations have been identified, no specific genotype-phenotype correlation has been found, suggesting that gene alteration leads to a loss of function irrespective of mutation type. Our aims were to understand the function of the XNP/ATR-X protein better, with specific attention to the functional consequences of mutations to the zinc finger domain. We used monoclonal antibodies directed against the XNP/ATR-X protein and performed immunocytochemical and western blot analyses, which showed altered or absent XNP/ATR-X expression in cells of affected patients. In addition, we used in vitro experiments to show that the zinc finger domain can mediate double stranded DNA binding and found that the DNA binding capacity of mutant forms in ATR-X patients is severely reduced. These data provide insights into the understanding of the functional significance of XNP/ATR-X mutations.
Subject(s)
Cell Nucleus/metabolism , Intellectual Disability/genetics , Mutation/genetics , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Thalassemia/genetics , Active Transport, Cell Nucleus , Antibodies, Monoclonal/immunology , Antibody Specificity/immunology , Blotting, Western , Cells, Cultured , DNA/genetics , DNA/metabolism , DNA Helicases/chemistry , DNA Helicases/genetics , DNA Helicases/immunology , DNA Helicases/metabolism , DNA-Binding Proteins/chemistry , DNA-Binding Proteins/genetics , DNA-Binding Proteins/immunology , DNA-Binding Proteins/metabolism , Epitopes/immunology , Fluorescent Antibody Technique , Gene Expression , Humans , Male , Nuclear Proteins/chemistry , Nuclear Proteins/immunology , Protein Binding , Syndrome , X-linked Nuclear Protein , Zinc Fingers/genetics , Zinc Fingers/physiologyABSTRACT
Na+/K+-ATPase during diabetes may be regulated by synthesis of its alpha and beta subunits and by changes in membrane fluidity and lipid composition. As these mechanisms were unknown in liver, we studied in rats the effect of streptozotocin-induced diabetes on liver Na+/K+-ATPase. We then evaluated whether fish oil treatment prevented the diabetes-induced changes. Diabetes mellitus induced an increased Na+/K+-ATPase activity and an enhanced expression of the beta1 subunit; there was no change in the amount of the alpha1 and beta3 isoenzymes. Biphasic ouabain inhibition curves were obtained for diabetic groups indicating the presence of low and high affinity sites. No alpha2 and alpha3 isoenzymes could be detected. Diabetes mellitus led to a decrease in membrane fluidity and a change in membrane lipid composition. The diabetes-induced changes are not prevented by fish oil treatment. The results suggest that the increase of Na+/K+-ATPase activity can be associated with the enhanced expression of the beta1 subunit in the diabetic state, but cannot be attributed to changes in membrane fluidity as typically this enzyme will increase in response to an enhancement of membrane fluidity. The presence of a high-affinity site for ouabain (IC50 = 10-7 M) could be explained by the presence of (alphabeta)2 diprotomeric structure of Na+/K+-ATPase or an as yet unknown alpha subunit isoform that may exist in diabetes mellitus. These stimulations might be related, in part, to the modification of fatty acid content during diabetes.
