Human immunodeficiency virus type 1 (HIV-1) tat induces nitric-oxide synthase in human astroglia.
Human immunodeficiency virus type 1 (HIV-1) infection is known to cause neuronal injury and dementia in a significant proportion of patients. However, the mechanism by which HIV-1 mediates its deleterious effects in the brain is poorly defined. The present study was undertaken to investigate the effect of the HIV-1 tat gene on the expression of inducible nitric-oxide synthase (iNOS) in human U373MG astroglial cells and primary astroglia. Expression of the tat gene as RSV-tat but not that of the CAT gene as RSV-CAT in U373MG astroglial cells led to the induction of NO production and the expression of iNOS protein and mRNA. Induction of NO production by recombinant HIV-1 Tat protein and inhibition of RSV-tat-induced NO production by anti-Tat antibodies suggest that RSV-tat-induced production of NO is dependent on Tat and that Tat is secreted from RSV-tat-transfected astroglia. Similar to U373MG astroglial cells, RSV-tat also induced the production of NO in human primary astroglia. The induction of human iNOS promoter-derived luciferase activity by the expression of RSV-tat suggests that RSV-tat induces the transcription of iNOS. To understand the mechanism of induction of iNOS, we investigated the role of NF-kappaB and C/EBPbeta, transcription factors responsible for the induction of iNOS. Activation of NF-kappaB as well as C/EBPbeta by RSV-tat, stimulation of RSV-tat-induced production of NO by the wild type of p65 and C/EBPbeta, and inhibition of RSV-tat-induced production of NO by deltap65, a dominant-negative mutant of p65, and deltaC/EBPbeta, a dominant-negative mutant of C/EBPbeta, suggest that RSV-tat induces iNOS through the activation of NF-kappaB and C/EBPbeta. In addition, we show that extracellular signal-regulated kinase (ERK) but not that p38 mitogen-activated protein kinase (MAPK) is involved in RSV-tat induced production of NO. Interestingly, PD98059, an inhibitor of the ERK pathway, and deltaERK2, a dominant-negative mutant of ERK2, inhibited RSV-tat-induced production of NO through the inhibition of C/EBPbeta but not that of NF-kappaB. This study illustrates a novel role for HIV-1 tat in inducing the expression of iNOS in human astrocytes that may participate in the pathogenesis of HIV-associated dementia.
Liu
Xiaojuan
X
Department of Oral Biology, University of Nebraska Medical Center, Lincoln, Nebraska 68583, USA.
Jana
Malabendu
M
Dasgupta
Subhajit
S
Koka
Sreenivas
S
He
Jun
J
Wood
Charles
C
Pahan
Kalipada
K
D000818:Animals; D001253:Astrocytes / Q000201:enzymology*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D015696:Gene Products, tat / Q000378:metabolism*; D005799:Genes, Dominant; D006801:Humans; D015151:Immunoblotting; D008156:Luciferases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D011401:Promoter Regions, Genetic; D013997:Time Factors; D015533:Transcriptional Activation; D014162:Transfection; D019892:eIF-2 Kinase / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D022782:CCAAT-Enhancer-Binding Protein-beta; D004791:Enzyme Inhibitors; D005419:Flavonoids; D015696:Gene Products, tat; D016328:NF-kappa B; D009569:Nitric Oxide; D008156:Luciferases; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D019892:eIF-2 Kinase; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one