Human Immunodeficiency Virus Type 1 (HIV-1) Tat Induces Nitric-oxide Synthase in Human Astroglia

Authors

Xiaojuan Liu, University of Nebraska Medical Center, Lincoln, Nebraska
Malabendu Jana, University of Nebraska Medical Center, Lincoln, Nebraska
Subhajit Dasgupta, University of Nebraska Medical Center, Lincoln, Nebraska
Sreenivas Koka, University of Nebraska Medical Center, Lincoln, Nebraska
Jun He, University of Nebraska-Lincoln
Charles Wood, University of Nebraska-LincolnFollow
Kalipada Pahan, University of Nebraska Medical Center, Lincoln, Nebraska

Date of this Version

2002

Comments

Published in THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 277, No. 42, Issue of October 18, pp. 39312–39319, 2002. Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc. Used by permission.

Abstract

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-κB and C/EBPβ, transcription factors responsible for the induction of iNOS. Activation of NF-κB as well as C/EBPβ by RSV-tat, stimulation of RSV-tat-induced production of NO by the wild type of p65 and C/EBPβ, and inhibition of RSV-tat-induced production of NO by Δp65, a dominant-negative mutant of p65, and ΔC/EBPβ, a dominant-negative mutant of C/EBPβ, suggest that RSV-tat induces iNOS through the activation of NF-κB and C/EBPβ. 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 ΔERK2, a dominant-negative mutant of ERK2, inhibited RSV-tat-induced production of NO through the inhibition of C/EBPβ but not that of NF-κB. 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.