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Journal of Virology, February 2000, p. 1632-1640, Vol. 74, No. 4
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Human Immunodeficiency Virus Type 1 Tat Protein Up-Regulates the Promoter Activity of the Beta-Chemokine Monocyte Chemoattractant Protein 1 in the Human Astrocytoma Cell Line U-87 MG: Role of SP-1, AP-1, and NF-kappa B Consensus Sites

Siew Pheng Lim1 and Alfredo Garzino-Demo2,*

Institute of Molecular and Cell Biology, Singapore 117609, Singapore,1 and Institute of Human Virology, University of Maryland Biotechnology Institute, Baltimore, Maryland 212012

Received 12 March 1999/Accepted 12 November 1999

It has been shown that the human immunodeficiency virus type 1 (HIV-1) Tat protein can specifically enhance expression and release of monocyte chemoattractant protein 1 (MCP-1) from human astrocytes. In this study, we show evidence that Tat-induced MCP-1 expression is mediated at the transcriptional level. Transient transfection of an expression construct encoding the full-length Tat into the human glioblastoma-astrocytoma cell line U-87 MG enhances reporter gene activity from cotransfected deletion constructs of the MCP-1 promoter. HIV-1 Tat exerts its effect through a minimal construct containing 213 nucleotides upstream of the translational start site. Site-directed mutagenesis studies indicate that an SP1 site (located between nucleotides -123 and -115) is critical for both constitutive and Tat-enhanced expression of the human MCP-1 promoter, as mutation of this SP1 site significantly diminished reporter gene expression in both instances. Gel retardation experiments further demonstrate that Tat strongly enhances the binding of SP1 protein to its DNA element on the MCP-1 promoter. Moreover, we also observe an increase in the binding activities of transcriptional factors AP1 and NF-kappa B to the MCP-1 promoter following Tat treatment. Mutagenesis studies show that an upstream AP1 site and an adjacent NF-kappa B site (located at -128 to -122 and -150 to -137, respectively) play a role in Tat-mediated transactivation. In contrast, a further upstream AP1 site (-156 to -150) does not appear to be crucial for promoter activity. We postulate that a Tat-mediated increase in SP1 binding activities augments the binding of AP1 and NF-kappa B, leading to synergistic activation of the MCP-1 promoter.

* Corresponding author. Mailing address: Institute of Human Virology, University of Maryland Biotechnology Institute, 725 W. Lombard St., Baltimore, MD 21201-1192. Phone: (410) 706-4676. Fax: (410) 706-4694. E-mail: ihvinfo{at}umbi.umd.edu.

Journal of Virology, February 2000, p. 1632-1640, Vol. 74, No. 4
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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