Transforming Growth Factor β Stimulates the Human Immunodeficiency Virus 1 Enhancer and Requires NF-κB Activity

ABSTRACT

Transforming growth factor β (TGF-β) is the prototype of a large superfamily of signaling molecules involved in the regulation of cell growth and differentiation. In certain patients infected with human immunodeficiency virus type 1 (HIV-1), increased levels of TGF-β promoted the production of virus and also impaired the host immune system. In an effort to understand the signaling events linking TGF-β action and HIV production, we show here that TGF-β can stimulate transcription from the HIV-1 long terminal repeat (LTR) promoter through NF-κB binding sites in both HaCaT and 300.19 pre-B cells. When introduced into a minimal promoter, NF-κB binding sites supported nearly 30-fold activation from the luciferase reporter upon TGF-β treatment. Electrophoretic mobility shift assay indicated that a major factor binding to the NF-κB site is the p50-p65 heterodimeric NF-κB in HaCaT cells. Coexpression of Gal4-p65 chimeric proteins supported TGF-β ligand-dependent gene expression from a luciferase reporter gene driven by Gal4 DNA binding sites. NF-κB activity present in HaCaT cells was not affected by TGF-β treatment as judged by the unchanged DNA binding activity and concentrations of p50 and p65 proteins. Consistently, steady-state levels of IκBα and IκBβ proteins were not changed by TGF-β treatment. Our results demonstrate that TGF-β is able to stimulate transcription from the HIV-1 LTR promoter by activating NF-κB through a mechanism distinct from the classic NF-κB activation mechanism involving the degradation of IκB proteins.

ACKNOWLEDGMENTS

We thank Albert S. Baldwin, Jr., for critical reading of the manuscript and for many valuable suggestions related to potential involvement of IκBα, Lishan Su for critical reading of the manuscript and helpful discussions, and Yong Yu for excellent technical support. We also thank Brian Cullen for HIV-chloramphenicol acetyltransferase and CMV-Tat plasmids, M. Lienhard Schmitz for the Gal4-p65 and Gal4-p65TA1 constructs, Rik Derynck for the pCAL2 plasmid, Tony Koleske for the pCDM8-p50 and pCDM8-p65 plasmids, and Rene Bernards for antiserum against MBP2.

This work was supported by grants from NIH (DK45746) and the Council for Tobacco Research (3613A). X.-F.W. is a Leukemia Society Scholar.

The first two authors contributed equally to this work.