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

Abstract

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.