In vitro activation of the HIV-1 enhancer in extracts from cells treated with a phorbol ester tumor promoter.

Abstract

The transition from persistent to lytic infection by the human immunodeficiency virus, HIV, is marked by a burst of viral replication and gene expression that occurs when infected cells are stimulated by physiological inducers or tumor promoters like 12‐O‐tetradecanoyl phorbol acetate (TPA). We report here that the HIV enhancer is activated specifically by TPA in several non‐lymphoid cell types, and that this transcriptional regulation can be reproduced in a cell‐free system. In vitro transcription experiments revealed a 6‐fold activation of the HIV promoter in nuclear extracts prepared from TPA‐induced HeLa tk‐ cells, whereas a control (human alpha‐globin) promoter was transcribed with equal efficiency in either induced or uninduced cell extracts. A corresponding increase in the activity of a cellular DNA‐binding protein that interacts with the HIV enhancer was detected in TPA‐treated cells with DNase I footprint experiments. This increase occurred in the absence of de novo protein synthesis, suggesting a post‐transcriptional activation mechanism. Analysis of HIV deletion mutants suggests that the enhancer is the target for the TPA effect both in vitro and in vivo. The cell‐free system described here should facilitate studies on the mechanism of phorbol ester induction of gene‐specific transcription factors.