Characterization and purification of a novel transcriptional repressor from HeLa cell nuclear extracts recognizing the negative regulatory element region of human immunodeficiency virus-1 long terminal repeat

Abstract

Cellular transcription factors play critical roles in regulating human immunodeficiency virus (HIV) gene transcription, although the precise mechanism(s) defining their roles are not well established. Primarily it has been suggested that sequence-specific interaction of trans-activating proteins with cis-acting DNA elements plays a crucial role in regulating the target genes. The negative regulatory element (NRE) of HIV-1 long terminal repeat (LTR) is one such defined region that has been reported to down-regulate LTR-directed HIV gene expression. Information regarding the role of this region in the regulation of HIV expression is lacking. Here we describe an attempt to further characterize the role of NRE cis-elements and define any sequence-specific interaction with cellular factors. Using gel mobility shift DNA-binding and Southwestern blot assays, we have mapped a distinct region of NRE (-290 to -260, a 30-base pair (bp) domain of NRE-A) sequences of HIV-1 LTR, which recognizes a specific DNA-binding protein from HeLa cell nuclear extracts. This factor is a 38-kDa polypeptide which can be affinity-purified to near homogeneity by this 30-bp specific oligonucleotide in affinity chromatography. The cellular factor from HeLa cell nuclear extract exhibits specific interaction only with the 30-bp NRE-A domain of HIV-1 LTR and acts as a strong transcriptional repressor/inhibitor molecule in the DNA-protein gel binding, as well as in vitro transcriptional studies with the nuclear extracts from cells with productive HIV-1 infection. To our knowledge, this is the first report of a factor recognizing a distinct segment within NRE that has been shown to exert an inhibitory effect on transcriptionally active DNA-protein "pre-initiation" complex formation, suggesting a possible role in HIV-1 gene regulation.