The sequence and structure of the 3' arm of the first stem-loop of the human immunodeficiency virus type 2 trans-activation responsive region mediate Tat-2 transactivation

GLI-2 modulates retroviral gene expression

GLI proteins are involved in the development of mice, humans, zebrafish, Caenorhabditis elegans, Xenopus, and Drosophila. While these zinc finger-containing proteins bind to TG-rich promoter elements and are known to regulate gene expression in C. elegans and Drosophila, mechanistic understanding of how regulation is mediated through naturally occurring transcriptional promoters is lacking. One isoform of human GLI-2 appears to be identical to a factor previously called Tax helper protein (THP), thus named due to its ability to interact with a TG-rich element in the human T-lymphotropic virus type 1 (HTLV-1) enhancer thought to mediate transcriptional stimulation by the Tax protein of HTLV-1. We now demonstrate that, working through its TG-rich binding site and adjacent elements, GLI-2/THP actually suppresses gene expression driven by the HTLV-1 promoter. GLI-2/THP has no effect on the HTLV-2 promoter, activates expression from the promoters of human immunodeficiency virus types 1 and (HIV-1 and -2), and stimulates HIV-1 replication. Both effective suppression and activation of gene expression and viral replication require the first of the five zinc fingers, which is not necessary for DNA binding, to be intact. Thus, not only can GLI-2/THP either activate or suppress gene expression, depending on the promoter, but the same domain (first zinc finger) mediates both effects. These findings suggest a role for GLI-2 in retroviral gene regulation and shed further light on the mechanisms by which GLI proteins regulate naturally occurring promoters.

Human GLI-2 is a tat activation response element-independent Tat cofactor

Zinc finger-containing GLI proteins are involved in the development of Caenorhabditis elegans, Xenopus, Drosophila, zebrafish, mice, and humans. In this study, we show that an isoform of human GLI-2 strongly synergizes with the Tat transactivating proteins of human immunodeficiency virus types 1 and 2 (HIV-1 and -2) and markedly stimulates viral replication. GLI-2 also synergizes with the previously described Tat cofactor cyclin T1 to stimulate Tat function. Surprisingly, GLI-2/Tat synergy is not dependent on either a typical GLI DNA binding site or an intact Tat activation response element but does require an intact TATA box. Thus, GLI-2/Tat synergy results from a mechanism of action which is novel both for a GLI protein and for a Tat cofactor. These findings link the GLI family of transcriptional and developmental regulatory proteins to Tat function and HIV replication.

Potent inhibition of human immunodeficiency virus type 1 (HIV-1) gene expression and virus production by an HIV-2 tat activation-response RNA decoy

Tat activation-response region (TAR) decoys have been developed for use in gene therapy for people infected with human immunodeficiency virus type 1 (HIV-1). When a TAR RNA decoy is overexpressed, it will bind Tat, thus leaving less of this crucial protein to bind to and activate the natural transcriptional promoter of HIV-1. Previous TAR decoy constructs have used HIV-1 TAR. However, recent epidemiological and biological data began to suggest that the TAR region from the human immunodeficiency virus type 2 (HIV-2) may suppress HIV-1 transcription and hence replication. We created a vector which overexpresses TAR-2 under the control of the human U6 small nuclear RNA gene promoter and here show that the U6-TAR-2 decoy construct potently inhibits both HIV-2 and HIV-1 gene expression. Further, this decoy construct is able to markedly suppress HIV-1 replication. Thus, we have directly proven that TAR-2 can suppress HIV-1 replication and suggest that the HIV-2 TAR decoy may prove useful for combating HIV-1 infection.