Interaction of Virion Protein Vpr of Human Immunodeficiency Virus Type 1 with Cellular Transcription Factor Sp1 and trans-Activation of Viral Long Terminal Repeat

Abstract

Acquired immunodeficiency syndrome (AIDS) is a result of replication of the human immunodeficiency virus type 1 (HIV-1) predominantly in CD4؉ T lymphocytes and macrophages. However, most of these cells in vivo are immunologically quiescent, a condition restricting HIV-1 replication. Vpr is an HIV-1 virion protein suspected to enhance HIV-1 replication in vivo. We demonstrate in this report that Vpr specifically activates HIV-1 long terminal repeat (LTR)-directed transcription. This effect is most pronounced on a minimal promoter from HIV-1 LTR containing the TATA box and binding motifs for the ubiquitous cellular transcription factor Sp1. Evidence is presented that Vpr interacts with Sp1 when Sp1 is bound to the Sp1 motifs within the HIV-1 LTR. Both Vpr-Sp1 interaction and Vpr trans-activation require a central Leu/Ile-rich domain in Vpr. Our findings suggest that Vpr trans-activation through Sp1 is most critical for the immediate early transcription of HIV-1 when other positive regulators, such as NF-B, are limited or inactive, a condition presumably present in vivo. By interacting with Sp1, Vpr also has the potential to influence cellular gene expression and cellular functions. Thus, therapeutic approaches directed toward blocking the Vpr trans-activation function could prove valuable in treating AIDS. HIV-11 is the etiological agent of AIDS. The hallmark of AIDS is the slow but progressive depletion of CD4 ϩ -T cells, a class of T cells crucial for immune functions. Depletion of CD4 ϩ -T cell results in immunodeficiency and AIDS-related disorders, including encephalopathy, dementia, and malignancies (1). Despite tremendous efforts in the past, the mechanism of these AIDS-related disorders has remained unclear. However, it is clear that these are a consequence of function of HIV-1 encoded gene products. For example, the HIV-1 envelope glycoprotein was implicated to be involved in toxic effects on neuronal cells (2). Recently, the HIV-1 Vpr protein in peripheral blood of HIV-1-infected people was shown to activate HIV-1 replication in latently infected cells (3,4). This effect of Vpr was suggested to contribute to HIV-1 pathogenesis in vivo.The HIV-1 genome encodes structural as well as regulatory gene products (5, 6). Recently, great efforts have been made toward understanding the function of the so-called accessory regulatory genes, namely vif, vpr, vpu, and nef. These genes are generally non-essential for HIV-1 to replicate in activated T cells. Yet, animal model studies with two of these genes, vpr and nef, suggested that they are required for in vivo replication and pathogenesis of the simian immunodeficiency virus (7,8). The paradox between HIV-1 replication in vitro and that in vivo suggests that HIV-1 replication may be subjected to different modes of regulation in vivo compared to in vitro. For example, in vitro studies have shown that HIV-1 replication is highly dependent on cellular activation and availability of activated NF-B transcription factor (5, 6, 9). However, in vivo, the majority of the sus...

Molecular mimicry in inducing DNA damage between HIV-1 Vpr and the anticancer agent, cisplatin

“…Vpr can induce several promoters, including the HIV-1 LTR and p21 WAF1 (Wang et al, 1995;Amini et al, 2004). These studies suggest that cooperativity between several cellular proteins including Sp1 (Wang et al, 1995), p300 (Kino et al, 2002) and p53 (Sawaya et al, 1998) is necessary for Vpr-induced regulation of the HIV-LTR. Vpr was also shown to cause cell differentiation and DNA damage (Shimura et al, 1999a, b).…”

“…Several Vpr mutants containing either point mutations or deletion of several amino acids were used (Wang et al, 1995;Sawaya et al, 1998Sawaya et al, , 1999Zhou and Ratner, 2000). Vpr mutant expression plasmids were transfected Frag.…”

Suppression of HIV-1 transcription and replication by a Vpr mutant

“…and 76 (Cys to Ser) occur in the region which has been involved in interaction of Vpr with cellular proteins such as RIP and Sp1, 9,10 suggesting that communication of Vpr with other cellular transcription factors may dictate its regulatory activity. Of note, the above amino acid substitutions at the 73 and 76 residues had no effect on subcellular localization of Vpr and significant levels of the mutant Vpr were detected in the nuclei of the cells.…”

“…Several studies suggested that, while the helical domain I may serve as a binding site for interaction with other proteins, helical domain II may function as an activator of transcription of responsive viral and cellular promoters. [8][9][10] To investigate the importance of these domains in Vpr-mediated regulation of HIV-1 gene transcription, human lymphocytic (Jurkat) and astrocytic (U-87MG) cells were transfected with HIV-1 LTR reporter constructs alone or with expression plasmids that permit production of wild-type and various mutants of Vpr with amino acid substitutions in domains I and II and the C-terminus (Figure Correspondence 1b). Ectopic expression of wild-type Vpr in both human cell types increased transcriptional activity of the HIV-1 LTR.…”

Using death to one's advantage: HIV modulation of apoptosis

“…In dividing cells, Vpr has been shown to modestly trans-activate the HIV long terminal repeat (LTR) and heterologous viral promoters. 87,98 The exact mechanism by which Vpr increases protein synthesis is not clear, 99 however, it may be achieved by direct binding of Vpr to the transcription factors TFIIB and Sp1. 99,100 In proliferating T cells and stimulated peripheral blood mononuclear cells (PBMCs), Vpr appears to be dispensable for the in vitro replication of HIV.…”