Cloning of a long HIV-1 readthrough transcript and detection of an increased level of early growth response protein-1 (Egr-1) mRNA in chronically infected U937 cells

Abstract

To identify the pathways involved in HIV-1 modification of cellular gene expression, chronically infected U937 cells were screened by mRNA differential display. A chimeric transcript consisting of the 3' end of the LTR of a HIV-1 provirus, followed by 3.7 kb of cellular RNA was identified suggesting that long readthrough transcription might be one of the mechanisms by which gene expression could be modified in individual infected cells. Such a phenomenon may also be the first step towards the potential transduction of cellular sequences. Furthermore, the mRNA encoding for the transcription factor Egr-1 was detected as an over-represented transcript in infected cells. Northern blot analysis confirmed the increase of Egr-1 mRNA content in both HIV-1 infected promonocytic U937 cells and T cell lines such as Jurkat and CEM. Interestingly a similar increase of Egr-1 mRNA has previously been reported to occur in HTLV-1 and HTLV-2 infected T cell lines. Despite the consistent increase in the level of Egr-1 mRNA, the amount of the encoded protein did not appear to be modified in HIV-1 infected cells, suggesting an increased turn over of the protein in chronically infected cells.

Activation of Egr-1 Expression in Astrocytes by HIV-1 Tat: New Insights into Astrocyte-Mediated Tat Neurotoxicity

“…In this study, we identified Egr-1 as a Tat positive regulatory target gene in astrocytes, which functioned upstream of two other Tat positive regulatory genes p300 and GFAP in these cells. Egr-1 is induced in HIV-infected monocytic and human CD4+ T lymphocytes (Dron et al, 1999) and astrocytes that were infected with HIV as shown in this study and other viruses (Cai et al, 2006;Romagnoli et al, 2008). In contrast, two early studies have shown that HIV-1 Tat blocks nerve growth factor-induced Egr-1 expression in neurons (Darbinian et al, 2008;Darbinian-Sarkissian et al, 2006).…”

Different Roles of Sp Family Members in HIV-1 Tat-Mediated Manganese Superoxide Dismutase Suppression in Hepatocellular Carcinoma Cells

“…Using differential display, it has been reported that chronically HIV-infected cells have an increased Egr-1 mRNA level. However, the Egr-1 protein level could not be detected by Western analysis (Dron et al, 1999). Our results, which demonstrated that Egr-1 protein was undetectable in both controls and Tat-transfected HepG2 cells, also exclude the possibility that Egr-1 will be a cause for the reduced expression of MnSOD in HepG2 cells.…”

HTLV-1 Tax upregulates early growth response protein 1 through nuclear factor-κB signaling

“…Our results showed that higher EGR1 levels in Tax-positive cells further increased p65 expression and promoted its nuclear translocation, leading to enhanced NF-κB binding activity, which favors T cell transformation and EGR1 upregulation. Similar results were observed in cells expressing the HIV-encoded protein, Tat, suggesting that Tat-induced EGR1 interacts with p65 in vitro and regulates NF-κB transcriptional activity in vivo [ 24 , 45 ]. The NF-κB binding site is reportedly important for EGR1-mediated IL-8 upregulation, and EGR1 knockdown inhibits IL-8 production and IL-8-mediated prostate cancer cell invasion.…”

“…NF-κB p65 subunit-induced transcription of human immunodeficiency virus 1 (HIV) long terminal repeats was previously shown to be dependent on an interaction with the Sp1 zinc finger DNA-binding domain [ 22 ]. EGR1, whose DNA-binding domain shares a high degree of homology with that of Sp1, interacts with p65 in vitro and regulates NF-κB transcriptional activity in vivo [ 23 , 24 ]. However, the roles played by EGR1 in regulating NF-κB transcriptional activity in HTLV-1 infected cells also remain unclear.…”