Regulation of SIVmac239 Basal Long Terminal Repeat Activity and Viral Replication in Macrophages

Abstract

CCAAT/enhancer-binding protein (C/EBP) ␤ and C/EBP sites in the HIV-1 long terminal repeat (LTR) are crucial for HIV-1 replication in monocyte/macrophages and for the ability of interferon ␤ (IFN␤) to inhibit ongoing active HIV replication in these cells. This IFN␤-mediated down-regulation involves induction of the truncated, dominant-negative isoform of C/EBP␤ referred to as liver-enriched transcriptional inhibitory protein (LIP). Although binding of the C/EBP␤ isoform to C/EBP sites in the simian immunodeficiency virus (SIV) LTR has previously been examined, the importance of these sites in core promoter-mediated transcription, virus replication, IFN␤-mediated regulation, and the relative binding of the two isoforms (C/EBP␤ and LIP) has not been investigated. Here, we specifically examine two C/EBP sites, JC1 (؊100 bp) and DS1 (؉134 bp), located within the minimal region of the SIV LTR, required for core promoter-mediated transcription and virus replication in macrophages. Our studies revealed that the JC1 but not DS1 C/EBP site is important for basal level transcription, whereas the DS1 C/EBP site is imperative for productive virus replication in primary macrophages. In contrast, either JC1 or DS1 C/EBP site is sufficient to mediate IFN␤-induced down-regulation of SIV LTR activity and virus replication in these cells. We also characterized the differential binding properties of C/EBP␤ and LIP to the JC1 and DS1 sites. In conjunction with previous studies from our laboratory, we demonstrate the importance of these sites in virus gene expression, and we propose a model for their role in establishing latency and persistence in macrophages in the brain.

An avian leukosis virus subgroup J isolate with a Rous sarcoma virus-like 5′-LTR shows enhanced replication capability

“…Several studies have demonstrated that the CCAAT/enhancer binding protein sites in the human immunodeficiency virus type 1 (HIV-1) LTR are crucial for HIV-1 replication in monocyte/macrophages and for the ability of IFN-b to inhibit ongoing active HIV replication in these cells (Henderson & Calame, 1997;Henderson et al, 1995Henderson et al, , 1996Ravimohan et al, 2010). Moreover, mutations in CCAAT/ enhancer elements have been found in the LTR region of RSV.…”

Illuminating viral infections in the nervous system

“…In macrophage cell lines, IFNβ can induce the production of a dominant-negative form of CCAAT/enhancer-binding protein-β (C/EBPβ) that has been referred to as LIP 75,76 . LIP blocks the acetylation of histones bound to SIV DNA and reduces viral replication 75,77 . Interestingly, an inverse correlation between SIV viral loads and the ratio of C/EBPβ to LIP was observed in macaque brains 76 , suggesting a role for IFNβ-induced genes in CNS antiviral responses following SIV infection.…”

Early Emergence and Selection of a SIV-LTR C/EBP Site Variant in SIV-Infected Macaques That Increases Virus Infectivity

“…The DS1 C/EBP site in the SIV-LTR is particularly important for regulation by IFNβ [18]. The C-to-A substitution we identified in LTRs sequenced in vivo is within the DS1 C/EBP site.…”

“…We have previously shown using competition EMSAs that the affinity of LIP for the wild-type DS1 C/EBP site is 3.5-fold higher than that of LAP, which may contribute to the negative regulatory function of the wild-type DS1 C/EBP site with regard to SIV-LTR activity [18]. We therefore carried out competition EMSAs to determine whether the C-to-A substitution within the DS1 site alters the affinity of LAP (Figure 5) and/or LIP (Figure 6).…”

“…Our previous studies have demonstrated the critical roles of C/EBP sites, JC1 and DS1, in regulating SIV-LTR transcriptional activity [18]. Regulation of the SIV and HIV LTRs by C/EBPβ has been demonstrated in both CD4+ lymphocytes and macrophages [21], [22].…”