Induction of chromosomally integrated HIV-1 LTR requires RBF-2 (USF/TFII-I) and RAS/MAPK signaling

Abstract

The HIV-1 LTR is regulated by multiple signaling pathways responsive to T cell activation. In this study, we have examined the contribution of the MAPK, calcineurin-NFAT and TNFalpha-NF-kappaB pathways on induction of chromosomally integrated HIV-1 LTR reporter genes. We find that induction by T-cell receptor (CD3) cross-linking and PMA is completely dependent upon a binding site for RBF-2 (USF1/2-TFII-I), known as RBEIII at -120. The MAPK pathway is essential for induction of the wild type LTR by these treatments, as the MEK inhibitors PD98059 and U0126 block induction by both PMA treatment and CD3 cross-linking. Stimulation of cells with ionomycin on its own has no effect on the integrated LTR, indicating that calcineurin-NFAT is incapable of causing induction in the absence of additional signals, but stimulation with both PMA and ionomycin produces a synergistic response. In contrast, stimulation of NF-kappaB by treatment with TNFalpha causes induction of both the wild type and RBEIII mutant LTRs, an effect that is independent of MAPK signaling. USF1, USF2 and TFII-I from unstimulated cells are capable of binding RBEIII in vitro, and furthermore can be observed on the LTR in vivo by chromatin imunoprecipitation from untreated cells. DNA binding activity of USF1/2 is marginally stimulated by PMA/ ionomycin treatment, and all three factors appear to remain associated with the LTR throughout the course of induction. These results implicate major roles for the MAPK pathway and RBF-2 (USF1/2-TFII-I) in coordinating events necessary for transition of latent integrated HIV-1 to active transcription in response to T cell signaling.

Epigenetic Regulation of HIV-1 Latency in Astrocytes

“…(iv) The HIV LTR in astrocytes is subjected to classical pathways for gene silencing, including HDACs and HMTs. We provide evidence here to show that inhibition of class 1 HDACs and a specific HMT potently induce HIV promoter activity, indicating that HIV promoter activity in astrocytes is silenced by a mechanism similar to that reported to induce LTR repression in T cells (28)(29)(30)(31)(32)(33)(34). These collective criteria indicate that astrocytes are reservoirs for HIV.…”

“…HDACs are recruited to the HIV LTR, inducing LTR chromatin compaction and as a consequence viral latency (19,26,27). Several transcription factors and corepressor complexes are shown to recruit class I HDACs to the initiator and enhancer regions of the HIV-1 LTR (28)(29)(30)(31)(32)(33)(34). HDAC inhibitors reactivate HIV in cell culture models and in resting CD4 ϩ T cells from HIV ϩ patients (19)(20)(21)(22).…”

Inhibitors of Histone Deacetylases

“…However, only two studies have identified this HDAC isoform at the HIV-1 LTR (16,17). Accordingly, we performed ChIP assays in the J89GFP cells using antibodies specific for the class I HDAC isoforms (Fig.…”

“…To date, multiple studies have demonstrated that recruitment of HDAC1 to the HIV-1 LTR by different DNA-binding complexes is sufficient to induce viral latency (9 -14). However, HDAC2 and HDAC3 can also bind to the HIV-1 LTR and may also play an important role in viral latency (12,16,17).…”

Histone deacetylase inhibitor Scriptaid reactivates latent HIV-1 promoter by inducing histone modification in in vitro latency cell lines

“…Later studies demonstrated that nuclear factor (NF)-κB p50 homodimers (12), AP-4 (13), CTIP2 (14), Sp1 and c-Myc (15), and CBF-1 (16) can participate in HDAC-1 recruitment. HDAC-2 and -3 can also associate with the HIV long terminal repeat (LTR), and play a role in the repression of LTR expression (14,17). It has been shown that the disruption of HDAC-1 recruitment to LTR, resulting from the inhibition of HDAC activity by global HDAC inhibitors, leads to LTR activation and the escape of viral expression in both cell line models and primary cells obtained from patients (10,(18)(19)(20)(21)(22)(23)(24)(25)(26).…”