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Poly(ADP-ribose) polymerase 1 is necessary for coactivating hypoxia-inducible factor-1-dependent gene expression by Epstein-Barr virus latent membrane protein 1

ABSTRACT: Latent membrane protein 1 (LMP1) is the major transforming protein of Epstein-Barr virus (EBV) and is critical for EBV-induced B-cell transformation in vitro. Poly(ADP-ribose) polymerase 1 (PARP1) regulates accessibility of chromatin, alters functions of transcriptional activators and repressors, and has been directly implicated in transcriptional activation. Previously we showed that LMP1 activates PARP1 and increases Poly(ADP-ribos)ylation (PARylation) through PARP1. Therefore, to identify targets of LMP1 that are regulated through PARP1, LMP1 was ectopically expressed in an EBV-negative Burkitt’s lymphoma cell line. These LMP1-expressing cells were then treated with the PARP inhibitor olaparib and prepared for RNA sequencing. The LMP1/PARP targets identified through this RNA-seq experiment are largely involved in metabolism and signaling. Interestingly, Ingenuity Pathway Analysis of RNA-seq data suggests that hypoxia-inducible factor 1-alpha (HIF-1α) is an LMP1 target mediated through PARP1. PARP1 is acting as a coactivator of HIF-1α-dependent gene expression in B cells, and this co-activation is enhanced by LMP1-mediated activation of PARP1. HIF-1α forms a PARylated complex with PARP1 and both HIF-1α and PARP1 are present at promoter regions of HIF-1α downstream targets, leading to accumulation of positive histone marks at these regions. Complex formation, PARylation and binding of PARP1 and HIF-1α at promoter regions of HIF-1α downstream targets can all be attenuated by PARP1 inhibition, subsequently leading to a buildup of repressive histone marks and loss of positive histone marks. In addition, LMP1 switches cells to a glycolytic ‘Warburg’ metabolism, preferentially using aerobic glycolysis over mitochondrial respiration. Finally, LMP1+ cells are more sensitive to PARP1 inhibition and, therefore, targeting PARP1 activity may be an effective treatment for LMP1+ EBV-associated malignancies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE121476 | GEO | 2018/10/24

REPOSITORIES: GEO

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Project description:Epstein-Barr virus (EBV) establishes life-long latency in human B-cells by maintaining its chromatinized episomes within the nucleus. These circularized mini-chromosomes do not integrate into the host genome. Therefore, it is essential for EBV to organize its chromatin in a manner suitable for genomic stability, DNA replication, and efficient gene expression. Poly [ADP-ribose] polymerase 1 (PARP1) activity is significantly higher in B-cells infected with EBV than those without, and considerably higher in the transcriptionally active type III latency compared to the immunoevasive type I. In addition to its role in DNA damage response, PARP1 has been implicated in transcriptional regulation and structural maintenance of both the human and EBV genome at specific regions. To better understand PARP1's role in the regulation of the EBV episome, we have functionally characterized the effect of PARP enzymatic inhibition on total episomal structure through in situ Hi-C mapping, generating the first complete 3D structure of the EBV genome. We have also mapped intragenomic contact changes after PARP inhibition to global binding of the chromatin looping factors CTCF and cohesin across the EBV genome. Additionally, PARP inhibition was shown to alter gene expression at the regions where chromatin looping was most effected. Finally, we have identified a novel function of PARP, which regulates cohesin complex chromatin binding. In conclusion, PARP1 inhibition does not alter the location of cohesin binding but does increase its frequency of binding at these regions. Despite this, there are fewer overall unique intragenomic interactions after PARP inhibition, while some areas have new chromatin loops not seen in the untreated EBV episome, leading us to conclude that PARP does have an essential role in the regulation of global EBV chromatin structure. The altered expression profile after the structural rearrangement induced by PARP inhibition also supports the idea that PARP1 helps maintain EBV latency programs.

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Poly(ADP-ribose) polymerase 1 is necessary for coactivating hypoxia-inducible factor-1-dependent gene expression by Epstein-Barr virus latent membrane protein 1

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