Erratum: PARP1 promotes gene expression at the post-transcriptional level by modulating the RNA-binding protein HuR

Poly (ADP-ribose) polymerase 1 promotes HuR/ELAVL1 cytoplasmic localization and inflammatory gene expression by regulating p38 MAPK activity

Post-transcriptional regulation of cytokine/chemokine mRNA turnover is critical for immune processes and contributes to the mammalian cellular response to diverse inflammatory stimuli. The ubiquitous RNA-binding protein human antigen R (HuR) is an integral regulator of inflammation-associated mRNA fate. HuR function is regulated by various post-translational modifications that alter its subcellular localization and ability to stabilize target mRNAs. Both poly (ADP-ribose) polymerase 1 (PARP1) and p38 mitogen-activated protein kinases (MAPKs) have been reported to regulate the biological function of HuR, but their specific regulatory and crosstalk mechanisms remain unclear. In this study, we show that PARP1 acts via p38 to synergistically promote cytoplasmic accumulation of HuR and stabilization of inflammation-associated mRNAs in cells under inflammatory conditions. Specifically, p38 binds to auto-poly ADP-ribosylated (PARylated) PARP1 resulting in the covalent PARylation of p38 by PARP1, thereby promoting the retention and activity of p38 in the nucleus. In addition, PARylation of HuR facilitates the phosphorylation of HuR at the serine 197 site mediated by p38, which then increases the translocation of HuR to the cytoplasm, ultimately stabilizing the inflammation-associated mRNA expression at the post-transcriptional level.

Cell-Penetrating Peptide TAT-HuR-HNS3 Suppresses Proinflammatory Gene Expression via Competitively Blocking Interaction of HuR with Its Partners

Proinflammatory cytokines/chemokines are commonly regulated by RNA-binding proteins at posttranscriptional levels. Human Ag R (HuR)/embryonic lethal abnormal vision-like 1 (ELAVL1) is one of the well-characterized RNA-binding proteins that increases the stability of short-lived mRNAs, which encode proinflammatory mediators. HuR employs its nucleocytoplasmic shuttling sequence (HNS) domain, interacting with poly(ADP-ribose) polymerase 1 (PARP1), which accounts for the enhanced poly-ADP-ribosylation and cytoplasmic shuttling of HuR. Also by using its HNS domain, HuR undergoes dimerization/oligomerization, underlying the increased binding of HuR with proinflammatory cytokine/chemokine mRNAs and the disassociation of the miRNA-induced silencing complex from the targets. Therefore, competitively blocking the interactions of HuR with its partners may suppress proinflammatory mediator production. In this study, peptides derived from the sequence of the HuR-HNS domain were synthesized, and their effects on interfering HuR interacting with PARP1 and HuR itself were analyzed. Moreover, cell-penetrating TAT-HuR-HNS3 was delivered into human and mouse cells or administered into mouse lungs with or without exposure of TNF-α or LPS. mRNA levels of proinflammatory mediators as well as neutrophil infiltration were evaluated. We showed that TAT-HuR-HNS3 interrupts HuR-PARP1 interaction and therefore results in a lowered poly-ADP-ribosylation level and decreased cytoplasmic distribution of HuR. TAT-HuR-HNS3 also blocks HuR dimerization and promotes Argonaute 2-based miRNA-induced silencing complex binding to the targets. Moreover, TAT-HuR-HNS3 lowers mRNA stability of proinflammatory mediators in TNF-α-treated epithelial cells and macrophages, and it decreases TNF-α-induced inflammatory responses in lungs of experimental animals. Thus, TAT-HuR-HNS3 is a promising lead peptide for the development of inhibitors to treat inflammation-related diseases.

Muscone derivative ZM-32 inhibits breast tumor angiogenesis by suppressing HuR-mediated VEGF and MMP9 expression

Inhibition of tumor angiogenesis is a highly effective strategy for cancer treatment. Human antigen R (HuR), an RNA-binding protein, is overexpressed in many cancers and regulates the mRNAs of multiple angiogenic factors by binding to the adenylate-uridylate-rich element in their 3' untranslated region. HuR protein has been demonstrated to be an important regulatory factor in macrophage-mediated angiogenesis, a process in which macrophages are critical for tumor progression. Muscone is a synthetic equivalent of musk, and recent studies have shown that it has a regulatory effect on angiogenesis. In this study, we synthesized five series of muscone derivatives and discovered that compound ZM-32 was effective in preventing HuR RRM1/2-Vegf-a mRNA complex formation. ZM-32 bound to HuR RRM1/2 protein with a K_D value of 521.7 nmol/L. Furthermore, ZM-32 inhibited endothelial cell proliferation, migration, and tubule formation, and suppressed the VEGF/VEGFR2/ERK1/2 signaling axis mediated by macrophages in vitro. We also demonstrated that ZM-32 effectively prevented the proliferation and migration of breast cancer cells and inhibited the growth and angiogenesis of MDA-MB-231 xenograft tumors without any obvious toxicity in vivo. Mechanistically, exposure to ZM-32 influenced the mRNA stability of Vegf-a and Mmp9 in a HuR-dependent manner in both macrophages and MDA-MB-231 cells. Thus, in this study we identified a new muscone derivative, ZM-32, with anti-angiogenesis effects mediated via targeting HuR in breast cancer, that may become a potentially valuable lead compound for anti-cancer angiogenesis.

Poly(ADP-ribosyl)ation enhances HuR oligomerization and contributes to pro-inflammatory gene mRNA stabilization

Poly(ADP-ribosyl)ation (PARylation) is an important post-translational modification mainly catalyzed by poly-ADP-ribose polymerase 1 (PARP1). In addition to having important roles in DNA damage detection and repair, it functions in gene expression regulation, especially at the posttranscriptional level. Embryonic lethal abnormal vision-like 1/human antigen R (ELAVL/HuR), a canonical 3′ untranslated region AU-rich element-binding protein, is a crucial mRNA-stabilizing protein that protects target mRNAs from RNA-destabilizing protein- or microRNA-induced silencing complex (miRISC)-mediated degradation. Additionally, in some cases, HuR itself either promotes or suppresses translation. Here, we demonstrated that in response to inflammatory stimuli, the PARylation of HuR, mostly at the conserved D226 site, by PARP1 increased the formation of the HuR oligomer/multimer, and HuR oligomerization promoted the disassociation of miRISC and stabilized the pro-inflammatory gene mRNAs. The prevention of PARP1 activation or HuR oligomerization attenuated lipopolysaccharide-induced inflammatory gene expression and the airway recruitment of neutrophils in mouse lungs. The present study verified a novel mechanism of PARP1 and HuR PARylation in the RNA stability regulation, increasing our understanding of how PARP1 regulates gene expression.

c-Abl-Mediated Tyrosine Phosphorylation of PARP1 Is Crucial for Expression of Proinflammatory Genes

Poly(ADP-ribosyl)ation is a rapid and transient posttranslational protein modification mostly catalyzed by poly(ADP-ribose) polymerase-1 (PARP1). Fundamental roles of activated PARP1 in DNA damage repair and cellular response pathways are well established; however, the precise mechanisms by which PARP1 is activated independent of DNA damage, and thereby playing a role in expression of inflammatory genes, remain poorly understood. In this study, we show that, in response to LPS or TNF-α exposure, the nonreceptor tyrosine kinase c-Abl undergoes nuclear translocation and interacts with and phosphorylates PARP1 at the conserved Y829 site. Tyrosine-phosphorylated PARP1 is required for protein poly(ADP-ribosyl)ation of RelA/p65 and NF-κB-dependent expression of proinflammatory genes in murine RAW 264.7 macrophages, human monocytic THP1 cells, or mouse lungs. Furthermore, LPS-induced airway lung inflammation was reduced by inhibition of c-Abl activity. The present study elucidated a novel signaling pathway to activate PARP1 and regulate gene expression, suggesting that blocking the interaction of c-Abl with PARP1 or pharmaceutical inhibition of c-Abl may improve the outcomes of PARP1 activation-mediated inflammatory diseases.

The Role of PARPs in Inflammation-and Metabolic-Related Diseases: Molecular Mechanisms and Beyond

Poly(ADP-ribosyl)ation (PARylation) is an essential post-translational modification catalyzed by poly(ADP-ribose) polymerase (PARP) enzymes. Poly(ADP-ribose) polymerase 1 (PARP1) is a well-characterized member of the PARP family. PARP1 plays a crucial role in multiple biological processes and PARP1 activation contributes to the development of various inflammatory and malignant disorders, including lung inflammatory disorders, cardiovascular disease, ovarian cancer, breast cancer, and diabetes. In this review, we will focus on the role and molecular mechanisms of PARPs enzymes in inflammation- and metabolic-related diseases. Specifically, we discuss the molecular mechanisms and signaling pathways that PARP1 is associated with in the regulation of pathogenesis. Recently, increasing evidence suggests that PARP inhibition is a promising strategy for intervention of some diseases. Thus, our in-depth understanding of the mechanism of how PARPs are activated and how their signaling downstream effecters can provide more potential therapeutic targets for the treatment of the related diseases in the future is crucial.

Novel insights into PARPs in gene expression: regulation of RNA metabolism

Poly(ADP-ribosyl)ation (PARylation) is an important post-translational modification in which an ADP-ribose group is transferred to the target protein by poly(ADP-riboses) polymerases (PARPs). Since the discovery of poly-ADP-ribose (PAR) 50 years ago, its roles in cellular processes have been extensively explored. Although research initially focused on the functions of PAR and PARPs in DNA damage detection and repair, our understanding of the roles of PARPs in various nuclear and cytoplasmic processes, particularly in gene expression, has increased significantly. In this review, we discuss the current advances in understanding the roles of PARylation with a particular emphasis in gene expression through RNA biogenesis and processing. In addition to updating PARP's significance in transcriptional regulation, we specifically focus on how PARPs and PARylation affect gene expression, especially inflammation-related genes, at the post-transcriptional levels by modulating RNA processing and degrading. Increasing evidence suggests that PARP inhibition is a promising treatment for inflammation-related diseases besides conventional chemotherapy for cancer.