2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD)-Inducible Poly-ADP-Ribose Polymerase (TIPARP/PARP7) Catalytic Mutant Mice (TiparpH532A) Exhibit Increased Sensitivity to TCDD-Induced Hepatotoxicity and Lethality

Abstract

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP/PARP7), an aryl hydrocarbon receptor (AHR) target gene and mono-ADP-ribosyltransferase, acts as part of a negative feedback loop to repress AHR signaling. This process is prevented by a single H532A mutation in TIPARP that destroys its catalytic activity. We hypothesized that the loss of TIPARP catalytic activity would increase sensitivity to TCDD-induced toxicity in vivo. To test this, we created a catalytically deficient mouse line (TiparpH532A ) by introducing a single H532A mutation in TIPARP. Treatment of mouse embryonic fibroblasts or hepatocytes isolated from TiparpH532A mice confirmed the increased TCDD-induced expression of the AHR target genes Cyp1a1, Cyp1b1 and Tiparp. TiparpH532A mice given a single injection of 10 µg/kg TCDD, a non-lethal dose in Tiparp+/+ mice, did not survive beyond day 10. All Tiparp+/+ mice survived the 30-day treatment. TCDD-treated TiparpH532A mice displayed increased expression of AHR target genes, increased steatohepatitis and hepatotoxicity. Hepatic RNA-sequencing revealed 7-fold more differentially expressed genes (DEGs) in TiparpH532A mice than in Tiparp+/+ mice (4542 vs 647 genes) 6 days after TCDD treatment. DEGs included genes involved in xenobiotic metabolism, lipid homeostasis and inflammation. Taken together, these data further support TIPARP as a critical negative regulator of AHR activity and show that loss of its catalytic activity is sufficient to increase sensitivity to TCDD-induced steatohepatitis and lethality. Since TIPARP inhibition has recently emerged as a potential anti-cancer therapy, the impact on AHR signaling and aromatic hydrocarbon toxicity will need to be carefully considered under conditions of therapeutic TIPARP inhibition.

Reduced Colonic Mucosal Injury in 2,3,7,8-Tetrachlorodibenzo-p-Dioxin Poly ADP-Ribose Polymerase (TIPARP/PARP7)-Deficient Mice

“…Thus, decreases in PARP7 levels or inhibition of its catalytic activity results in increased AHR signaling [9,10,18]. In support of these findings, both PARP7 knockout mice and mutant mice harboring a catalytically deficient PARP7 show increased AHR activity and increased sensitivity to toxicities produced by the AHR ligand TCDD [19][20][21].…”

“…Increased AHR and IFN-I signaling is also phenocopied by a loss of PARP7's catalytic activity through the introduction of a single histidine to alanine mutation at amino acid 532 of the protein [6,9,21]. Recently, two small molecule inhibitors of PARP7 have been reported [10,56].…”

TIPARP is involved in the regulation of intraocular pressure

“…Other PARPs, including TIPARP, also known as mono(ADP-ribosyl) transferase (MART) enzymes, catalyse mono-ADP-ribosylation (MARylation), which is not well understood 9 . As a MART enzyme, TIPARP catalyses the mono-ADP-ribosylation of target proteins and exerts effects on the viral response, transcriptional regulation, stem cell pluripotency, neuronal function and cytoskeleton regulation [9][10][11][12][13][14] . In addition, TIPARP has been identified as a potential target of cancer therapy 12,15,16 .…”

“…TIPARP has important functions in many physiological processes, including gene regulation, viral response, and cytoskeleton regulation 9 . The dysregulation of TIPARP may induce neuronal developmental disorders, abnormal antiviral responses, some types of cancer, and dioxin-induced steatohepatitis [10][11][12][13][14][15][16] . Evidence of the association between TIPARP and POAG has been reported in a few studies.…”

Loss of PARP7 Increases Type I Interferon Signaling in EO771 Breast Cancer Cells and Prevents Mammary Tumor Growth by Increasing Antitumor Immunity

“…EO771 and NCI-H1373 cells (ATCC) were maintained in RPMI (1.0 g/L glucose), supplemented with 10% v/v heat-inactivated fetal bovine serum (FBS), 1% v/v L-glutamine, and 1% v/v penicillin-streptomycin (P/S). COS-1 cells (ATCC) and MEFs (described elsewhere [16,24]) were maintained in DMEM (1.0 g/L glucose) supplemented with 10% v/v FBS, 1% v/v L-glutamine, and 1% v/v P/S. Cells were cultured at 37 • C with 100% humidity and 5% CO 2 .…”