Interaction between PARP-1 and HIF-2α in the hypoxic response.

Hypoxia-inducible factors (HIFs) mediate the transcriptional adaptation of hypoxic cells. The extensive transcriptional programm regulated by HIFs involves the induction of genes controlling angiogenesis, cellular metabolism, cell growth, metastasis, apoptosis, extracellular matrix remodeling and others. HIF is a heterodimer of HIF-α and HIF-ß subunits. In addition to HIF-1α, HIF-2α has evolved as an isoform that contributes differently to the hypoxic adaptation by performing non-redundant functions. Poly (ADP-ribose) polymerase-1 (PARP-1) is a nuclear protein involved in the control of DNA repair and gene transcription by modulating chromatin structure and acting as part of gene-specific enhancer/promoter-binding complexes. Previous results have shown that PARP-1 regulates HIF-1 activity. In this study, we focused on the cross-talk between HIF-2α and PARP-1. By using different approaches to suppress PARP-1, we show that HIF-2α mRNA expression, protein levels and HIF-2-dependent gene expression, such as ANGPTL4 and erythropoietin (EPO), are regulated by PARP-1. This regulation occurs at both the transcriptional and post-trancriptional level. We also show a complex formation between HIF-2α with PARP-1. This complex is sensitive to PARP inhibition and seems to protect against the von Hippel-Lindau-dependent HIF-2α degradation. Finally, we show that parp-1(-/-) mice display a significant reduction in the circulating hypoxia-induced EPO levels, number of red cells and hemoglobin concentration. Altogether, these results reveal a complex functional interaction between PARP-1 and the HIF system and suggest that PARP-1 is involved in the fine tuning of the HIF-mediated hypoxic response in vivo.

Poly(ADP-ribose)polymerase-1 (PARP-1) in carcinogenesis: potential role of PARP inhibitors in cancer treatment.

Poly(ADP-ribose)polymerase-1 (PARP-1) is a nuclear, zinc-finger, deoxyribonucleic acid (DNA)-binding protein that detects specifically DNA strand breaks generated by different genotoxic agents. Whereas activation of PARP-1 by mild genotoxic stimuli facilitates DNA repair and cell survival, severe DNA damage triggers different pathways of cell death, including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. Pharmacological inhibition or genetic ablation of PARP-1 results in a clear benefit in cancer treatment by different mechanisms, including selective killing of homologous recombinationdeficient tumor cells, downregulation of tumor-related gene expression, and decrease in the apoptotic threshold in the cotreatment with chemo- and radiotherapy. We summarize in this review the findings and concepts for the role of PARP-1 and poly(ADP-ribosylation) in the regulation of carcinogenesis and some of the preclinical and clinical data available for these agents, together with the challenges facing the clinical development of these agents.

Poly(ADP-ribose)polymerase-1 (PARP-1) in carcinogenesis: potential role of PARP inhibitors in cancer treatment

Poly(ADP-ribose)polymerase-1 (PARP-1) is a nuclear, zinc-finger, deoxyribonucleic acid (DNA)-binding protein that detects specifically DNA strand breaks generated by different genotoxic agents. Whereas activation of PARP-1 by mild genotoxic stimuli facilitates DNA repair and cell survival, severe DNA damage triggers different pathways of cell death, including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. Pharmacological inhibition or genetic ablation of PARP-1 results in a clear benefit in cancer treatment by different mechanisms, including selective killing of homologous recombinationdeficient tumor cells, downregulation of tumor-related gene expression, and decrease in the apoptotic threshold in the cotreatment with chemo- and radiotherapy. We summarize in this review the findings and concepts for the role of PARP-1 and poly(ADP-ribosylation) in the regulation of carcinogenesis and some of the preclinical and clinical data available for these agents, together with the challenges facing the clinical development of these agents (AU)

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Modulation of transcription by PARP-1: consequences in carcinogenesis and inflammation.

Post-translational modification of proteins by poly(ADP-ribosyl)ation is involved in the regulation of a number of biological functions. While an 18 member superfamily of poly(ADP-ribose) polymerases (PARP)s has been described PARP-1 accounts for more than 90% of the poly(ADP-ribosyl)ating capacity of the cells. PARP-1 act as a DNA nick sensor and is activated by DNA breaks to cleave NAD(+) into nicotinamide and ADP-ribose to synthesize long branching poly(ADP-ribose) polymers (PAR) covalently attached to nuclear acceptor proteins. Whereas activation of PARP-1 by mild genotoxic stimuli facilitate DNA repair and cell survival, severe DNA damage triggers different pathways of cell death including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. PAR and PARP-1 have also been described as having a function in transcriptional regulation through their ability to modify chromatin-associated proteins and as a cofactor of different transcription factors, most notably NF-kappaB and AP-1. Pharmacological inhibition or genetic ablation of PARP-1 not only provided remarkable protection from tissue injury in various oxidative stress-related disease models but it result in a clear benefit in the treatment of cancer by different mechanisms including selective killing of homologous recombination-deficient tumor cells, down regulation of tumor-related gene expression and decrease in the apoptotic threshold in the co-treatment with chemo and radiotherapy. We will summarize in this review the current findings and concepts for the role of PARP-1 and poly(ADP-ribosyl)ation in the regulation of transcription, oxidative stress and carcinogenesis.