PARP-2 deficiency affects the survival of CD4+CD8+ double-positive thymocytes

On the way to selective PARP-2 inhibitors. Design, synthesis, and preliminary evaluation of a series of isoquinolinone derivatives

PARP-1 and PARP-2 are members of the family of poly(ADP-ribose)polymerases, which are involved in the maintenance of genomic integrity under conditions of genotoxic stimuli. The different roles of the two isoforms under pathophysiological conditions have not yet been fully clarified, and this is partially due to the lack of selective inhibitors. We report herein the synthesis and preliminary pharmacological evaluation of a large series of isoquinolinone derivatives as PARP-1/PARP-2 inhibitors. Among them, we identified the 5-benzoyloxyisoquinolin-1(2 H)-one derivative as the most selective PARP-2 inhibitor reported so far, with a PARP-2/PARP-1 selectivity index greater than 60.

Transcriptional regulation by poly(ADP-ribose) polymerase-1 during T cell activation

Background

Accumulating evidence suggests an important role for the enzyme poly(ADP-ribose) polymerase-1 (PARP-1) as an integral part of the gene expression regulatory machinery during development and in response to specific cellular signals. PARP-1 might modulate gene expression through its catalytic activity leading to poly(ADP-ribosyl)ation of nuclear proteins or by its physical association with relevant proteins. Recently, we have shown that PARP-1 is activated during T cell activation. However, the proposed role of PARP-1 in reprogramming T cell gene expression upon activation remains largely unexplored.

Results

In the present study we use oligonucleotide microarray analysis to gain more insight into the role played by PARP-1 during the gene expression reprogramming that takes place in T cells upon activation with anti-CD3 stimulation alone, or in combination with anti-CD28 co-stimulation. We have identified several groups of genes with expression modulated by PARP-1. The expression of 129 early-response genes to anti-CD3 seems to be regulated by PARP-1 either in a positive (45 genes) or in a negative manner (84 genes). Likewise, in the presence of co-stimulation (anti-CD3 + anti-CD28 stimulation), the expression of 203 genes is also regulated by PARP-1 either up (173 genes) or down (30 genes). Interestingly, PARP-1 deficiency significantly alters expression of genes associated with the immune response such as chemokines and genes involved in the Th1/Th2 balance.

Conclusion

This study provides new insights into changes in gene expression mediated by PARP-1 upon T cell activation. Pathway analysis of PARP-1 as a nuclear signalling molecule in T cells would be of relevance for the future development of new therapeutic approaches targeting PARP-1 in the acquired immune response.

Toward specific functions of poly(ADP-ribose) polymerase-2

Poly(ADP-ribose) polymerase-2 (PARP-2) belongs to a family of enzymes that catalyze poly(ADP-ribosyl)ation of proteins. PARP-1 and PARP-2 are so far the only PARP enzymes whose catalytic activity has been shown to be induced by DNA-strand breaks, providing strong support for key shared functions in the cellular response to DNA damage. Accordingly, clinical trials for cancer, using PARP inhibitors that target the conserved catalytic domain of PARP proteins, are now ongoing. However, recent data suggest unique functions for PARP-2 in specific processes, such as genome surveillance, spermatogenesis, adipogenesis and T cell development. Understanding these physiological roles might provide invaluable clues to the rational development and exploitation of specific PARP-2 inhibitor drugs in a clinical setting and the design of new therapeutic approaches in different pathophysiological conditions.

NAD+/NADH and NADP+/NADPH in cellular functions and cell death: regulation and biological consequences

Accumulating evidence has suggested that NAD (including NAD+ and NADH) and NADP (including NADP+ and NADPH) could belong to the fundamental common mediators of various biological processes, including energy metabolism, mitochondrial functions, calcium homeostasis, antioxidation/generation of oxidative stress, gene expression, immunological functions, aging, and cell death: First, it is established that NAD mediates energy metabolism and mitochondrial functions; second, NADPH is a key component in cellular antioxidation systems; and NADH-dependent reactive oxygen species (ROS) generation from mitochondria and NADPH oxidase-dependent ROS generation are two critical mechanisms of ROS generation; third, cyclic ADP-ribose and several other molecules that are generated from NAD and NADP could mediate calcium homeostasis; fourth, NAD and NADP modulate multiple key factors in cell death, such as mitochondrial permeability transition, energy state, poly(ADP-ribose) polymerase-1, and apoptosis-inducing factor; and fifth, NAD and NADP profoundly affect aging-influencing factors such as oxidative stress and mitochondrial activities, and NAD-dependent sirtuins also mediate the aging process. Moreover, many recent studies have suggested novel paradigms of NAD and NADP metabolism. Future investigation into the metabolism and biological functions of NAD and NADP may expose fundamental properties of life, and suggest new strategies for treating diseases and slowing the aging process.

DNA repair, damage signaling and carcinogenesis

The First joint meeting of the German DGDR (German Society for Research on DNA Repair) and the French SFTG (French Society of Genotoxicology) on DNA Repair was held in Toulouse, France, from September 15 to 19, 2007. It was organized by Lisa Wiesmüller and Bernard Salles together with the scientific committee consisting of Gilbert de Murcia, Jean-Marc Egly, Frank Grosse, Karl-Peter Hopfner, Georges Iliakis, Bernd Kaina, Markus Löbrich, Bernard Lopez, Daniel Marzin and Alain Sarasin. This report summarizes information presented by the speakers (invited lectures and oral communications) during the seven plenary sessions, which include (1) excision repair, (2) DNA repair and carcinogenesis, (3) double-strand break repair, (4) replication in repair and lesion bypass, (5) cellular responses to genotoxic stress, (6) DNA repair machinery within the chromatin context and (7) genotoxicology and testing. A total of 23 plenary lectures, 32 oral communications and 66 posters were presented in this rather intense 4 days meeting, which stimulated extensive discussions and highly interdisciplinary scientific exchanges among the approximately 250 participants.

Poly(ADP-ribose) polymerase-2 [corrected] controls adipocyte differentiation and adipose tissue function through the regulation of the activity of the retinoid X receptor/peroxisome proliferator-activated receptor-gamma [corrected] heterodimer

The peroxisome proliferator-activated receptor-gamma (PPARgamma, NR1C3) in complex with the retinoid X receptor (RXR) plays a central role in white adipose tissue (WAT) differentiation and function, regulating the expression of key WAT proteins. In this report we show that poly(ADP-ribose) polymerase-2 (PARP-2), also known as an enzyme participating in the surveillance of the genome integrity, is a member of the PPARgamma/RXR transcription machinery. PARP-2(-/-) mice accumulate less WAT, characterized by smaller adipocytes. In the WAT of PARP-2(-/-) mice the expression of a number of PPARgamma target genes is reduced despite the fact that PPARgamma1 and -gamma2 are expressed at normal levels. Consistent with this, PARP-2(-/-) mouse embryonic fibroblasts fail to differentiate to adipocytes. In transient transfection assays, PARP-2 small interference RNA decreases basal activity and ligand-dependent activation of PPARgamma, whereas PARP-2 overexpression enhances the basal activity of PPARgamma, although it does not change the maximal ligand-dependent activation. In addition, we show a DNA-dependent interaction of PARP-2 and PPARgamma/RXR heterodimer by chromatin immunoprecipitation. In combination, our results suggest that PARP-2 is a novel cofactor of PPARgamma activity.