Critical Role of the Automodification of Poly(ADP-ribose) Polymerase-1 in Nuclear Factor-κB-dependent Gene Expression in Primary Cultured Mouse Glial Cells

Abstract

Poly(ADP-ribose) polymerase-1 (PARP-1 1 ; EC 2.4.2.30) is an abundant nuclear protein that is activated by DNA strand breakage and that catalyzes the covalent attachment of poly-(ADP-ribose) (PAR) from NAD ϩ to numerous nuclear proteins and transcription factors, including histones; DNA polymerase ␣ and ␤; p53; and PARP-1, itself being the major target, via its automodification domain (1, 2). Besides PARP-1, another six PARPs have been identified: short PARP, PARP-2, PARP-3, tankylase-1/2, and vault PARP (2, 3). However, the physiological roles of poly(ADP-ribosyl)ation of nuclear proteins and transcription factors induced by PARPs are not completely understood. The initially identified subtype of the enzyme, PARP-1, has been thought to play a central role in the process of poly(ADP-ribosyl)ation because poly(ADP-ribosyl)ation is markedly reduced in most tissues of PARP-1 null mice (4). Transient poly(ADP-ribosyl)ation by PARP-1 can be induced by a wide variety of environmental stimuli, including reactive oxygen, ionizing radiation, and genotoxic stress (1, 2). Thus, PARP-1 has been suggested to regulate DNA repair (5). On the other hand, overactivation of PARP-1 by massively damaged DNA consumes NAD ϩ and consequently ATP, resulting in necrotic cell death by energy failure (3, 6).There are many reports suggesting that PARP-1 is also involved in regulation of gene expression at the transcriptional step (2, 3). PARP-1 seems to play dual roles in transcription. Poly(ADP-ribosyl)ation of transcription factors such as YinYang 1 (7), RNA polymerase II-associated factors (8), and p53 (9) results in reversible silencing of transcription by impairing the DNA binding of these proteins. In other instances, PARP-1 was found to have only one function, stimulating the DNA binding activity of transcription factors such as Oct-1 (10) and B-Myb (11). Recent reports have also shown that PARP-1 is required for specific nuclear factor-B (NF-B)-dependent gene expression and acts as a coactivator for 14). Indeed, the NF-B-dependent transcription of some inflammatory mediators in response to endotoxin (13) or pro-inflammatory cytokines such as tumor necrosis factor-␣ (TNF-␣) and interleukin-1␤ (IL-1␤) (12-14) is almost completely abrogated in PARP-1 null mice. Thus, anti-inflammatory effects of PARP-1 inhibitors have been extensively discussed in relation to various inflammation-related diseases (15, 16). However, the exact biochemical mechanism by which PARP-1 regulates NF-B-dependent transcription is obscure. To date, some groups have reported that the enzyme activity of PARP-1 might directly influence NF-B-dependent transcription. Kameoka et al. (17) showed that poly(ADP-ribosyl)ation markedly suppresses the DNA binding activity of NF-B via direct modification in vitro. demonstrated that the DNA binding activity of NF-B p50 is NAD ϩ -dependent and reversibly regulated by the automodification of PARP-1 under cell-free conditions. In contrast, Hassa et al. (14) concluded that neither the enzyme activity nor the DNA binding

Inhibition of Poly(ADP-Ribose) Polymerase Suppresses Inflammation and Promotes Recovery after Ischemic Injury

“…There is disagreement as to whether PARP-1 enzymatic activity is required for this interaction with NF-kB. Some reports show that enzymatically nonfunctional PARP-1 can facilitate NF-kB activation (reviewed in Kraus and Lis, 2003), but others have shown that inhibition of enzymatic PARP-1 activity suppresses NF-kB-driven gene transcription in a variety of cell types, including microglia (Chiarugi and Moskowitz, 2003;Nakajima et al, 2004). It remains possible, however, that the antiinflammatory actions of PJ34 could be mediated by enzymatic inhibition of PARP species other than PARP-1, or by blocking the effect of PARP-1 at transcription sites other than NF-kB (Jagtap and Szabo, 2005).…”

Microglial Activation in Stroke: Therapeutic Targets

“…[215][216][217] PARP-1 enzymatic activity is required for NF-B-mediated gene transcription and for many of the inflammatory responses in microglia. 22,214,218,219 Several PARP inhibitors are now commercially available. Most of these do not discriminate well between PARP-1 and several of the other PARP species, but studies using PARP-1 Ϫ/Ϫ cells indicate a major, though perhaps not exclusive role for the PARP-1 isoform in microglial activation.…”

Caspases in cell survival, proliferation and differentiation

“…On the one hand, it is shown that co-activation of NF-kB by p300 in TNF-or LPS-stimulated primary fibroblasts or macrophages does not depend on the enzymatic activity of PARP-1, whereas on the other hand, studies using PARP-1 inhibitors do indicate a role for PARP-1 enzymatic activity in the enhancement of NF-kB transcriptional activity. 21,22 Further analysis is required to clarify this intriguing issue.…”