Poly(ADP-ribose) polymerase enhances activator-dependent transcription in vitro

In vivo regulation of the chicken cardiac troponin T gene promoter in zebrafish embryos

The chicken cardiac troponin T (cTnT) gene is representative of numerous cardiac and skeletal muscle-specific genes that contain muscle-CAT (MCAT) elements within their promoters. We examined the regulation of the chicken cTnT gene in vivo in zebrafish embryos, and in vitro in cardiomyocyte, myoblast, and fibroblast cultures. Defined regions of the cTnT promoter were linked to the green fluorescent protein (GFP) gene for in vivo analysis, and the luciferase gene for in vitro analysis. Injection of the cTnT promoter constructs into fertilized zebrafish eggs resulted in GFP expression in both heart and skeletal muscle cells reproducing the pattern of expression of the endogenous cTnT gene in the chicken embryo. Promoter deletion analysis revealed that the cis-regulatory regions responsible for cardiac and skeletal muscle-specific expression functioned in an equivalent manner in both in vitro and in vivo environments. In addition, we show that mutation of the poly-ADP ribose polymerase-I (PARP-I) binding site adjacent to the distal MCAT element in the chicken cTnT promoter produced a non-cell-specific promoter in vitro and in the zebrafish. Thus, the PARP-I transcriptional regulatory mechanism that governs muscle specificity of the chicken cTnT promoter is conserved across several chordate classes spanning at least 350 million years of evolution.

Active poly(ADPribose) metabolism in DNAase- and salt-resistant rat testis chromatin with high transcriptional activity/competence

A chromatin fraction, named pP fraction, was prepared from rat testis nuclei, which had been digested with nuclease in order to separate soluble and insoluble chromatin. This fraction resembled nuclear matrix as it was highly resistant to DNAase digestion, had a high content of proteins compared to the low DNA percentage, and a noticeable transcriptional activity. Moreover, poly(ADPribosyl)ation system (i.e., poly(ADPR)polymerase, poly(ADPribose), and acceptor proteins) was still present at high levels. In order to study whether it might be identified as the protein support surrounding chromatin loops, this pP fraction was further analyzed after 3 M NaCl extraction. The 3 M NaCl extract and the highly insoluble pellet, named Nuclear Matrix Pellet, were characterized as it regards DNA, newly synthesized RNA and proteins. Furthermore, poly(ADPribose) metabolism was analyzed by measuring both poly(ADPribose) polymerase and poly(ADPribose) glycohydrolase activities, poly(ADPribose) distribution and by identifying protein acceptors. The final pellet had features of nuclear matrix containing less than 10% DNA and high percentage of proteins; 28% of newly synthesized RNA was still associated with this fraction. Long and branched polyADPribose were found in the nuclear matrix-like pellet, although ADPribose acceptors (mainly H1 and core histones) appeared to be modified mostly with short ADPribose oligomers. Longest and branched polymers were retained on the top of protein gel, likely bound to automodified poly(ADPribose) polymerase.

PARP goes transcription

PARP-1, an enzyme that catalyzes the attachment of ADP ribose units to target proteins, plays at least two important roles in transcription regulation. First, PARP-1 modifies histones and creates an anionic poly(ADPribose) matrix that binds histones, thereby promoting the decondensation of higher-order chromatin structures. Second, PARP-1 acts as a component of enhancer/promoter regulatory complexes. Recent studies have shown that both of these activities are critical for gene regulation in vivo.

Inhibitors of poly (ADP-ribose) polymerase modulate signal transduction pathways in colitis

During inflammatory bowel diseases, oxidative and nitrosative stress induces DNA damage and activation of the nuclear enzyme poly (ADP-ribose) polymerase (PARP), resulting in depletion of intracellular energetics, intestinal barrier dysfunction and cellular death. The aim of our study was to evaluate the therapeutic efficacy of in vivo inhibition of PARP in experimental colitis, which was induced by rectal instillation of trinitrobenzene sulfonic acid (TNBS) in rats. In vehicle-treated rats, TNBS treatment resulted in colonic erosion and ulceration. Neutrophil infiltration (indicated by myeloperoxidase activity in the colon) was associated with formation of nitrotyrosine and marked apoptosis. Elevated levels of plasma nitrate/nitrite, metabolites of nitric oxide (NO), were also found. These inflammatory events were associated with the activation of nuclear factor-kappa B (NF-kappa B) and activator protein-1 (AP-1) in the colon; NF-kappa B was maximally activated at 3 and 7 days, whereas AP-1 increased 1 day after TNBS administration and declined thereafter. Treatment of the rats with the PARP inhibitors, 3-aminobenzamide or 1,5-dihydroxyisoquinoline, resolved colonic damage and reduced plasma levels of NO metabolites. Resolution of the damage was associated with reduction of neutrophil infiltration, nitrotyrosine formation and apoptosis. Treatment with PARP inhibitors also reduced DNA binding of NF-kappa B and AP-1 in the colon. These data demonstrate that pharmacological inhibition of PARP ameliorates colitis. Reduction of the inflammatory process is associated with modification of the activation of signal transduction pathways.

Nuclear receptor coactivator thyroid hormone receptor-binding protein (TRBP) interacts with and stimulates its associated DNA-dependent protein kinase

Nuclear receptors mediate gene activation through ligand-dependent interaction with coactivators. We previously cloned and characterized thyroid hormone receptor-binding protein, TRBP (NcoA6: AIB3/ASC-2/RAP250/PRIP/TRBP/NRC), as an LXXLL-containing coactivator that associates with coactivator complexes through its C terminus. To search for protein factors involved in TRBP action, we identified a distinct set of proteins from HeLa nuclear extract that interacts with the C terminus of TRBP. Analysis by mass spectrometric protein sequencing revealed a DNA-dependent protein kinase (DNA-PK) complex including its catalytic subunit and regulatory subunits, Ku70 and Ku86. DNA-PK is a heterotrimeric nuclear phosphatidylinositol 3-kinase that functions in DNA repair, recombination, and transcriptional regulation. DNA-PK phosphorylates TRBP at its C-terminal region, which directly interacts with Ku70 but not Ku86 in vitro. In addition, in the absence of DNA, TRBP itself activates DNA-PK, and the TRBP-stimulated DNA-PK activity has an altered phosphorylation pattern from DNA-stimulated activity. An anti-TRBP antibody inhibits TRBP-induced kinase activity, suggesting that protein content of TRBP is responsible for the stimulation of DNA-independent kinase activity. Furthermore, in DNA-PK-deficient scid cells, TRBP-mediated transactivation is significantly impaired, and nuclear localization of TRBP is altered. The activation of DNA-PK in the absence of DNA ends by the coactivator TRBP suggests a novel mechanism of coactivator-stimulated DNA-PK phosphorylation in transcriptional regulation.

Overexpression of a protein fragment of RNA helicase A causes inhibition of endogenous BRCA1 function and defects in ploidy and cytokinesis in mammary epithelial cells

The breast- and ovarian-specific tumor suppressor, BRCA1, has been implicated to function in many nuclear processes, including DNA damage repair, recombination, transcription, ubiquitination, cell cycle checkpoint enforcement, and centrosome regulation. Utilizing a previously described interaction between BRCA1 and RNA helicase A (RHA), we have developed a dominant-negative approach to block BRCA1 function in human breast epithelial cells. Overexpression of a truncated RHA peptide that can bind to the BRCA1 carboxy-terminus prevents normal BRCA1 function, such as BRCA1 association with nuclear foci following DNA damage. Overexpression of this dominant-negative protein induces pleomorphic nuclei, aberrant mitoses with extra centrosomes, and tetraploidy. This model system allows us to observe changes to mammary epithelial cells that occur acutely following loss of BRCA1 function. Furthermore, inhibition of BRCA1 via overexpressing the RHA fragment coincides with a reduction in PARP-1 protein expression, suggesting a possible mechanism for BRCA1 in the maintenance of genomic integrity.

Role of PARP under stress conditions: cell death or protection?

A great deal of increasing evidence designs PARP as a multifunctional protein implicated in many cellular functions. Much interest is emerging to understand the precise mechanisms by which PARP mediates genome stabilization and protection against damage, as well as its involvement in cell death, either apoptotic or necrotic. Aside from the clearly established role of PARP hyperactivation in necrotic cell death, after excessive DNA damage and energy failure, it appears to be actively involved in the phenomenon of apoptosis. However, its exact role is still controversial. The identification of several enzymes sharing the poly(ADP-ribose) polymerase catalytic domain (PARPs), but with different features and subcellular localization, has opened a new perspective in the field of poly(ADP-ribosyl)ation. The picture of the role of PARP in the control of cell homeostasis became even more complex after demonstration of its implication in the regulation of gene transcription. The notion that energy failure is the sole mechanism by which PARP promotes cell death is therefore under reevaluation.

Activation of Poly(adenosine diphosphate–ribose) Polymerase in Mouse Tumors Treated by Photodynamic Therapy¶

Poly(adenosine diphosphate-ribose) polymerase (PARP) has recently been characterized as a key regulator of cell death-survival transcriptional programs associated with stress and inflammation. Possible participation of this enzyme in the response of tumors to photodynamic therapy (PDT) was investigated in this study. Immunohistochemical analysis of mouse FsaR tumors treated by PDT based on photosensitizers Photofrin or 5,10,15,20-tetra-(m-hydroxyphenyl)chlorine (mTHPC) revealed a strong positive staining for PARP product poly(ADP-ribose) at 30 min and 1 h after PDT, respectively, and even more intense positivity at 2 h after PDT with both photosensitizers. Flow cytometry-based examination showed the induction of poly-ADP-ribosylation in FsaR tumors at 30 min after PDT, with a trend for a further increase in the intensity by 2 h after PDT in both cancer cells and tumor-associated leukocytes. In FsaR cells treated in vitro by mTHPC-based PDT, flow cytometric analysis indicated that the activation of PARP concentrated in cells undergoing apoptosis and reached a maximum by 30 min after PDT. The administration of PARP inhibitors, 3-aminobenzamide or 1,5-isoquinolinediol, to FsaR tumor-bearing mice before PDT light treatment increased the resistance of these tumors to PDT. PARP appears to control the balance between apoptotic and necrotic cell death in PDT-treated tumors and regulate the progression of PDT-induced inflammatory or innate immune response.

Fine tuning the transcriptional regulation of the CXCL1 chemokine

Constitutive activation of the transcription factor nuclear factor-κB (NF-κB) plays a major role in inflammatory diseases as well as cancer by inducing the endogenous expression of many proinflammatory proteins such as chemokines, and facilitating escape from apoptosis. The constitutive expression of chemokines such as CXCL1 has been correlated with growth, angiogenesis, and metastasis of cancers such as melanoma. The transcription of CXCL1 is regulated through interactions of NF-κB with other transcriptional regulatory molecules such as poly(ADP-ribose) polymerase-1 (PARP-1) and cAMP response element binding protein (CREB)-binding protein (CBP). It has been proposed that these two proteins interact with NF-κB and other enhancers to form an enhanceosome at the promoter region of CXCL1 and modulate CXCL1 transcription. In addition to these positive cofactors, a negative regulator, CAAT displacement protein (CDP), may also be involved in the transcriptional regulation of CXCL1. It has been postulated that the elevated expression of CXCL1 in melanomas is due to altered interaction between these molecules. CDP interaction with the promoter down-regulates transcription, whereas PARP and/or CBP interactions enhance transcription. Thus, elucidation of the interplay between components of the enhanceosome of this gene is important in finding more efficient and new therapies for conditions such as cancer as well as acute and chronic inflammatory diseases.

Endogenous mono-ADP-ribosylation mediates smooth muscle cell proliferation and migration via protein kinase N-dependent induction of c-fos expression

ADP-ribosylation has been coupled to intracellular events associated with smooth muscle cell vasoreactivity, cytoskeletal integrity and free radical damage. Additionally, there is evidence that ADP-ribosylation is required for smooth muscle cell proliferation. Our investigation employed selective inhibitors to establish that mono-ADP-ribosylation and not poly(ADP-ribosyl)ation was necessary for the stimulation of DNA synthesis by mitogens. Mitogen treatment increased concomitantly the activity of both soluble and particulate mono-ADP-ribosyltransferase, as well as the number of modified proteins. Inclusion of meta-iodobenzylguanidine (MIBG), a selective decoy substrate of arginine-dependent mono-ADP-ribosylation, prevented the modification of these proteins. MIBG also blocked the stimulation of DNA and RNA synthesis, prevented smooth muscle cell migration and suppressed the induction of c-fos and c-myc gene expression. An examination of relevant signal transduction pathways showed that MIBG did not interfere with MAP kinase and phosphatidylinositol 3-kinase stimulation; however, it did inhibit phosphorylation of the Rho effector, PRK1/2. This novel observation suggests that mono-ADP-ribosylation participates in a Rho- dependent signalling pathway that is required for immediate early gene expression.

Poly(ADP-ribose) polymerase triggers the microvascular mechanisms of hepatic ischemia-reperfusion injury

Activation of poly(ADP-ribose) polymerase (PARP) mediates oxidative stress-induced cell injury. We tested the hypothesis that PARP contributes to ischemia-reperfusion (I/R) damage of the liver by triggering the mechanisms of microcirculatory failure. Leukocyte- and platelet-endothelial cell interactions as well as sinusoidal perfusion were analyzed by intravital fluorescence microscopy after lobar hepatic I/R (90 min/30 min) in C57BL/6 x 129/Sv wild-type (PARP+/+) and PARP-deficient (PARP-/-) mice. Hepatic I/R induced leukocyte/platelet-endothelial cell interactions and tissue injury in PARP+/+ mice, as indicated by impaired sinusoidal perfusion and increased alanine aminotransferase (ALT)/aspartate aminotransferase (AST) serum activities. In PARP-/- mice, however, the postischemic increase in the numbers of rolling/adherent leukocytes and platelets was significantly lower. In addition, I/R-induced translocation of CD62P as well as mRNA expression of CD62E, CD54, and CD106 were attenuated. The degree of perfusion failure was reduced and the increase in the ALT/AST activities was lower in PARP-/- mice compared with PARP+/+ mice. We conclude that PARP contributes to hepatic microvascular injury by triggering the expression/translocation of adhesion molecules and modulating leukocyte/platelet-endothelial cell interactions.

Functional interaction between human papillomavirus type 18 E2 and poly(ADP-ribose) polymerase 1

Human papillomavirus E2 protein is a transcription factor of viral gene expression and DNA replication. Here we show that PARP is a positive regulator of the E2 protein of human papillomavirus type 18 (HPV-18). PARP interacted with the COOH terminal region of HPV-18 E2 in vitro. The E2 interaction domain within PARP is located in the NH(2)-terminal zinc finger motif and the BRCT motif included in the automodification domain. Overexpression of either wild type or the NH(2)-terminal region of PARP containing zinc finger and BRCT stimulated E2-dependent transcription. Gel retardation assay indicates that PARP augments DNA binding activity of E2 in vitro. We also show that PARP-1 is recruited to E2-dependent promoter in vivo using ChIP assay. These results suggest that PARP serves a transcriptional co-activator in E2-dependent transcription by interacting directly with the HPV E2 protein.

Hyperphosphorylated C-terminal repeat domain-associating proteins in the nuclear proteome link transcription to DNA/chromatin modification and RNA processing

Using an interaction blot approach to search in the human nuclear proteome, we identified eight novel proteins that bind the hyperphosphorylated C-terminal repeat domain (phosphoCTD) of RNA polymerase II. Unexpectedly, five of the new phosphoCTD-associating proteins (PCAPs) represent either enzymes that act on DNA and chromatin (topoisomerase I, DNA (cytosine-5) methyltransferase 1, poly(ADP-ribose) polymerase-1) or proteins known to bind DNA (heterogeneous nuclear ribonucleoprotein (hnRNP) U/SAF-A, hnRNP D). The other three PCAPs represent factors involved in pre-mRNA metabolism as anticipated (CA150, NSAP1/hnRNP Q, hnRNP R) (note that hnRNP U/SAF-A and hnRNP D are also implicated in pre-mRNA metabolism). Identifying as PCAPs proteins involved in diverse DNA transactions suggests that the range of phosphoCTD functions extends far beyond just transcription and RNA processing. In view of the activities possessed by the DNA-directed PCAPs, it is likely that the phosphoCTD plays important roles in genome integrity, epigenetic regulation, and potentially nuclear structure. We present a model in which the phosphoCTD association of the PCAPs poises them to act either on the nascent transcript or on the DNA/chromatin template. We propose that the phosphoCTD of elongating RNA polymerase II is a major organizer of nuclear functions.

GPI 6150, a PARP inhibitor, reduces the colon injury caused by dinitrobenzene sulfonic acid in the rat

Poly (ADP-ribose) polymerase, a nuclear enzyme activated by DNA strand breaks, has been shown to play an important role in the pathogenesis of inflammatory bowel disease. Here we investigate the effects of 1,11b-dihydro-[2H]benzopyrano [4,3,2-de]isoquinolin-3-one (GPI 6150), a new poly (ADP-ribose) polymerase inhibitor, in animal models of experimental colitis. Colitis was induced in rats by intra-colonic instillation of dinitrobenzene sulfonic acid. Rats experienced hemorrhagic diarrhea and weight loss. At 4 days after administration of dinitrobenzensulfonic acid, the mucosa of the colon exhibited large areas of necrosis. Neutrophil infiltration (determined by histology and an increase in myeloperoxidase activity in the mucosa) was associated with up-regulation of ICAM-1. Immunohistochemistry for poly (ADP-ribose) showed an intense staining in the inflamed colon. GPI 6150 (20 or 40 mg/kg daily, i.p.) significantly reduced the degree of hemorrhagic diarrhea and weight loss caused by administration of dinitrobenzensulfonic acid. GPI 6150 also caused a substantial reduction of (i) the degree of colon injury, (ii) the rise in myeloperoxidase activity (mucosa), (iii) the increase in the tissue levels of malondialdehyde, (iv) the increase in staining (immunohistochemistry) for poly (ADP-ribose), as well as (v) the upregulation of ICAM-1 and P-selectin caused by dinitrobenzensulfonic acid in the colon. Thus, GPI 6150 reduces the degree of colitis caused by dinitrobenzensulfonic acid. We propose that GPI 6150 may be useful in the treatment of inflammatory bowel disease.

The inhibition of poly(ADP-ribose) polymerase enhances growth rates of ataxia telangiectasia cells

Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme which is activated in response to genotoxic insults by binding damaged DNA and attaching polymers of ADP-ribose to nuclear proteins at the expense of its substrate NAD+. In persons affected with ataxia telangiectasia (A-T), associated mutations in the ataxia telangiectasia mutated gene render cells unable to cope with the genotoxic stresses from ionizing radiation and oxidative damage, thus resulting in a higher concentration of unrepaired DNA damage and the activation of PARP in an uncontrolled manner. In primary A-T fibroblasts, we observed a 58-96% increase in PARP activity and a concomitant loss of cellular NAD+ and ATP content. PARP protein by Western blot analysis increased only slightly in these cells, supporting the observation that the steady state levels of DNA damage is higher in A-T cells than in normals. When treated with PARP inhibitors 3-aminobenzamide or 1,5-dihydroisoquinoline, cellular growth rates reached those observed in normal fibroblast cultures. The improvement of cellular growth and NAD+ levels in A-T cells with PARP inhibition suggests that the cellular metabolic status of A-T cells is compromised and the inhibition of PARP may relieve some of the drain on cellular pyridine nucleotides and ATP. Thus, therapy utilizing PARP inhibitors may provide a benefit for individuals affected with A-T.

Nitric oxide-peroxynitrite-poly(ADP-ribose) polymerase pathway in the skin

In the last decade it has become well established that in the skin, nitric oxide (NO), a diffusable gas, mediates various physiologic functions ranging from the regulation of cutaneous blood flow to melanogenesis. If produced in excess, NO combines with superoxide anion to form peroxynitrite (ONOO-), a cytotoxic oxidant that has been made responsible for tissue injury during shock, inflammation and ischemia-reperfusion. The opposite effects of NO and ONOO- on various cellular processes may explain the 'double-edged sword' nature of NO depending on whether or not cellular conditions favour peroxynitrite formation. Peroxynitrite has been shown to activate the nuclear nick sensor enzyme, poly(ADP-ribose) polymerase (PARP). Overactivation of PARP depletes the cellular stores of NAD+, the substrate of PARP, and the ensuing 'cellular energetic catastrophy' results in necrotic cell death. Whereas the role of NO in numerous skin diseases including wound healing, burn injury, psoriasis, irritant and allergic contact dermatitis, ultraviolet (UV) light-induced sunburn erythema and the control of skin infections has been extensively documented, the intracutaneous role of peroxynitrite and PARP has not been fully explored. We have recently demonstrated peroxynitrite production, DNA breakage and PARP activation in a murine model of contact hypersensitivity, and propose that the peroxynitrite-PARP route represents a common pathway in the pathomechanism of inflammatory skin diseases. Here we briefly review the role of NO in skin pathology and focus on the possible roles played by peroxynitrite and PARP in various skin diseases.

Sequence-specific binding of poly(ADP-ribose) polymerase-1 to the human T cell leukemia virus type-I tax responsive element

We have previously identified poly(ADP-ribose) polymerase-1 (PARP-1) as a coactivator for the human T cell leukemia virus type I (HTLV-I) transcription activator Tax. While PARP-1 is believed to contribute to DNA repair, PARP-1 has been described as a coactivator for other transcription factors. Recent evidence suggests that PARP-1 forms complexes on cellular promoters, so we investigated PARP-1 complexes on the HTLV-I Tax responsive elements (TxREs) using an end-blocked DNA binding assay. We observed sequence-specific binding of PARP-1 to the TxREs. The DNA binding domain of PARP-1 was fused to the transcriptional activation domain of VP16, and this fusion protein activated the HTLV-I promoter in a TxRE-dependent manner. Internal, sequence-specific binding of PARP-1 to DNA provides a mechanism for transcriptional regulation of the HTLV-I promoter. The mechanism of PARP-1 function in the HTLV-I system may have common mechanistic steps with other cellular promoters, including the formation of active complexes on the promoter.

Poly(ADP-ribose) polymerase: killer or conspirator? The 'suicide hypothesis' revisited

Poly(ADP-ribose) polymerase 1 (PARP-1) is an abundant nuclear enzyme involved in DNA repair. The therapeutic efficacy of drugs that inhibit PARP-1 in various disorders underscores the active role of PARP-1 in cell death. Although it is well established that excessive DNA damage causes PARP-1 hyperactivation, which leads to cell death by energy failure, a new mechanistic perspective is emerging following the identification of various PARPs that exhibit different features and subcellular distributions. Studies demonstrating the significant role of PARP-1 in the regulation of gene transcription have further increased the intricacy of poly(ADP-ribosyl)ation in the control of cell homeostasis and challenge the notion that energy collapse is the sole mechanism by which poly(ADP-ribose) formation contributes to cell death. The hypothesis that PARPs might regulate cell fate as essential modulators of death and survival transcriptional programs will be discussed with particular focus on the regulation of transcription factors such as nuclear factor kappaB and p53. (An animation depicting the involvement of PARP-1 in the 'suicide hypothesis' is available at http://archive.bmn.com/supp/tips/tips2303a.html)

Rapid activation of poly(ADP-ribose) polymerase contributes to Sindbis virus and staurosporine-induced apoptotic cell death

Poly(ADP-ribose) polymerase-1 (PARP-1) is a chromatin-associated enzyme that is activated by DNA strand breaks and catalyzes the transfer of ADP-ribose groups from NAD to itself and other nuclear proteins. Although caspase-mediated PARP-1 cleavage occurs during almost all forms of apoptosis, the contribution of PARP-1 activation and cleavage to this cell death process remains unclear. Using immortalized fibroblasts from wild-type (PARP-1(+/+)) and PARP-1 knockout (PARP-1(-/-)) mice, and a mouse neuroblastoma cell line (N18), the role that poly(ADP-ribosyl)ation plays in Sindbis virus (SV)-induced apoptosis was examined. Robust PARP-1 activation occurred in SV-infected cells prior to morphologic changes associated with apoptotic cell death and PARP-1 activity ceased simultaneously with caspase-3 activation and PARP-1 proteolysis. PARP-1 activity was maximal before detectable DNA fragmentation, but was absent when DNA damage was most intense. SV and staurosporine-induced cell death was delayed in fibroblasts lacking PARP-1 activity, suggesting that PARP-1 activation contributes to apoptotic cell death induced by these stimuli. SV replication was not affected by lack of PARP-1 activity, but DNA fragmentation and caspase-3 activation were delayed and occurred at lower levels in PARP-1-deficient fibroblasts. Early virus-induced PARP-1 activation may represent a novel way by which cells signal to the nucleus to regulate protein function by poly(ADP-ribosyl)ation in response to virus infection.

Anti-cancer action of 4-iodo-3-nitrobenzamide in combination with buthionine sulfoximine: inactivation of poly(ADP-ribose) polymerase and tumor glycolysis and the appearance of a poly(ADP-ribose) polymerase protease

E-ras 20 tumorigenic malignant cells and CV-1 non-tumorigenic cells were treated with a drug combination of 4-iodo-3-nitrobenzamide (INO(2)BA) and buthionine sulfoximine (BSO). Growth inhibition of E-ras 20 cells by INO(2)BA was augmented 4-fold when cellular GSH content was diminished by BSO, but the growth rate of CV-1 cells was not affected by the drug combination. Analyses of the intracellular fate of the prodrug INO(2)BA revealed that in E-ras 20 cells about 50% of the intracellular reduced drug was covalently protein-bound, and this binding was dependent upon BSO, whereas in CV-1 cells BSO did not influence protein binding. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was identified as the protein that covalently binds the reduction product of INO(2)BA, which is 4-iodo-3-nitrosobenzamide. Since only the enzymatically reduced drug INOBA bound covalently to GAPDH, the BSO-dependent covalent protein-drug association indicated an apparent nitro-reductase activity present in E-ras 20 cells, but not in CV-1 cells, explaining the selective toxicity. Covalent binding of INOBA to GAPDH inactivated this enzyme in vitro; INO(2)BA+BSO also inactivated cellular glycolysis in E-ras 20 cells because it provided the precursor to the inhibitory species: INOBA. Another event that occurred in INO(2)BA+BSO-treated E-ras 20 cells was the progressive appearance of a poly(ADP-ribose) polymerase protease. This enzyme was partially purified and characterized by the polypeptide degradation product generated from PARP I, which exhibited a 50kDa mass. This pattern of proteolysis of PARP I is consistent with a drug-induced necrotic cell killing pathway.

Poly(ADP-Ribose) polymerase inhibition reduces reperfusion injury after heart transplantation

The aim of the present study was to investigate the effects of the novel poly(ADP-ribose) polymerase (PARP) inhibitor PJ34 (N-(6-oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylacetamide) on myocardial and endothelial function after hypothermic ischemia and reperfusion in a heterotopic rat heart transplantation model. After a 1-hour ischemic preservation, reperfusion was started either after application of placebo or PJ34 (3 mg/kg). The assessment of left ventricular pressure-volume relations, total coronary blood flow, endothelial function, myocardial high energy phosphates, and histological analysis were performed at 1 and 24 hours of reperfusion. After 1 hour, myocardial contractility and relaxation, coronary blood flow, and endothelial function were significantly improved and myocardial high energy phosphate content was preserved in the PJ34-treated animals. Improved transplant function was also seen with treatment with another, structurally different PARP inhibitor, 5-aminoisoquinoline. The PARP inhibitors did not affect baseline cardiac function. Immunohistological staining confirmed that PJ34 prevented the activation of PARP in the transplanted hearts. The activation of P-selectin and ICAM-1 was significantly elevated in the vehicle-treated heart transplantation group. Thus, pharmacological PARP inhibition reduces reperfusion injury after heart transplantation due to prevention of energy depletion and downregulation of adhesion molecules and exerts a beneficial effect against reperfusion-induced graft coronary endothelial dysfunction.

Transcriptional repression by binding of poly(ADP-ribose) polymerase to promoter sequences

Poly(ADP-ribose) polymerase (PARP) is a DNA-binding enzyme that plays roles in response to DNA damage, apoptosis, and genetic stability. Recent evidence has implicated PARP in transcription of eukaryotic genes. However, the existing paradigm tying PARP function to the presence of DNA strand breaks does not provide a mechanism by which it may be recruited to gene-regulating domains in the absence of DNA damage. Here we report that PARP can bind to the DNA secondary structures (hairpins) in heteroduplex DNA in a DNA end-independent fashion and that automodification of PARP in the presence of NAD+ inhibited its hairpin binding activity. Atomic force microscopic images show that in vitro PARP protein has a preference for the promoter region of the PARP gene in superhelical DNA where the dyad symmetry elements likely form hairpins according to DNase probing. Using a chromatin cross-linking and immunoprecipitation assay we show that PARP protein binds to the chromosomal PARP promoter in vivo. Reporter gene assays have revealed that the transcriptional activity of the PARP promoter is 4-5-fold greater in PARP knockout cells than in wild type fibroblasts. Reintroduction of vectors expressing full-length PARP protein or its truncated mutant (DNA-binding domain retained but lacking catalytic activity) into PARP(-/-) cells has conferred transcriptional down-regulation of the PARP gene promoter. These data provide support for PARP protein as a potent regulator of transcription including down-regulation of its own promoter.

The sequence-specific DNA binding of NF-kappa B is reversibly regulated by the automodification reaction of poly (ADP-ribose) polymerase 1

Recent studies suggest that the synthesis of protein-bound ADP-ribose polymers catalyzed by poly(ADP-ribose) polymerase-1 (PARP-1) regulates eucaryotic gene expression, including the NF-kappaB-dependent pathway. Here, we report the molecular mechanism by which PARP-1 activates the sequence-specific binding of NF-kappaB to its oligodeoxynucleotide. We co-incubated pure recombinant human PARP-1 and the p50 subunit of NF-kappaB (NF-kappaB-p50) in the presence or absence of betaNAD+ in vitro. Electrophoretic mobility shift assays showed that, when PARP-1 was present, NF-kappaB-p50 DNA binding was dependent on the presence of betaNAD+. DNA binding by NF-kappaB-p50 was not efficient in the absence of betaNAD+. In fact, the binding was not efficient in the presence of 3-aminobenzamide (3-AB) either. Thus, we conclude that NF-kappaB-p50 DNA binding is protein-poly(ADP-ribosyl)ation dependent. Co-immunoprecipitation and immunoblot analysis revealed that PARP-1 physically interacts with NF-kappaB-p50 with high specificity in the absence of betaNAD+. Because NF-kB-p50 was not an efficient covalent target for poly(ADP-ribosyl)ation, our results are consistent with the conclusion that the auto-poly(ADP-ribosyl)ation reaction catalyzed by PARP-1 facilitates the binding of NF-kappaB-p50 to its DNA by inhibiting the specific protein.protein interactions between NF-kappaB-p50 and PARP-1. We also report the activation of NF-kappaB DNA binding by the automodification reaction of PARP-1 in cultured HeLa cells following exposure to H(2)O(2). In these experiments, preincubation of HeLa cells with 3-AB, prior to oxidative damage, strongly inhibited NF-kappaB activation in vivo as well.

The enzymatic and DNA binding activity of PARP-1 are not required for NF-kappa B coactivator function

Poly(ADP-ribose) polymerase 1 (PARP-1)-deficient mice are protected against septic shock, diabetes type I, stroke, and inflammation. We report that primary cells from PARP-1(-/-) animals are impaired in kappa B-dependent transcriptional activation induced by different stimuli involved in inflammatory and genotoxic stress signaling. PARP-1 was also required for p65-mediated transcriptional activation. PARP-1 enzymatic inhibitors did not inhibit the transcriptional activation of a kappa B-dependent reporter gene in wild type cells. Remarkably, neither the enzymatic activity nor the DNA binding activity of PARP-1 was required for kappa B-dependent transcriptional activation in PARP-1(-/-) cells complemented with different PARP-1 mutants. However, PARP-1 interacted in vitro directly with both subunits of NF-kappa B (p50 and p65), and mapping of the interaction domains revealed that both subunits bind to different PARP-1 domains. Furthermore, a PARP-1 mutant lacking the enzymatic and DNA binding activity interacted comparably to the wild type PARP-1 with p65 or p50. Finally, we showed that PARP-1 is activating the natural inducible nitric-oxide synthase and P-selectin promoter in a kappa B-dependent manner upon stimulation of the cells with inflammatory stimuli or cotransfection of p65. Our results provide evidence that neither the DNA binding nor the enzymatic activity of PARP-1 but its direct protein-protein interaction with both subunits of NF-kappa B is required for its coactivator function, thus expanding the role of PARP-1 as an essential and novel classical transcriptional coactivator for kappa B-dependent gene expression in vivo.

Inhibition of host cell apoptosis by Toxoplasma gondii is accompanied by reduced activation of the caspase cascade and alterations of poly(ADP-ribose) polymerase expression

The obligate intracellular protozoan parasite Toxoplasma gondii has been shown to protect different cell types from apoptosis induced by a variety of pro-apoptotic treatments. However, the precise cell biological mechanisms of this inhibition remained unknown. As shown in this study, apoptosis in human-derived HL-60 and U937 cells induced by treatment with actinomycin D or TNF-α in combination with cycloheximide, respectively, was indeed dose-dependently downregulated by prior infection with T. gondii, as determined by DNA fragmentation assays. Cleavage of caspase 3 and caspase 9 after treatment with pro-apoptotic stimuli was considerably diminished by T. gondii. Furthermore, release of mitochondrial cytochrome c during apoptosis in HL-60 cells was prevented by intracellular parasites and this was correlated with the absence of DNA strand breaks on the single cell level. Inhibition of cytochrome c release coincided with a twofold upregulation of Mcl-1 protein levels in HL-60 and U937 cells, while Bcl-2 expression did not increase after infection. Parasitic interference with the caspase cascade led to a reduced proteolytic cleavage of the nuclear target molecule protein kinase Cδ. In parallel, poly(ADP-ribose) polymerase protein levels were prominently downregulated by T. gondii, irrespective of whether HL-60 and U937 cells had been treated with pro-apototic stimuli or left untreated. However, poly(ADP-ribose) polymerase mRNA levels remained unchanged after infection as determined by RT-PCR analyses. These observations suggest that T. gondii has evolved different mechanisms that may contribute to downregulation of host cell apoptosis, namely inhibition of cytochrome c release and subsequent caspase activation as well as downregulation of poly(ADP-ribose) polymerase protein levels.

Poly(ADP-ribosyl)ation of transcription factor Yin Yang 1 under conditions of DNA damage

Under conditions of severe DNA damage the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1) is activated, catalyzing the modification of proteins by forming and attaching to them poly(ADP-ribose) chains. A specific physical interaction between PARP-1 and transcription factor Yin Yang 1 (YY1) in vitro was shown previously, which had important consequences for the activities of both proteins. It is demonstrated here that YY1 and PARP-1 form complexes in vivo. YY1 was transiently poly(ADP-ribosyl)ated immediately after genotoxic treatment of HeLa cells. The narrow time frame of the modification coincides with that known for the activation of PARP-1 under these conditions. This immediate modification correlated with a decreased affinity of YY1 to its cognate DNA binding sites.

Maintenance of connexin 32 and 26 expression in primary cultured rat hepatocytes treated with 3-acetylpyridine

BACKGROUND AND AIM

We recently reported that primary rat hepatocytes treated with 3-acetylpyridine (3-AP), an analog of nicotinic acid, could maintain hepatic differentiated functions such as albumin, tryptophan 2,3-dioxygenase, and connexin 32 (Cx32) mRNA expressions for more than a week. In the present experiment, we investigated the expression of not only Cx32, but also Cx26 in cells treated with 10 mmol/L 3-AP in detail.

METHODS

We examined the expression of Cx32 and Cx26 in primary rat hepatocytes by using the methods of immunocytochemistry, immunoelectron microscopy, northern blotting, and dye-transfer.

RESULTS

The hepatocytes treated with 3-AP were polygonal with a large cytoplasm from day 3, and were maintained for approximately 2 weeks, whereas the cells without 3-AP began to die from day 4. Immunocytochemically in the cells with 3-AP, many Cx32- and Cx26-positive spots were observed between most adjacent cells, and the intensity of positive spots increased with time in culture, whereas in the cells without 3-AP, Cx32- and Cx26-positive spots disappeared at day 4. Furthermore, most Cx26-positive spots were colocalized with Cx32-positive ones. The amounts of Cx32 and Cx26 mRNA transcripts in the cells with 3-AP at day 14 were more than 80% and approximately 30% of those of Cx32 and Cx26 mRNA transcripts in the cells at day 1, respectively. Gap junctional intercellular communication was maintained in the cells treated with 3-AP at day 8, although it was lost in the cells without 3-AP.

CONCLUSION

Thus, the addition of 10 mmol/L 3-AP to the medium enhanced the maintenance of Cx32 and Cx26 expression, which is one of the hepatic differentiated functions, in primary rat hepatocytes for a long time.

Transcription factor Yin Yang 1 stimulates poly(ADP-ribosyl)ation and DNA repair

Poly(ADP-ribose) polymerase 1 (PARP-1) is a nuclear enzyme that catalyzes the synthesis of ADP-ribose polymers from NAD(+). The function of PARP-1 is related to important nuclear processes including DNA repair and transcription. Previous studies demonstrated a specific physical interaction between PARP-1 and the transcription factor Yin Yang 1 (YY1) in vitro. In this study, a functional relationship between both proteins in response to genotoxic treatment of cells is presented. The interaction of YY1 with PARP-1 greatly stimulates the enzymatic activity of PARP-1. Consistent with this, the overexpression of YY1 in HeLa cells resulted in an enhanced synthesis of poly(ADP-ribose) and an acceleration of DNA repair in response to a treatment with methyl-N'-nitro-N'-nitrosoguanidine.

Nuclear factor 1 interferes with Sp1 binding through a composite element on the rat poly(ADP-ribose) polymerase promoter to modulate its activity in vitro

Poly(ADP-ribose) polymerase-1 (PARP-1) catalyzes the rapid and extensive poly(ADP-ribosyl)ation of nuclear proteins in response to DNA strand breaks, and its expression, although ubiquitous, is modulated from tissue to tissue and during cellular differentiation. PARP-1 gene promoters from human, rat, and mouse have been cloned, and they share a structure common to housekeeping genes, as they lack a functional TATA box and contain multiple GC boxes, which bind the transcriptional activator Sp1. We have previously shown that, although Sp1 is important for rat PARP1 (rPARP) promoter activity, its finely tuned modulation is likely dependent on other transcription factors that bind the rPARP proximal promoter in vitro. In this study, we identified one such factor as NF1-L, a rat liver isoform of the nuclear factor 1 family of transcription factors. The NF1-L site on the rPARP promoter overlaps one of the Sp1 binding sites previously identified, and we demonstrated that binding of both factors to this composite element is mutually exclusive. Furthermore, we provide evidence that NF1-L has no effect by itself on rPARP promoter activity, but rather down-regulates the Sp1 activity by interfering with its ability to bind the rPARP promoter in order to modulate transcription of the rPARP gene.

A cellular survival switch: poly(ADP-ribosyl)ation stimulates DNA repair and silences transcription

Poly(ADP-ribosyl)ation is a post-translational modification occurring in the nucleus. The most abundant and best-characterized enzyme catalyzing this reaction, poly(ADP-ribose) polymerase 1 (PARP1), participates in fundamental nuclear events. The enzyme functions as molecular "nick sensor". It binds with high affinity to DNA single-strand breaks resulting in the initiation of its catalytic activity. Activated PARP1 promotes base excision repair. In addition, PARP1 modifies several transcription factors and thereby precludes their binding to DNA. We propose that a major function of PARP1 includes the silencing of transcription preventing expression of damaged genes. Concomitant stimulation of DNA repair suggests that PARP1 acts as a switch between transcription and DNA repair. Another PARP-type enzyme, tankyrase, is involved in the regulation of telomere elongation. Tankyrase modifies a telomere-associated protein and thereby prevents it masking telomeric repeats providing access of telomerase for telomere elongation. Therefore, poly(ADP-ribosyl)ation reactions may act as molecular switches in DNA metabolism.

Poly(ADP-ribosyl)ation of p53 in vitro and in vivo modulates binding to its DNA consensus sequence

The tumor-suppressor p53 undergoes extensive poly(ADP-ribosyl)ation early during apoptosis in human osteosarcoma cells, and degradation of poly(ADP-ribose) (PAR) attached to p53 coincides with poly(ADP-ribose)polymerase-1, (PARP-1) cleavage, and expression of p53 target genes. The mechanism by which poly(ADP-ribosyl)ation may regulate p53 function has now been investigated. Purified wild-type PARP-1 catalyzed the poly(ADP-ribosyl) of full-length p53 in vitro. In gel supershift assays, poly(ADP-ribosyl)ation suppressed p53 binding to its DNA consensus sequence; however, when p53 remained unmodified in the presence of inactive mutant PARP-1, it retained sequence-specific DNA binding activity. Poly(ADP-ribosyl)ation of p53 by PARP-1 during early apoptosis in osteosarcoma cells also inhibited p53 interaction with its DNA consensus sequence; thus, poly(ADP-ribosyl)ation may represent a novel means for regulating transcriptional activation by p53 in vivo.

Functional competition between poly(ADP-ribose) polymerase and its 24-kDa apoptotic fragment in DNA repair and transcription

Poly(ADP-ribose) polymerase is a 113-kDa nuclear enzyme that binds to both damaged DNA and to RNA associated with actively transcribed regions of chromatin. Binding of poly(ADP-ribose) polymerase to DNA lesions activates it, catalyzing the covalent addition of multiple ADP-ribose polymers to the enzyme (automodification). During apoptosis, poly(ADP-ribose) polymerase is cleaved by caspase-3, resulting in the formation of an N-terminal 24-kDa fragment, containing the DNA binding domain, and a C-terminal 89-kDa catalytic fragment. The functional relevance of this cleavage is not well understood. We therefore prepared a recombinant 24-kDa poly(ADP-ribose) polymerase fragment and investigated the role of this fragment in DNA repair and transcription. The 24-kDa fragment retained its binding affinity for both DNA breaks and RNA. In an in vitro cell-free DNA repair assay, this fragment inhibited rejoining of DNA breaks and suppressed ADP-ribose polymer formation by competing with poly(ADP-ribose) polymerase in binding to DNA breaks. With regard to transcription, it has recently been demonstrated that binding of poly(ADP-ribose) polymerase to transcribed RNA reduces the rate of transcript elongation and that automodification of poly(ADP-ribose) polymerase bound to DNA breaks results in up-regulation of transcription. We tested the 24-kDa fragment for its ability to suppress transcript elongation, and we found that it competed against the up-regulation of transcription mediated by full-length poly(ADP-ribose) polymerase. The ability of the 24-kDa fragment to inhibit DNA repair, ADP-ribose polymer formation, and damage-dependent up-regulation of transcription may contribute to the apoptotic shift from cell survival to cell death mode.

A role for poly(ADP-ribose) polymerase in the transcriptional regulation of the melanoma growth stimulatory activity (CXCL1) gene expression

The melanoma growth stimulatory activity/growth-regulated protein, CXCL1, is constitutively expressed at high levels during inflammation and progression of melanocytes into malignant melanoma. It has been shown previously that CXCL1 overexpression in melanoma cells is due to increased transcription as well as stability of the CXCL1 message. The transcription of CXCL1 is regulated through several cis-acting elements including Sp1, NF-kappaB, HMGI(Y), and the immediate upstream region (IUR) element (nucleotides -94 to -78), which lies immediately upstream to the nuclear factor kappaB (NF-kappaB) element. Previously, it has been shown that the IUR is necessary for basal and cytokine-induced transcription of the CXCL1 gene. UV cross-linking and Southwestern blot analyses indicate that the IUR oligonucleotide probe selectively binds a 115-kDa protein. In this study, the IUR element has been further characterized. We show here that proximity of the IUR element to the adjacent NF-kappaB element is critical to its function as a positive regulatory element. Using binding site oligonucleotide affinity chromatography, we have selectively purified the 115-kDa IUR-F. Mass spectrometry/mass spectrometry/matrix-assisted laser desorption ionization/time of flight spectroscopy and amino acid analysis as well as microcapillary reverse phase chromatography electrospray ionization tandem mass spectrometry identified this protein as the 114-kDa poly(ADP-ribose) polymerase (PARP1). Furthermore, 3-aminobenzamide, an inhibitor of PARP-specific ADP-ribosylation, inhibits CXCL1 promoter activity and reduces levels of CXCL1 mRNA. The data point to the possibility that PARP may be a coactivator of CXCL1 transcription.

Inhibition of poly(ADP-ribose) polymerase activity is insufficient to induce tetraploidy

Poly(ADP-ribose) polymerase (PARP) knockout mice are resistant to murine models of human diseases such as cerebral and myocardial ischemia, traumatic brain injury, diabetes, Parkinsonism, endotoxic shock and arthritis, implicating PARP in the pathogenesis of these diseases. Potent selective PARP inhibitors are therefore being evaluated as novel therapeutic agents in the treatment of these diseases. Inhibition or depletion of PARP, however, increases genomic instability in cells exposed to genotoxic agents. We recently demonstrated the presence of a genomically unstable tetraploid population in PARP(-/-) fibroblasts and its loss after stable transfection with PARP cDNA. To elucidate whether the genomic instability is attributable to PARP deficiency or lack of PARP activity, we investigated the effects of PARP inhibition on development of tetraploidy. Immortalized wild-type and PARP(-/-) fibroblasts were exposed for 3 weeks to 20 microM GPI 6150 (1,11b-dihydro-[2H:]benzopyrano[4,3,2-de]isoquinolin-3-one), a novel small molecule specific competitive inhibitor of PARP (K(i) = 60 nM) and one of the most potent PARP inhibitors to date (IC(50) = 0.15 microM). Although GPI 6150 initially decreased cell growth in wild-type cells, there was no effect on cell growth or viability after 24 h. GPI 6150 inhibited endogenous PARP activity in wild-type cells by approximately 91%, to about the residual levels in PARP(-/-) cells. Flow cytometric analysis of unsynchronized wild-type cells exposed for 3 weeks to GPI 6150 did not induce the development of tetraploidy, suggesting that, aside from its catalytic function, PARP may play other essential roles in the maintenance of genomic stability.

Noncovalent binding of poly(ADP-ribose) to nuclear matrix proteins: developmental changes and tissue specificity

Poly(ADP-ribose) is a nuclear polynucleotide involved in the regulation of chromatin functions via covalent and/or noncovalent modification of nuclear proteins. Using a binding assay on protein blots, we searched for poly(ADP-ribose) binding proteins in nuclear matrices from testes of differently aged rats as well as from various adult rat tissues (brain, liver, spleen). We found that nuclear matrix proteins represent a significant subset of the nuclear proteins that can establish noncovalent interactions with poly(ADP-ribose). The profiles of poly(ADP-ribose) binding nuclear matrix proteins appeared to be tissue-specific and changed during postnatal development in the testis. The isolation and analysis of endogenous poly-(ADP-ribose) from rat testes showed that the ADP-ribose polymers that bind nuclear matrix proteins in vitro are also present under physiologic conditions in vivo. These results further substantiate the possibility that poly(ADP-ribose) may affect chromatin functions through noncovalent interaction with specific protein targets, including nuclear matrix components.

Misregulation of gene expression in primary fibroblasts lacking poly(ADP-ribose) polymerase

Poly(ADP-ribose) polymerase (PARP) is implicated in the maintenance of genomic integrity, given that inhibition or depletion of this enzyme increases genomic instability in cells exposed to genotoxic agents. We previously showed that immortalized fibroblasts derived from PARP(-/-) mice exhibit an unstable tetraploid population, and partial chromosomal gains and losses in PARP(-/-) mice and immortalized fibroblasts are accompanied by changes in the expression of p53, Rb, and c-Jun, as well as other proteins. A tetraploid population has also now been detected in primary fibroblasts derived from PARP(-/-) mice. Oligonucleotide microarray analysis was applied to characterize more comprehensively the differences in gene expression between asynchronously dividing primary fibroblasts derived from PARP(-/-) mice and their wild-type littermates. Of the 11,000 genes monitored, 91 differentially expressed genes were identified. The loss of PARP results in down-regulation of the expression of several genes involved in regulation of cell cycle progression or mitosis, DNA replication, or chromosomal processing or assembly. PARP deficiency also up-regulates genes that encode extracellular matrix or cytoskeletal proteins that are implicated in cancer initiation or progression or in normal or premature aging. These results provide insight into the mechanism by which PARP deficiency impairs mitotic function, thereby resulting in the genomic alterations and chromosomal abnormalities as well as in altered expression of genes that may contribute to genomic instability, cancer, and aging.

A fast signal-induced activation of Poly(ADP-ribose) polymerase: a novel downstream target of phospholipase c

We present the first evidence for a fast activation of the nuclear protein poly(ADP-ribose) polymerase (PARP) by signals evoked in the cell membrane, constituting a novel mode of signaling to the cell nucleus. PARP, an abundant, highly conserved, chromatin-bound protein found only in eukaryotes, exclusively catalyzes polyADP-ribosylation of DNA-binding proteins, thereby modulating their activity. Activation of PARP, reportedly induced by formation of DNA breaks, is involved in DNA transcription, replication, and repair. Our findings demonstrate an alternative mechanism: a fast activation of PARP, evoked by inositol 1,4,5,-trisphosphate-Ca(2+) mobilization, that does not involve DNA breaks. These findings identify PARP as a novel downstream target of phospholipase C, and unveil a novel fast signal-induced modification of DNA-binding proteins by polyADP-ribosylation.

Thyroid hormone receptor-binding protein, an LXXLL motif-containing protein, functions as a general coactivator

Nuclear hormone receptors activate gene transcription through ligand-dependent association with coactivators. Specific LXXLL sequence motifs present in these cofactors are sufficient to mediate these ligand-induced interactions. A thyroid hormone receptor (TR)-binding protein (TRBP) was cloned by a Sos-Ras yeast two-hybrid system using TRbeta1-ligand binding domain as bait. TRBP contains 2063 amino acid residues, associates with TR through a LXXLL motif, and is ubiquitously expressed in a variety of tissues and cells. TRBP strongly transactivates through TRbeta1 and estrogen receptor in a dose-related and ligand-dependent manner, and also exhibits coactivation through AP-1, CRE, and NFkappaB-response elements, similar to the general coactivator CBP/p300. The C terminus of TRBP binds to CBP/p300 and DRIP130, a component of the DRIP/TRAP/ARC complex, which suggests that TRBP may activate transcription by means of such interactions. Further, the association of TRBP with the DNA-dependent protein kinase (DNA-PK) complex and DNA-independent phosphorylation of TRBP C terminus by DNA-PK point to a potential connection between transcriptional control and chromatin architecture regulation.

Characterization of sPARP-1. An alternative product of PARP-1 gene with poly(ADP-ribose) polymerase activity independent of DNA strand breaks

Poly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear enzyme that catalyzes the synthesis of poly(ADP-ribose) (pADPr) from its substrate NAD(+) upon binding to DNA strand breaks. Poly(ADP-ribosyl)ation has been implicated in many cellular processes including replication, transcription, and the maintenance of genomic stability. However, studies with mice and cells lacking PARP-1 reveal a critical role for the enzyme in the maintenance of genomic integrity only. Recently, a significant level of poly(ADP-ribose) polymerase activity has been detected in fibroblasts derived from mice lacking PARP-1 following treatment with genotoxic agents (Shieh, W. M., Amé, J-C., Wilson, M. V., Wang, Z-Q., Koh, D. W., Jacobson, M. K., and Jacobson, E. L. (1998) J. Biol. Chem. 273, 30069-30072). We have isolated a cDNA that originates from PARP-1 (-/-) fibroblasts and encodes a polypeptide of 493 amino acid residues bearing poly(ADP-ribose) polymerase activity. This protein, that we named sPARP-1 for short poly(ADP-ribose) polymerase-1, has a calculated mass of 55.3 kDa and is identical in deduced amino acid sequence to the catalytic domain of PARP-1. Radiation hybrid analysis assigned the sPARP-1 gene to the chromosome 1H5-H6 in an immediate proximity to the known location of PARP-1 gene, indicating that sPARP-1 and PARP-1 are most probably products of the same gene. Active sPARP-1 is present in both PARP-1 (+/+) and PARP-1 (-/-) cells as demonstrated by activity-Western blotting and immunostaining using a specific antibody developed against sPARP-1. Like PARP-1, sPARP-1 is localized in the cell nucleus, uses NAD(+) as a substrate and is inhibited by nicotinamide analogues. sPARP-1 produces pADPr of similar length and structure to that of PARP-1. However, contrary to PARP-1, sPARP-1 does not require DNA strand breaks for its activation, although it is stimulated following genotoxic treatments.

Transcriptional regulation of the MHC II gene DRA in untransformed human thyrocytes

MHC class II molecules are heterodimeric, polymorphic transmembrane glycoproteins physiologically expressed on cells of the immune system and pathologically expressed on the affected target cells of autoimmunity. Their function is to present processed peptides to antigen-specific CD4(+) T cells. To understand the molecular mechanism of the regulation of class II genes in autoimmune target cell thyrocytes, we investigated the transcriptional regulation of DRA on untransformed, differentiated human thyroid cells following IFN-gamma stimulation, which is potentially relevant to the inappropriate class II expression found in Graves' disease. Data from this study show that IFN-gamma enhances a promoter Y box binding protein and induces an X box binding protein in untransformed thyrocytes, but not in SV-40-transfected thyrocytes. Initial characterization of the proteins has indicated that the Y box binding protein is approximately 132 kDa in size while the X box binding protein binds to the X2 region and is approximately 116 kDa. The X box binding protein may correspond to poly(ADP-ribose) polymerase, a recently described component of the X2 box binding protein, X2BP. In addition, the signal transducer and activator of transcription 1alpha protein (STAT1alpha) is also induced by IFN-gamma in these cells. These results further suggest that there are differences in class II gene regulation between differentiated cells and transformed cell lines.

Evidence for regulation of NF-kappaB by poly(ADP-ribose) polymerase

The DNA-binding activity of NF-kappaB in nuclear extracts of poly(ADP-ribose) polymerase (PARP)-defective mutant L1210 cell clones was markedly increased and was inversely correlated with the PARP content in these cells. The DNA-binding activity of NF-kappaB in a clone with the lowest PARP content (Cl-3527, contained 6% of PARP of wild type cells) was about 35-fold of that of the wild-type cells, whereas the change in the DNA-binding activity of AP-1 and SP-1 in the mutant was relatively small or not so significant. Transfection of a PARP-expressing plasmid to the mutant cells decreased the abnormally high levels of NF-kappaB complexes, especially p50/p65(Rel A) complex, to near the normal level. Moreover, poly(ADP-ribosyl)ation of nuclear extracts in vitro suppressed the ability of NF-kappaB to form a complex with its specific DNA probe by approx. 80%. Further analysis with purified recombinant NF-kappaB proteins revealed that both rp50 and rMBP-p65 (Rel A) proteins, but not rGST-IkappaB, could be poly(ADP-ribosyl)ated in vitro and that the modification resulted in a marked decrease in the DNA-binding activity of rMBP-p65, whereas a slight activation was observed in rp50. Poly(ADP-ribosyl)ated p65/NF-kappaB was detected in the cytosol of wild type L1210 cells by immunoblotting with anti-poly(ADP-ribose) and anti-p65 antibodies. Taken together, these results strongly suggest that PARP is involved in the regulation of NF-kappaB through the protein modification.

Identification of poly(ADP-ribose) polymerase as a transcriptional coactivator of the human T-cell leukemia virus type 1 Tax protein

Human T-cell leukemia virus type 1 (HTLV-1) encodes a transcriptional activator, Tax, whose activity is believed to contribute significantly to cellular transformation. Tax stimulates transcription from the proviral promoter as well as from promoters for a variety of cellular genes. The mechanism through which Tax communicates to the general transcription factors and RNA polymerase II has not been completely determined. We investigated whether Tax could function directly through the general transcription factors and RNA polymerase II or if other intermediary factors or coactivators were required. Our results show that a system consisting of purified recombinant TFIIA, TFIIB, TFIIE, TFIIF, CREB, and Tax, along with highly purified RNA polymerase II, affinity-purified epitope-tagged TFIID, and semipurified TFIIH, supports basal transcription of the HTLV-1 promoter but is not responsive to Tax. Two additional activities were required for Tax to stimulate transcription. We demonstrate that one of these activities is poly(ADP-ribose) polymerase (PARP), a molecule that has been previously identified to be the transcriptional coactivator PC1. PARP functions as a coactivator in our assays at molar concentrations approximately equal to those of the DNA and equal to or less than those of the transcription factors in the assay. We further demonstrate that PARP stimulates Tax-activated transcription in vivo, demonstrating that this biochemical approach has functionally identified a novel target for the retroviral transcriptional activator Tax.

New functions of a long-known molecule. Emerging roles of NAD in cellular signaling

Over the past decades, the pyridine nucleotides have been established as important molecules in signaling pathways, besides their well known function in energy transduction. Similarly to another molecule carrying such dual functions, ATP, NAD(P)+ may serve as substrate for covalent protein modification or as precursor of biologically active compounds. Protein modification is catalyzed by ADP-ribosyl transferases that attach the ADP-ribose moiety of NAD+ to specific amino-acid residues of the acceptor proteins. For a number of ADP ribosylation reactions the specific transferases and their target proteins have been identified. As a result of the modification, the biological activity of the acceptor proteins may be severely changed. The cell nucleus contains enzymes catalyzing the transfer of ADP-ribose polymers (polyADP-ribose) onto the acceptor proteins. The best known enzyme of this type is poly(ADP-ribose) polymerase 1 (PARP1), which has been implicated in the regulation of several important processes including DNA repair, transcription, apoptosis, neoplastic transformation and others. The second group of reactions leads to the synthesis of an unusual cyclic nucleotide, cyclic ADP-ribose (cADPR). Moreover, the enzymes catalyzing this reaction may also replace the nicotinamide of NADP+ by nicotinic acid resulting in the synthesis of nicotinic acid adenine dinucleotide phosphate (NAADP+). Both cADPR and NAADP+ have been reported to be potent intracellular calcium-mobilizing agents. In concert with inositol 1,4,5-trisphosphate, they participate in cytosolic calcium regulation by releasing calcium from intracellular stores.

Poly(ADP-ribosyl)ation basally activated by DNA strand breaks reflects glutamate-nitric oxide neurotransmission

Poly(ADP-ribose) polymerase (PARP) transfers ADP ribose groups from NAD(+) to nuclear proteins after activation by DNA strand breaks. PARP overactivation by massive DNA damage causes cell death via NAD(+) and ATP depletion. Heretofore, PARP has been thought to be inactive under basal physiologic conditions. We now report high basal levels of PARP activity and DNA strand breaks in discrete neuronal populations of the brain, in ventricular ependymal and subependymal cells and in peripheral tissues. In some peripheral tissues, such as skeletal muscle, spleen, heart, and kidney, PARP activity is reduced only partially in mice with PARP-1 gene deletion (PARP-1(-/-)), implicating activity of alternative forms of PARP. Glutamate neurotransmission involving N-methyl-d-aspartate (NMDA) receptors and neuronal nitric oxide synthase (nNOS) activity in part mediates neuronal DNA strand breaks and PARP activity, which are diminished by NMDA antagonists and NOS inhibitors and also diminished in mice with targeted deletion of nNOS gene (nNOS(-/-)). An increase in NAD(+) levels after treatment with NMDA antagonists or NOS inhibitors, as well as in nNOS(-/-) mice, indicates that basal glutamate-PARP activity regulates neuronal energy dynamics.

Effects of nicotinamide-related agents on the growth of primary rat hepatocytes and formation of small hepatocyte colonies

AIMS/BACKGROUND

We report in this study that, 10 mM nicotinamide can stimulate the proliferation of primary rat hepatocytes in serum-free Dulbecco's modified Eagle's medium supplemented with 10 ng/ml epidermal growth factor and that small hepatocyte colonies appear from 4 to 5 days after plating. We examined the effects of nicotinamide-related agents on the growth and differentiation of primary rat hepatocytes and on the appearance of small hepatocyte colonies.

METHODS

As nicotinamide is an aqueous vitamin named niacin and known to act as an inhibitor of poly (ADP-ribose) polymerase (PARP), we therefore chose to examine the effects on hepatocytes of three nicotinamide-related agents, nicotinic acid (NA) which is also a niacin, 3-aminobenzamide (3-AB) which is a strong inhibitor of PARP but is not a niacin, and 3-acetylpyridine (3-AP) which is a weak inhibitor of PARP and also not a niacin. To examine their effects on the growth of the cells and on the formation of the colony, immunocytochemistry for BrdU was carried out. Expression of albumin, tryptophan 2,3-dioxygenase (TO), and connexin 32 (Cx32) mRNAs were used as marks of hepatic differentiation. Intracellular NAD+ content was also measured.

RESULTS

At concentration of 10 mM, NA could not enhance the proliferation of mature hepatocytes but induced the appearance of small hepatocyte colonies. At concentration of 5 mM, 3-AB enhanced the proliferation of the hepatocytes but did not induce small hepatocyte colonies. On the other hand, although 10 mM 3-AP remarkably inhibited the DNA synthesis of the cells, the expression not only of albumin but also of TO and Cx32 mRNAs in the cells was well maintained for more than one week. The intracellular NAD+ concentration was correlated with the proliferation of the hepatocytes.

CONCLUSION

These results suggest that the intracellular NAD+ content may be correlated with the proliferation of primary hepatocytes and that the supplementation of niacin in the medium may be important for the appearance of small hepatocyte colonies.

Syncytiotrophoblastic giant cells in teratocarcinoma-like tumors derived from Parp-disrupted mouse embryonic stem cells

The enzyme poly(ADP-ribose) polymerase (Parp) catalyzes poly(ADP-ribosyl)ation reaction and is involved in DNA repair and cell death induction upon DNA damages. Meanwhile, poly(ADP-ribosyl)ation of chromosome-associated proteins is suggested to be implicated in the regulation of gene expression and cellular differentiation, both of which are important in tumorigenesis. To investigate directly the role of Parp deficiency in tumorigenicity and differentiation of embryonic stem (ES) cells during tumor formation, studies were conducted by using wild-type J1 (Parp(+/+)) ES cells and Parp(+/-) and Parp(-/-) ES clones generated by disrupting Parp exon 1. These ES cells, irrespective of the Parp genotype, produced tumors phenotypically similar to teratocarcinoma when injected s.c. into nude mice. Remarkably, all tumors derived from Parp(-/-) clones contained syncytiotrophoblastic giant cells (STGCs), which possess single or multiple megalo-nuclei. The STGCs were present within large areas of intratumoral hemorrhage. In contrast, neither STGC nor hemorrhage was observed in tumors of both wild-type J1 cells and Parp(+/-) clones. Electron microscopic examination showed that the STGCs possess microvilli on the cell surface and contained secretory granules in the cytoplasm. Furthermore, the cytoplasms of STGCs were strongly stained with antibody against mouse prolactin, which could similarly stain trophoblasts in placenta. These morphological and histochemical features indicate that the STGCs in teratocarcinoma-like tumors derived from Parp(-/-) clones belong to the trophoblast cell lineage. Our findings thus suggest that differentiation of ES cells into STGCs was possibly induced by the lack of Parp during the development of teratocarcinoma.

Poly(ADP-ribosyl)ation reactions in the regulation of nuclear functions

Poly(ADP-ribosyl)ation is a post-translational modification of proteins. During this process, molecules of ADP-ribose are added successively on to acceptor proteins to form branched polymers. This modification is transient but very extensive in vivo, as polymer chains can reach more than 200 units on protein acceptors. The existence of the poly(ADP-ribose) polymer was first reported nearly 40 years ago. Since then, the importance of poly(ADP-ribose) synthesis has been established in many cellular processes. However, a clear and unified picture of the physiological role of poly(ADP-ribosyl)ation still remains to be established. The total dependence of poly(ADP-ribose) synthesis on DNA strand breaks strongly suggests that this post-translational modification is involved in the metabolism of nucleic acids. This view is also supported by the identification of direct protein-protein interactions involving poly(ADP-ribose) polymerase (113 kDa PARP), an enzyme catalysing the formation of poly(ADP-ribose), and key effectors of DNA repair, replication and transcription reactions. The presence of PARP in these multiprotein complexes, in addition to the actual poly(ADP-ribosyl)ation of some components of these complexes, clearly supports an important role for poly(ADP-ribosyl)ation reactions in DNA transactions. Accordingly, inhibition of poly(ADP-ribose) synthesis by any of several approaches and the analysis of PARP-deficient cells has revealed that the absence of poly(ADP-ribosyl)ation strongly affects DNA metabolism, most notably DNA repair. The recent identification of new poly(ADP-ribosyl)ating enzymes with distinct (non-standard) structures in eukaryotes and archaea has revealed a novel level of complexity in the regulation of poly(ADP-ribose) metabolism.