The transient receptor potential melastatin-related channel 2 (TRPM2) is a nonselective cation channel, whose prolonged activation by oxidative and nitrative agents leads to cell death. Here, we show that the drug puromycin selectively targets TRPM2-expressing cells, leading to cell death. Our data suggest that the silent information regulator 2 (Sir2 or sirtuin) family of enzymes mediates this susceptibility to cell death. Sirtuins (2). This influx is thought to occur as a consequence of TRPM2 channel activation via ADP-ribose (ADPr) binding to the cytoplasmic, C-terminal domain of the channel. This domain, termed NudT9-H (NudT9 homology), contains an apparent Nudix enzymatic motif and shares significant homology to the mitochondrial NudT9 enzyme (4, 5), a member of the Nudix ADPr hydrolase family. Indeed, electrophysiology experiments have shown that low micromolar levels of ADPr activate the TRPM2 channel (4, 6), and that this activation is mediated through the NudT9-H domain (7, 8), implicating a direct ADPr and NudT9-H interaction.The NudT9-H domain has been reported to have hydrolytic activity toward ADPr, albeit at a ϳ100-fold lower rate than NudT9 (4, 9). Although it was initially thought that the ADPr hydrolase activity of TRPM2 might have a role in regulating TRPM2 gating via hydrolysis of bound ADPr, recent data have demonstrated that mutations in putative catalytic residues of NudT9-H do not affect TRPM2 channel gating, leaving the function of this activity unclear (8). Some studies suggest that hydrogen peroxide directly activates the TRPM2 channel (3, 10); however, it has been reported recently that this oxidative agent acts indirectly by triggering the release of ADPr from an intracellular compartment (8, 11). The mechanism of TRPM2 activation by hydrogen peroxide may prove to be more complex, as hydrogen peroxide and ADPr have also been suggested to act cooperatively in TRPM2 channel activation (12).In this article, we have investigated the ability of TRPM2 to sensitize cells to cellular insults other than those inducing oxidative stress. Here, we demonstrate that puromycin, a well known pleiotropic cell stress agent, selectively targets TRPM2-expressing cells, leading to cell death. Our studies suggest that Sir2 enzymes play an important role in mediating this response. We found that TRPM2 has the capacity to sense OAADPr, the unique metabolite of the Sir2 protein deacetylase reaction, and induce cell death in response to puromycin. Furthermore, we report the first direct evidence that OAADPr binds to the NudT9-H domain and modulates TRPM2 channel activity. Our data have important implications for the potential physiological roles of ADPr-related molecules as secondary messengers. This report links Sir2 enzymes (sirtuins) with the TRPM2 channel through the Sir2 metabolite OAADPr. This newly discovered association provides a plausible mechanism for previously described sirtuin functions, which include control of stress response pathways and metabolic regulation. EXPERIMENTAL PROCEDURESCell Cul...

The Sir2 family of NAD ؉ -dependent histone/protein deacetylases has been implicated in a wide range of biological activities, including gene silencing, life span extension, and chromosomal stability. Recent evidence has indicated that these proteins produce a novel metabolite O-acetyl-ADP-ribose (OAADPr) during deacetylation. Cellular studies have demonstrated that this metabolite exhibits biological effects when microinjected in living cells. However, the molecular targets of OAADPr remain to be identified. Here we have analyzed the ADP-ribose-specific Nudix family of hydrolases as potential in vivo metabolizing enzymes of OAADPr. In vitro, we found that the ADP-ribose hydrolases (yeast YSA1, mouse NudT5, and human NUDT9) cleaved OAADPr to the products AMP and acetylated ribose 5-phosphate. Steady-state kinetic analyses revealed that YSA1 and NudT5 hydrolyzed OAADPr with similar kinetic constants to those obtained with ADP-ribose as substrate. In dramatic contrast, human NUDT9 was 500-fold less efficient (k cat /K m values) at hydrolyzing OAADPr compared with ADP-ribose. The inability of OAADPr to inhibit the reaction of NUDT9 with ADPribose suggests that NUDT9 binds OAADPr with low affinity, likely due to steric considerations of the additional acetylated-ribose moiety. We next explored whether Nudix hydrolytic activities against OAADPr could be observed in cell extracts from yeast and human. Using a detailed analysis of the products generated during the consumption of OAADPr in extracts, we identified two robust enzymatic activities that were not consistent with the known Nudix hydrolases. Instead, we identified cytoplasmic esterase activities that hydrolyze OAADPr to acetate and ADP-ribose, whereas a distinct activity residing in the nucleus is consistent with an OAADPr-specific acetyltransferase. These findings establish for the first time that select members of the ADP-ribose hydrolases are potential targets of OAADPr metabolism. However, the predominate endogenous activities observed from diverse cell extracts represent novel enzymes.

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Platelet-derived growth factor (PDGF) is a broadly expressed mitogenic and chemotactic factor with diverse roles in a number of physiologic and pathologic settings. The zinc finger transcription factors Sp1, Sp3 and Egr-1 bind to overlapping elements in the proximal PDGF B-chain promoter and activate transcription of this gene. The anthracycline nogalamycin has previously been reported to inhibit the capacity of Egr-1 to bind DNA in vitro. Here we used electrophoretic mobility shift assays to show that nogalamycin added to cells in culture did not alter the interaction of Egr-1 with the PDGF-B promoter. Instead, it enhanced the capacity of Sp1 to bind DNA. Nogalamycin increased PDGF-B mRNA expression at the level of transcription, which was abrogated by mutation of the Sp1 binding site in the PDGF-B promoter or overexpression of mutant Sp1. Rather than increasing total levels of Sp1, nogalamycin altered the phosphorylation state of the transcription factor. Overexpression of dominant-negative PKC-zeta blocked nogalamycin-inducible Sp1 phosphorylation and PDGF-B promoter-dependent expression. Nogalamycin stimulated the phosphorylation of PKC-zeta (on residue Thr(410)). These findings demonstrate for the first time that PKC-zeta and Sp1 phosphorylation mediate the inducible expression of this growth factor.

Platelet-derived growth factor (PDGF) is a mitogen and chemoattractant for a wide variety of cell types. The genes encoding PDGF A chain (PDGF-A) and PDGF B chain (PDGF-B) reside on separate chromosomes and are independently regulated at the level of transcription. Regulatory events underlying inducible PDGF-A expression have been the focus of much investigation. However, mechanisms that inhibit transcription of this gene are not well understood. In this study, we report the capacity of a newly cloned DNA binding factor, GC factor 2 (GCF2), to repress expression driven by the human PDGF-A promoter. 5' Deletion and transient cotransfection analysis in vascular endothelial cells revealed that GCF2 repression is mediated by a nucleotide region located in the proximal region of the PDGF-A promoter. Electrophoretic mobility shift assays demonstrate that GCF2 binds to this region in a specific and dose-dependent manner. Interestingly, the site bound by GCF2 overlaps those for specificity protein-1 (Sp1) and early growth response factor-1 (Egr-1), zinc finger transcription factors that direct basal and inducible expression of the PDGF-A gene. Gel shift experiments revealed that GCF2 competes with these factors for interaction with the PDGF-A promoter. Overexpression of GCF2 suppressed endogenous PDGF-A expression in vascular endothelial cells and smooth muscle cells. GCF2 was induced on mechanical injury of cells in culture as well as after balloon injury of the rat carotid artery wall. Time course studies revealed the sustained induction of GCF2 after injury while PDGF-A levels sharply returned to baseline. Smooth muscle cell proliferation was inhibited by GCF2, an effect reversed by the addition of exogenous PDGF-AA. These findings demonstrate negative regulation of PDGF-A expression by GCF2. This is the first report of the induction of an endogenous transcriptional repressor in the rat vessel wall.

The regulatory mechanisms mediating basal and inducible platelet-derived growth factor (PDGF)-A expression have been the focus of intense recent investigation, but repression of PDGF-A expression is largely unexplored. Here we isolated a nuclear factor that interacts with the proximal region of the PDGF-A promoter using bulk binding assays and chromatography techniques. Peptide mass ®ngerprint and supershift analysis revealed this DNA-binding protein to be NF1/X. NF1/X repressed PDGF-A promoterdependent transcription and endogenous mRNA expression, which was reversible by oligonucleotide decoys bearing an NF1/X-binding site. Mutation in the DNA-binding domain of NF1/X abolished its repression of PDGF-A promoter. NF1/X antagonized the activity of a known activator of the PDGF-A chain, Sp1, by inhibiting its occupancy of the proximal PDGF-A promoter. NF1/X physically and speci®cally interacts with Sp1 via its subtype-speci®c domain and blocks Sp1 induction of the promoter. NF1/X residues 311±416 mediated NF1/X suppression of basal PDGF-A transcription, whereas residues 243±416 were required for NF1/X repression of Sp1-inducible promoter activity. These ®ndings demonstrate that repression of PDGF-A gene transcription is governed by interplay between NF1/X and Sp1.

Angiotensin II (ATII) and platelet-derived growth factor (PDGF) are two vasoconstrictors implicated in the maintenance of normal vascular homeostasis. PDGF Achain levels increase in cultured vascular smooth muscle cells (SMCs) exposed to ATII. The molecular mechanisms underlying this induction are not known. We used transient transfection analysis to show that ATII can increase reporter gene activity driven by fragments of the PDGF-A promoter bearing recognition elements for the transcription factor, Egr-1. Nuclear run-off experiments indicate that ATII induces Egr-1 expression at the level of transcription. Gel shift and supershift studies show that Egr-1 protein accumulates in the nuclei of SMCs exposed to ATII and binds to the proximal region of the PDGF-A promoter in a specific, time-dependent manner. ATII induced extracellular-signal regulated kinase (p42/44 ERK) activity as did phorbol 12-myristate 13-acetate. The specific MEK1/2 inhibitor, PD98059, suppressedbothPDGF-AandEgr-1endogenousandpromoter-dependent expression inducible by ATII. The ATII type 1 receptor (AT1) antagonist, Losartan, inhibited ATII-induction of p42/44 ERK, as well as Egr-1 and PDGF-A, whereas neither PD123319, an AT2 receptor antagonist, nor wortmannin, an inhibitor of phosphatidylinositol 3-kinase and c-Jun N-terminal kinase, had any effect. ATII-induction of Egr-1 and PDGF-A was blocked by SIN-1, a NO donor. In addition, this pathway was blocked by overexpression of NO synthase. Collectively, these findings demonstrate that ATII activation of the PDGF-A promoter is mediated via the MEK/ERK/Egr-1 pathway and AT1 receptor and that this process is antagonized by NO.Angiotensin II (ATII), 1 a peptide hormone with potent vasoconstrictor activity, has long been implicated in the pathobiology of hypertension. In vascular smooth muscle cells (SMCs), ATII stimulates protein synthesis (1), cellular hypertrophy (2-5), migration (6), extracellular matrix synthesis (7,8), and the activation of a large number of transcription factors. These include Jak/STAT (9), Ets-1 (10), SRF (11), MHox (11), c-Jun (12, 13), JunB (12), and c-Fos (14). ATII is produced in the vessel wall by the actions of renin, which converts angiotensinogen to ATI, which is then cleaved to ATII by angiotensin-converting enzyme. Two ATII receptor subtypes have been described, AT1 and AT2. Signal transduction through G-protein-coupled AT1 receptors involves phospholipase C, phospholipase A 2 , phospholipase D, adenylate cyclase, and the release of intracellular calcium (reviewed in Refs. 15 and 16). The AT1 receptor also regulates neointimal thickening after mechanical injury to the rat carotid artery wall and ATII infusion (17). AT2 receptor signaling is less well understood, but evidence suggests that this receptor is involved in growth inhibition (18), Bcl-2 dephosphorylation (19), and apoptosis (20, 21). Platelet-derived growth factor (PDGF) consists of an A-chain and B-chain held together in homo-or heterodimeric configuration by disulfide bonds (reviewed in Refs. 22 and 2...

Platelet-derived growth factor (PDGF) B-chain gene is differentially expressed in smooth muscle cells (SMCs) derived from the rat aortic wall. SMCs cultured from two week-old rats (pups) express high levels of PDGF-B mRNA, whereas cells isolated from three month-old rats (adults) express low levels of PDGF-B. Nuclear run-off experiments indicate that increased PDGF-B gene expression in pups is mediated, at least in part, at the transcriptional level. We used electrophoretic mobility shift assays and Western blot analysis to demonstrate that levels of Sp1 and Sp3, two zinc finger transcription factors which mediate basal expression of the PDGF-B gene, are elevated in pup nuclei compared with adult nuclei. The immediate-early transcription factor, Egr-1, which footprints the PDGF-B promoter, is also constitutively expressed in these cells. Platelet-derived growth factor (PDGF)1 consists of an Achain and a B-chain held together in heterodimeric or homodimeric configuration by disulfide bonds (1). Multiple cell types, including vascular smooth muscle cells (SMCs) (2), produce and respond to this potent mitogen and chemoattractant in culture. Seifert et al. (3) observed over a decade ago that PDGF may be developmentally regulated in these cells. SMCs cultured from the aortae of 2-week-old rats (pups) (WKY12-22 cells) secreted almost 200-fold greater levels of PDGF than cells isolated from 3-month-old rats (adults) (WKY3M-22 cells). Subsequent Northern blot analysis determined that PDGF-B gene expression is at least 60-fold greater in cultured pup SMCs than adult cells (4). Evidence that differential PDGF-B expression is mediated at the level of transcription was obtained from nuclear run-off analysis (5). Several other genes, such as tropoelastin and ␣ 1 -procollagen (type I), were found to be overexpressed in pup cells relative to adult cells by cDNA library screening strategies. Cloning pup cells by dilution plating revealed that subpopulations expressed high levels of elastin, CYPIA1 and osteopontin mRNA (6). Cultured pup and adult SMCs also display marked differences in morphology. The epithelioid and cobblestone shape of pup cells contrasts with the spindle-like, elongated bipolar nature of adult SMCs (4).Basal and inducible expression of the PDGF-B gene is mediated by nucleotide elements located approximately 40 bp upstream of the TATA box. We and others showed that Sp1 binds to the 5Ј-CCACCC-3Ј motif and drives basal expression in vascular endothelial (7) and osteosarcoma cells (8). This is consistent with in vivo footprinting studies which indicate that this region is occupied by nuclear factors in intact cells (9). The related zinc finger transcription factor, Sp3, also interacts with this region of the promoter and activates transcription (8, 10). Egr-1, also known as TIS8, zif268, and NGFI-A (11), plays a positive regulatory role in PDGF-B promoter-dependent expression in cells exposed to phorbol esters or subjected to mechanical injury (12, 13). Egr-1 binds to a cryptic recognition element in the PDGF-B...