The phenylpropanoid-derived natural product salicylic acid (SA) plays a key role in disease resistance. However, SA administered in the absence of a pathogen is a paradoxically weak inductive signal, often requiring concentrations of 0.5 to 5 mM to induce acquired resistance or related defense mechanisms or to precondition signal systems. In contrast, endogenous SA accumulates to concentrations of <70 pM at the site of attempted infection. Here, we show that although 10 to 100 p M SA had negligible effects when administered to soybean cell suspensions in the absence of a pathogen, physiological concentrations of SA markedly enhanced the induction of defense gene transcripts, H202 accumulation, and hypersensitive cell death by an avirulent strain of Pseudomonas syringae pv glycinea, with optimal effects being at -50 pM. SA also synergistically enhanced H202 accumulation in response to the protein phosphatase type 2A inhibitor cantharidin in the absence of a pathogen. The synergistic effect of SA was potent, rapid, and insensitive to the protein synthesis inhibitor cycloheximide, and we conclude that SA stimulates an agonist-dependent gain control operating at an early step in the signal pathway for induction of the hypersensitive response. This fine control mechanism differs from previously described time-dependent, inductive coarse control mechanisms for SA action in the absence of a pathogen. Induction of H202 accumulation and hypersensitive cell death by avirulent P. s. glycinea was blocked by the phenylpropanoid synthesis inhibitor a-aminooxy-P-phenylpropionic acid, and these responses could be rescued by exogenous SA. Because the agonist-dependent gain control operates at physiological levels of SA, we propose that rapid fine control signal amplification makes an important contribution to SA function in the induction of disease resistance mechanisms.

Recent studies have revealed that the redox-sensitive glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), is involved in neuronal cell death that is triggered by oxidative stress. GAPDH is locally deposited in disulfidebonded aggregates at lesion sites in certain neurodegenerative diseases. In this study, we investigated the molecular mechanism that underlies oxidative stress-induced aggregation of GAPDH and the relationship between structural abnormalities in GAPDH and cell death. Under nonreducing in vitro conditions, oxidants induced oligomerization and insoluble aggregation of GAPDH via the formation of intermolecular disulfide bonds. Because GAPDH has four cysteine residues, including the active site Cys 149 , we prepared the cysteine-substituted mutants C149S, C153S, C244A, C281S, and C149S/C281S to identify which is responsible for disulfide-bonded aggregation. Whereas the aggregation levels of C281S were reduced compared with the wild-type enzyme, neither C149S nor C149S/C281S aggregated, suggesting that the active site cysteine plays an essential role. Oxidants also caused conformational changes in GAPDH concomitant with an increase in ␤-sheet content; these abnormal conformations specifically led to amyloid-like fibril formation via disulfide bonds, including Cys 149 . Additionally, continuous exposure of GAPDH-overexpressing HeLa cells to oxidants produced disulfide bonds in GAPDH leading to both detergent-insoluble and thioflavin-S-positive aggregates, which were associated with oxidative stress-induced cell death. Thus, oxidative stresses induce amyloid-like aggregation of GAPDH via aberrant disulfide bonds of the active site cysteine, and the formation of such abnormal aggregates promotes cell death.In both prokaryotic and eukaryotic cells, glyceraldehyde-3-phosphate dehydrogenase (GAPDH 2 ; EC 1.2.1.12) plays a central role in glycolysis, catalyzing the reversible conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in a reaction that is accompanied by the reduction of NAD ϩ to NADH. Mammalian GAPDH is a homotetramer composed of four identical subunits. Recent studies show that mammalian GAPDH has diverse activities unrelated to its glycolytic function (1, 2), including roles in membrane fusion, microtubule bundling, nuclear RNA transport (2), regulation of Ca 2ϩ homeostasis (3), and transcription (4). In addition to the various functions of GAPDH described above, particular attention is paid to its role in apoptosis (5-7). Although the proapoptotic role(s) of GAPDH seems to depend upon its accumulation in the particulate fractions, including the nucleus (5, 7), the detailed mechanism is still unclear.Recently, it has been suggested that a wide variety of neurodegenerative diseases are characterized by the accumulation of intracellular and extracellular protein aggregates (8,9). An initializing event in protein aggregation is thought to be the formation of an abnormal oligomer. For instance, ␤-amyloid and ␣-synuclein undergo conformational changes in Alzheimer disea...

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)2 is a classic glycolytic enzyme that also mediates cell death by its nuclear translocation under oxidative stress. Meanwhile, we previously presented that oxidative stress induced disulfide-bonded GAPDH aggregation in vitro. Here, we propose that GAPDH aggregate formation might participate in oxidative stress-induced cell death both in vitro and in vivo. We show that human GAPDH amyloidlike aggregate formation depends on the active site cysteine-152 (Cys-152) in vitro. In SH-SY5Y neuroblastoma, treatment with dopamine decreases the cell viability concentration-dependently (IC 50 ‫؍‬ 202 M). Low concentrations of dopamine (50 -100 M) mainly cause nuclear translocation of GAPDH, whereas the levels of GAPDH aggregates correlate with high concentrations of dopamine (200 -300 M)-induced cell death. Doxycycline-inducible overexpression of wild-type GAPDH in SH-SY5Y, but not the Cys-152-substituted mutant (C152A-GAPDH), accelerates cell death accompanying both endogenous and exogenous GAPDH aggregate formation in response to high concentrations of dopamine. Deprenyl, a blocker of GAPDH nuclear translocation, fails to inhibit the aggregation both in vitro and in cells but reduced cell death in SH-SY5Y treated with only a low concentration of dopamine (100 M). These results suggest that GAPDH participates in oxidative stress-induced cell death via an alternative mechanism in which aggregation but not nuclear translocation of GAPDH plays a role. Moreover, we observe endogenous GAPDH aggregate formation in nigra-striatum dopaminergic neurons after methamphetamine treatment in mice. In transgenic mice overexpressing wildtype GAPDH, increased dopaminergic neuron loss and GAPDH aggregate formation are observed. These data suggest a critical role of GAPDH aggregates in oxidative stress-induced brain damage.Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a classic glycolytic enzyme that is also involved in cell death and neuropsychiatric conditions (1, 2). GAPDH mediates cell death under oxidative stress conditions at least in part through nuclear translocation together with Siah (3). In the nucleus, GAPDH activates p300/CBP and regulates gene transcription (4). The pathway can be blocked by deprenyl (Selegiline), a neuroprotective compound (5). Although nuclear translocation of GAPDH is known to cause cell death, other mechanisms of GAPDH-associated cell death may also exist.Several neurodegenerative diseases are characterized by the accumulation of misfolded proteins, resulting in intracellular and extracellular protein aggregates (6, 7). For instance, conformational changes in ␤-amyloid (A␤) in Alzheimer disease and ␣-synuclein in Parkinson disease lead to the formation of abnormal oligomers and amyloid fibrils (8). Similar to A␤ and ␣-synuclein, GAPDH is also amyloidogenic (9 -14). We previously reported the molecular mechanism underlying oxidative stressinduced amyloid-like aggregation of GAPDH using the purified rabbit GAPDH and demonstrated the critical role of the act...

The finding that IL-19 drives pathogenic innate immune responses in the colon suggests that the selective targeting of IL-19 may be an effective therapeutic approach in the treatment of human IBD.

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