Plant respiratory burst oxidase homolog (rboh) proteins, which are homologous to the mammalian 91-kDa glycoprotein subunit of the phagocyte oxidase (gp91 phox ) or NADPH oxidase 2 (NOX2), have been implicated in the production of reactive oxygen species (ROS) both in stress responses and during development. Unlike mammalian gp91 phox /NOX2 protein, plant rboh proteins have hydrophilic N-terminal regions containing two EF-hand motifs, suggesting that their activation is dependent on Ca 2؉ . However, the significance of Ca 2؉ binding to the EF-hand motifs on ROS production has been unclear. By employing a heterologous expression system, we showed that ROS production by Arabidopsis thaliana rbohD (AtrbohD) was induced by ionomycin, which is a Ca 2؉ ionophore that induces Ca 2؉ influx into the cell. This activation required a conformational change in the EF-hand region, as a result of Ca 2؉ binding to the EF-hand motifs. We also showed that AtrbohD was directly phosphorylated in vivo, and that this was enhanced by the protein phosphatase inhibitor calyculin A (CA). Moreover, CA itself induced ROS production and dramatically enhanced the ionomycin-induced ROS production of AtrbohD. Our results suggest that Ca 2؉ binding and phosphorylation synergistically activate the ROS-producing enzyme activity of AtrbohD.Photosynthetic plants have developed various mechanisms to cope with oxidative stress, such as the production of antioxidants and enzymes that scavenge reactive oxygen species (ROS).3 Plants are also equipped with mechanisms for producing ROS in response to internal and external stimuli. ROS production is induced during many physiological processes, including stress responses, cell growth, hormonal responses, stomatal closure, and disease resistance (see Refs. 1-4 and references therein).ROS production is induced in plants in response to recognition of pathogenic signals, such as pathogen/microbe-associated molecular patterns (PAMPs/MAMPs) or elicitors. Elicitor-induced ROS production is preceded by a rapid increase in the cytosolic free Ca 2ϩ concentration ([Ca 2ϩ ] cyt ) (5-7) and is inhibited both by Ca 2ϩ chelators such as EGTA and BAPTA, and by Ca 2ϩ channel blockers such as La 3ϩ (6,8). The overexpression of rice two-pore channel 1 (OsTPC1), which is a putative voltage-gated Ca 2ϩ channel, enhanced elicitor-induced ROS production (9). Elicitor-induced ROS production is also inhibited by diphenylene iodonium (DPI), which is known to inhibit NADPH oxidase activity (6, 10). NADPH oxidase activity in the microsomal membrane fraction from tomato and tobacco was activated by adding Ca 2ϩ in vitro (11), suggesting that elicitor-induced ROS production by plant NADPH oxidase might be dependent on Ca 2ϩ . In mammalian phagocytes, ROS production is mediated by the NADPH-dependent phagocytic oxidase (phox) complex, which consists of the catalytic subunit gp91 phox /NADPH oxidase (NOX) 2, together with the regulatory subunits p22 phox , p40 phox , p47 phox , p67 phox , and the small GTP-binding protein Rac (12). In...

The vacuole-type ATPases (V-ATPases) exist in various intracellular compartments of eukaryotic cells to regulate physiological processes by controlling the acidic environment. The crystal structure of the subunit C of Thermus thermophilus V-ATPase, homologous to eukaryotic subunit d of V-ATPases, has been determined at 1.95-Å resolution and located into the holoenzyme complex structure obtained by single particle analysis as suggested by the results of subunit cross-linking experiments. The result shows that VATPase is substantially longer than the related F-type ATPase, due to the insertion of subunit C between the V 1 (soluble) and the Vo (membrane bound) domains. Subunit C, attached to the Vo domain, seems to have a socket like function in attaching the central-stalk subunits of the V 1 domain. This architecture seems essential for the reversible association͞dissociation of the V 1 and the Vo domains, unique for V-ATPase activity regulation.T he vacuole-type ATPases (V-ATPases) are commonly found in many organisms involved in a variety of physiological processes (1). V-ATPases in eukaryotic cells (eukaryotic VATPases) translocate protons across the membrane consuming ATP. They reside within intracellular compartments, including endosomes, lysosomes, and secretory vesicles, and within plasma membranes of certain cells including renal intercalated cells, osteoclasts, and macrophages. Eukaryotic V-ATPases are responsible for various cell functions including the acidification of intracellular compartments, renal acidification, born resorption, and tumor metastasis (2).V-ATPase and the F-type ATP synthase (F-ATPase) are evolutionary related and share the rotary mechanism coupling ATP synthesis͞hydrolysis and proton translocation across the membrane (2-4). However, these two types of ATPase show significant differences. Reversible association͞dissociation of the V 1 domain (soluble) and the V o domain (membrane bound) is a unique activity regulation mechanism compared to FATPase (Fig. 1). For example, glucose deprivation has been shown to cause a rapid dissociation of the yeast V-ATPase into free V 1 and V o domains, which is reversible and independent of de novo protein synthesis (5, 6). Similar observations have been reported for Manduca sexta and mammalian complexes (7-9). Subunit composition and structure in the stalk region of VATPase, which connects the V o and V 1 domains, are suggested to be significantly different from those in F-ATPase (10) (Fig. 1). Thus, this region is possibly responsible for the association͞ dissociation of the complex.V-ATPases are also found in archaea and some eubacteria (prokaryotic V-ATPases) (11). The V-ATPase from Thermus thermophilus is solely responsible for aerobic ATP synthesis in this bacteria, which lacks F-ATPase (12). The Thermus VATPase is composed of nine different subunits, which are arranged within the atp operon in the order of G-I-L-E-C-F-A-B-D, which encodes proteins with molecular sizes of 13, 71,8,20,35,12, 64, 54, and 25 kDa, respectively (10) (Fig. 1). This A...

Background: Many patients with invasive ductal carcinoma of the pancreas (IDC) have a poor outcome. MUC4 expression has been implicated as a marker for diagnosis and progression of IDC, but there are no studies of the relation between MUC4 expression and patient prognosis in IDC. Aims: To investigate the prognostic significance of MUC4 expression in IDC. Methods: The expression profiles of MUC4, ErbB2, p27, and MUC1 were investigated in IDC tissues from 135 patients by means of immunohistochemistry. Results: MUC4 was expressed in 43 of the 135 patients with IDC (31.9%). The survival of 21 patients with high MUC4 expression (.20% of neoplastic cells stained) was significantly worse than that of the 114 patients with low MUC4 expression (,20% of neoplastic cells stained) (p = 0.0043). Univariate analysis showed that high MUC4 expression (p = 0.0061), large primary tumour status (.T2) (p = 0.0436), distant metastasis (p = 0.0383), lymphatic invasion (p = 0.0243), and surgical margins (p = 0.0333) were significant risk factors affecting the outcome of patients with IDC. Backward stepwise multivariate analysis showed that MUC4 expression (p = 0.0121), lymph node metastasis (p = 0.0245), and lymphatic invasion (p = 0.0239) were significant independent risk factors. ErbB2, p27, and MUC1 were not independent risk factors. Conclusions: This study shows that MUC4 expression in IDC is a new independent factor for poor prognosis and predicts the outcome of patients with IDC.

Previously it has been found that the MUC2 gene for intestinal type secretory mucin is highly expressed in intraductal papillary mucinous tumors (IPMT), which are characterized by non-invasive growth and a favorable outcome. In contrast, MUC2 mRNA is rarely expressed in invasive ductal carcinomas (IDC), which have poor outcomes. The gastric type secretory mucin, MUC5AC, is strongly expressed in the surface mucous cells of gastric mucosa. As both MUC2 and MUC5AC mucins share the characteristics of forming highly viscous gels, it is expected that not only MUC2 mucin expression but also MUC5AC mucin expression may be associated with a favorable prognosis in patients with pancreatic tumors. MUC5AC mucin gene expression was examined in 24 cases of IPMT and 38 cases of IDC by in situ hybridization using a digoxigenin-labeled oligonucleotide. The results were compared with MUC2 mucin gene expression. Neither MUC5AC mRNA nor MUC2 mRNA was detected in normal pancreatic tissues. MUC5AC mRNA was expressed in 20 of 24 cases of IPMT (83%) and in five of 38 cases of IDC (13%). In contrast, MUC2 mRNA was expressed in 14 of 24 cases of IPMT (58%) and in none of the 38 cases of IDC (0%). The expression rates of MUC5AC mRNA and MUC2 mRNA in IPMT were significantly higher than those in IDC (P< 0.001, respectively). Intraductal papillary mucinous tumors are characterized by three histological types: (i) villous dark cell type; (ii) papillary clear cell type; and (iii) compact cell type. The villous dark cell type generally expressed both MUC5AC+ and MUC2+ genes. Alternatively, the papillary clear cell type and the compact cell type usually showed MUC5AC+ and MUC2- expression. Patients with MUC5AC mRNA expression had a significantly better survival prognosis than those with no MUC5AC mRNA expression (P< 0.005). In conclusion, MUC5AC gene expression occurs in a majority of IPMT cases, even in those with no MUC2 production. MUC5AC expression can be

The three-dimensional structure of oryzacystatin-I, a cysteine proteinase inhibitor of the rice, Oryza sativa L. japonica, has been determined in solution at pH 6.8 and 25 degrees C by (1)H and (15)N NMR spectroscopy. The main body (Glu13-Asp97) of oryzacystatin-I is well-defined and consists of an alpha-helix and a five-stranded antiparallel beta-sheet, while the N- and C-terminal regions (Ser2-Val12 and Ala98-Ala102) are less defined. The helix-sheet architechture of oryzacystatin-I is stabilized by a hydrophobic cluster formed between the alpha-helix and the beta-sheet and is considerably similar to that of monellin, a sweet-tasting protein from an African berry, as well as those of the animal cystatins studied, e.g., chicken egg white cystatin and human stefins A and B (also referred to as human cystatins A and B). Detailed structural comparison indicates that oryzacystatin-I is more similar to chicken cystatin, which belongs to the type-2 animal cystatins, than to human stefins A and B, which belong to the type-1 animal cystatins, despite different loop length.