Kyushu University

About: Kyushu University is a education organization based out in Fukuoka, Japan. It is known for research contribution in the topics: Population & Catalysis. The organization has 68284 authors who have published 135190 publications receiving 3055928 citations. The organization is also known as: Kyūshū Daigaku.

Direct Evidence for Increased Hydroxyl Radicals Originating From Superoxide in the Failing Myocardium

Abstract: —Experimental and clinical studies have suggested an increased production of reactive oxygen species (ROS) in the failing myocardium. The present study aimed to obtain direct evidence for increased ROS and to determine the contribution of superoxide anion (·O2−), H2O2, and hydroxy radical (·OH) in failing myocardial tissue. Heart failure was produced in adult mongrel dogs by rapid ventricular pacing at 240 bpm for 4 weeks. To assess the production of ROS directly, freeze-clamped myocardial tissue homogenates were reacted with the nitroxide radical, 4-hydroxy-2,2,6,6,-tetramethyl-piperidine- N -oxyl, and its spin signals were detected by electron spin resonance spectroscopy. The rate of electron spin resonance signal decay, proportional to ·OH level, was significantly increased in heart failure, which was inhibited by the addition of dimethylthiourea (·OH scavenger) into the reaction mixture. Increased ·OH in the failing heart was abolished to the same extent in the presence of desferrioxamine (iron chelator), catalase (H2O2 scavenger), and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; LaMotte) (·O2− scavenger), indicating that ·OH originated from H2O2 and ·O2−. Further, ·O2− produced in normal myocardium in the presence of antimycin A (mitochondrial complex III inhibitor) could reproduce the increase of H2O2 and ·OH seen in the failing tissue. There was a significant positive relation between myocardial ROS level and left ventricular contractile dysfunction. In conclusion, in the failing myocardium, ·OH was produced as a reactive product of ·O2− and H2O2, which might play an important role in left ventricular failure.

Regulation of Rice NADPH Oxidase by Binding of Rac GTPase to Its N-Terminal Extension

Abstract: Reactive oxygen species (ROS) produced by NADPH oxidase play critical roles in various cellular activities, including plant innate immunity response. In contrast with the large multiprotein NADPH oxidase complex of phagocytes, in plants, only the homologs of the catalytic subunit gp91phox and the cytosolic regulator small GTPase Rac are found. Plant homologs of the gp91phox subunit are known as Rboh (for respiratory burst oxidase homolog). Although numerous Rboh have been isolated in plants, the regulation of enzymatic activity remains unknown. All rboh genes identified to date possess a conserved N-terminal extension that contains two Ca2+ binding EF-hand motifs. Previously, we ascertained that a small GTPase Rac (Os Rac1) enhanced pathogen-associated molecular pattern–induced ROS production and resistance to pathogens in rice (Oryza sativa). In this study, using yeast two-hybrid assay, we found that interaction between Rac GTPases and the N-terminal extension is ubiquitous and that a substantial part of the N-terminal region of Rboh, including the two EF-hand motifs, is required for the interaction. The direct Rac–Rboh interaction was supported by further studies using in vitro pull-down assay, a nuclear magnetic resonance titration experiment, and in vivo fluorescence resonance energy transfer (FRET) microscopy. The FRET analysis also suggests that cytosolic Ca2+ concentration may regulate Rac–Rboh interaction in a dynamic manner. Furthermore, transient coexpression of Os Rac1 and rbohB enhanced ROS production in Nicotiana benthamiana, suggesting that direct Rac–Rboh interaction may activate NADPH oxidase activity in plants. Taken together, the results suggest that cytosolic Ca2+ concentration may modulate NADPH oxidase activity by regulating the interaction between Rac GTPase and Rboh.

Cytoplasmic ubiquitin ligase KPC regulates proteolysis of p27Kip1 at G1 phase

Abstract: The cyclin-dependent kinase inhibitor p27(Kip1) is degraded at the G0-G1 transition of the cell cycle by the ubiquitin-proteasome pathway. Although the nuclear ubiquitin ligase (E3) SCF(Skp2) is implicated in p27(Kip1) degradation, proteolysis of p27(Kip1) at the G0-G1 transition proceeds normally in Skp2(-/-) cells. Moreover, p27(Kip1) is exported from the nucleus to the cytoplasm at G0-G1 (refs 9-11). These data suggest the existence of a Skp2-independent pathway for the degradation of p27(Kip1) at G1 phase. We now describe a previously unidentified E3 complex: KPC (Kip1 ubiquitination-promoting complex), consisting of KPC1 and KPC2. KPC1 contains a RING-finger domain, and KPC2 contains a ubiquitin-like domain and two ubiquitin-associated domains. KPC interacts with and ubiquitinates p27(Kip1) and is localized to the cytoplasm. Overexpression of KPC promoted the degradation of p27(Kip1), whereas a dominant-negative mutant of KPC1 delayed p27(Kip1) degradation. The nuclear export of p27(Kip1) by CRM1 seems to be necessary for KPC-mediated proteolysis. Depletion of KPC1 by RNA interference also inhibited p27(Kip1) degradation. KPC thus probably controls degradation of p27(Kip1) in G1 phase after export of the latter from the nucleus.