Senescence of Rice Leaves XXIV. Involvement of Calcium and Calmodulin in the Regulation of Senescence

Effects of compounds that influenced calcium uptake and calmodulininhibitors on the senescence of detached rice leaves were examined.Chelators, ethyleneglycol-bis-(ß-aminoethyl ether)-N,N,N',N'-tetraaceticacid (EGTA) and l,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraaceticacid (BAPTA), significantly promoted senescence of detachedrice leaves in the dark and light. The effect of EGTA can bereversed by treating detached rice leaves with calcium. Verapamil,a calcium channel blocker, and lanthanum chloride, a calciumantagonist, promoted dark-induced, and suppressed BA- and light-retardedsenescence of detached rice leaves. Calcium ionophore A23187 [GenBank] and ruthenium red, believed to raise cytosolic level of Ca²⁺,were quite effective in retarding dark-induced and ABA-promotedsenescence of detached rice leaves. Calmodulin inhibitors, W-7,compound 48/80, chlorpromazine and trifluoperazine, significantlypromoted dark-induced, and suppressed BA- and light-retardedsenescence of detached rice leaves. It is concluded that cytosoliclevel of Ca²⁺ may regulate senescence of detached rice leavesthrough a calmodulin-dependent mechanism. (Received June 13, 1990; Accepted August 3, 1990)     

Comparative Study of the Metabolism of 1-Aminocyclopropane-1-carboxylic Acid and Senescence of Water-Stressed and ABA-Treated Excised Rice Leaves

Changes in the metabolism of 1-aminocyclopropane-l-carboxylicacid (ACC) during senescence in the light in turgid, water-stressed,and ABA-treated, excised rice leaves were examined. The decreasesin levels of Chl and protein were more rapid in the water-stressedand in the ABA-treated leaves than in the turgid leaves. Inturgid leaves, levels of proline remained very low, but theyincreased considerably as a result of water stress or treatmentwith ABA. The production of ethylene was strongly inhibitedby water stress and by ABA through the inhibition of the synthesisof ACC and/or the conversion of ACC to ethylene. In turgid leaves,the level of 1-(malonylamino)cyclopropane-l-carboxylic acid(MACC) increased with time during incubation in the light. Waterstress resulted in a pattern of accumulation of MACC similarto that in the turgid control. However, ABA blocked the malonylationof ACC. (Received July 27, 1989; Accepted March 12, 1990)     

Nitric oxide produced by iNOS is associated with collagen synthesis in keloid scar formation

Nitric oxide (NO) has emerged as an important mediator of many physiological functions. Recent reports have shown that NO participates in the wound healing process, however, its role in keloid formation remains unclear. This study aimed to investigate the effect of NO on keloid fibroblasts (KF) and to determine the levels of inducible nitric oxide synthase (iNOS) expression in clinical specimens of keloid. Scar tissue from seven keloid patients with matched perilesion skin tissue controls was studied for inducible nitric oxide synthase expression and location. In addition, primary keloid and normal scar skin fibroblast cultures were set up to investigate the effects of NO in inducing collagen type I expression. Inducible nitric oxide synthase expression, and NO production were elevated in keloid scar tissues but not in matched perilesion skin tissues. Furthermore, exposure of KF to exogenous NO resulted in increased expression of collagen type I in a dose-dependent manner. NO exposure also induced time-course dependent collagen I expression that peaked at 24h in KF. Taken together, these results indicate that excess collagen formations in keloid lesion may be attributed to iNOS overexpression.     

Versatile modes of peptide recognition by the ClpX N domain mediate alternative adaptor‐binding specificities in different bacterial species

ClpXP, an AAA+ protease, plays key roles in protein‐quality control and many regulatory processes in bacteria. The N‐terminal domain of the ClpX component of ClpXP is involved in recognition of many protein substrates, either directly or by binding the SspB adaptor protein, which delivers specific classes of substrates for degradation. Despite very limited sequence homology between the E. coli and C. crescentus SspB orthologs, each of these adaptors can deliver substrates to the ClpXP enzyme from the other bacterial species. We show that the ClpX N domain recognizes different sequence determinants in the ClpX‐binding (XB) peptides of C. crescentus SspBα and E. coli SspB. The C. crescentus XB determinants span 10 residues and involve interactions with multiple side chains, whereas the E. coli XB determinants span half as many residues with only a few important side chain contacts. These results demonstrate that the N domain of ClpX functions as a highly versatile platform for peptide recognition, allowing the emergence during evolution of alternative adaptor‐binding specificities. Our results also reveal highly conserved residues in the XB peptides of both E. coli SspB and C. crescentus SspBα that play no detectable role in ClpX‐binding or substrate delivery.     

Upregulation of the Chemokine (C-C Motif) Ligand 2 via a Severe Acute Respiratory Syndrome Coronavirus Spike-ACE2 Signaling Pathway

Severe acute respiratory syndrome coronavirus (SARS-CoV) was identified to be the causative agent of SARS with atypical pneumonia. Angiotensin-converting enzyme 2 (ACE2) is the major receptor for SARS-CoV. It is not clear whether ACE2 conveys signals from the cell surface to the nucleus and regulates expression of cellular genes upon SARS-CoV infection. To understand the pathogenesis of SARS-CoV, human type II pneumocyte (A549) cells were incubated with the viral spike protein or with SARS-CoV virus-like particles containing the viral spike protein to examine cytokine modulation in lung cells. Results from oligonucleotide-based microarray, real-time PCR, and enzyme-linked immunosorbent assays indicated an upregulation of the fibrosis-associated chemokine (C-C motif) ligand 2 (CCL2) by the viral spike protein and the virus-like particles. The upregulation of CCL2 by SARS-CoV spike protein was mainly mediated by extracellular signal-regulated kinase 1 and 2 (ERK1/2) and AP-1 but not the IκBα-NF-κB signaling pathway. In addition, Ras and Raf upstream of the ERK1/2 signaling pathway were involved in the upregulation of CCL2. Furthermore, ACE2 receptor was activated by casein kinase II-mediated phosphorylation in cells pretreated with the virus-like particles containing spike protein. These results indicate that SARS-CoV spike protein triggers ACE2 signaling and activates fibrosis-associated CCL2 expression through the Ras-ERK-AP-1 pathway.Severe acute respiratory syndrome (SARS) is an atypical pneumonia that occurred in several countries during late 2002 and the first half of 2003. A novel coronavirus, SARS-coronavirus (SARS-CoV), isolated from SARS patients was identified to be the causative agent of SARS. SARS-CoV infected more than 8,000 people, with a worldwide mortality rate of 9.6% (8, 20). The virus contains a positive-sense single-stranded RNA genome of approximately 30,000 nucleotides. Four major structural proteins including spike (S), membrane (M), envelope (E), and nucleocapsid (N) make up the SARS-CoV particles (31, 36). Angiotensin (Ang)-converting enzyme 2 (ACE2) and CD209L (L-SIGN) have been identified to be the receptors for SARS-CoV (15, 27). SARS-CoV spike protein induced ACE2-mediated interleukin-8 (IL-8) release from lung cells via activation of activation protein 1 (AP-1) (4). Nevertheless, involvement of ACE2 in virus pathogenesis is not fully understood.Dysregulation of inflammatory cytokines and adhesion molecules may be involved in lung injury that causes acute respiratory distress syndrome. High levels of proinflammatory cytokines such as interleukin-6, transforming growth factor β (TGF-β), and tumor necrosis factor alpha (TNF-α) were detected in the sera and ACE2⁺ cells of SARS patients (12, 45). Elevated levels of cytokines, including alpha interferon (IFN-α), IFN-β, IFN-γ, CCL3, CCL5, and CXCL10, were also detected in SARS-CoV-infected macrophages, dendritic cells, and a colon carcinoma cell line (1, 5, 25). It is possible that the high fatality rate of SARS results from a severe immune response caused by cytokines and chemokines.CCL2 [chemokine (C-C motif) ligand 2; monocyte chemoattractant protein-1, (MCP-1)] is a CC chemokine that attracts monocytes, memory T lymphocytes, and basophils. CCL2 and its receptor CCR2 are involved in inflammatory reactions, including monocyte/macrophage migration, Th2 cell polarization, and the production of TGF-β and procollagen in fibroblast cells (9, 10). CCL2 is thus associated with several lung inflammatory disorders including acute respiratory distress syndrome, asthma, and pulmonary fibrosis (35). These inflammatory disorders and pulmonary infiltration are known to account for the progressive respiratory failure and death of SARS patients. In addition, upregulation of CCL2 was detected in the sera of SARS patients and the supernatant of a SARS-CoV-infected culture system (5, 16). However, mechanisms by which SARS-CoV is involved in the upregulation of CCL2 are not known.In this study, we have taken a step forward in understanding the pathogenesis of SARS-CoV by examining SARS-CoV-mediated cytokine modulation in human type II pneumocyte (A549) cells and monkey kidney Vero E6 cells. Both pretreatment of A549 cells with SARS-CoV virus-like particles (VLPs) and preincubation of the cells with the viral spike protein upregulate the expression of fibrosis-associated CCL2. SARS-CoV may interact with ACE2 receptor and activate casein kinase II-mediated ACE2 phosphorylation, which is critical for SARS-CoV-induced CCL2 upregulation. In addition, Ras, Raf, MEK, extracellular signal-regulated kinase 1 and 2 (ERK1/2), and AP-1 are directly involved in SARS-CoV-induced CCL2 upregulation. These data suggest that the intracellular ACE2 signaling pathway in the pneumocytes of SARS-CoV-infected patients confers risks of lung fibrosis leading to respiratory failure.     

Herb–drug interaction of Andrographis paniculata extract and andrographolide on the pharmacokinetics of theophylline in rats

Herb–drug interaction has become a serious problem since herbal medicine is extensively used in the modern world. This study investigates effects of Andrographis paniculata extract (APE) and its major component, andrographolide (AG), on the pharmacokinetics of theophylline, a typical substrate of cytochrome P450 1A2 enzyme, in rats. After APE or AG pretreatment for 3 days, on the fourth day rats were administered theophylline via femoral vein cannula. The blood theophylline levels were monitored by microdialysis sampling combined with HPLC-UV. The results indicated that the clearance of theophylline was significantly increased and the area under concentration–time curve (AUC) was reduced in both AG and APE pretreated groups at low-dose theophylline administration (1 mg/kg). The elimination half-life (t_1/2β) and mean residence time (MRT) of theophylline were shortened by 14% and 17%, respectively, in the AG pretreated group when high-dose theophylline (5 mg/kg) was given. However, theophylline accumulated in rat of the group with APE pretreatment. This phenomenon suggests that some other herbal components contained in APE may interact with theophylline and retard its elimination when theophylline was administered at a high dose. Our results suggest that patients who want to use CYP1A2-metabolized drugs such as caffeine and theophylline should be advised of the potential herb–drug interaction, to reduce therapeutic failure or increased toxicity of conventional drug therapy.