Interaction of the estrogen receptors with the Fas ligand promoter in human monocytes

The predominance of autoimmune diseases among women suggests that estrogen may modulate immune function. Monocytes and macrophages are important in initiating, maintaining, and resolving inflammatory responses through cell-signaling molecules, which control immune cell survival. One important mechanism of cell survival is mediated by the Fas/Fas ligand (FasL) system. In this study, the link between estrogen, monocytes/macrophages, and the Fas/FasL system was investigated. Estrogen treatment increased FasL expression in monocytes through the binding of the estrogen receptors (ER) to the estrogen recognizing elements and AP-1 motifs present at the FasL promoter. Furthermore, estrogen induced apoptosis in monocytes expressing ERbeta, but not in monocyte-differentiated macrophages expressing ERalpha. The expression of either ERalpha or ERbeta and their response to estrogen in monocytes was found to be dependent on the their stage of cell differentiation. Previously, we have shown that estrogen replacement therapy in postmenopausal women decreased the number of circulating monocytes. In this study, we have characterized the molecular mechanism by which estrogen regulates monocytes homeostasis. These findings indicate that estrogen may regulate immune cell survival through the Fas/FasL system. There is biological relevance to these findings in view of studies showing that accumulation of activated monocytes is involved in the pathogenesis of conditions such as vasculititis, arteriosclerosis, and rheumatoid arthritis.     

Phosphorylated claspin interacts with a phosphate-binding site in the kinase domain of Chk1 during ATR-mediated activation

Claspin is essential for the ATR-dependent activation of Chk1 in Xenopus egg extracts containing incompletely replicated or UV-damaged DNA. The activated form of Claspin contains two repeated phosphopeptide motifs that mediate its binding to Chk1. We show that these phosphopeptide motifs bind to Chk1 by means of its N-terminal kinase domain. The binding site on Chk1 involves a positively charged cluster of amino acids that contains lysine 54, arginine 129, threonine 153, and arginine 162. Mutagenesis of these residues strongly compromises the ability of Chk1 to interact with Claspin. These amino acids lie within regions of Chk1 that are involved in various aspects of its catalytic function. The predicted position on Chk1 of the phosphate group from Claspin corresponds to the location of activation-loop phosphorylation in various kinases. In addition, we have obtained evidence that the C-terminal regulatory domain of Chk1, which does not form a stable complex with Claspin under our assay conditions, nonetheless has some role in Claspin-dependent activation. Overall, these results indicate that Claspin docks with a phosphate-binding site in the catalytic domain of Chk1 during activation by ATR. Phosphorylated Claspin may mimic an activating phosphorylation of Chk1 during this process.     

A functional interaction between chromogranin B and the inositol 1,4,5-trisphosphate receptor/Ca2+ channel

Chromogranins A and B (CGA and CGB) are high capacity, low affinity calcium (Ca2+) storage proteins found in many cell types most often associated with secretory granules of secretory cells but also with the endoplasmic reticulum (ER) lumen of these cells. Both CGA and CGB associate with inositol 1,4,5-trisphosphate receptor (InsP3R) in a pH-dependent manner. At an intraluminal pH of 5.5, as found in secretory vesicles, both CGA and CGB bind to the InsP3R. When the intraluminal pH is 7.5, as found in the ER, CGA totally dissociates from InsP3R, whereas CGB only partially dissociates. To investigate the functional consequences of the interaction between the InsP3R and CGB monomers or CGA/CGB heteromers, purified mouse InsP3R type I were fused to planar lipid bilayers and activated by 2 microM InsP3. In the presence of luminal CGB monomers or CGA/CGB heteromers the InsP3R/Ca2+ channel open probability and mean open time increased significantly. The channel activity remained elevated when the pH was changed to 7.5, a reflection of CGB binding to the InsP3R even at pH 7.5. These results suggest that CGB may play an important modulatory role in the control of Ca2+ release from the ER. Furthermore, the difference in the ability of CGA and CGB to regulate the InsP3R/Ca2+ channel and the variability of CGA/CGB ratios could influence the pattern of InsP3-mediated Ca2+ release.     

Crystal structure of Drosophila angiotensin I-converting enzyme bound to captopril and lisinopril

This study provides evidence that treatment with preclustered ephrin A5-Fc results in a substantial increase in the stability of the p110γ PI-3 kinase associated with EphA8, thereby enhancing PI-3 kinase activity and cell migration on a fibronectin substrate. In contrast, co-expression of a lipid kinase-inactive p110γ mutant together with EphA8 inhibits ligand-stimulated PI-3 kinase activity and cell migration on a fibronectin substrate, suggesting that the mutant has a dominant negative effect against the endogenous p110γ PI-3 kinase. Significantly, the tyrosine kinase activity of EphA8 is not important for either of these processes. Taken together, our results demonstrate that the stimulation of cell migration on a fibronectin substrate by the EphA8 receptor depends on the p110γ PI-3 kinase but is independent of a tyrosine kinase activity.     

Slow and persistent increase of [Ca2+]c in response to ligation of surface IgM in WEHI-231 cells

WEHI-231 and Bal 17 B cell lines are representative models for immature and mature B cells, respectively. Their regulation of cytosolic Ca(2+) concentration ([Ca(2+)](c)) was compared using fura-2 fluorescence ratiometry. The ligation of B cell antigen receptor (BCR) by anti-IgM antibody induced a slow but large increase of [Ca(2+)](c) in WEHI-231 cells while not in Bal 17 cells. The thapsigargin-induced store-operated Ca(2+) entry (SOCE) of Bal 17 cells reached a steady state which was blocked by 2-aminoethoxydiphenyl borate (2-APB). On the contrary, the thapsigargin-induced SOCE of WEHI-231 cells increased continuously, which was accelerated by 2-APB. The increase of [Ca(2+)](c) by BCR ligation was also enhanced by 2-APB in WEHI-231 cells while blocked in Bal 17 cells. The Mn(2+) quenching study showed that the thapsigargin-, or the BCR ligation-induced Ca(2+) influx pathway of WEHI-231 was hardly permeable to Mn(2+). The intractable increase of [Ca(2+)](c) may explain the mechanism of BCR-driven apoptosis of WEHI-231 cells, a well-known model of clonal deletion of autoreactive immature B cells.     

Crystal structure of the YchF protein reveals binding sites for GTP and nucleic acid

The bacterial protein encoded by the gene ychF is 1 of 11 universally conserved GTPases and the only one whose function is unknown. The crystal structure determination of YchF was sought to help with the functional assignment of the protein. The YchF protein from Haemophilus influenzae was cloned and expressed, and the crystal structure was determined at 2.4 A resolution. The polypeptide chain is folded into three domains. The N-terminal domain has a mononucleotide binding fold typical for the P-loop NTPases. An 80-residue domain next to it has a pronounced alpha-helical coiled coil. The C-terminal domain features a six-stranded half-barrel that curves around an alpha-helix. The crablike three-domain structure of YchF suggests the binding site for a double-stranded nucleic acid in the cleft between the domains. The structure of the putative GTP-binding site is consistent with the postulated guanine specificity of the protein. Fluorescence measurements have demonstrated the ability of YchF to bind a double-stranded nucleic acid and GTP. Taken together with other experimental data and genomic analysis, these results suggest that YchF may be part of a nucleoprotein complex and may function as a GTP-dependent translation factor.     

Strain-specific patterns of autonomic nervous system activity and heart failure susceptibility in mice

Transgenic mice are widely used to study cardiac function, but strain-dependent differences in autonomic nervous system activity (ANSA) have not been explored. We compared 1) short-term pharmacological responses of cardiac rhythm in FVB vs. C57Black6/SV129 wild-type mice and 2) long-term physiological dynamics of cardiac rhythm and survival in tumor necrosis factor (TNF)-alpha transgenic mice with heart failure (TNF-alpha mice) on defined backgrounds. Ambulatory telemetry electrocardiographic recordings and response to saline, adrenergic, and cholinergic agents were examined in FVB and C57Black6/SV129 mice. In FVB mice, baseline heart rate (HR) was higher and did not change after injection of isoproterenol or atropine but decreased with propranolol. In C57Black6/SV129 mice, HR did not change with propranolol but increased with isoproterenol or atropine. Mean HR, but not indexes of HR variability, was an excellent predictor of response to autonomic agents. The proportion of surviving animals was higher in TNF-alpha mice on an FVB background than on a mixed FVB/C57Black6 background. The homeostatic states of ANSA are strain specific, which can explain the interstrain differences in mean HR, pharmacological responses, and survival of animals with congestive heart failure. Strain-specific differences should be considered in selecting the strains of mice used for transgenic and gene targeting experiments.     

Construction of DNA-shuffled and incrementally truncated libraries by a mutagenic and unidirectional reassembly method: changing from a substrate specificity of phospholipase to that of lipase

A method of mutagenic and unidirectional reassembly (MURA) that can generate libraries of DNA-shuffled and randomly truncated proteins was developed. The method involved fragmenting the template gene(s) randomly by DNase I and reassembling the small fragments with a unidirectional primer by PCR. The MURA products were treated with T4 DNA polymerase and subsequently with a restriction enzyme whose site was located on the region of the MURA primer. The N-terminal-truncated and DNA-shuffled library of a Serratia sp. phospholipase A(1) prepared by this method had an essentially random variation of truncated size and also showed point mutations associated with DNA shuffling. After high-throughput screening on triglyceride-emulsified plates, several mutants exhibiting absolute lipase activity (NPL variants) were obtained. The sequence analysis and the lipase activity assay on the NPL variants revealed that N-terminal truncations at a region beginning with amino acids 61 to 71, together with amino acid substitutions, resulted in the change of substrate specificity from a phospholipase to a lipase. We therefore suggest that the MURA method, which combines incremental truncation with DNA shuffling, can contribute to expanding the searchable sequence space in directed evolution experiments.     

ABA and polyamines act independently in primary leaves of cold-stressed tomato (Lycopersicon esculentum)

The effects of ABA and putrescine, a polyamine, on cold-induced membrane leakage were investigated using primary leaves of wild-type and an ABA-deficient mutant, flacca , of tomato ( Lycopersicon esculentum Mill.). The amount of chilling-induced electrolyte leakage from flacca leaves was much higher than that from the wild-type leaves. When applied exogenously ABA reduced cold-induced electrolyte leakage from leaves of both wild-type and the flacca mutant. However, the cold-induced electrolyte leakage from flacca leaves was not as pronounced as in the wild-type indicating that ABA is an important mediator in response to cold stress in the leaves. Putrescine reduced cold-induced electrolyte leakage from both wild-type and flacca leaves. Synthesis of putrescine in the leaves was increased by cold treatment. DFMO, a biosynthetic inhibitor of the polyamine, increased electrolyte leakage from cold-treated leaves, and exogenously applied putrescine decreased the enhanced leakage to the control level. Therefore, this polyamine is thought also to be involved in the response to cold stress of tomato leaves. Both ABA and putrescine were protective against cold stress, but exogenously applied ABA decreased the endogenous level of putrescine in the leaves. Furthermore, the DMFO-increased electrolyte leakage in cold-stressed leaves was completely abolished by the application of ABA. These results suggest that ABA is a major regulator in the response to cold stress in tomato leaves and that it does not exert its role via putrescine in the response to cold stress.