Bilayer interfacial properties modulate the binding of amphipathic peptides

The free energy of transfer (DeltaG degrees ) from water to lipid bilayers was measured for two amphipathic peptides, the presequence of the mitochondrial peptide rhodanese (MPR) and melittin. Experiments were designed to determine the effects on peptide partitioning of the addition of lipids that produce structural modifications to the bilayer/water interface. In particular, the addition of cholesterol or the cholesterol analog 6-ketocholestanol increases the bilayer area compressibility modulus, indicating that these molecules modify lipid-lipid interactions in the plane of the bilayer. The addition of 6-ketocholestanol or lipids with attached polyethylene glycol chains (PEG-lipids) modify the effective thickness of the interfacial region; 6-ketocholestanol increases the width of hydrophilic headgroup region in the direction of the acyl chains whereas the protruding PEG chains of PEG-lipids increase the structural width of the headgroup region into the surrounding aqueous phase. The incorporation of PEG-lipids with PEG molecular weights of 2000 or 5000 had no appreciable effect on peptide partitioning that could not be accounted for by the presence of surface charge. However, for both MPR and melittin DeltaG degrees decreased linearly with increasing bilayer compressibility modulus, demonstrating the importance of bilayer mechanical properties in the binding of amphipathic peptides.     

Human genome-wide RNAi screen for host factors that modulate intracellular Salmonella growth

Salmonella enterica is a bacterial pathogen of humans that can proliferate within epithelial cells as well as professional phagocytes of the immune system. While much has been learned about the microbial genes that influence the infectious process through decades of intensive research, relatively little is known about the host factors that affect infection. We performed a genome-wide siRNA screen to identify host genes that Salmonella enterica serovar Typhimurium (S. typhimurium) utilizes to facilitate growth within human epithelial cells. In this screen, with siRNAs targeting every predicted gene in the human genome, we identified 252 new human-host-susceptibility factors (HSFs) for S. typhimurium. We also identified 39 genes whose silencing results in increased intracellular growth of S. typhimurium. The HSFs identified are regulated most centrally by NFκB and associate with each other through an extremely dense network of interactions that center around a group of kinases. Most genes identified were not previously appreciated as playing roles in the intracellular lifecycle of S. enterica. Numerous HSFs identified with interesting characteristics that could play plausible roles in mediating intracellular microbial growth are discussed. Importantly, this study reveals significant overlap between the host network that supports S. typhimurium growth within human epithelial cells and the one that promotes the growth of Mycobacterium tuberculosis within human macrophages. In addition to providing much new information about the molecular mechanisms underlying S. enterica-host cell interplay, all 252 HSFs identified are candidates for new anti-microbial targets for controlling S. enterica infections, and some may provide broad-spectrum anti-microbial activity.     

Structural features in heparin that interact with VEGF165 and modulate its biological activity.

The 165 amino acid form of vascular endothelial growth factor (VEGF165) is a heparin-binding growth factor with mitogenic activity for vascular endothelial cells. We examined activities of various heparin derivatives toward their interactions with VEGF165 using an enzyme-linked immunosorbent assay and elucidated the structural features in heparin for the interactions. Native heparin interacted with VEGF165, whereas N-desulfated, N-acetylated (N-DS, N-Ac-) heparin, and 6-O-desulfated (6-O-DS-) heparin did not. The 2-O-desulfated (2-O-DS-) heparin retained the ability for the interaction with VEGF165. In contrast, the 2-O-DS-heparin exhibited no ability for the interaction with FGF-2 and HGF. Thus, structural requirements in heparin for the specific interaction with VEGF165 are distinct from those with FGF-2 and HGF which require a high content of 2-O-sulfate groups. In a cell proliferation assay, native heparin and 2-O-DS-heparin exhibited inhibitory abilities for VEGF165-induced proliferation of human umbilical vein endothelial cells (HUVECs) with their high concentrations (more than 64 microg/ml), while only native heparin could enhance the proliferation of the chlorate-treated cells. These results suggested that a high content of 2-O-sulfate groups is not required for the specific interaction with VEGF165alone, although it is essential for the mitogenic activity of the growth factor.     

The brain in vivo expresses the 2',3'-cAMP-adenosine pathway

Although multiple biochemical pathways produce adenosine, studies suggest that the 2',3'-cAMP-adenosine pathway (2',3'-cAMP→2'-AMP/3'-AMP→adenosine) contributes to adenosine production in some cells/tissues/organs. To determine whether the 2',3'-cAMP-adenosine pathway exists in vivo in the brain, we delivered to the brain (gray matter and white matter separately) via the inflow perfusate of a microdialysis probe either 2',3'-cAMP, 3',5'-cAMP, 2'-AMP, 3'-AMP, or 5'-AMP and measured the recovered metabolites in the microdialysis outflow perfusate with mass spectrometry. In both gray and white matter, 2',3'-cAMP increased 2'-AMP, 3'-AMP and adenosine, and 3',5'-cAMP increased 5'-AMP and adenosine. In both brain regions, 2'-AMP, 3-AMP and 5'-AMP were converted to adenosine. Microdialysis experiments in 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase) wild-type mice demonstrated that traumatic brain injury (controlled cortical impact model) activated the brain 2',3'-cAMP-adenosine pathway; similar experiments in CNPase knockout mice indicated that CNPase was involved in the metabolism of endogenous 2',3'-cAMP to 2'-AMP and to adenosine. In CSF from traumatic brain injury patients, 2',3'-cAMP was significantly increased in the initial 12 h after injury and strongly correlated with CSF levels of 2'-AMP, 3'-AMP, adenosine and inosine. We conclude that in vivo, 2',3'-cAMP is converted to 2'-AMP/3'-AMP, and these AMPs are metabolized to adenosine. This pathway exists endogenously in both mice and humans.     

Molecular evidence that human ocular ciliary epithelium expresses components involved in phototransduction

Here we report the expression, in the human ocular ciliary epithelium and in a human nonpigmented (NPE) ciliary epithelial cell line, of genes usually restricted to cone and rod photoreceptor cells of the retina. By RT-PCR and DNA sequencing we identified the expression of rhodopsin and components linked to its deactivation, including rhodopsin kinase, recoverin, and visual arrestin. We also detected the expression of transducin (T-alpha), phosphodiesterase (PDE-alpha), and cGMP-gated channel alpha-subunits. Cultured NPE cells responded to treatment with phorbol ester by enhancing the expression of rhodopsin mRNA three- to fourfold. Indirect immunofluorescence of the intact ciliary epithelium with monoclonal antibodies (MAbs) against rhodopsin, rhodopsin kinase, and visual arrestin revealed labeling preferentially restricted to the NPE cells. Furthermore, Western blot analysis of whole lysates from the pars plicata region of the human ciliary epithelium with MAbs demonstrated immunochemical cross-reactivity with proteins of molecular mass similar to rhodopsin (36 kDa), rhodopsin kinase (64 to 66 kDa), and arrestin (48-52 kDa) from the human retina. These results provide the first molecular evidence that components of a non-visual phototransduction pathway are expressed in the human ocular NPE ciliary epithelium, which may be linked to circadian entrainment tasks.     

Human endostatin-derived synthetic peptides possess potent antiangiogenic properties in vitro and in vivo

Pharmacological control of the angiogenic process (i.e., the neovascularization necessary for the growth and progression of tumors and metastases) is considered to be one of the most promising approaches to antineoplastic therapy. Endostatin, a 20-kDa protein derived from collagen XVIII, is one of the first recently discovered endogeneous antiangiogenic substances, but its cell targets and mechanism(s) of action are still unknown. We thought it would be interesting to test whether shorter peptides derived from endostatin might preserve its antiangiogenic activity. Four synthetic peptides corresponding to the sequences 6-49 (I), 50-92 (II), 93-133 (III), and 134-178 (IV) of human endostatin were tested for their ability to inhibit endothelial cell proliferation, migration, and both in vitro and in vivo angiogenesis. Fragment I (and fragment IV in the tests performed) was found to be fully biologically active in all of the angiogenesis assays, and sometimes showed even greater potency and efficacy than full-length human endostatin itself.     

Tenascin-R plays a role in neuroprotection via its distinct domains that coordinate to modulate the microglia function

Microglia are one of the main cell types activated by brain injury. In the present study, we have investigated how domains of the extracellular matrix molecule tenascin-R (TN-R) modulate microglia function. We found that epidermal growth factor-like repeats inhibited adhesion and migration of microglia via a protein kinase A-dependent mechanism. In contrast, fibronectin 6-8 repeats promoted adhesion and migration of the primary microglia via a protein kinase C-dependent mechanism. Both domains of TN-R induced an up-regulation in the secretion of cytokines, such as chemokine-induced cytokine 3 and tumor neurosis factor alpha. Interestingly, epidermal growth factor-like repeats and fibronectin 6-8 induced a dramatic up-regulation in the secretion of brain-derived neurotrophic factor/transforming growth factor-beta and nerve growth factor/transforming growth factor-beta, respectively, and conditioned medium from activated microglia was able to promote neurite outgrowth of N1E-115 cells and primary cortical neurons. These results suggest that TN-R plays a role in neuroprotection through distinct domains coordinating to modulate microglia function.     

Gyrase and Topo IV modulate chromosome domain size in vivo

In bacteria, DNA supercoil movement is restricted to subchromosomal regions or 'domains.' To elucidate the nature of domain boundaries, we analysed reaction kinetics for γδ site-specific resolution in six chromosomal intervals ranging in size from 14 to 90 kb. In stationary cultures of Salmonella typhimurium , resolution kinetics were rapid for both short and long intervals, suggesting that random stationary barriers occur with a 30% probability at approximately 80 kb intervals along DNA. To test the biochemical nature of domain barriers, a genetic screen was used to look for mutants with small domains. Rare temperature-sensitive alleles of DNA gyrase and Topo IV (the two essential type II topoisomerases) had more supercoil barriers than wild-type strains in all growth states. The most severe gyrase mutants were found to have twice as many barriers in growing cells as wild type throughout a 90 kb interval of the chromosome. We propose that knots and tangles in duplex DNA restrain supercoil diffusion in living bacteria.     

Cellular metabolites modulate in vivo signaling of Arabidopsis cryptochrome-1

Cryptochromes are blue-light absorbing flavoproteins with multiple signaling roles. In plants, cryptochrome (cry1, cry2) biological activity has been linked to flavin photoreduction via an electron transport chain to the protein surface comprising 3 evolutionarily conserved tryptophan residues known as the ‘Trp triad.’ Mutation of any of the Trp triad residues abolishes photoreduction in isolated cryptochrome protein in vitro and therefore had been suggested as essential for electron transfer to the flavin. However, photoreduction of the flavin in Arabidopsis cry2 proteins occurs in vivo even with mutations in the Trp triad, indicating the existence of alternative electron transfer pathways to the flavin. These pathways are potentiated by metabolites in the intracellular environment including ATP, ADP, AMP, and NADH. In the present work we extend these observations to Arabidopsis cryptochrome 1 and demonstrate that Trp triad substitution mutants at W400F and W324F positions which are not photoreduced in vitro can be photoreduced in whole cell extracts, albeit with reduced efficiency. We further show that the flavin signaling state (FADH°) is stabilized in an in vivo context. These data illustrate that in vivo modulation by metabolites in the cellular environment may play an important role in cryptochrome signaling, and are discussed with respect to possible effects on the conformation of the C-terminal domain to generate the biologically active conformational state.     

甘丙肽及其受体在中枢神经系统疾病中的作用

中枢神经系统疾病因其发病机制复杂而难以找到药物作用的有效靶点。甘丙肽(galanin, GAL)因其广泛的中枢神经系统分布并与多种神经系统疾病密切相关而进入人们的视线。现已证明,GAL与三种G蛋白偶联受体(GALR1-3)结合后,通过抑制cAMP/PKA(GALR1、GALR3)和激活磷脂酶C(GALR2)等信号通路调节众多生理和病理过程。本文概述了近年来GAL及其受体在中枢神经系统疾病中的作用的研究进展,旨在为理解这些疾病的发病机制以及靶向药物的研发提供新的指导。     

In vivo screening for secreted proteins that modulate glucose handling identifies interleukin-6 family members as potent hypoglycemic agents

Diabetes is a disease of abnormal glucose homeostasis characterized by chronic hyperglycemia and a broad array of consequent organ damage. Because normal glucose homeostasis is maintained by a complex interaction between behavior (feeding and physical activity) and metabolic activity that is modulated by inter-organ signaling through secreted factors, disease modeling in vitro is necessarily limited. In contrast, in vivo studies allow complex metabolic phenotypes to be studied but present a barrier to high throughput studies. Here we present the development of a novel in vivo screening platform that addresses this primary limitation of in vivo experimentation. Our platform leverages the large secretory capacity of the liver and the hepatocyte transfection technique of hydrodynamic tail vein injection to achieve supraphysiologic blood levels of secreted proteins. To date, the utility of hydrodynamic transfection has been limited by the deleterious impact of the variable transfection efficiency inherent to this technique. We overcome this constraint by co-transfection of a secreted luciferase cDNA whose product can be easily monitored in the blood of a living animal and used as a surrogate marker for transfection efficiency and gene expression levels. To demonstrate the utility of our strategy, we screened 248 secreted proteins for the ability to enhance glucose tolerance. Surprisingly, interleukin-6 and several of its family members but not other well-recognized insulin sensitizing agents were identified as potent hypoglycemic factors. We propose this experimental system as a powerful and flexible in vivo screening platform for identifying genes that modulate complex behavioral and metabolic phenotypes.     

Three suppressor systems in human blood that modulate lymphoproliferation.

Three suppressor system of T lymphocyte proliferation found in normal blood were characterized. The adherent cell suppressor system (ACSS) is effected by a steroid and radioresistant monocyte that survives well in culture. The prostaglandin-related suppressor system (PgSS) is effected by a similar cell but is distinct from the ACSS in terms of magnitude of suppression, effective monocyte concentration, and carrageenan or indomethacin sensitivity. The induced suppressor system (ISS) is effected by a T lymphocyte that is partially radiosensitive and loses activity after 24 hr in culture. Although the ISS is unaffected by age, ACSS and PgSS activity is, overall, higher among elderly than among young adult subjects. Activation of these three suppressor systems does not require cell replication. They are not restricted by histocompatibility barriers.     

Inhibitory Fc receptors modulate in vivo cytotoxicity against tumor targets

Inhibitory receptors have been proposed to modulate the in vivo cytotoxic response against tumor targets for both spontaneous and antibody-dependent pathways. Using a variety of syngenic and xenograft models, we demonstrate here that the inhibitory FcgammaRIIB molecule is a potent regulator of antibody-dependent cell-mediated cytotoxicity in vivo, modulating the activity of FcgammaRIII on effector cells. Although many mechanisms have been proposed to account for the anti-tumor activities of therapeutic antibodies, including extended half-life, blockade of signaling pathways, activation of apoptosis and effector-cell-mediated cytotoxicity, we show here that engagement of Fcgamma receptors on effector cells is a dominant component of the in vivo activity of antibodies against tumors. Mouse monoclonal antibodies, as well as the humanized, clinically effective therapeutic agents trastuzumab (Herceptin(R)) and rituximab (Rituxan(R)), engaged both activation (FcgammaRIII) and inhibitory (FcgammaRIIB) antibody receptors on myeloid cells, thus modulating their cytotoxic potential. Mice deficient in FcgammaRIIB showed much more antibody-dependent cell-mediated cytotoxicity; in contrast, mice deficient in activating Fc receptors as well as antibodies engineered to disrupt Fc binding to those receptors were unable to arrest tumor growth in vivo. These results demonstrate that Fc-receptor-dependent mechanisms contribute substantially to the action of cytotoxic antibodies against tumors and indicate that an optimal antibody against tumors would bind preferentially to activation Fc receptors and minimally to the inhibitory partner FcgammaRIIB.     

The metal ion binding properties of calreticulin modulate its conformational flexibility and thermal stability

Calreticulin (CRT) is a soluble chaperone involved in the conformational maturation of glycoproteins in the endoplasmic reticulum. Using biochemical and biophysical techniques including circular dichroism, proteolysis, and analytical ultracentrifugation, we have determined the effects of calcium and zinc ions on the structural properties of human CRT. Circular dichroism analysis has shown that the binding of calcium and zinc ions to CRT induces no significant changes in the secondary structure of the protein but affects in very distinct ways the local tertiary packing of these elements. More specifically, these studies have revealed that CRT adopts a more rigid and thermally stable structure upon binding calcium ions and a more loosely packed and thermally destabilized structure upon binding zinc ions. Consistent with these results, proteolysis experiments demonstrated that the intrinsic conformational flexibility of CRT can be modulated toward either a decrease or an increase in susceptibility to cleavage by chymotrypsin upon binding calcium or zinc ions, respectively. Results from sedimentation analysis indicated that the global three-dimensional structure of CRT is essentially unchanged upon binding calcium ions. In marked contrast, CRT self-associates reversibly to form dimers upon binding zinc ions. Collectively, our results provide evidence that calcium and zinc ions induce strikingly different changes in the biochemical and structural properties of CRT.     

Endogenous factors that modulate yeast glucan synthetase in cell-free extracts

Yeast 1,3-beta-D-glucan synthetase (EC 2.4.1.34) activity is modulated by endogenous factors obtained by the extraction of different subcellular fractions with hot water. Cell wall fractions were enriched in activators while supernatant fractions also contained appreciable amounts of inhibitors. The action of these compounds requires the presence of EDTA. Maximal activation by the stimulatory material was reached when assayed in sonicated enzymatic preparations that had been obtained by mechanical breakage of cells in water. The activating material derived from cell wall fractions contained a mixture of low molecular weight compounds. They were found to be different from GTP as deduced from their resistance to alkaline phosphatase and different elution profile in gel filtration. The supernatant material was also heterogeneous with regard to both activators and inhibitors. The combined effect of GTP and activating material derived from cell wall fractions was supraadditive. The polymers synthesized in the absence and in the presence of the endogenous activator were characterized as beta-1,3-glucans on the base of their resistance to periodate and susceptibility to beta-glucanases. However, the length of the radioactive chains was greater when synthesized in the presence of the activator. This was mediated by an increase in the Vmax of the synthetase.