Four A6-TCR/peptide/HLA-A2 structures that generate very different T cell signals are nearly identical

The interactions of three singly substituted peptide variants of the HTLV-1 Tax peptide bound to HLA-A2 with the A6 T cell receptor have been studied using T cell assays, kinetic and thermodynamic measurements, and X-ray crystallography. The three peptide/MHC ligands include weak agonists and antagonists with different affinities for TCR. The three-dimensional structures of the three A6-TCR/peptide/HLA-A2 complexes are remarkably similar to each other and to the wild-type agonist complex, with minor adjustments at the interface to accommodate the peptide substitutions (P6A, V7R, and Y8A). The lack of correlation between structural changes and the type of T cell signals induced provides direct evidence that different signals are not generated by different ligand-induced conformational changes in the alphabeta TCR.

Activation of protease-activated receptor (PAR)-1, PAR-2, and PAR-4 stimulates IL-6, IL-8, and prostaglandin E2 release from human respiratory epithelial cells

Epithelia from many tissues express protease-activated receptors (PARs) that play a major role in several different physiological processes. In this study, we examined their capacity to modulate IL-6, IL-8, and PGE(2) production in both the A459 and BEAS-2B cell lines and primary human bronchial epithelial cells (HBECs). All three cell types expressed PAR-1, PAR-2, PAR-3, and PAR-4, as judged by RT-PCR and immunocytochemistry. Agonist peptides corresponding to the nascent N termini of PAR-1, PAR-2, and PAR-4 induced the release of cytokines from A549, BEAS-2B, and HBECs with a rank order of potency of PAR-2 > PAR-4 > PAR-1 at 400 microM. PAR-1, PAR-2, and PAR-4 also caused the release of PGE(2) from A549 and HBECs. The PAR-3 agonist peptide was inactive in all systems tested. PAR-1, PAR-2, or PAR-4, in combination, caused additive IL-6 release, but only the PAR-1 and PAR-2 combination resulted in an additive IL-8 response. PAR peptide-induced responses were accompanied by changes in intracellular calcium ion concentrations. However, Ca(2+) ion shutoff was approximately 2-fold slower with PAR-4 than with PAR-1 or PAR-2, suggesting differential G protein coupling. Combined, these data suggest an important role for PAR in the modulation of inflammation in the lung.

House dust mite allergens induce proinflammatory cytokines from respiratory epithelial cells: the cysteine protease allergen, Der p 1, activates protease-activated receptor (PAR)-2 and inactivates PAR-1

In previous studies, we demonstrated that allergenic house dust mite proteases are potent inducers of proinflammatory cytokines from the respiratory epithelium, although the precise mechanisms involved were unclear. In this study, we investigated whether this was achieved through activation of protease-activated receptor (PAR)-1 or -2. Pretreatment of A549 respiratory epithelial cells with the clinically important cysteine protease allergen, Der p 1, ablated subsequent PAR-1, but not PAR-2 agonist peptide-induced IL-6 and IL-8 release. HeLa cells transfected with the plasmid coding for PAR-2, in contrast to PAR-1, released significant concentration of IL-6 after exposure to Der p 1. Exposure of HeLa cells transfected with either PAR-1/enhanced yellow fusion protein or PAR-2/enhanced yellow fusion protein to Der p 1 caused receptor internalization in the latter cells only, as judged by confocal microscopy with re-expression of the receptor within 120-min postenzyme exposure. Der p 1-induced cytokine release from both A549 and transfected HeLa cells was accompanied by changes in intracellular Ca(2+) concentrations. Desensitization studies showed that Der p 1 pretreatment of the A549 cells resulted in the abolition of both trypsin- and PAR-2 agonist peptide-induced Ca(2+) release, but not that induced by subsequent exposure to either thrombin or PAR-1 agonist peptide. These data indicate for the first time that the house dust mite allergen Der p 1-induced cytokine release from respiratory epithelial cells is, in part, mediated by activation of PAR-2, but not PAR-1.

Spatial and temporal dynamics of T cell receptor signaling with a photoactivatable agonist

The precise timing of signals downstream of the T cell receptor (TCR) is poorly understood. To address this problem, we prepared major histocompatibility complexes containing an antigenic peptide that is biologically inert until exposed to ultraviolet (UV) light. UV irradiation of these complexes in contact with cognate T cells enabled the high-resolution temporal analysis of signaling. Phosphorylation of the LAT adaptor molecule was observed in 4 s, and diacylglycerol production and calcium flux was observed in 6-7 s. TCR activation also induced cytoskeletal polarization within 2 min. Antibody blockade of CD4 reduced the intensity of LAT phosphorylation and the speed of calcium flux. Furthermore, strong desensitization of diacylglycerol production, but not LAT phosphorylation, occurred shortly after TCR activation, suggesting that different molecular events play distinct signal-processing roles. These results establish the speed and localization of early signaling steps, and have important implications regarding the overall structure of the network.

Interleukin-6 production by endothelial cells via stimulation of protease-activated receptors is amplified by endotoxin and tumor necrosis factor-alpha

Human endothelial cells respond to extracellular proteases, endotoxin (lipopolysaccharide, LPS), and inflammatory cytokines. Endothelial cells express several protease-activated receptors (PAR), including the thrombin-activated receptors PAR-1 and PAR-3 and a thrombin-independent, protease-activated receptor, PAR-2. To examine the potential cooperation between PAR and inflammatory stimuli, we investigated the effects of the PAR-1 agonist peptide Ser-Phe-Leu-Leu-Arg-Asn (SFLLRN) and PAR-2 agonist peptide Ser-Leu-Ile-Gly-Lys-Val (SLIGKV) on endothelial cells. Human umbilical vein endothelial cells (HUVEC) were cultured in vitro with SFLLRN or SLIGKV in the presence and absence of LPS or tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) levels in the culture supernatants were assayed. Both SFLLRN and SLIGKV induced detectable levels of IL-6 production in a dose-dependent fashion, with the PAR-1 receptor agonist being more potent. In the presence of all stimulatory concentrations of LPS or TNF-alpha tested, both peptides were found to further enhance IL-6 production. The effects of SFLLRN and SLIGKV were specific, as related peptides with identical amino acid compositions, but lacking in consensus sequences, were biologically inactive either alone or in the presence of LPS. Both the direct and the amplifying effects of PAR agonist peptides on IL-6 production were pertussis toxin sensitive and caused an increase in the intracellular levels of calcium, implicating G-proteins and calcium mobilization in these pathways. Furthermore, the amplifying effect of LPS or TNF-alpha on PAR-mediated cytokine production was associated with corresponding increases in nuclear NF-kappaB proteins. The results demonstrate significant potentiation of PAR-induced signaling by LPS and TNF-alpha and indicate the potential cooperation of proteases and inflammatory stimuli in amplifying vascular inflammation.

CD28, Ox-40, LFA-1, and CD4 modulation of Th1/Th2 differentiation is directly dependent on the dose of antigen

The involvement of specific accessory/costimulatory molecules in differentiation to Th1 and Th2 phenotypes is controversial. Reports suggest that molecules such as CD4, CD28, and Ox-40 support Th2 differentiation and suppress Th1 differentiation, whereas others such as LFA-1 support Th1 responses and suppress Th2 responses. We have previously defined an in vitro model of differentiation that is absolutely dependent on the initial dose and affinity of peptide presented to a naive CD4 cell. The dose and affinity of Ag regulate autocrine production of IL-2, IL-4, and IFN-gamma, which in turn govern differentiation to Th1 and Th2 phenotypes. We have used this system to confirm that CD4, CD28, and Ox-40 interactions can promote, and LFA-1 interactions can suppress, differentiation of cells secreting the Th2 cytokines IL-5 and IL-13. However, for CD4 and LFA-1, this is only seen over a certain range of peptide doses. In addition, CD28 and Ox-40 interactions also promote Th1 differentiation. In general, agonist Abs to accessory molecules shifted the response curves for IFN-gamma, IL-5, and IL-13 to lower doses, whereas antagonist reagents resulted in similar curves shifted toward the higher doses. We conclude that ligation of cell surface accessory receptors enables low doses of Ag to promote responses normally induced only by higher doses. Individual receptors do not intrinsically regulate one cytokine phenotype or another, suggesting that differentiation is controlled by the level of expression of multiple accessory molecule pairs integrated with the number and affinity of peptide/MHC complexes.

Human peptidoglycan recognition proteins require zinc to kill both gram-positive and gram-negative bacteria and are synergistic with antibacterial peptides

Mammals have four peptidoglycan recognition proteins (PGRPs or PGLYRPs), which are secreted innate immunity pattern recognition molecules with effector functions. In this study, we demonstrate that human PGLYRP-1, PGLYRP-3, PGLYRP-4, and PGLYRP-3:4 have Zn(2+)-dependent bactericidal activity against both Gram-positive and Gram-negative bacteria at physiologic Zn(2+) concentrations found in serum, sweat, saliva, and other body fluids. The requirement for Zn(2+) can only be partially replaced by Ca(2+) for killing of Gram-positive bacteria but not for killing of Gram-negative bacteria. The bactericidal activity of PGLYRPs is salt insensitive and requires N-glycosylation of PGLYRPs. The LD(99) of PGLYRPs for Gram-positive and Gram-negative bacteria is 0.3-1.7 muM, and killing of bacteria by PGLYRPs, in contrast to killing by antibacterial peptides, does not involve permeabilization of cytoplasmic membrane. PGLYRPs and antibacterial peptides (phospholipase A(2), alpha- and beta-defensins, and bactericidal permeability-increasing protein), at subbactericidal concentrations, synergistically kill Gram-positive and Gram-negative bacteria. These results demonstrate that PGLYRPs are a novel class of recognition and effector molecules with broad Zn(2+)-dependent bactericidal activity against both Gram-positive and Gram-negative bacteria that are synergistic with antibacterial peptides.

Single-cell analyses reveal two defects in peptide-specific activation of naive T cells from aged mice

Confocal fluorescent microscopy was used to study redistribution of membrane-associated proteins in naive T cells from young and old mice from a transgenic stock whose T cells express a TCR specific for a peptide derived from pigeon cytochrome C. About 50% of the T cells from young mice that formed conjugates with peptide-pulsed APC were found to form complexes, at the site of binding to the APC, containing CD3epsilon, linker for activation of T cells (LAT), and Zap-70 in a central area and c-Cbl, p95(vav), Grb-2, PLC gamma, Fyn, and Lck distributed more uniformly across the interface area. Two-color staining showed that those cells that were able to relocalize c-Cbl, LAT, CD3epsilon, or PLC gamma typically relocalized all four of these components of the activation complex. About 75% of conjugates that rearranged LAT, c-Cbl, or PLC gamma also exhibited cytoplasmic NF-AT migration to the T cell nucleus. Aging had two effects. First, it led to a diminution of approximately 2-fold in the proportion of T cell/APC conjugates that could relocalize any of the nine tested proteins to the immune synapse. Second, aging diminished by approximately 2-fold the frequency of cytoplasmic NF-AT migration among cells that could generate immune synapses containing LAT, c-Cbl, or PLC gamma. Thus naive CD4 T cells from old mice exhibit at least two separable defects in the earliest stages of activation induced by peptide/MHC complexes.

SH2 and SH3 domains: potential targets for anti-cancer drug design

Protein-tyrosine kinases interact with a diverse group of signaling molecules that share common structural elements known as Src homology 2 and 3 (SH2 and SH3) domains. SH2 domains bind with high affinity to peptide sequences within target proteins that contain phosphorylated tyrosine residues, but have no affinity for the unphosphorylated sequence. This property allows activated tyrosine kinases to initiate signal transduction by recruiting downstream effectors with SH2 domains. SH3 domains also mediate protein-protein interaction. Target sequences for SH3 domains are rich in proline and hydrophobic amino acids, but do not require phosphorylation. SH2- and SH3-mediated protein-protein interactions are required for the transmission of proliferative signals initiated by tyrosine kinases (e.g., Ras activation or stimulation of phosphatidylinositol-3' kinase activity). Peptidomimetic ligands based on the sequence of target proteins for SH2 and SH3 domains may represent new lead compounds for the therapy of proliferative diseases that are dependent upon constitutively activated tyrosine kinases (e.g., BCR/ABL in chronic myelogenous and acute lymphocytic leukemias or HER-2/Neu in breast and ovarian cancer.

Peptide therapeutics for CNS indications

Neuropeptides play a crucial role in the normal function of the central nervous system and peptide receptors hold great promise as therapeutic targets for the treatment of several CNS disorders. In general, the development of peptide therapeutics has been limited by the lack of drug-like properties of peptides and this has made it very difficult to transform them into marketable therapeutic molecules. Some of these challenges include poor in vivo stability, poor solubility, incompatibility with oral administration, shelf stability, cost of manufacture. Recent technical advances have overcome many of these limitations and have led to rapid growth in the development of peptides for a wide range of therapeutic indications such as diabetes, cancer and pain. This review examines the therapeutic potential of peptide agonists for the treatment of major CNS disorders such as schizophrenia, anxiety, depression and autism. Both clinical and preclinical data has been accumulated supporting the potential utility of agonists at central neurotensin, cholecystokinin, neuropeptide Y and oxytocin receptors. Some of the successful approaches that have been developed to increase the stability and longevity of peptides in vivo and improve their delivery are also described and potential strategies for overcoming the major challenge that is unique to CNS therapeutics, penetration of the blood-brain barrier, are discussed.

Inhibition of experimental allergic airways disease by local application of a cell-penetrating dominant-negative STAT-6 peptide

Allergic airways disease is initiated and perpetuated by an aberrant Th2 inflammatory response regulated in part by the cytokines IL-4 and IL-13, each of which induces activation of the STAT-6 transcription factor. Data from murine models indicate that the clinical manifestations of acute asthma are STAT-6 dependent, and thus, STAT-6 is a target for drug development in allergic airways disease. We designed a novel chimeric peptide (STAT-6 inhibitory peptide (STAT-6-IP)) comprised of a sequence predicted to bind to and inhibit STAT-6, fused to a protein transduction domain, to facilitate cellular uptake of the STAT-6-binding peptide. Our data demonstrate that the STAT-6-IP inhibited OVA-induced production of Th2 cytokines IL-4 and IL-13 in vitro. In contrast, the STAT-6-IP did not affect production of IFN-gamma, demonstrating specificity for Th2 cytokine inhibition. Following intranasal administration, the STAT-6-IP was localized to epithelial cells in the airways. Finally, in in vivo murine models of allergic rhinitis and asthma, intranasal delivery of the STAT-6-IP inhibited OVA-induced lung inflammation and mucus production as well as accumulation of eosinophils and IL-13 in bronchoalveolar lavage fluid and OVA-dependent airway hyperresponsiveness. Together these data show that local application of cell-penetrating peptide inhibitors of STAT-6 has significant potential for the treatment of allergic rhinitis and asthma.

Peptide YY derivatives as selective neuropeptide Y/peptide YY Y1 and Y2 agonists devoided of activity for the Y3 receptor sub-type

Peptide YY derivatives were evaluated for their respective ability to bind and activate the NPY/PYY receptor sub-types (Y1, Y2 and Y3) present in various preparations. The analogue [Leu31,Pro34]PYY demonstrated high (nM) affinity in rat frontoparietal cortical membrane preparations (Y1-enriched tissue) and the rabbit saphenous vein (Y1 in vitro bioassay) but only low affinity in a Y2-enriched preparation (rat hippocampus). In contrast, PYY C-terminal fragments such as PYY3-36 and PYY13-36 were more potent in Y2 than Y1 assays. Interestingly, and in contrast to [Leu31,Pro34]NPY and NPY13-36, the PYY derivatives [Leu31,Pro34]PYY and PYY3-36 were inactive in a purported Y3 bioassay (rat colon). These results suggest that [Leu31,Pro34]PYY and PYY3-36 respectively represent the first selective and potent Y1 and Y2 agonists, devoided of significant affinity/activity for the Y3 receptor class.

Peptide agonist docking in the N-terminal ectodomain of a class II G protein-coupled receptor, the VPAC1 receptor. Photoaffinity, NMR, and molecular modeling

The neuropeptide vasoactive intestinal peptide (VIP) strongly impacts on human pathophysiology and does so through interaction with class II G protein-coupled receptors named VIP pituitary adenylate cyclase-activating peptide (PACAP) receptors (VPACs). The molecular nature of VIP binding to receptors remains elusive. In this work, we have docked VIP in the human VPAC1 receptor by the following approach. (i) VIP probes containing photolabile residues in positions 6, 22, and 24 of VIP were used to photolabel the receptor. After receptor cleavage and Edman sequencing of labeled receptor fragments, it was shown that Phe6, Tyr22, and Asn24 of VIP are in contact with Asp107, Gly116, and Cys122 in the N-terminal ectodomain (N-ted) of the receptor, respectively. (ii) The structure of VIP was determined by NMR showing a central alpha helix, a disordered N-terminal His1-Phe6 segment and a 3(10) Ser25-Asn28 helix termination. (iii) A three-dimensional model of the N-ted of hVPAC1 was constructed by using the NMR structure of the N-ted of corticotropin-releasing factor receptor 2beta as a template. As expected, the fold is identified as a short consensus repeat with two antiparallel beta sheets and is stabilized by three disulfide bonds. (iv) Taking into account the constraints provided by photoaffinity, VIP was docked into the hVPAC1 receptor N-ted. The 6-28 fragment of VIP nicely lies in the N-ted C-terminal part, but the N terminus region of VIP is free for interacting with the receptor transmembrane region. The data provide a structural rationale to the proposed two-step activation mechanism of VPAC receptor and more generally of class II G protein-coupled receptors.

Dihydromunduletone Is a Small-Molecule Selective Adhesion G Protein-Coupled Receptor Antagonist

Adhesion G protein-coupled receptors (aGPCRs) have emerging roles in development and tissue maintenance and is the most prevalent GPCR subclass mutated in human cancers, but to date, no drugs have been developed to target them in any disease. aGPCR extracellular domains contain a conserved subdomain that mediates self-cleavage proximal to the start of the 7-transmembrane domain (7TM). The two receptor protomers, extracellular domain and amino terminal fragment (NTF), and the 7TM or C-terminal fragment remain noncovalently bound at the plasma membrane in a low-activity state. We recently demonstrated that NTF dissociation liberates the 7TM N-terminal stalk, which acts as a tethered-peptide agonist permitting receptor-dependent heterotrimeric G protein activation. In many cases, natural aGPCR ligands are extracellular matrix proteins that dissociate the NTF to reveal the tethered agonist. Given the perceived difficulty in modifying extracellular matrix proteins to create aGPCR probes, we developed a serum response element (SRE)-luciferase-based screening approach to identify GPR56/ADGRG1 small-molecule inhibitors. A 2000-compound library comprising known drugs and natural products was screened for GPR56-dependent SRE activation inhibitors that did not inhibit constitutively active Gα13-dependent SRE activation. Dihydromunduletone (DHM), a rotenoid derivative, was validated using cell-free aGPCR/heterotrimeric G protein guanosine 5'-3-O-(thio)triphosphate binding reconstitution assays. DHM inhibited GPR56 and GPR114/ADGRG5, which have similar tethered agonists, but not the aGPCR GPR110/ADGRF1, M3 muscarinic acetylcholine, or β2 adrenergic GPCRs. DHM inhibited tethered peptide agonist-stimulated and synthetic peptide agonist-stimulated GPR56 but did not inhibit basal activity, demonstrating that it antagonizes the peptide agonist. DHM is a novel aGPCR antagonist and potentially useful chemical probe that may be developed as a future aGPCR therapeutic.

NCAM 180 acting via a conserved C-terminal domain and MLCK is essential for effective transmission with repetitive stimulation

NCAM 180 isoform null neuromuscular junctions are unable to effectively mobilize and exocytose synaptic vesicles and thus exhibit periods of total transmission failure during high-frequency repetitive stimulation. We have identified a highly conserved C-terminal (KENESKA) domain on NCAM that is required to maintain effective transmission and demonstrate that it acts via a pathway involving MLCK and probably myosin light chain (MLC) and myosin II. By perfecting a method of introducing peptides into adult NMJs, we tested the hypothesized role of proteins in this pathway by competitive disruption of protein-protein interactions. The effects of KENESKA and other peptides on MLCK and MLC activation and on failures in both wild-type and NCAM 180 null junctions supported this pathway, and serine phosphorylation of KENESKA was critical. We propose that this pathway is required to replenish synaptic vesicles utilized during high levels of exocytosis by facilitating myosin-driven delivery of synaptic vesicles to active zones or their subsequent exocytosis.

Differential TCR signaling regulates apoptosis and immunopathology during antigen responses in vivo

Clonal selection theories postulate that lymphocyte fate is regulated by antigen receptor specificity. However, lymphocyte apoptosis is induced through nonantigen-specific receptors such as Fas (CD95/APO-1) or TNFR. We define a selective TCR that controls apoptosis by Fas or TNFR stimulation. Variant ligands can deliver this "competence to die" signal without the full TCR signals necessary for cytokine synthesis. These partial agonists regulate T cell deletion in vivo even when Fas or TNF is provided by T cells of unrelated specificity, but they do not cause the liver necrosis that is associated with T cell elimination by the full agonist. Thus, selective signaling ligands regulate T cell deletion and immune damage in vivo and may be important for peripheral T cell tolerance.

gamma-Conotoxin-PnVIIA, a gamma-carboxyglutamate-containing peptide agonist of neuronal pacemaker cation currents

A novel gamma-carboxyglutamate-containing peptide, designated gamma-conotoxin-PnVIIA, is described from the venom of the molluscivorous snail Conus pennaceus. gamma PnVIIA, triggers depolarization and firing of action potential bursts in the caudodorsal neurons of Lymnaea. This effect is due to activation or enhancement of a slow inward cation current that may underly endogenous bursting activity of these neurons. The amino acid sequence of gamma PnVIIA was determined as DCTSWFGRCTVNS gamma CCSNSCDQTYC gamma-LYAFOS (where gamma is gamma-carboxyglutamate, O is trans-4-hydroxyproline), thus gamma PnVIIA belongs to the six cysteine four loop structural family of conotoxins, and is most homologous to the previously described excitatory conotoxin-TxVIIA. Interestingly, TxVIIA did not induce action potentials in Lymnaea caudodorsal neurons. gamma PnVIIA is the prototype of a new class of gamma-conotoxins that will provide tools for the study of voltage-gated pacemaker channels, which underly bursting processes in excitable systems.

TCR signaling for initiation and completion of thymocyte positive selection has distinct requirements for ligand quality and presenting cell type

Thymocyte selection involves signaling by TCR engaging diverse self-peptide:MHC molecule ligands on various cell types in the cortex and medulla. Here we separately analyze early and late stages of selection to better understand how presenting cell type, ligand quality, and the timing of TCR signaling contribute to intrathymic differentiation. TCR transgenic CD4+CD8+ thymocytes (double positive (DP)) from MHC-deficient mice were stimulated using various presenting cells and ligands. The resulting CD69high cells were isolated and evaluated for maturation in reaggregate cultures with wild-type or MHC molecule-deficient thymic stroma with or without added hemopoietic dendritic cells (DC). Production of CD4+ T cells required TCR signaling in the reaggregates, indicating that transient recognition of self-ligands by DP is inadequate for full differentiation. DC bearing a potent agonist ligand could initiate positive selection, producing activated thymocytes that matured into agonist-responsive T cells in reaggregates lacking the same ligand. DC could also support the TCR signaling necessary for late maturation. These results argue that despite the negative role assigned to DC in past studies, neither the peptide:MHC molecule complexes present on DC nor any other signals provided by these cells stimulate only thymocyte death. These findings also indicate that unique epithelial ligands are not necessary for positive selection. They provide additional insight into the role of ligand quality in selection events and support the concept that following initiation of maturation from the DP state, persistent TCR signaling is characteristic of and perhaps required by T cells.

Discovery of a novel thrombopoietin mimic agonist peptide

A random phage peptide library was constructed for the filamentous bacteriophage fuse5. The library was made by inserting a degenerate oligonucleotide which encodes 15 variable amino acids into the NH2-terminal region of the phage gene III protein. This library, containing 1x10(9) different phages, was screened with a human immunoglobulin fusion protein containing the extracellular region of human thrombopoietin receptor. Several phages were isolated following four cycles of enrichment and amplification. These phages specifically bound to the fusion protein. One phage peptide acted as an agonist of the thrombopoietin receptor, since it stimulated the proliferation of thrombopoietin-dependent cells and the differentiation of mouse bone marrow cells to megakaryocytes. The amino acid sequence of this peptide is not present in the primary amino acid sequence of thrombopoietin. This discovery may lead to the design of a small-molecular mimic of thrombopoietin.

Calmodulin-independent, agonistic properties of a peptide containing the calmodulin binding site of estrogen receptor alpha

Calmodulin (CaM) contributes to estrogen receptor alpha (ER)-mediated transcription. In order to study the underlying mechanisms, we synthesized a peptide including the CaM binding site: ERalpha17p (P(295)-T(311)). This peptide inhibited ER-CaM association, unlike two analogs in which two amino acids required for CaM binding were substituted. Exposure of MCF-7 cells to ERalpha17p down regulated ER, stimulated ER-dependent transcription and enhanced the proliferation of ER-positive breast cancer cell lines. Interestingly, ERalpha17p analogs unable to bind to CaM induced similar responses, demonstrating that ERalpha17p-mediated effects are mainly relevant to mechanisms independent of ER-CaM dissociation. The P(295)-T(311) motif is indeed a platform for multiple post-translational modifications not necessarily CaM-dependent. The additional finding that deletion of the P(295)-T(311) sequence in ER produced a constitutive transcriptional activity revealed that this platform motif has autorepressive functions. With regard to cell function, association of CaM to ER would counteract this autorepression, leading thereby to enhanced ER-mediated transactivation.

Tethered ligand library for discovery of peptide agonists

We exploited the mechanism underlying thrombin receptor activation to develop a novel screening method to identify peptide agonists. The thrombin receptor is activated by limited proteolysis of its amino-terminal exodomain. Thrombin cleaves this domain to unmask a new amino terminus, which then functions as a tethered peptide agonist, binding intramolecularly to the body of the receptor to trigger signaling. The thrombin receptor's amino-terminal exodomain can also donate the tethered agonist intermolecularly to activate nearby thrombin receptors. We utilized this ability by co-expressing a "tethered ligand library," which displayed the thrombin receptor's amino-terminal exodomain bearing random pentapeptides in place of the native tethered ligand together with target receptors in Xenopus oocytes. Clones that conferred thrombin-dependent signaling by intermolecular ligation of the target receptor were isolated by sib selection. Agonists for the thrombin receptor itself (GFIYF) and for the formyl peptide receptor (MMWLL) were identified. Surprisingly, the latter agonist was quite active at the formyl peptide receptor even without N-formylation, and its formylated form, fMMWLL, was more potent than the classical formyl peptide receptor agonist fMLF. In addition to identifying novel peptide agonists for targets of pharmacological interest, this method might be used to discover agonists for orphan receptors. It also suggests a possible evolutionary path from peptide to protease-activated receptors.

Amino acids that specify structure through hydrophobic clustering and histidine-aromatic interactions lead to biologically active peptidomimetics

Acyclic beta-sheet structure can be nucleated in heptapeptides when the 4-(2-aminoethyl)-6-dibenzofuranpropanoic acid residue (1) is flanked in sequence by two His residues, a His residue and a hydrophobic residue or by two hydrophobic residues. Acyclic beta-sheet peptidomimetics having an appropriate sequence have sufficient structural integrity to exhibit antimicrobial activity equivalent to that of gramicidin S.

The CD8 beta polypeptide is required for the recognition of an altered peptide ligand as an agonist

T cell activation is triggered by the specific recognition of cognate peptides presented by MHC molecules. Altered peptide ligands are analogs of cognate peptides which have a high affinity for MHC molecules. Some of them induce complete T cell responses, i.e. they act as agonists, whereas others behave as partial agonists or even as antagonists. Here, we analyzed both early (intracellular Ca2+ mobilization), and late (interleukin-2 production) signal transduction events induced by a cognate peptide or a corresponding altered peptide ligand using T cell hybridomas expressing or not the CD8 alpha and beta chains. With a video imaging system, we showed that the intracellular Ca2+ response to an altered peptide ligand induces the appearance of a characteristic sustained intracellular Ca2+ concentration gradient which can be detected shortly after T cell interaction with antigen-presenting cells. We also provide evidence that the same altered peptide ligand can be seen either as an agonist or a partial agonist, depending on the presence of CD8beta in the CD8 co-receptor dimers expressed at the T cell surface.

Central pre-proglucagon derived peptides: opportunities for treatment of obesity

Modern societies have moved from famine to feast and obesity and its co-morbidities now sweep the world as a global epidemic. Numerous scientific laboratories and pharmaceutical companies have taken the challenge and are now exploiting novel molecular targets for treatment of obesity. The pre-proglucagon system constitutes interesting candidates as potential targets for new anti-obesity drugs. In the periphery, pre-proglucagon derived peptides, Glucagon-Like Peptide-1 (GLP-1), Glucagon-Like Peptide-2 (GLP-2) and oxyntomodulin (OXM) are involved in a wide variety of physiological functions, including glucose homeostasis, gastric emptying, intestinal growth, insulin secretion as well as the regulation of food intake. Peripheral administration of GLP-1 derivatives and analogues to both rodents and man have shown promising effects on food intake and body weight suggesting that such therapies constitute potential anti-obesity treatment. In the central nervous system, pre-proglucagon and hence GLP-1, GLP-2 and OXM are exclusively found in a small population of nerve cells in the nucleus of the solitary tract. These constitute a neural pathway linking the "viscero-sensory" brainstem to hypothalamic nuclei involved in energy homeostasis. Intracerebroventricular administration of all of the three derived peptides robustly decrease food intake. It is evident that central GLP-1 agonism probably in combination with GLP-2 and/or OXM agonism constitute a potential pharmacological tool to reduce food intake and maybe also enhance energy expenditure. This and other aspects of the current state of the role of central pre-proglucagon in energy homeostasis are reviewed.

Partial activation of human T cells by peptide analogs on live APC: induction of clonal anergy associated with protein tyrosine dephosphorylation

T-cell clonal anergy induced by peptide analogs in the presence of live APC in murine systems was reported to be associated with incomplete tyrosine phosphorylation of the CD3 zeta chain followed by a lack of subsequent ZAP-70 recruitment. Furthermore, protein tyrosine phosphatase SHP-1 was associated with ZAP-70 upon T-cell activation, leading to a dominant negative signaling. In this study, we used nonself BCGa-specific human ThO clones and investigated the antagonistic/partial agonistic activities of one-residue-substituted analog peptides. The results showed that (a) certain one-residue-substituted analogs can partially activate T cells to produce lymphokines, without proliferation; (b) a peptide with a conservative one-residue substitution can induce T-cell anergy in the presence of live APC, but T cells are capable of responding to exogenously added IL-2; and (c) the induction of anergy is accompanied by marked dephosphorylation of a 110-kDa protein, without either upregulation of CD25 or any changes in CD3 zeta phosphorylation patterns, suggesting that TCR-mediated dominant negative signaling through phosphatase(s) in another mechanism that may lead to the induction of T-cell clonal anergy by altered TCR ligands.