Molecular evidence for multiple origins of Insectivora and for a new order of endemic African insectivore mammals

The traditional views regarding the mammalian order Insectivora are that the group descended from a single common ancestor and that it is comprised of the following families: Soricidae (shrews), Tenrecidae (tenrecs), Solenodontidae (solenodons), Talpidae (moles), Erinaceidae (hedgehogs and gymnures), and Chrysochloridae (golden moles). Here we present a molecular analysis that includes representatives of all six families of insectivores, as well as 37 other taxa representing marsupials, monotremes, and all but two orders of placental mammals. These data come from complete sequences of the mitochondrial 12S rRNA, tRNA-Valine, and 16S rRNA genes (2.6 kb). A wide range of different methods of phylogenetic analysis groups the tenrecs and golden moles (both endemic to Africa) in an all-African superordinal clade comprised of elephants, sirenians, hyracoids, aardvark, and elephant shrews, to the exclusion of the other four remaining families of insectivores. Statistical analyses reject the idea of a monophyletic Insectivora as well as traditional concepts of the insectivore suborder Soricomorpha. These findings are supported by sequence analyses of several nuclear genes presented here: vWF, A2AB, and alpha-beta hemoglobin. These results require that the order Insectivora be partitioned and that the two African families (golden moles and tenrecs) be placed in a new order. The African superordinal clade now includes six orders of placental mammals.

Binding and functional properties of recombinant and endogenous CXCR3 chemokine receptors

IP10 and MIG are two members of the CXC branch of the chemokine superfamily whose expression is dramatically up-regulated by interferon (IFN)-gamma. The proteins act largely on natural killer (NK)-cells and activated T-cells and have been implicated in mediating some of the effects of IFN-gamma and lipopolysaccharides (LPSs), as well as T-cell-dependent anti-tumor responses. Recently both chemokines have been shown to be functional agonists of the same G-protein-coupled receptor, CXCR3. We now report the pharmacological characterization of CXCR3 and find that, when heterologously expressed, CXCR3 binds IP10 and MIG with Ki values of 0.14 and 4.9 nM, respectively. The receptor has very modest affinity for SDF-1alpha and little or no affinity for other CXC-chemokines. The properties of the endogenous receptor expressed on activated T-cells are similar. Surprisingly, several CC-chemokines, particularly eotaxin and MCP-4, also compete with moderate affinity for the binding of IP10 to CXCR3. Eotaxin does not activate CXCR3 but, in CXCR3-transfected cells, can block IP10-mediated receptor activation. Eotaxin, therefore, may be a natural CXCR3 antagonist.

Highly congruent molecular support for a diverse superordinal clade of endemic African mammals

A solution to higher level mammalian phylogeny is going to depend on the congruent establishment of superordinal groupings followed by a linking together of these clades. We present congruent and convincing evidence from four disparate nuclear protein coding genes and from a tandem alignment of the 12S-16S mitochondrial region, for a superordinal clade of endemic African mammals that includes elephant shrews, aardvarks, golden mole, elephants, sirenians, and hyraxes. Because of strong support for golden mole as part of this clade, the Insectivora are rendered paraphyletic or polyphyletic, with constrained monophyly of the insectivores judged significantly worse in the vast majority of tests. Branching arrangement within this clade remains highly uncertain; however, a tandem alignment of the protein coding genes suggests elephant shrew is the earliest African lineage. None of the individual data sets or combinations of data sets support the widely held view of a mirorder Tethytheria (Sirenia/Proboscidea), although only a tandem alignment of protein coding and mitochondrial loci significantly rejects this association. The majority of the data sets and analyses provide strong support for Caviomorpha as part of a monophyletic Rodentia.

The interphotoreceptor retinoid binding protein gene in therian mammals: implications for higher level relationships and evidence for loss of function in the marsupial mole

The subclass Theria of Mammalia includes marsupials (infraclass Metatheria) and placentals (infraclass Eutheria). Within each group, interordinal relationships remain unclear. One limitation of many studies is incomplete ordinal representation. Here, we analyze DNA sequences for part of exon 1 of the interphotoreceptor retinoid binding protein gene, including 10 that are newly reported, for representatives of all therian orders. Among placentals, the most robust clades are Cetartiodactyla, Paenungulata, and an expanded African clade that includes paenungulates, tubulidentates, and macroscelideans. Anagalida, Archonta, Altungulata, Hyracoidea + Perissodactyla, Ungulata, and the "flying primate" hypothesis are rejected by statistical tests. Among marsupials, the most robust clade includes all orders except Didelphimorphia. The phylogenetic placement of the monito del monte and the marsupial mole remains unclear. However, the marsupial mole sequence contains three frameshift indels and numerous stop codons in all three reading frames. Given that the interphotoreceptor retinoid binding protein gene is a single-copy gene that functions in the visual cycle and that the marsupial mole is blind with degenerate eyes, this finding suggests that phenotypic degeneration of the eyes is accompanied by parallel changes at the molecular level as a result of relaxed selective constraints.

Enhanced expression of eotaxin and CCR3 mRNA and protein in atopic asthma. Association with airway hyperresponsiveness and predominant co-localization of eotaxin mRNA to bronchial epithelial and endothelial cells

Eotaxin is a newly discovered C-C chemokine which preferentially attracts and activates eosinophil leukocytes by acting specifically on its receptor CCR3. The airway inflammation characteristic of asthma is believed to be, at least in part, the result of eosinophil-dependent tissue injury. This study was designed to determine whether there is increased expression of eotaxin and CCR3 in the bronchial mucosa of asthmatics and whether this is associated with disease severity. The major sources of eotaxin and CCR3 mRNA were determined by co-localization experiments. Bronchial mucosal biopsy samples were obtained from atopic asthmatics and normal non-atopic controls. Eotaxin and CCR3 mRNA were identified in tissue sections by in situ hybridization (ISH) using radiolabeled riboprobes and their protein product visualized by immunohistochemistry (IHC). Co-localization experiments were performed by double ISH/IHC. Eotaxin and CCR3 (mRNA and protein) were significantly elevated in atopic asthmatics compared with normal controls. In the asthmatics there was a highly significant inverse correlation between eotaxin mRNA+ cells and the histamine provocative concentration causing a 20% fall in FEV1 (PC20). Cytokeratin-positive epithelial cells and CD31+ endothelial cells were the major source of eotaxin mRNA whereas CCR3 co-localized predominantly to eosinophils. These data are consistent with the hypothesis that damage to the bronchial mucosa in asthma involves secretion of eotaxin by epithelial and endothelial cells resulting in eosinophil infiltration mediated via CCR3. Since selective (eotaxin) and non-selective C-C chemokines such as RANTES, MCP-3 and MCP-4 all stimulate eosinophils via CCR3, this receptor is potentially a prime therapeutic target in the spectrum of diseases involving eosinophil-mediated tissue damage.

Endemic African mammals shake the phylogenetic tree

The order Insectivora, including living taxa (lipotyphlans) and archaic fossil forms, is central to the question of higher-level relationships among placental mammals. Beginning with Huxley, it has been argued that insectivores retain many primitive features and are closer to the ancestral stock of mammals than are other living groups. Nevertheless, cladistic analysis suggests that living insectivores, at least, are united by derived anatomical features. Here we analyse DNA sequences from three mitochondrial genes and two nuclear genes to examine relationships of insectivores to other mammals. The representative insectivores are not monophyletic in any of our analyses. Rather, golden moles are included in a clade that contains hyraxes, manatees, elephants, elephant shrews and aardvarks. Members of this group are of presumed African origin. This implies that there was an extensive African radiation from a single common ancestor that gave rise to ecologically divergent adaptive types. 12S ribosomal RNA transversions suggest that the base of this radiation occurred during Africa's window of isolation in the Cretaceous period before land connections were developed with Europe in the early Cenozoic era.

Blockade of the voltage-gated potassium channel Kv1.3 inhibits immune responses in vivo

The voltage activated K+ channel (Kv1.3) has recently been identified as the molecule that sets the resting membrane potential of peripheral human T lymphoid cells. In vitro studies indicate that blockage of Kv1.3 inhibits T cell activation, suggesting that Kv1.3 may be a target for immunosuppression. However, despite the in vitro evidence, there has been no in vivo demonstration that blockade of Kv1.3 will attenuate an immune response. The difficulty is due to species differences, as the channel does not set the membrane potential in rodent peripheral T cells. In this study, we show that the channel is present on peripheral T cells of miniswine. Using the peptidyl Kv1.3 inhibitor, margatoxin, we demonstrate that Kv1.3 also regulates the resting membrane potential, and that blockade of Kv1.3 inhibits, in vivo, both a delayed-type hypersensitivity reaction and an Ab response to an allogeneic challenge. In addition, prolonged Kv1.3 blockade causes reduced thymic cellularity and inhibits the thymic development of T cell subsets. These results provide in vivo evidence that Kv1.3 is a novel target for immunomodulation.

Blockade of the voltage-gated potassium channel Kv1.3 inhibits immune responses in vivo

The voltage activated K+ channel (Kv1.3) has recently been identified as the molecule that sets the resting membrane potential of peripheral human T lymphoid cells. In vitro studies indicate that blockage of Kv1.3 inhibits T cell activation, suggesting that Kv1.3 may be a target for immunosuppression. However, despite the in vitro evidence, there has been no in vivo demonstration that blockade of Kv1.3 will attenuate an immune response. The difficulty is due to species differences, as the channel does not set the membrane potential in rodent peripheral T cells. In this study, we show that the channel is present on peripheral T cells of miniswine. Using the peptidyl Kv1.3 inhibitor, margatoxin, we demonstrate that Kv1.3 also regulates the resting membrane potential, and that blockade of Kv1.3 inhibits, in vivo, both a delayed-type hypersensitivity reaction and an Ab response to an allogeneic challenge. In addition, prolonged Kv1.3 blockade causes reduced thymic cellularity and inhibits the thymic development of T cell subsets. These results provide in vivo evidence that Kv1.3 is a novel target for immunomodulation.

Old World fruitbat phylogeny: evidence for convergent evolution and an endemic African clade

Knud Andersen (1912, Catalogue of the Chiroptera in the Collections of the British Museum: I. Megachiroptera, British Museum of Natural History, London) divided Old World fruitbats (family Pteropodidae) into the rousettine, cynopterine, epomophorine, eonycterine, and notopterine sections. The latter two sections comprise the subfamily Macroglossinae; members of this subfamily exhibit specializations for nectarivory (e.g., elongated, protrusible, brushy tongues) and cluster together in cladistic analyses based on anatomical characters. Other evidence, including single-copy DNA hybridization, suggests that macroglossines are either paraphyletic or polyphyletic; this implies that adaptations for pollen and nectar feeding evolved independently in different macroglossine lineages or were lost in nonmacroglossines after evolving in a more basal common ancestor. Hybridization data also contradict Andersen's phylogeny in providing support for an endemic African clade that includes representatives of three of Andersen's sections. Here, we present complete mitochondrial 12S rRNA and valine tRNA gene sequences for 20 pteropodids, including representatives of all of Andersen's sections, and examine the aforementioned controversies. Maximum likelihood, minimum evolution, and maximum parsimony analyses all contradict macroglossine monophyly and provide support for an African clade that associates Megaloglossus and Lissonycteris and those two with Epomophorus. In conjunction with the DNA hybridization results, there are now independent lines of molecular evidence suggesting: (i) convergent evolution of specializations for nectarivory, at least in Megaloglossus versus other macroglossines, and (ii) a previously unrecognized clade of endemic Africa taxa. Estimates of divergence time based on 12S rRNA and DNA hybridization data are also in good agreement and suggest that extant fruitbats trace back to a common ancestor 25 million to 36 million years ago.

Secondary structure and patterns of evolution among mammalian mitochondrial 12S rRNA molecules

Forty-nine complete 12S ribosomal RNA (rRNA) gene sequences from a diverse assortment of mammals (one monotreme, 11 marsupials, 37 placentals), including 11 new sequences, were employed to establish a "core" secondary structure model for mammalian 12S rRNA. Base-pairing interactions were assessed according to the criteria of potential base-pairing as well as evidence for base-pairing in the form of compensatory mutations. In cases where compensatory evidence was not available among mammalian sequences, we evaluated evidence among other vertebrate 12S rRNAs. Our results suggest a core model for secondary structure in mammalian 12S rRNAs with deletions as well as additions to the Gutell (1994: Nucleic Acids Res. 22) models for Bos and Homo. In all, we recognize 40 stems, 34 of which are supported by at least some compensatory evidence within Mammalia. We also investigated the occurrence and conservation in mammalian 12S rRNAs of nucleotide positions that are known to participate in the decoding site in E. coli. Twenty-four nucleotide positions known to participate in the decoding site in E. coli also occur among mammalian 12S rRNAs and 17 are invariant for the same base as in E. coli. Patterns of nucleotide substitution were assessed based on our secondary structure model. Transitions in loops become saturated by approximately 10-20 million years. Transitions in stems, in turn, show partial saturation at 20 million years but divergence continues to increase beyond 100 million years. Transversions accumulate linearly beyond 100 million years in both stems and loops although the rate of accumulation of transversions is three- to fourfold higher in loops. Presumably, this difference results from constraints to maintain pairing in stems.

Interordinal mammalian relationships: evidence for paenungulate monophyly is provided by complete mitochondrial 12S rRNA sequences

The complete mitochondrial 12S rRNA sequences of 5 placental mammals belonging to the 3 orders Sirenia, Proboscidea, and Hyracoidea are reported together with phylogenetic analyses (distance and parsimony) of a total of 51 mammalian orthologues. This 12S rRNA database now includes the 2 extant proboscideans (the African and Asiatic elephants Loxodonta africana and Elephas maximus), 2 of the 3 extant sirenian genera (the sea cow Dugong dugon and the West Indian manatee Trichechus manatus), and 2 of the 3 extant hyracoid genera (the rock and tree hyraxes Procavia capensis and Dendrohyrax dorsalis). The monophyly of the 3 orders Sirenia, Proboscidea, and Hyracoidea is supported by all kinds of analysis. There are 23 and 3 diagnostic subsitutions shared by the 2 proboscideans and the 2 hyracoids, respectively, but none by the 2 sirenians. The 2 proboscideans exhibit the fastest rates of 12S rRNA evolution among the 11 placental orders studied. Based on various taxonomic sampling methods among eutherian orders and marsupial outgroups, the most strongly supported clade in our comparisons clusters together the 3 orders Sirenia, Proboscidea, and Hyracoidea in the superorder Paenungulata. Within paenungulates, the grouping of sirenians and proboscideans within the mirorder Tethytheria is observed. This branching pattern is supported by all analyses by high bootstrap percentages (BPs) and decay indices. When only one species is selected per order or suborder, the taxonomic sampling leads to a relative variation in bootstrap support of 53% for Tethytheria (BPs ranging from 44 to 93%) and 7% for Paernungulata (92-99%). When each order or suborder is represented by two species, this relative variation decreased to 10% for Tethytheria (78-87%) and 3% for Paenungulata (96-99%). Two nearly exclusive synapomorphies for paenungulates are identified in the form of one transitional compensatory change, but none were detected for tethytherians. Such a robust and reliable resolution of the paenungulate node implies a long history of the common ancestors, allowing time for synapomorphies to accumulate. This observation suggests a Late Cretaceous/Early Paleocene origin for the Paenungulata.

Cloning, expression, and characterization of the human eosinophil eotaxin receptor

Although there is a mounting body of evidence that eosinophils are recruited to sites of allergic inflammation by a number of beta-chemokines, particularly eotaxin and RANTES, the receptor that mediates these actions has not been identified. We have now cloned a G protein-coupled receptor, CC CKR3, from human eosinophils which, when stably expressed in AML14.3D10 cells bound eotaxin, MCP-3 and RANTES with Kds of 0.1, 2.7 and 3.1 nM, respectively. CC CKR3 also bound MCP-1 with lower affinity, but did not bind MIP-1 alpha or MIP-1 beta. Eotaxin, RANTES, and to a lessor extent MCP-3, but not the other chemokines, activated CC CKR3 as determined by their ability to stimulate a Ca(2+) -flux. Competition binding studies on primary eosinophils gave binding affinities for the different chemokines which were indistinguishable from those measured with CC CKR3. Since CC CKR3 is prominently expressed in eosinophils we conclude that CC CKR3 is the eosinophil eotaxin receptor. Eosinophils also express a much lower level of a second chemokine receptor, CC CKR1, which appears to be responsible for the effects of MIP-1 alpha.

Compensatory substitutions and the evolution of the mitochondrial 12S rRNA gene in mammals

12S ribosomal RNA (rRNA) gene sequences from a suite of mammalian taxa (13 placentals, 4 marsupials, 1 monotreme), for which phylogenetic relationships are well established based on independent criteria, were employed to study the evolution of this gene. Phylogenetic analysis of 12S sequences produces a phylogeny that agrees with expectations. Base composition provides evidence for directional symmetrical substitution pressure in loops; in stems, base composition is much more even. Rates of nucleotide substitution are lower in stems than loops. Patterns of nucleotide substitution show an overall preference for transitions over transversions, with this difference more profound in stems than loops. Among different transversion pathways, there is a wide range of transformation frequencies. An analysis of compensatory substitutions shows that there is strong evidence for their occurrence and that a weighting factor of 0.61 should be applied in phylogenetic analyses to account for the dependence of mutations at stem positions relative to positions where changes are independent. Among stem variables (i.e., stem length, interaction distance, substitution rates, G+C content, and the percentage of bases that are paired), several significant correlations were discovered, but stem length and interaction distance are uncorrelated with other variables.

Arginine 206 of the C5a receptor is critical for ligand recognition and receptor activation by C-terminal hexapeptide analogs

C5a is a 74-amino-acid glycoprotein whose receptor is a member of the rhodopsin superfamily. While antagonists have been generated to many of these receptors, similar efforts directed at family members whose natural ligands are proteins have met with little success. The recent development of hexapeptide analogs of C5a has allowed us to begin elucidation of the molecular events that lead to activation by combining a structure/activity study of the ligand with receptor mutagenesis. Removal of the hexapeptide's C-terminal arginine reduces affinity by 100-fold and eliminates the ability of the ligand to activate the receptor. Both the guanidino side chain and the free carboxyl of the arginine participate in the interaction. The guanidino group makes the energy-yielding contact with the receptor, while the free carboxylate negates "electrostatic" interference with Arg-206 of the receptor. It is the apparent movement Arg-206 induced by this set of interactions that is responsible for activation, since conversion of Arg-206 to alanine eliminates the agonist activity of the hexapeptides. Surprisingly, activation is a nearly energy-neutral event and may reflect the binding process rather than the final resting site of the ligand.

Phylogeny, rates of evolution, and patterns of codon usage among sea urchin retroviral-like elements, with implications for the recognition of horizontal transfer

Phylogenetic relationships, rates of evolution, and codon usage were investigated in a family of retrotransposons (SURL elements) found in echinoids. The phylogeny of SURL element reverse transcriptase sequences from 10 echinoid species clearly shows the phylogenetic signature of the host taxa as well as paralogous sequences that diverged prior to speciation events. Two subfamilies (1 and 5) of SURL element reverse transcriptase sequences are recognized that diverged prior to the radiation of the Echinometridae. Comparisons of synonymous versus nonsynonymous substitutions indicate that SURL elements have been active in echinoid genomes and have evolved under purifying selection for millions of years. Rates of synonymous substitution for reverse transcriptase are similar to rates of single-copy DNA evolution and to rates of synonymous substitution for the H3 and H4 histone genes, contradicting the assumption that rates of evolution are accelerated in retrotransposons. Finally, codon usage in SURL elements is biased for codons ending in A or U relative to 42 sea urchin nuclear genes. Biased codon usage is sometimes cited as evidence for horizontal transfer, but in the case of SURL elements this bias occurs in spite of a long history of vertical transmission rather than because of horizontal transfer.

Phylogeny of the Pteropodidae (Mammalia, Chiroptera) Based on Dna Hybridization, With Evidence for Bat Monophyly

We constructed DNA-hybridisation matrices comparing 18 genera of Megachiroptera and an outgroup microchiropteran, and eight species of Pteropus and two related genera. Three species each of Megachiroptera and Microchiroptera, two of Primates, and an outgroup armadillo were compared in another matrix; additional representatives of other mammalian orders figured in a further set of experiments. Among the megachiropterans examined, Nyctimene and Paranyctimene comprise the sister-group to other pteropodids. Of the 'macroglossines', only Macroglossus and Syconycteris are associated apart from typical pteropodines, while the four remaining nectar-feeders (Eonycteris, Megaloglossus, Melonycteris, Notopteris) are independently linked with non-nectar-feeding clades. Thus, Megaloglossus is the nearest relative of Lissonycteris, with Epomophorus and Rousettus successive sister-groups to both, while Eonycteris is the sister of all four; Melonycteris and Pteralopex form a trichotomy with the closely related Acerodon and Pteropus, and Notopteris is the sister-taxon to all four. It therefore appears that anatomical specialisations for nectar- and pollen-feeding evolved (or were lost) several times within Pteropodidae. Cynopterus and Dobsonia represent additional clades within the Pteropodinae, with which Thoopterus and Aproteles are respectively paired. Comparisons among species of Pteropus and related genera suggest that Acerodon may be congeneric with Pteropus, but that Pteralopex clearly is not. The ordinal-level matrices support bat monophyly: no order tested is closer to either of the chiropteran suborders than they are to each other, and bats are separated from Primates by at least two nodes. On the basis of previous rate determinations for mammals, we estimate that the African grouping (Epomophorus, Megaloglossus, Lissonycteris) is mid-Miocene in origin, that the two major pteropodid subfamilies (Nyctimeninae and Pteropodinae, including 'Macroglossinae') separated in the Early Miocene, and that the divergence of chiropteran suborders dates from the latest Cretaceous or earliest Palaeocene. Arrangement of genera within Pteropodidae supports the family's Australo-Pacific or south-east Asian origin.

Phylogeny, Molecules Versus Morphology, and Rates of Character Evolution Among Fruitbats (Chiroptera: Megachiroptera)

Andersen's 1912 monograph on megachiropterans remains the definitive work on the systematics of this group. Andersen argued that the Macroglossinae, containing the eonycterine and notopterine sections, are a monophyletic sister-group to other fruitbats (i.e. Andersen's Rousettus, Cynopterus and Epomophorus sections). Two recent molecular studies (DNA hybridisation and restriction mapping of ribosomal cistrons), as well as an analysis of female reproductive characters, challenge the monophyly of the Macroglossinae and several of Andersen's other conclusions such as the phylogenetic position of Nyctimene. We performed a cladistic analysis on 36 morphological characters, including 33 that were gleaned from Andersen, to determine whether phylogenetic hypotheses based on modem phylogenetic methods are in agreement with Andersen's original conclusions and to compare morphological and molecular phylogenetic hypotheses. Minimum-length trees based on parsimony are largely consistent with Andersen and support (1) a monophyletic Macroglossinae, within which the eonycterine section is paraphyletic with respect to a monophyletic notopterine section, (2) a monophyletic Cynopterus section, excepting the exclusion of Myonycteris, (3) a monophyletic Epomophorus section, excepting the exclusion of Plerotes, and (4) a paraphyletic Rousettus section, with several of the Rousettus-like forms branching off near the base of the tree. Bootstrapping analyses on a reduced data-set that included taxa shared in common with the DNA hybridisation study did not provide strong support (greater than or equal to 95%) for any clades but did provide moderate support (greater than or equal to 70) for several clades, including a monophyletic Macroglossinae. These findings are in marked contrast to the DNA hybridisation phylogeny. A high index of between-data-set incongruence is further evidence for the clash between DNA hybridisation and morphology. A phylogenetic framework was constructed on the basis of morphological data and DNA hybridisation data using a criterion of moderate support and shows little resolution, whereas employing a criterion of strong support produced a framework resolving several additional nodes. One implication of this framework is that characteristic macroglossine features such as a long tongue with a thick carpet of filiform papillae have evolved independently on several occasions (or evolved once and were lost several times). Rates of character evolution for the morphological characters employed in our analysis were calculated using divergence times estimated from DNA hybridisation data. Rates have apparently been fastest in the interior branches, and slower along the external branches, which suggests an early adaptive radiation in the history of fruitbats.

Development of C5a receptor antagonists. Differential loss of functional responses

C5a is a 74-amino acid glycoprotein generated on activation of the C system. The responses evoked by C5a, both in vitro and in vivo, and its association with inflammatory diseases, suggest that a receptor antagonist would be of considerable therapeutic importance. However, efforts at generating antagonists have so far been unsuccessful. Structure/activity studies of the C terminus of C5a have generated peptide analogues with nanomolar affinities, but all of these retain strong agonist properties. We now report hexapeptides of the form NMePhe-Lys-Pro-dCha-X-dArg in which increasing aromaticity at position 5 leads to a progressive loss of agonism with little change in binding affinity. The different responses induced by C5a are lost in the order: degranulation before Ca(2+)-flux before chemotaxis. We also describe the first full antagonist of C5a, because the peptide in which x = Trp is not only devoid of all agonist properties, but it inhibits C5a induced degranulation and C5a stimulated G protein activation.

Development of C5a receptor antagonists. Differential loss of functional responses

C5a is a 74-amino acid glycoprotein generated on activation of the C system. The responses evoked by C5a, both in vitro and in vivo, and its association with inflammatory diseases, suggest that a receptor antagonist would be of considerable therapeutic importance. However, efforts at generating antagonists have so far been unsuccessful. Structure/activity studies of the C terminus of C5a have generated peptide analogues with nanomolar affinities, but all of these retain strong agonist properties. We now report hexapeptides of the form NMePhe-Lys-Pro-dCha-X-dArg in which increasing aromaticity at position 5 leads to a progressive loss of agonism with little change in binding affinity. The different responses induced by C5a are lost in the order: degranulation before Ca(2+)-flux before chemotaxis. We also describe the first full antagonist of C5a, because the peptide in which x = Trp is not only devoid of all agonist properties, but it inhibits C5a induced degranulation and C5a stimulated G protein activation.

The amino terminus of the human C5a receptor is required for high affinity C5a binding and for receptor activation by C5a but not C5a analogs

The binding domain of the human C5a receptor consists of two distinct and physically separable subsites. One of these sites binds the C-terminal 8 amino acids of C5a and is as yet undefined, while the second site lies in the N terminus of the receptor and interacts with the core of C5a. Two deletion mutants were prepared to probe the importance of this second site. Removal of residues 2-22 decreased the binding affinity for C5a by 600-fold, while extending the deletion through residue 30 caused a further 75-fold decrease. Thus, the N terminus is responsible for at least 45% of the total energy for the binding of C5a. The five aspartic acids present in the deleted segments appear to be critical residues, as their conversion to alanines accounts for most of the affinity lost in the two truncations. Despite its importance for binding, the N terminus is not necessary for signal transduction, as a C-terminal peptide analog of C5a was able to stimulate G protein activation and to generate a Ca2+ flux through a receptor lacking residues 2-22. However, intact C5a was a very poor activator of this truncated receptor. These results imply that interaction between the N terminus of the receptor and C5a produces a conformational change in C5a that allows it's C terminus to properly interact with and activate the receptor.

Induction, characterization, and functional coupling of the high affinity chemokine receptor for RANTES and macrophage inflammatory protein-1 alpha upon differentiation of an eosinophilic HL-60 cell line

Eosinophilic differentiation of a pro-eosinophilic HL-60 cell line resulted in the induction of a high affinity RANTES/macrophage inflammatory protein-1 alpha receptor. The induced receptor is biochemically indistinguishable in RANTES equilibrium-binding studies from the monocytic receptor expressed on THP-1 cell membranes. Continued expression of the receptor requires the continuous presence of the inducing stimulus, and receptor site number declines without a loss of binding affinity with a t1/2 of 11.5 h on withdrawal of the inducing stimulus. The induced receptor is capable of three physiologic measures of receptor coupling, namely, ligand-induced Ca2+ fluxes, priming of the respiratory burst, and chemotaxis. Dose-dependent Ca2+ fluxes were elicited upon increasing concentrations of RANTES and MIP-1 alpha whereas no response was measured upon addition of MIP-1 beta or MCP-1. In addition, desensitization studies demonstrated that previous exposure to either RANTES or MIP-1 alpha almost completely inhibits a Ca2+ flux upon subsequent exposure to either ligand. Priming of the respiratory burst to PMA in differentiated cells by human rRANTES was more effective than priming by IL-5 or granulocyte-macrophage-CSF, whereas undifferentiated cells failed to secrete superoxide anion. In addition, differentiated cells underwent chemotaxis in response to RANTES. This provides the first evidence for the induction of a C-C chemokine receptor upon eosinophilic differentiation of a leukocyte cell line, and is in keeping with the demonstrated ability of human RANTES to induce the rapid formation of eosinophilic inflammatory sites.

Induction, characterization, and functional coupling of the high affinity chemokine receptor for RANTES and macrophage inflammatory protein-1 alpha upon differentiation of an eosinophilic HL-60 cell line

Eosinophilic differentiation of a pro-eosinophilic HL-60 cell line resulted in the induction of a high affinity RANTES/macrophage inflammatory protein-1 alpha receptor. The induced receptor is biochemically indistinguishable in RANTES equilibrium-binding studies from the monocytic receptor expressed on THP-1 cell membranes. Continued expression of the receptor requires the continuous presence of the inducing stimulus, and receptor site number declines without a loss of binding affinity with a t1/2 of 11.5 h on withdrawal of the inducing stimulus. The induced receptor is capable of three physiologic measures of receptor coupling, namely, ligand-induced Ca2+ fluxes, priming of the respiratory burst, and chemotaxis. Dose-dependent Ca2+ fluxes were elicited upon increasing concentrations of RANTES and MIP-1 alpha whereas no response was measured upon addition of MIP-1 beta or MCP-1. In addition, desensitization studies demonstrated that previous exposure to either RANTES or MIP-1 alpha almost completely inhibits a Ca2+ flux upon subsequent exposure to either ligand. Priming of the respiratory burst to PMA in differentiated cells by human rRANTES was more effective than priming by IL-5 or granulocyte-macrophage-CSF, whereas undifferentiated cells failed to secrete superoxide anion. In addition, differentiated cells underwent chemotaxis in response to RANTES. This provides the first evidence for the induction of a C-C chemokine receptor upon eosinophilic differentiation of a leukocyte cell line, and is in keeping with the demonstrated ability of human RANTES to induce the rapid formation of eosinophilic inflammatory sites.

Two-site binding of C5a by its receptor: an alternative binding paradigm for G protein-coupled receptors

The guanine nucleotide-binding protein-coupled receptor superfamily binds a vast array of biological messengers including lipids, odorants, catecholamines, peptides, and proteins. While some small molecules bind to these receptors at a single interhelical site, we find that the binding domain on the receptor for the inflammatory protein C5a is more complex and consists of two distinct subsites. This more elaborate motif appears to be an evolutionary adaptation of the simpler paradigm to which a second interaction site has been added in the receptor N terminus. Surprisingly, occupation of only one of the subsites is required for receptor activation. The two-site motif is not unique to the C5a receptor but appears to be widely used by the superfamily to accommodate macromolecular ligands.

Formation of eosinophilic and monocytic intradermal inflammatory sites in the dog by injection of human RANTES but not human monocyte chemoattractant protein 1, human macrophage inflammatory protein 1 alpha, or human interleukin 8

Equilibrium binding studies on canine mononuclear and granulocytic cells allow the identification of a single high affinity receptor for the human C-C chemokine RANTES (dissociation constant, 14 +/- 8 pM), that, in contrast to the human RANTES receptor, has no affinity for human macrophage inflammatory protein 1 alpha (hMIP-1 alpha). A single intradermal injection of hRANTES in dog resulted in eosinophil- and macrophage-rich inflammatory sites within 4 h. Cell infiltration peaked at 16-24 h after hRANTES injection. There was histological evidence of intravascular activation of eosinophils at 4 h, although eosinophils in the vasculature and interstitium contained apparently intact granules. Monocytes were the predominant cells adherent to venular endothelium at 16-24 h. Human MIP-1 alpha elicited no response in canine dermis, whereas monocyte chemoattractant protein 1 caused mild perivascular cuffing with monocytes. In contrast, human interleukin 8 induced a neutrophilic dermal infiltrate that was maximal by 4 h after challenge. This provides the first direct evidence in vivo that RANTES has significant proinflammatory activity and, in addition, could be a mediator in atopic pathologies characterized by eosinophilic and monocytic inflammatory responses.