Cloning and characterization of the guinea pig eosinophil eotaxin receptor, C-C chemokine receptor-3: blockade using a monoclonal antibody in vivo.

Certain C-C chemokines, signaling via the eotaxin receptor C-C chemokine receptor-3 (CCR3), are thought to be central mediators of eosinophil accumulation in allergic inflammation. To investigate the role of CCR3 in vivo, we cloned the guinea pig eotaxin receptor (guinea pig CCR3) from a genomic DNA library. We isolated a single-exon open reading frame coding for a 358-amino acid chemokine receptor protein with 67 and 69% homology to human and murine CCR3, respectively. When expressed in stable transfectants, this receptor bound 125I-labeled guinea pig eotaxin, 125I-labeled human monocyte chemotactic protein-3, and 125I-labeled human RANTES. In chemotaxis assays, guinea pig CCR3 transfectants responded only to guinea pig eotaxin, with a maximal effect at 100 nM. mAbs were raised that bound selectively to both guinea pig CCR3 transfectants and guinea pig eosinophils. One of these mAbs, 2A8, blocked both ligand binding to transfectants and their chemotaxis in response to eotaxin. The Ab also inhibited chemotaxis and the elevation of cytosolic calcium in guinea pig eosinophils in response to eotaxin. F(ab')2 fragments of 2A8 were prepared that retained the ability to inhibit eosinophil calcium responses to eotaxin. Pretreatment of (111)In-labeled eosinophils in vitro with F(ab')2 2A8 selectively inhibited their accumulation in response to eotaxin in vivo. These data demonstrate that functional blockade of eosinophil chemokine receptors can be achieved in vivo and provide further support for the development of novel anti-inflammatory drugs targeting eosinophil recruitment through chemokine receptor antagonism.

Mouse astrocytes respond to the chemokines MCP-1 and KC, but reverse transcriptase-polymerase chain reaction does not detect mRNA for the KC or new MCP-1 receptor.

Previous studies demonstrated the involvement of astrocytes in the development of astrogliosis, a condition in which these cells undergo proliferation and hypertrophy. To examine whether astrocytes could migrate into lesions, we tested the influence of the murine chemokines MCP-1, KC, TCA3, and MIP-1 beta on migration of cultured neonatal mouse astrocytes. Subnanomolar concentrations of MCP-1 and KC were active chemoattractants indicating that these molecules were effective at physiologic concentrations. Specificity of MCP-1 was demonstrated by antibody inhibition and by the finding that the chemokine MIP-1 beta failed to induce astrocyte migration. The migratory responses were sensitive to pertussis toxin; this finding is consistent with involvement of G protein-coupled receptors. To examine the receptors for these chemokines further, we cloned the mouse homolog of the human MCP-1 receptor from a mouse peritoneal exudate cell cDNA library. The gene had 78% nucleotide sequence homology with the human MCP-1 receptor (the nucleotide sequence of clone 1 encoding the mouse MCP-1 receptor can be obtained from the GenBank database, accession number U56819). However, reverse transcriptase-polymerase chain reaction (RT-PCR) failed to detect message for either the MCP-1 or KC receptors in astrocytes. The combined data suggest that mouse astrocytes use novel receptors to recognize these chemokines.

Molecular cloning and characterization of a human eotaxin receptor expressed selectively on eosinophils.

The chemokine eotaxin is unusual in that it appears to be a highly specific chemoattractant for eosinophils. Ligand-binding studies with radiolabeled eotaxin demonstrated a receptor on eosinophils distinct from the known chemokine receptors CKR-1 and -2. The distinct eotaxin binding site on human eosinophils also bound RANTES (regulated on activation T expressed and secreted) and monocyte chemotactic protein (MCP)3. We have now isolated a cDNA from eosinophils, termed CKR-3, with significant sequence similarity to other well characterized chemokine receptors. Cells transfected with CKR-3 cDNA bound radiolabeled eotaxin specifically and with high affinity, comparable to the binding affinity observed with eosinophils. This receptor also bound RANTES and MCP-3 with high affinity, but not other CC or CXC chemokines. Furthermore, receptor transfectants generated in a murine B cell lymphoma cell line migrated in transwell chemotaxis assays to eotaxin, RANTES, and MCP-3, but not to any other chemokines. A monoclonal antibody recognizing CKR-3 was used to show that eosinophils, but not other leukocyte types, expressed this receptor. This pattern of expression was confirmed by Northern blot with RNA from highly purified leukocyte subsets. The restricted expression of CKR-3 on eosinophils and the fidelity of eotaxin binding to CKR-3, provides a potential mechanism for the selective recruitment and migration of eosinophils within tissues.

Molecular characterization of two murine eosinophil beta chemokine receptors.

beta or C-C chemokines including RANTES, MCP-3, MIP-1 alpha, and eotaxin have been implicated in the pathogenesis of eosinophilic inflammation. Two human beta chemokine receptors have been cloned and characterized: the MIP-1 alpha/RANTES receptor or C-C chemokine receptor 1 (CCR-1) and the MCP-1 receptor or C-C chemokine receptor 2 (CCR-2). However, no murine beta chemokine receptors have thus far been reported. Molecular cloning from mouse genomic DNA and cDNA libraries yielded two murine beta chemokine receptors with 79% and 65% sequence identity with human CCR-1, and 50% and 55% with human CCR-2. COS cells transiently transfected with the murine homologue of human CCR-1 bind murine MIP-1 alpha and human RANTES with Kds of 3.4 nM and 4.2 nM and murine MIP-1 beta with an EC50 of 8.9 nM. The other murine beta chemokine receptor, which we have designated murine CCR-3, also binds murine MIP-1 alpha. The mRNAs for both receptors are expressed in eosinophils from IL-5 transgenic mice. The level of murine CCR-3 mRNA in these mouse eosinophils exceeds that of CCR-1 mRNA and approaches actin levels. Murine MIP-1 alpha was found to be a potent chemoattractant for murine eosinophils. Our findings suggest that the murine MIP-1 alpha ligand/receptor system is an important mediator of murine eosinophil trafficking.

Analysis of the human regulators of complement activation (RCA) gene cluster with yeast artificial chromosomes (YACs).

The human regulators of complement activation gene cluster (RCA cluster) have been partially characterized with yeast artificial chromosomes (YACs). While the data confirm many points previously elucidated, the finer resolution of YAC mapping has allowed the discovery and/or localization of partial gene duplications, the determination of gene orientations, and the measurement of gaps between known genes. Here nine overlapping YACs that encompass a genomic region of 800 kb, encoding four RCA genes and three gene-like elements, are described. The encoded genes and two of the gene-like elements share the same orientation and are ordered (5' to 3') DAF, CR2, CR1, MCP-like, CR1-like, and MCP. A C4bp-like region lies upstream from DAF and is likely to correspond to one recently observed by F. Pardo-Manuel, J. Rey-Campos, A. Hillarp, B. Dahlback, and S. Rodriguez de Cordoba (1990, Proc. Natl. Acad. Sci. USA 87: 4529-4533). MCP-like, a new genetic element, was discovered and found to be homologous to the 5' portion of the MCP gene. Two large gaps of 85 kb (between CR2 and DAF) and 110 kb (between DAF and the C4bp-like element) could carry additional RCA genes. The arrangement of CR1, MCP-like, CR1-like, and MCP, in that order, strongly suggests that this region was generated by a single duplication of neighboring CR1/CR1-like and MCP/MCP-like forerunners. The RCA YACs will now serve as convenient DNA sources for the subcloning and further characterization of this region.

Membrane cofactor protein of the complement system: alternative splicing of serine/threonine/proline-rich exons and cytoplasmic tails produces multiple isoforms that correlate with protein phenotype.

Membrane cofactor protein (MCP) is a complement regulatory protein that is expressed on human cells and cell lines as two relatively broad species with Mr of 58,000-68,000 and 48,000-56,000. The structure of a previously reported cDNA clone indicated that MCP was a type 1 membrane glycoprotein and a member of the regulators of complement activation gene/protein cluster. However, it did not provide an explanation for the unusual phenotypic pattern of MCP. Therefore, in parallel with an analysis of the gene, additional cDNAs were cloned and characterized. Six different MCP cDNA classes were identified. All encode the same 5' untranslated signal peptide, four SCRs, transmembrane domain, and basic amino acid anchor. However, they differ in the length and composition of an extracellular serine/threonine/proline (STP)-rich area, a site of heavy O-glycosylation, and cytoplasmic tail. Analysis of the MCP gene demonstrated that the variation in cDNA structure was a result of alternative splicing. Peripheral blood cells and cell lines predominantly expressed four of the six isoforms. These varied by the presence or absence of an STP-rich segment of 15 amino acids (STPB) and by the use of one of two cytoplasmic domains. Analysis by polymerase chain reaction, Northern blots, and transfection indicated that the predominance of MCP cDNA isoforms with STPB correlated with the high molecular weight protein phenotype, while the predominance of isoforms without STPB correlated with the lower molecular weight phenotype. The expression in a single cell of four distinct protein species with variable STP-rich regions and cytoplasmic tails represents an interesting example of the use of alternative splicing to provide variability in a mammalian protein.

Membrane cofactor protein of the complement system. A HindIII restriction fragment length polymorphism that correlates with the expression polymorphism.

An RFLP was found in the DNA of 25 unrelated persons, two families, and five cell lines that correlated with their membrane cofactor protein phenotype. If restricted with HindIII, DNA derived from upper band predominant protein (U) phenotypes had a band at 2 kb, whereas DNA of lower band predominant (L) phenotypes had a 4-kb band. The equal band protein phenotype, in which equal quantities of the two species are expressed, had bands at both 4 and 2 kb. The polymorphic HindIII site was localized to an intron within the membrane cofactor protein gene between exon 1 (codes for 5'UT/signal peptide) and exon 2 (codes for the first short consensus repeat). Using the polymerase chain reaction (PCR), sequences around this site were amplified and a single band of 260 bp was produced. In the U phenotype, the PCR product was restricted with HindIII into 200- and 60-bp fragments. In the L phenotype, there was no change in the size of 260 bp upon restriction with HindIII. For the equal band protein phenotype, the PCR product was partially cleaved. The 260-bp PCR product was subcloned and sequenced. DNA from the U phenotype demonstrated an intact HindIII site (AAGCTT), whereas in the DNA of the L phenotype, this site was altered because a "G" was substituted for a "C" (AAGGTT).

Membrane cofactor protein (MCP or CD46): newest member of the regulators of complement activation gene cluster.

Membrane cofactor protein (MCP; CD46) is a widely distributed C3b/C4b-binding cell surface glycoprotein which serves as an inhibitor of complement activation on host cells. The protein has been purified, multiple cDNAs cloned and sequenced, and the genomic organization determined. MCP belongs to a family known as the regulators of complement activation (RCA) gene cluster. The RCA members are related structurally [possess approximately 60 amino acid repeating motifs termed short consensus repeats (SCR)], functionally (bind C3b/C4b), and genetically (genes are tightly clustered on chromosome 1 at q3.2). Beginning at its amino-terminus, MCP is composed of four SCRs, a ser/thr/pro-enriched region, an area of undefined function, a transmembrane hydrophobic domain, a cytoplasmic anchor and cytoplasmic tail. On SDS-PAGE, MCP migrates as two broad forms with Mrs of 59,000-68,000 and 51,000-58,000. The quantity of each form expressed is inherited in an autosomal codominant fashion. This structural heterogeneity is partly explained by the expression of multiple cDNA/protein isoforms that arise by alternative splicing of ser/thr/pro-rich exons (sites of heavy O-glycosylation) and of cytoplasmic tails. This protein is of interest to immunologists and clinicians because of its role in regulation of the complement pathways and, therefore, inflammation in immune complex-mediated syndromes; to reproductive immunologists on account of its expression on sperm and at the maternal-fetal interface; and to tumor immunologists because of its high expression on malignant cells. The availability of monoclonal and polyclonal antibodies and molecular probes will be helpful in addressing questions about the biology of MCP in these and other areas.

Structure of the gene for human complement protein decay accelerating factor.

Decay accelerating factor (DAF) is a glycophospholipid-anchored membrane protein that is part of the regulators of complement activation (RCA) gene family located on human chromosome 1, band q32. These proteins, beginning at their amino terminus, consist largely of multiple copies of an approximately 60 amino acid short consensus repeat (SCR). A DAF cDNA clone was used to identify overlapping bacteriophage genomic clones. The human DAF gene spans approximately 40 kb and consists of 11 exons. The length of these exons and introns varies considerably, with the exons ranging from 21 to 956 bp and the introns ranging from approximately 0.5 to 19.8 kb. SCR I, II, and IV are all encoded by single exons; however, SCR III is encoded by two separate exons, with the splice junction occurring after the second nucleotide of the codon for the glycine residue at position 34 of the consensus sequence. This feature has also been found in CR1, CR2, membrane cofactor protein, and murine factor H. Following the SCR in DAF is a 76 amino acid serine/threonine-rich domain encoded on three separate exons. Exon 10 encodes the Alu family sequence that has been found as an insert in a minor class of DAF cDNA, thus indicating that this mRNA arises by standard alternative splicing. The last DAF exon, which comes after the largest intron of 19.8 kb, encodes the hydrophobic carboxy terminus and the 3'UT region. The nature of the signal that directs posttranslational attachment of a glycophospholipid anchor to DAF is not known, but that signal is apparently spread over three exons and greater than 20 kb. An analysis of the DAF gene provides additional evidence for the common evolutionary heritage of the RCA gene family. The exon/intron structure of this gene will facilitate experiments aimed at understanding the functions of the various domains of DAF.

Polymorphisms of the regulators of complement activation gene cluster.

The regulators of complement activation (RCA) constitute a tightly linked gene family that controls the activity of the complement system. Genetic polymorphisms have been reported for all of RCA genes at the DNA, RNA and/or protein levels. In addition, multiple RNA and/or protein products have been observed for most of these genes. These polymorphisms and variants are instrumental in the study of the structure, evolution and function of the RCA family.

Molecular cloning and chromosomal localization of human membrane cofactor protein (MCP). Evidence for inclusion in the multigene family of complement-regulatory proteins.

Membrane cofactor protein (MCP), a regulatory molecular of the complement system with cofactor activity for the factor I-mediated inactivation of C3b and C4b, is widely distributed, being present on leukocytes, platelets, endothelial cells, epithelial cells, and fibroblasts. MCP was purified from a human T cell line (HSB2) and the NH2-terminal 24-amino acid sequence obtained by Edman degradation. An oligonucleotide probe based on this sequence was used to identify a clone from a human monocytic (U937) cDNA library. Nucleotide sequencing showed a 43-bp 5'-untranslated region, an open reading frame of 1,152 bp, and a 335-bp 3'-untranslated region followed by a 16-bp poly(A) track. The deduced full-length MCP protein consists of a 34-amino acid signal peptide and a 350-amino acid mature protein. The protein has, beginning at the NH2 terminus, four approximately 60-amino acid repeat units that match the consensus sequence found in a multigene family of complement regulatory proteins (C3b-receptor or CR1, C3d-receptor or CR2, decay-accelerating factor, C4-binding protein, and factor H), as well as several other complement and non-complement proteins. The remainder of the MCP protein consists of 25 amino acids that are rich in serine and threonine (probable site of heavy O-linked glycosylation of MCP), 17 amino acids of unknown significance, and a 23-amino acid transmembrane hydrophobic region followed by a 33-amino acid cytoplasmic tail. The MCP gene was localized to human chromosome 1, bands 1q31-41, by analysis of human x rodent somatic cell hybrid clones and by in situ hybridization. This same genetic region contains the multigene family of complement-regulatory proteins, which is thereby enlarged to include the functionally and structurally related MCP.