Molecular cloning of cDNAs encoding a LD78 receptor and putative leukocyte chemotactic peptide receptors

Abstract

Several cDNA clones encoding receptors for leukocyte chemoattractants, including IL-8, C5a, N-formyl peptides (FP), and platelet-activating factor, have been isolated in the past 3 years. The primary structure of these receptors revealed that they are members of the superfamily of G protein-coupled receptors containing seven transmembrane domains. In this study the polymerase chain reaction was carried out to isolate novel cDNA clones encoding human receptors of IL-8 related cytokines, chemokines, from a human monocyte cDNA library using degenerate oligonucleotide primers devised from conserved sequences among the cDNAs encoding the human receptors for IL-8, FP and C5a. Four novel cDNA clones (HM63, HM74, HM89, and HM145) in addition to cDNAs for FP and C5a receptors were isolated. All polypeptides encoded by the cloned cDNAs share common features with the G protein-coupled receptor superfamily, such as seven putative hydrophobic transmembrane domains and, except for HM74, N-linked glycosylation sites near the N-terminus. The amino acid sequence identities among HM63, HM89, HM145, IL-8 receptors, FP receptor, and C5a receptor are in the range of 24-68%, higher than those of other members of the G protein-coupled receptor superfamily. Moreover, the number of amino acids between the fifth and sixth transmembrane domains, which varies within this superfamily, is the same in these receptors. Thus, three of the newly identified proteins probably belong to a 'leukocyte chemotactic peptide receptor family'. HM74 differs from the other clones with respect to the amino acid homology, suggesting that this may be the receptor for a different type of ligand. Furthermore, it was confirmed that HM145 is a functional receptor for LD78, one of the C-C chemokines, as revealed by the measurement of decrease of cAMP accumulation as well as calcium influx using stable transfectants.