Organization and Differential Expression of the Human Monocyte Chemoattractant Protein 1 Receptor Gene

Abstract

Two forms of the monocyte chemoattractant protein-1 receptors (the type A monocyte chemoattractant protein 1 (MCP-1) receptor CCR-2A and the type B MCP-1 receptor (CCR-2B) have been recently cloned and found to differ only in their terminal carboxyl tails. Here, we report that the two isoforms are alternatively spliced variants of a single MCP-1 receptor gene. Sequencing of the gene revealed that the 47-amino acid carboxyl tail of CCR2B was located in the same exon as the seven transmembrane domains of the receptor, and the 61-amino acid tail of CCR2A was in a downstream exon. Examination of freshly isolated human monocytes by reverse transcriptase-polymerase chain reaction revealed that CCR2B was the predominant isoform and that message levels of both CCR2A and CCR2B decreased as the monocytes differentiated into macrophages. In stably transfected cell lines, CCR2B trafficked well to the cell surface, but CCR2A was found predominately in the cytoplasm. Equilibrium binding studies revealed that those CCR2A receptors that successfully trafficked to the cell surface bound MCP-1 with high affinity (K d ‫؍‬ 310 pM), similar to CCR2B. In signaling studies, both CCR2A and CCR2B mediated agonist-dependent calcium mobilization, as well as inhibition of adenylyl cyclase. Creation of chimeras between CCR2A and the human thrombin receptor revealed that the cytoplasmic retention of CCR2A was due to its terminal carboxyl tail. Progressive truncation of the carboxyl tail indicated that a cytoplasmic retention signal(s) was located between residues 316 and 349. These data indicate that the alternatively spliced form of the human MCP-1 receptor (CCR2A) binds MCP-1 with high affinity and is a functional receptor and that expression at the cell surface is controlled by amino acid sequences located in the terminal carboxyl tail.

JM4 is a four‐transmembrane protein binding to the CCR5 receptor

“…Sequence prediction suggested that JM4 is a four-transmembrane-spanning protein with a preferential localisation at the endoplasmic reticulum (ER). JM4 shares sequence similarity with human JWA and the rat homologue glutamate transporter-associated protein [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], which regulates glutamate uptake by interacting with the ten-transmembrane-spanning excitatory amino acid carrier 1 (EAAC1) [16]. We show that JWA, like JM4, binds to CCR5.…”

“…Like CCR5D32, this truncated receptor is not efficiently expressed at the cell surface and interferes with HIV infection [10]. Evidence for the role of the cytoplasmic tail in receptor trafficking to the plasma membrane has recently been demonstrated for the CCR2 receptor isoforms [11]. Furthermore, the palmitoylation of the C-terminal tail of CCR5 has a significant influence on targeting the receptor to the plasma membrane, on signalling, internalisation, and intracellular trafficking [12][13][14][15].…”

Variants of chemokine receptor 2 and interleukin 4 receptor, but not interleukin 10 or Fas ligand, increase risk of cervical cancer

“…[8][9][10] Two alternatively spliced isoforms of CCR-2, CCR-2A and B are described where CCR-2A is found mostly in the cytoplasm while CCR-2B migrates to the cell surface. 11 A V64I polymorphism in the first transmembrane domain of CCR-2 affects stability of the CCR-2A isoform with the I-allele increasing stability and thereby expression of CCR-2A on the cell surface. 12 CCR-2 is a co-receptor for HIV-1 entry into host cells and the 64I-variant is associated with decreased risk for progression from HIV-1 infection to AIDS.…”

Identification and Partial Characterization of a Variant of Human CXCR3 Generated by Posttranscriptional Exon Skipping

“…Evidence exists that such regulation might also be important in CKR biology. Differentially processed mRNA messages have indeed been observed for CXCR4 (CXCR4 and CXCR4-Lo) (2), CCR9 (A and B) (3), and CCR2 (A and B) (4). We now report on the discovery of a posttranscriptionally altered variant of human CXCR3, the designated receptor for non-ELR-CXC-chemokines IFN-inducible protein 10/CXCL10, monokine induced by IFN-␥/ CXCL9 (5), and IFN-inducible T cell ␣ chemoattractant/CXCL11 (6).…”