Two novel fully functional isoforms of CX3CR1 are potent HIV coreceptors

Alexandre Garin; Nadine Tarantino; Sophie Faure; Mehdi Daoudi; Cédric Lécureuil; Anne Bourdais; Patrice Debré; Philippe Deterre; Christophe Combadiere

doi:10.4049/jimmunol.171.10.5305

Two novel fully functional isoforms of CX3CR1 are potent HIV coreceptors

J Immunol. 2003 Nov 15;171(10):5305-12. doi: 10.4049/jimmunol.171.10.5305.

Authors

Alexandre Garin¹, Nadine Tarantino, Sophie Faure, Mehdi Daoudi, Cédric Lécureuil, Anne Bourdais, Patrice Debré, Philippe Deterre, Christophe Combadiere

Affiliation

¹ Laboratoire d'Immunologie Cellulaire et Tissulaire, Institut National de la Santé et de la Recherche Médicale, Unité 543, Hôpital Pitié-Salpêtriere, Paris, France.

PMID: 14607932
DOI: 10.4049/jimmunol.171.10.5305

Abstract

We identified two novel isoforms of the human chemokine receptor CX3CR1, produced by alternative splicing and with N-terminal regions extended by 7 and 32 aa. Expression of the messengers coding these isoforms, compared with that of previously described V28 messengers, is lower in monocytes and NK cells, but higher in CD4(+) T lymphocytes. CX3CR1 and its extended isoforms were expressed in HEK-293 cells and compared for expression, ligand binding, and cellular responses. In steady state experiments, all three CX3CR1 isoforms bound CX3CL1 with similar affinity. In kinetic binding studies, however, k(on) and k(off) were significantly greater for the extended CX3CR1 isoforms, thereby suggesting that the N-terminal extensions may alter the functions induced by CX3CL1. In signaling studies, all three CX3CR1 isoforms mediated agonist-dependent calcium mobilization, but the EC(50) was lower for the extended than for the standard isoforms. In addition, chemotactic responses for these extended isoforms shifted left, also indicating a more sensitive response. Finally, the longer variants appeared to be more potent HIV coreceptors when tested in fusion and infection assays. In conclusion, we identified and characterized functionally two novel isoforms of CX3CR1 that respond more sensitively to CX3CL1 and HIV viral envelopes. These data reveal new complexity in CX3CR1 cell activation and confirm the critical role of the N-terminal domain of the chemokine receptors in ligand recognition and cellular response.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Alternative Splicing / immunology
Amino Acid Sequence
Base Sequence
CX3C Chemokine Receptor 1
Cell Line
Cells, Cultured
Chemokine CX3CL1
Chemokine CXCL1
Chemokines, CX3C / biosynthesis
Chemokines, CX3C / genetics
Chemokines, CX3C / isolation & purification
Chemokines, CX3C / metabolism*
Chemokines, CXC / agonists
Chemokines, CXC / metabolism
Chemotaxis, Leukocyte / genetics
Chemotaxis, Leukocyte / immunology
Gene Expression Regulation / immunology
Humans
Intercellular Signaling Peptides and Proteins / agonists
Intercellular Signaling Peptides and Proteins / metabolism
Membrane Proteins / biosynthesis
Membrane Proteins / genetics
Membrane Proteins / isolation & purification
Membrane Proteins / metabolism*
Molecular Sequence Data
Protein Binding / genetics
Protein Binding / immunology
Protein Isoforms / biosynthesis
Protein Isoforms / genetics
Protein Isoforms / isolation & purification
Protein Isoforms / metabolism
RNA, Messenger / biosynthesis
Receptors, Chemokine / agonists
Receptors, Chemokine / biosynthesis
Receptors, Chemokine / genetics
Receptors, Chemokine / metabolism
Receptors, HIV / physiology*
Transfection

Substances

CX3C Chemokine Receptor 1
CX3CL1 protein, human
CXCL1 protein, human
Chemokine CX3CL1
Chemokine CXCL1
Chemokines, CX3C
Chemokines, CXC
Cx3cl1 protein, mouse
Cx3cr1 protein, mouse
Intercellular Signaling Peptides and Proteins
Membrane Proteins
Protein Isoforms
RNA, Messenger
Receptors, Chemokine
Receptors, HIV