Two novel fully functional isoforms of CX3CR1 are potent HIV coreceptors.
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.
Garin
Alexandre
A
Laboratoire d'Immunologie Cellulaire et Tissulaire, Institut National de la Santé et de la Recherche Médicale, Unité 543, Hôpital Pitié-Salpêtriere, Paris, France.
Tarantino
Nadine
N
Faure
Sophie
S
Daoudi
Mehdi
M
Lécureuil
Cédric
C
Bourdais
Anne
A
Debré
Patrice
P
Deterre
Philippe
P
Combadiere
Christophe
C
D017398:Alternative Splicing / Q000276:immunology; D000595:Amino Acid Sequence; D001483:Base Sequence; D000073883:CX3C Chemokine Receptor 1; D002460:Cell Line; D002478:Cells, Cultured; D054428:Chemokine CX3CL1; D054360:Chemokine CXCL1; D020523:Chemokines, CX3C / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D019743:Chemokines, CXC / Q000819:agonists / Q000378:metabolism; D002634:Chemotaxis, Leukocyte / Q000235:genetics / Q000276:immunology; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000819:agonists / Q000378:metabolism; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D019707:Receptors, Chemokine / Q000819:agonists / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015728:Receptors, HIV / Q000502:physiology*; D014162:Transfection
D000073883:CX3C Chemokine Receptor 1; C515538:CX3CL1 protein, human; C475829:CXCL1 protein, human; D054428:Chemokine CX3CL1; D054360:Chemokine CXCL1; D020523:Chemokines, CX3C; D019743:Chemokines, CXC; C515539:Cx3cl1 protein, mouse; C471885:Cx3cr1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D019707:Receptors, Chemokine; D015728:Receptors, HIV