The chemokine receptor CCR1 is constitutively active, which leads to G protein-independent, β-arrestin-mediated internalization.
Activation of G protein-coupled receptors by their associated ligands has been extensively studied, and increasing structural information about the molecular mechanisms underlying ligand-dependent receptor activation is beginning to emerge with the recent expansion in GPCR crystal structures. However, some GPCRs are also able to adopt active conformations in the absence of agonist binding that result in the initiation of signal transduction and receptor down-modulation. In this report, we show that the CC-type chemokine receptor 1 (CCR1) exhibits significant constitutive activity leading to a variety of cellular responses. CCR1 expression is sufficient to induce inhibition of cAMP formation, increased F-actin content, and basal migration of human and murine leukocytes. The constitutive activity leads to basal phosphorylation of the receptor, recruitment of β-arrestin-2, and subsequent receptor internalization. CCR1 concurrently engages Gαi and β-arrestin-2 in a multiprotein complex, which may be accommodated by homo-oligomerization or receptor clustering. The data suggest the presence of two functional states for CCR1; whereas receptor coupled to Gαi functions as a canonical GPCR, albeit with high constitutive activity, the CCR1·β-arrestin-2 complex is required for G protein-independent constitutive receptor internalization. The pertussis toxin-insensitive uptake of chemokine by the receptor suggests that the CCR1·β-arrestin-2 complex may be related to a potential scavenging function of the receptor, which may be important for maintenance of chemokine gradients and receptor responsiveness in complex fields of chemokines during inflammation.
From the Skaggs School of Pharmacy and Pharmaceutical Sciences.
C Taylor
CT
Gilliland
From the Skaggs School of Pharmacy and Pharmaceutical Sciences.
Catherina L
CL
Salanga
From the Skaggs School of Pharmacy and Pharmaceutical Sciences.
Tetsuya
T
Kawamura
the Department of Pharmacology, School of Medicine, University of California, San Diego, La Jolla, California 92093.
JoAnn
J
Trejo
From the Skaggs School of Pharmacy and Pharmaceutical Sciences. Electronic address: thandel@ucsd.edu.
Tracy M
TM
Handel
D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D019556:COS Cells; D018925:Chemokines / Q000235:genetics / Q000378:metabolism; D002522:Chlorocebus aethiops; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000235:genetics; D054389:Receptors, CCR1 / Q000235:genetics / Q000378:metabolism*; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
C000605254:ARRB2 protein, human; C000605258:Arrb2 protein, mouse; D019390:Arrestins; C515300:CCR1 protein, human; C515301:Ccr1 protein, mouse; D018925:Chemokines; D044385:GTP-Binding Protein alpha Subunits; D046912:Multiprotein Complexes; D054389:Receptors, CCR1; D000071560:beta-Arrestin 2; D000071557:beta-Arrestins
Arrestin; Bioluminescence Resonance Energy Transfer (BRET); CCR1; Cell Migration; Chemokines; Constitutive Activity; G Protein-coupled Receptors (GPCR); Internalization