Role of the intracellular domains of CXCR4 in SDF-1-mediated signaling.
The CXCR4 chemokine receptor is a G(i) protein-coupled receptor that triggers multiple intracellular signals in response to stromal cell-derived factor 1 (SDF-1), including calcium mobilization and p44/42 extracellular signal-regulated kinases (ERK1/2). Transduced signals lead to cell chemotaxis and are terminated through receptor internalization depending on phosphorylation of the C terminus part of CXCR4. Receptor endocytosis is also required for some receptors to stimulate ERK1/2 and to migrate through a chemokine gradient. In this study, we explored the role played by the 3 intracellular loops (ICL1-3) and the C terminus domain of CXCR4 in SDF-1-mediated signaling by using human embryonic kidney (HEK)-293 cells stably expressing wild-type or mutated forms of CXCR4. ICL3 of CXCR4 is specifically involved in G(i)-dependent signals such as calcium mobilization and ERK activation, but does not trigger CXCR4 internalization after SDF-1 binding, indicating that ERK phosphorylation is independent of CXCR4 endocytosis. Surprisingly, ICL2, with or without the aspartic acid, arginine, and tyrosine (DRY) motif, is dispensable for G(i) signaling. However, ICL2 and ICL3, as well as the C terminus part of CXCR4, are needed to transduce SDF-1-mediated chemotaxis, suggesting that this event involves multiple activation pathways and/or cooperation of several cytoplasmic domains of CXCR4.
Roland
Joachim
J
Laboratoire Infections Rétrovirales et Signalisation Cellulaire CNRS UMR 5121, Institut de Biologie, Montpellier, France.
Murphy
Brendan J
BJ
Ahr
Barbara
B
Robert-Hebmann
Véronique
V
Delauzun
Vincent
V
Nye
Keith E
KE
Devaux
Christian
C
Biard-Piechaczyk
Martine
M
D020013:Calcium Signaling; D002460:Cell Line; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000502:physiology*; D002633:Chemotaxis; D003593:Cytoplasm; D004705:Endocytosis; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D017434:Protein Structure, Tertiary; D019718:Receptors, CXCR4 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D014162:Transfection
C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D019718:Receptors, CXCR4; D020928:Mitogen-Activated Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go