Role of the intracellular domains of CXCR4 in SDF-1-mediated signaling

The CXCR4 chemokine receptor is a G, 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 chemo kine 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. kine 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 sphosphorylation is independent of CXCR4-endocytosis. Surprisingly, ICL2, with or without the aspartic acid, arginine, and tyrosine (DRY) motif, is dispensable for G, signaling. However, ICL2 and ICL3, as well as the C terminus part of CXCR4, are needed to transcluce SDF-1-mediated chemotaxis, suggesting that this event involves multiple activation pathways and/or cooperation of several cytoplasmic domains of CXCR4. (Blood. 2003;101:399-406) (C) 2003 by The American Society of Hematology