title: Identification of the cytoplasmic domains of CXCR4 involved in Jak2 and STAT3 phosphorylation.
abstract: The chemokine SDF-1alpha transduces G(i)-dependent and -independent signals through CXCR4. Activation of Jak2/STAT3, a G(i)-independent signaling pathway, which plays a major role in survival signals, is known to be activated after SDF-1alpha binding to CXCR4 but the domains of CXCR4 involved in this signaling remain unexplored. Using human embryonic kidney HEK-293 cells stably expressing wild-type or mutated forms of CXCR4, we demonstrated that STAT3 phosphorylation requires the N-terminal part of the third intracellular loop (ICL3) and the tyrosine 157 present at the end of the second intracellular loop (ICL2) of CXCR4. In contrast, neither the conserved Tyr(135) in the DRY motif at the N terminus of ICL2 nor the Tyr(65) and Tyr(76) in the first intracellular loop (ICL1) are involved in this activation. ICL3, which does not contain any tyrosine residues, is needed to activate Jak2. These results demonstrate that two separate domains of CXCR4 are involved in Jak2/STAT3 signaling. The N-terminal part of ICL3 is needed to activate Jak2 after SDF-1alpha binding to CXCR4, leading to phosphorylation of only one cytoplasmic Tyr, present at the C terminus of ICL2, which triggers STAT3 activation. This work has profound implications for the understanding of CXCR4-transduced signaling.
authors.affiliation: Laboratoire Infections Rétrovirales et Signalisation Cellulaire, CNRS UMR 5121, Institut de Biologie, 4, Bd Henri IV, CS 89508, 34960 Montpellier Cedex 2, France.
authors.forename: Barbara
authors.initials: B
authors.lastname: Ahr
authors.forename: Mélanie
authors.initials: M
authors.lastname: Denizot
authors.forename: Véronique
authors.initials: V
authors.lastname: Robert-Hebmann
authors.forename: Anne
authors.initials: A
authors.lastname: Brelot
authors.forename: Martine
authors.initials: M
authors.lastname: Biard-Piechaczyk
mesh_terms: D001665:Binding Sites; D002460:Cell Line; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D053614:Janus Kinase 2; D009154:Mutation; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019718:Receptors, CXCR4 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D019718:Receptors, CXCR4; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2