title: CXCL12 signaling is independent of Jak2 and Jak3.
abstract: Janus kinases (Jaks) are a small family of cytoplasmic tyrosine kinases, critical for signaling by Type I and II cytokine receptors. The importance of Jaks in signaling by these receptors has been firmly established by analysis of mutant cell lines, the generation of Jak knock-out mice, and the identification of patients with Jak3 mutations. While a number of other ligands that do not bind Type I and II cytokine receptors have also been reported to activate Jaks, the requirement for Jaks in signaling by these receptors is less clear. Chemokines for example, which bind seven transmembrane receptors, have been reported to activate Jaks, and principally through the use of pharmacological inhibitors, it has been argued that Jaks are essential for chemokine signaling. In the present study, we focused on CXCR4, which binds the chemokine CXCL12 or stromal cell-derived factor-1, a chemokine that has been reported to activate Jak2 and Jak3. We found that the lack of Jak3 had no effect on CXCL12 signaling or chemotaxis nor did overexpression of wild-type versions of the kinase. Similarly, overexpression of wild-type or catalytically inactive Jak2 or "knocking-down" Jak2 expression using siRNA also had no effect. We also found that in primary lymphocytes, CXCL12 did not induce appreciable phosphorylation of any of the Jaks compared with cytokines for which these kinases are required. Additionally, little or no Stat (signal transducer and activator of transcription) phosphorylation was detected. Thus, we conclude that in contrast to previous reports, Jaks, especially Jak3, are unlikely to play an essential role in chemokine signaling.
authors.affiliation: Molecular Immunology and Inflammation Branch, NIAMS, Laboratory of Host Defenses, NIAID, and Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Masato
authors.initials: M
authors.lastname: Moriguchi
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Hissong
authors.forename: Massimo
authors.initials: M
authors.lastname: Gadina
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Yamaoka
authors.forename: H Lee
authors.initials: HL
authors.lastname: Tiffany
authors.forename: Philip M
authors.initials: PM
authors.lastname: Murphy
authors.forename: Fabio
authors.initials: F
authors.lastname: Candotti
authors.forename: John J
authors.initials: JJ
authors.lastname: O'Shea
mesh_terms: D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D002461:Cell Line, Transformed; D054377:Chemokine CXCL12; D018925:Chemokines / Q000378:metabolism; D019743:Chemokines, CXC / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D047468:Immunoprecipitation; D007376:Interleukin-2 / Q000378:metabolism; D053614:Janus Kinase 2; D053616:Janus Kinase 3; D019169:Jurkat Cells; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000378:metabolism; D008024:Ligands; D008214:Lymphocytes / Q000378:metabolism; D009154:Mutation; D020125:Mutation, Missense; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D018925:Chemokines; D019743:Chemokines, CXC; D016207:Cytokines; D018076:DNA, Complementary; D007376:Interleukin-2; D008024:Ligands; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507933:JAK3 protein, human; D053614:Janus Kinase 2; D053616:Janus Kinase 3; D002118:Calcium