title: SDF-1 synergistically enhances IL-3-induced activation of the Raf-1/MEK/Erk signaling pathway through activation of Rac and its effector Pak kinases to promote hematopoiesis and chemotaxis.
abstract: Stromal cell-derived factor 1 (SDF-1) cooperates with cytokines to promote hematopoiesis. Here we demonstrate that SDF-1 activates Erk synergistically with interleukin-3 (IL-3) in hematopoietic cells. Small GTPases Ras and Rac were prominently activated by IL-3 and SDF-1, respectively. In accordance with this, Raf-1 was significantly activated by IL-3 but not by SDF-1. SDF-1 strongly induced phosphorylation of Raf-1 on S338, the target site for the Rac effector Paks, and enhanced the IL-3-induced activation of Raf-1 and MEK. Furthermore, the synergistic activation of Erk was inhibited by expression of a dominant-negative mutant of Pak1 or that of Rac and was enhanced by an activated mutant of Pak1. SDF-1 and IL-3 also showed synergistic effects on expansion of hematopoietic cells and on induction of chemotaxis, which were both inhibited by the MEK inhibitor PD98059. These results suggest that SDF-1 synergistically enhances IL-3-induced Erk activation by up-regulating Raf-1 activity through the Rac effector Pak kinases to promote hematopoiesis.
authors.affiliation: Department of Hematology, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan. ara.hema@tmd.ac.jp
authors.forename: Ayako
authors.initials: A
authors.lastname: Arai
authors.forename: Aishun
authors.initials: A
authors.lastname: Jin
authors.forename: Weihua
authors.initials: W
authors.lastname: Yan
authors.forename: Daisuke
authors.initials: D
authors.lastname: Mizuchi
authors.forename: Koh
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Nanki
authors.forename: Osamu
authors.initials: O
authors.lastname: Miura
mesh_terms: D000818:Animals; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000502:physiology*; D002633:Chemotaxis; D004357:Drug Synergism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000201:enzymology / Q000378:metabolism; D007377:Interleukin-3 / Q000494:pharmacology*; D020935:MAP Kinase Signaling System; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D054377:Chemokine CXCL12; D019743:Chemokines, CXC; C515256:Cxcl12 protein, mouse; D007377:Interleukin-3; C515905:Pak1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D054462:p21-Activated Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020744:rac GTP-Binding Proteins