title: The M-Ras-RA-GEF-2-Rap1 pathway mediates tumor necrosis factor-alpha dependent regulation of integrin activation in splenocytes.
abstract: The Rap1 small GTPase has been implicated in regulation of integrin-mediated leukocyte adhesion downstream of various chemokines and cytokines in many aspects of inflammatory and immune responses. However, the mechanism for Rap1 regulation in the adhesion signaling remains unclear. RA-GEF-2 is a member of the multiple-member family of guanine nucleotide exchange factors (GEFs) for Rap1 and characterized by the possession of a Ras/Rap1-associating domain, interacting with M-Ras-GTP as an effector, in addition to the GEF catalytic domain. Here, we show that RA-GEF-2 is specifically responsible for the activation of Rap1 that mediates tumor necrosis factor-alpha (TNF-alpha)-triggered integrin activation. In BAF3 hematopoietic cells, activated M-Ras potently induced lymphocyte function-associated antigen 1 (LFA-1)-mediated cell aggregation. This activation was totally abrogated by knockdown of RA-GEF-2 or Rap1. TNF-alpha treatment activated LFA-1 in a manner dependent on M-Ras, RA-GEF-2, and Rap1 and induced activation of M-Ras and Rap1 in the plasma membrane, which was accompanied by recruitment of RA-GEF-2. Finally, we demonstrated that M-Ras and RA-GEF-2 were indeed involved in TNF-alpha-stimulated and Rap1-mediated LFA-1 activation in splenocytes by using mice deficient in RA-GEF-2. These findings proved a crucial role of the cross-talk between two Ras-family GTPases M-Ras and Rap1, mediated by RA-GEF-2, in adhesion signaling.
authors.affiliation: Division of Molecular Biology, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yoshikawa
authors.forename: Takaya
authors.initials: T
authors.lastname: Satoh
authors.forename: Takashi
authors.initials: T
authors.lastname: Tamura
authors.forename: Ping
authors.initials: P
authors.lastname: Wei
authors.forename: Shymaa E
authors.initials: SE
authors.lastname: Bilasy
authors.forename: Hironori
authors.initials: H
authors.lastname: Edamatsu
authors.forename: Atsu
authors.initials: A
authors.lastname: Aiba
authors.forename: Koko
authors.initials: K
authors.lastname: Katagiri
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kinashi
authors.forename: Kazuki
authors.initials: K
authors.lastname: Nakao
authors.forename: Tohru
authors.initials: T
authors.lastname: Kataoka
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects; D002449:Cell Aggregation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D018390:Gene Targeting; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D013154:Spleen / Q000166:cytology* / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: C508086:CNrasGEF protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D016023:Integrins; D016169:Lymphocyte Function-Associated Antigen-1; C109523:MRAS protein, human; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; C109418:Mras protein, mouse; D020559:Monomeric GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins