title: A novel regulator of G-protein signaling bearing GAP activity for Galphai and Galphaq in megakaryocytes.
abstract: The regulator of G-protein signaling (RGS) negatively regulates the alpha subunit of G proteins by accelerating their intrinsic guanosine triphosphatase (GTPase) activity. Here are reported the isolation and characterization of a novel mouse RGS, termed RGS18, which is a new member of RGS subfamily B. Northern blot analysis showed that RGS18 messenger RNA was detected predominantly in spleen and hematopoietic cells, and immunohistochemical studies demonstrated that RGS18 was expressed in megakaryocytes, platelets, granulocytes/monocytes, and, weakly, in hematopoietic stem cells, but not in lymphocytes or erythrocytes. Although various subcellular localizations of RGS have been reported, RGS18 was found to be localized in cytoplasm in megakaryocytes. In vitro binding assays of RGS18 with megakaryocyte cell lysates with or without AlF(4)(-) treatment demonstrated that RGS18 specifically binds to 2 alpha subunits of the G protein, Galphai and Galphaq. Furthermore, RGS18 clearly exhibited GTPase-activating protein (GAP) activity for Galphai and Galphaq but not for Galphas or Galpha12. In addition, chemokine stromal-derived factor 1 (SDF-1), which has been reported to stimulate megakaryocyte colony formation in the presence of thrombopoietin, affected the binding of RGS18 to Galphai but not to Galphaq. Therefore, the newly isolated RGS18 turned out to be a new member of the RGS family bearing GAP activity for Galphai, which might be stimulated by SDF-1 in megakaryocytes, as well as for Galphaq. Thus, RGS18 may play an important role in proliferation, differentiation, and/or migration of megakaryocytes.
authors.affiliation: Tsukuba Life Science Center, The Institute of Physical and Chemical Research, Japan. nagata@rtc.riken.go.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Nagata
authors.forename: M
authors.initials: M
authors.lastname: Oda
authors.forename: H
authors.initials: H
authors.lastname: Nakata
authors.forename: Y
authors.initials: Y
authors.lastname: Shozaki
authors.forename: T
authors.initials: T
authors.lastname: Kozasa
authors.forename: K
authors.initials: K
authors.lastname: Todokoro
mesh_terms: D017607:Aluminum Compounds / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001792:Blood Platelets / Q000737:chemistry; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D054377:Chemokine CXCL12; D019743:Chemokines, CXC / Q000494:pharmacology; D003593:Cytoplasm / Q000737:chemistry; D005260:Female; D005459:Fluorides / Q000494:pharmacology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D006098:Granulocytes / Q000737:chemistry; D006412:Hematopoietic Stem Cells / Q000737:chemistry; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008533:Megakaryocytes / Q000737:chemistry / Q000648:ultrastructure; D051379:Mice; D008969:Molecular Sequence Data; D009000:Monocytes / Q000737:chemistry; D020710:RGS Proteins; D012333:RNA, Messenger / Q000032:analysis; D013154:Spleen / Q000737:chemistry
chemical_list: D017607:Aluminum Compounds; D002352:Carrier Proteins; D054377:Chemokine CXCL12; D019743:Chemokines, CXC; C515256:Cxcl12 protein, mouse; D020690:GTPase-Activating Proteins; D047908:Intracellular Signaling Peptides and Proteins; D020710:RGS Proteins; D012333:RNA, Messenger; C422991:Rgs18 protein, mouse; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins; D005459:Fluorides; C032311:aluminum fluoride