title: Activation of RasGRP3 by phosphorylation of Thr-133 is required for B cell receptor-mediated Ras activation.
abstract: The Ras signaling pathway plays a critical role in B lymphocyte development and activation, but its activation mechanism has not been well understood. At least one mode of Ras regulation in B cells involves a Ras-guanyl nucleotide exchange factor, RasGRP3. We demonstrate here that RasGRP3 undergoes phosphorylation at Thr-133 upon B cell receptor cross-linking, thereby resulting in its activation. Deletion of phospholipase C-gamma2 or pharmacological interference with conventional PKCs resulted in marked reduction in both Thr-133 phosphorylation and Ras activation. Moreover, mutation of Thr-133 in RasGRP3 alone severely impaired its ability to activate Ras in B cell receptor signaling. Hence, our data suggest that PKC, after being activated by diacylglycerol, phosphorylates RasGRP3, thereby contributing to its full activation.
authors.affiliation: Laboratories of Lymphocyte Differentiation and Immunogenomics, RIKEN Research Center for Allergy and Immunology, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Aiba
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Oh-hora
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kiyonaka
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Kimura
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hijikata
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Mori
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Kurosaki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002645:Chickens; D003432:Cross-Linking Reagents; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D009154:Mutation; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011487:Protein Conformation; D011493:Protein Kinase C / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D055672:Static Electricity; D013912:Threonine / Q000737:chemistry; D010738:Type C Phospholipases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D003432:Cross-Linking Reagents; D020662:Guanine Nucleotide Exchange Factors; D011947:Receptors, Antigen, B-Cell; D011994:Recombinant Proteins; D013912:Threonine; D011493:Protein Kinase C; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D018631:ras Proteins