title: Btk regulation in human and mouse B cells via protein kinase C phosphorylation of IBtkγ.
abstract: The inhibitor of Bruton tyrosine kinase γ (IBtkγ) is a negative regulator of the Bruton tyrosine kinase (Btk), which plays a major role in B-cell differentiation; however, the mechanisms of IBtkγ-mediated regulation of Btk are unknown. Here we report that B-cell receptor (BCR) triggering caused serine-phosphorylation of IBtkγ at protein kinase C consensus sites and dissociation from Btk. By liquid chromatography and mass-mass spectrometry and functional analysis, we identified IBtkγ-S87 and -S90 as the critical amino acid residues that regulate the IBtkγ binding affinity to Btk. Consistently, the mutants IBtkγ carrying S87A and S90A mutations bound constitutively to Btk and down-regulated Ca(2+) fluxes and NF-κB activation on BCR triggering. Accordingly, spleen B cells from Ibtkγ(-/-) mice showed an increased activation of Btk, as evaluated by Y551-phosphorylation and sustained Ca(2+) mobilization on BCR engagement. These findings identify a novel pathway of Btk regulation via protein kinase C phosphorylation of IBtkγ.
authors.affiliation: Department of Experimental and Clinical Medicine, University of Catanzaro Magna Graecia, Catanzaro, Italy.
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Janda
authors.forename: Camillo
authors.initials: C
authors.lastname: Palmieri
authors.forename: Antonio
authors.initials: A
authors.lastname: Pisano
authors.forename: Marilena
authors.initials: M
authors.lastname: Pontoriero
authors.forename: Enrico
authors.initials: E
authors.lastname: Iaccino
authors.forename: Cristina
authors.initials: C
authors.lastname: Falcone
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Fiume
authors.forename: Marco
authors.initials: M
authors.lastname: Gaspari
authors.forename: Maria
authors.initials: M
authors.lastname: Nevolo
authors.forename: Emanuela
authors.initials: E
authors.lastname: Di Salle
authors.forename: Annalisa
authors.initials: A
authors.lastname: Rossi
authors.forename: Annamaria
authors.initials: A
authors.lastname: De Laurentiis
authors.forename: Adelaide
authors.initials: A
authors.lastname: Greco
authors.forename: Daniele
authors.initials: D
authors.lastname: Di Napoli
authors.forename: Elwin
authors.initials: E
authors.lastname: Verheij
authors.forename: Domenico
authors.initials: D
authors.lastname: Britti
authors.forename: Luca
authors.initials: L
authors.lastname: Lavecchia
authors.forename: Ileana
authors.initials: I
authors.lastname: Quinto
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Scala
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution / Q000502:physiology; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002477:Cells / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense / Q000502:physiology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012694:Serine / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C437966:IBtk protein, human; D047908:Intracellular Signaling Peptides and Proteins; D012694:Serine; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse; D011493:Protein Kinase C; D000409:Alanine