title: Two distinct waves of membrane-proximal B cell antigen receptor signaling differentially regulated by Src homology 2-containing inositol polyphosphate 5-phosphatase.
abstract: The phosphatidylinositol 3-kinase (PI3K) pathway plays a critical role in B cell activation and differentiation. Recruitment of pleckstrin homology (PH) domain-containing signal transduction proteins to the plasma membrane through binding to 3-phosphoinositide second messengers represents a major effector mechanism for PI3Ks. We have found that the PH domains of Bam32 and tandem PH domain-containing protein 2 (TAPP2) specify a temporally distinct wave of membrane recruitment compared with that of Bruton's tyrosine kinase (Btk), with recruitment of these two adaptors representing a later stage of the response. In this study we provide direct evidence that PH domain-dependent recruitment of Btk to the membrane is blocked by coligation of the inhibitory receptor FcgammaRII in human B lymphoma cells. In contrast, recruitment specified by the Bam32 or TAPP2 PH domains is completely insensitive to FcgammaRII inhibition. This differential regulation can be accounted for by Src homology 2-containing inositol polyphosphate 5-phosphatase (SHIP) activity alone, as expression of membrane-targeted SHIP completely abrogated Btk recruitment, but had no inhibitory effect on Bam32 or TAPP2 recruitment. Strikingly, kinetic analysis revealed that membrane recruitment of Bam32 and TAPP2 is actually more rapid under "inhibitory" signaling conditions. Analysis of 3-phosphoinositide generation under activating and inhibitory signaling conditions indicated that recruitment of Bam32 and TAPP2 is inversely correlated with the SHIP substrate/product ratio (phosphatidylinositol 3,4,5-trisphosphate/phosphatidylinositol 3,4-bisphosphate). Overexpression of TAPP2 in B cells led to an increase in the sustained phase of the calcium response and increased NF-AT-dependent transcriptional activation after B cell Ag receptor ligation. Together, these results suggest that Bam32 and TAPP2 adaptors define a novel group of SHIP-activated targets of PI3K that regulate B cell Ag receptor signaling.
authors.affiliation: Department of Immunology, University of Manitoba, 730 William Avenue, Winnipeg, Manitoba, Canada R3E 0W3.
authors.forename: Allyson K
authors.initials: AK
authors.lastname: Krahn
authors.forename: Kewei
authors.initials: K
authors.lastname: Ma
authors.forename: Sen
authors.initials: S
authors.lastname: Hou
authors.forename: Vincent
authors.initials: V
authors.lastname: Duronio
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Marshall
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001402:B-Lymphocytes / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D001798:Blood Proteins / Q000502:physiology; D020013:Calcium Signaling / Q000235:genetics / Q000276:immunology; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008024:Ligands; D008074:Lipoproteins; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000502:physiology; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000502:physiology*; D021381:Protein Transport / Q000276:immunology; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D017452:Receptors, IgG / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D014157:Transcription Factors / Q000502:physiology; D015533:Transcriptional Activation / Q000276:immunology; D018909:src Homology Domains / Q000502:physiology*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D001798:Blood Proteins; D002352:Carrier Proteins; C486555:DAPP1 protein, human; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008074:Lipoproteins; D008565:Membrane Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; C461494:PLEKHA2 protein, human; D018129:Phosphatidylinositol Phosphates; D010750:Phosphoproteins; D011947:Receptors, Antigen, B-Cell; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C060974:phosphatidylinositol 3,4,5-triphosphate; C060980:phosphatidylinositol 3,4-diphosphate; C039077:platelet protein P47; D019869:Phosphatidylinositol 3-Kinases; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases