title: CD19 amplification of B lymphocyte Ca2+ responses: a role for Lyn sequestration in extinguishing negative regulation.
abstract: B lymphocyte antigen receptor (BCR) signals are regulated by CD19, with BCR-induced intracellular calcium ([Ca(2+)](i)) responses enhanced by CD19 co-ligation. In this study, CD19 engagement using a dimeric anti-CD19 antibody induced [Ca(2+)](i) mobilization and significantly enhanced BCR-induced [Ca(2+)](i) responses without a requirement for CD19/BCR co-ligation. Although simultaneous CD19 and BCR engagement significantly enhanced CD19/Lyn complex formation and [Ca(2+)](i) responses, downstream tyrosine phosphorylation of CD22 and multiple other cellular proteins was inhibited, as was SHP1 recruitment to phosphorylated CD22. CD19 overexpression also enhanced BCR-induced [Ca(2+)](i) responses, but down-regulated tyrosine phosphorylation of CD22 and multiple other cellular proteins following BCR ligation. Because CD19 and Lyn expression are genetically titrated in B cells, CD19 engagement may augment BCR-induced [Ca(2+)](i) responses by sequestering the available pool of functional Lyn away from downstream negative regulatory proteins such as CD22. Consistent with this, simultaneous CD19 engagement did not further enhance the BCR-induced [Ca(2+)](i) responses of Lyn- or CD22-deficient B cells. Thus, CD19 recruitment of Lyn may preferentially activate selective signaling pathways downstream of the CD19/Lyn complex to the exclusion of other downstream regulatory and effector pathways. Other receptors may also utilize a similar strategy to regulate kinase availability and downstream intermolecular signaling.
authors.affiliation: Department of Immunology, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: M
authors.initials: M
authors.lastname: Fujimoto
authors.forename: J C
authors.initials: JC
authors.lastname: Poe
authors.forename: M
authors.initials: M
authors.lastname: Hasegawa
authors.forename: T F
authors.initials: TF
authors.lastname: Tedder
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D018941:Antigens, CD19 / Q000096:biosynthesis*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism; D001402:B-Lymphocytes / Q000378:metabolism*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D015815:Cell Adhesion Molecules; D002455:Cell Division; D002867:Chromones / Q000494:pharmacology; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D007070:Immunoglobulin A / Q000378:metabolism; D007075:Immunoglobulin M / Q000378:metabolism; D037102:Lectins; D008213:Lymphocyte Activation; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D051918:Sialic Acid Binding Ig-like Lectin 2; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018941:Antigens, CD19; D000944:Antigens, Differentiation, B-Lymphocyte; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D002867:Chromones; D004791:Enzyme Inhibitors; D007070:Immunoglobulin A; D007075:Immunoglobulin M; D037102:Lectins; D009025:Morpholines; D051918:Sialic Acid Binding Ig-like Lectin 2; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D002118:Calcium