Phosphorylation of CD19 Y484 and Y515, and linked activation of phosphatidylinositol 3-kinase, are required for B cell antigen receptor-mediated activation of Bruton's tyrosine kinase.
Bruton's tyrosine kinase (Btk) plays a critical role in B cell Ag receptor (BCR) signaling, as indicated by the X-linked immunodeficiency and X-linked agammaglobulinemia phenotypes of mice and men that express mutant forms of the kinase. Although Btk activity can be regulated by Src-family and Syk tyrosine kinases, and perhaps by phosphatidylinositol 3,4,5-trisphosphate, BCR-coupled signaling pathways leading to Btk activation are poorly understood. In view of previous findings that CD19 is involved in BCR-mediated phosphatidylinositol 3-kinase (PI3-K) activation, we assessed its role in Btk activation. Using a CD19 reconstituted myeloma model and CD19 gene-ablated animals we found that BCR-mediated Btk activation and phosphorylation are dependent on the expression of CD19, while BCR-mediated activation of Lyn and Syk is not. Wortmannin preincubation inhibited the BCR-mediated activation and phosphorylation of Btk. Btk activation was not rescued in the myeloma by expression of a CD19 mutant in which tyrosine residues previously shown to mediate CD19 interaction with PI3-K, Y484 and Y515, were changed to phenylalanine. Taken together, the data presented indicate that BCR aggregation-driven CD19 phosphorylation functions to promote Btk activation via recruitment and activation of PI3-K. Resultant phosphatidylinositol 3,4,5-trisphosphate probably functions to localize Btk for subsequent phosphorylation and activation by Src and Syk family kinases.
Buhl
A M
AM
Division of Basic Sciences, Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206, USA.
Cambier
J C
JC
D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D018941:Antigens, CD19 / Q000378:metabolism* / Q000502:physiology; D001402:B-Lymphocytes / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D020013:Calcium Signaling / Q000276:immunology; D004789:Enzyme Activation / Q000235:genetics / Q000276:immunology; D004792:Enzyme Precursors / Q000378:metabolism / Q000502:physiology; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000201:enzymology* / Q000235:genetics / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism* / Q000502:physiology; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D013154:Spleen / Q000166:cytology / Q000201:enzymology; D000072377:Syk Kinase; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism* / Q000502:physiology; D014960:X Chromosome / Q000276:immunology; D019061:src-Family Kinases / Q000378:metabolism / Q000502:physiology
D018941:Antigens, CD19; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D011947:Receptors, Antigen, B-Cell; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; C000625951:Btk protein, mouse; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma