Syk and Bruton's tyrosine kinase are required for B cell antigen receptor-mediated activation of the kinase Akt.
Activation of Akt by multiple stimuli including B cell antigen receptor (BCR) engagement requires phosphatidylinositol 3-kinase and regulates processes including cell survival, proliferation, and metabolism. BCR cross-linking activates three families of non-receptor protein tyrosine kinases (PTKs) and these are transducers of signaling events including phospholipase C and mitogen-activated protein kinase activation; however, the relative roles of PTKs in BCR-mediated Akt activation are unknown. We examined Akt activation in Lyn-, Syk- and Btk-deficient DT40 cells and B cells from Lyn(-/-) mice. BCR-mediated Akt activation required Syk and was partially dependent upon Btk. Increased BCR-induced Akt phosphorylation was observed in Lyn-deficient DT40 cells and Lyn(-/-) mice compared with wild-type cells suggesting that Lyn may negatively regulate Akt function. BCR-induced tyrosine phosphorylation of the phosphatidylinositol 3-kinase catalytic subunit was abolished in Syk-deficient cells consistent with a receptor-proximal role for Syk in BCR-mediated phosphatidylinositol 3-kinase activation; in contrast, it was maintained in Btk-deficient cells, suggesting Btk functions downstream of phosphatidylinositol 3-kinase. Calcium depletion did not influence BCR-induced Akt phosphorylation/activation, showing that neither Syk nor Btk mediates its effects via changes in calcium levels. Thus, BCR-mediated Akt stimulation is regulated by multiple non-receptor PTK families which regulate Akt both proximal and distal to phosphatidylinositol 3-kinase activation.
Craxton
A
A
Department of Microbiology, University of Washington, Seattle, Washington 98195, USA. andyuk@u.washington.edu
Jiang
A
A
Kurosaki
T
T
Clark
E A
EA
D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018345:Mice, Knockout; D008956:Models, Chemical; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011947:Receptors, Antigen, B-Cell / Q000276:immunology / Q000502:physiology*; D013154:Spleen / Q000276:immunology; D000072377:Syk Kinase; D019061:src-Family Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
D000077329:Agammaglobulinaemia Tyrosine Kinase; D002118:Calcium; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011947:Receptors, Antigen, B-Cell; D000072377:Syk Kinase; D019061:src-Family Kinases; C000625951:Btk protein, mouse; C000606897:Syk protein, mouse; C060902:lyn protein-tyrosine kinase