The tyrosine kinases Syk and Lyn exert opposing effects on the activation of protein kinase Akt/PKB in B lymphocytes.

The protein kinase Akt/PKB is a crucial regulator of cell survival in response to mitogenic signals. The increased kinase activity of v-akt, an oncogenic form of Akt/PKB, causes mouse T cell lymphoma, and overexpression of Akt/PKB is associated with progression of several tumor types in human. In this study, we demonstrate that ligation of B cell antigen receptor (BCR) leads to activation of Akt/PKB in B lymphocytes. BCR-induced activation of Akt/PKB required the tyrosine kinase Syk, which was not previously known to regulate Akt/PKB. In contrast, BCR crosslinking of Lyn-deficient B cells resulted in markedly enhanced hyperphosphorylation and activation of Akt/PKB compared with wild-type B cells, indicating that this Src-family kinase acts as an endogenous antagonist of BCR-induced Akt/PKB activation. Lyn inhibited Akt/PKB additively with an okadaic acid-sensitive endogenous phosphatase(s). Expression of exogenous Lyn in mutant cells restored normal BCR-induced phosphorylation of Akt/PKB. Negative regulation of Akt/PKB by Lyn was not dependent on the protein phosphatases SHP-1, SHP-2, or SHIP. Our results show that Lyn provides a mechanism for negative regulation and opposes the effect of Syk on BCR-mediated activation of Akt/PKB. Deregulation of Akt/PKB correlates with the hyperresponsiveness of B cells from Lyn-deficient mice stimulated by BCR crosslinking and may contribute to the autoimmune syndrome that develops in Lyn-deficient animals.

[1]  N. Hay,et al.  The PI 3-kinase/Akt signaling pathway delivers an anti-apoptotic signal. , 1997, Genes & development.

[2]  P. Tsichlis,et al.  Transduction of interleukin-2 antiapoptotic and proliferative signals via Akt protein kinase. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[3]  J. Brugge,et al.  Phosphatidylinositol 3-kinase is required for integrin-stimulated AKT and Raf-1/mitogen-activated protein kinase pathway activation , 1997, Molecular and cellular biology.

[4]  R. Geahlen,et al.  Syk- and Lyn-dependent phosphorylation of Syk on multiple tyrosines following B cell activation includes a site that negatively regulates signaling. , 1998, Journal of immunology.

[5]  José Luis de la Pompa,et al.  Negative Regulation of PKB/Akt-Dependent Cell Survival by the Tumor Suppressor PTEN , 1998, Cell.

[6]  Kenneth G. C. Smith,et al.  Inhibition of the B Cell by CD22: A Requirement for Lyn , 1998, The Journal of experimental medicine.

[7]  Frank McCormick,et al.  Akt activation by growth factors is a multiple-step process: the role of the PH domain , 1998, Oncogene.

[8]  J. Unkeless,et al.  Inhibitory receptors, ITIM sequences and phosphatases. , 1997, Current opinion in immunology.

[9]  E. Puré,et al.  Syk Is Required for BCR-mediated Activation of p90Rsk, but Not p70S6k, via a Mitogen-activated Protein Kinase-independent Pathway in B Cells* , 1997, The Journal of Biological Chemistry.

[10]  Philippe Soriano,et al.  Characterization of the B lymphocyte populations in Lyn-deficient mice and the role of Lyn in signal initiation and down-regulation. , 1997, Immunity.

[11]  T. Kurosaki,et al.  Deletion of SHIP or SHP-1 Reveals Two Distinct Pathways for Inhibitory Signaling , 1997, Cell.

[12]  D. Jelinek,et al.  Phosphatidylinositol 3-kinase activation in normal human B lymphocytes. , 1996, Journal of immunology.

[13]  A. Hata,et al.  Tyrosine kinases Lyn and Syk regulate B cell receptor‐coupled Ca2+ mobilization through distinct pathways. , 1994, The EMBO journal.

[14]  F. McCormick,et al.  Dual role of phosphatidylinositol-3,4,5-trisphosphate in the activation of protein kinase B. , 1997, Science.

[15]  Ornella Parolini,et al.  Deficient expression of a B cell cytoplasmic tyrosine kinase in human X-linked agammaglobulinemia , 1993, Cell.

[16]  E. Puré,et al.  Suboptimal Cross-linking of Antigen Receptor Induces Syk-dependent Activation of p70S6 Kinase through Protein Kinase C and Phosphoinositol 3-Kinase* , 1999, The Journal of Biological Chemistry.

[17]  D. Parker,et al.  Differential coupling of membrane Ig and CD40 to the extracellularly regulated kinase signaling pathway. , 1998, Journal of Immunology.

[18]  M. Gold,et al.  Differential activation of the ERK, JNK, and p38 mitogen-activated protein kinases by CD40 and the B cell antigen receptor. , 1996, Journal of immunology.

[19]  K. Horikawa,et al.  A Double-Edged Kinase Lyn: A Positive and Negative Regulator for Antigen Receptor–mediated Signals , 1998, The Journal of experimental medicine.

[20]  S. Staal.  Molecular cloning of the akt oncogene and its human homologues AKT1 and AKT2: amplification of AKT1 in a primary human gastric adenocarcinoma. , 1987, Proceedings of the National Academy of Sciences of the United States of America.

[21]  L. Peso,et al.  Interleukin-3-induced phosphorylation of BAD through the protein kinase Akt. , 1997, Science.

[22]  J. Downward.  Mechanisms and consequences of activation of protein kinase B/Akt. , 1998, Current opinion in cell biology.

[23]  J. Cheng,et al.  Molecular alterations of the AKT2 oncogene in ovarian and breast carcinomas , 1995, International journal of cancer.

[24]  P. Cohen,et al.  Characterization of a 3-phosphoinositide-dependent protein kinase which phosphorylates and activates protein kinase Bα , 1997, Current Biology.

[25]  C. Turck,et al.  Membrane Ig cross-linking regulates phosphatidylinositol 3-kinase in B lymphocytes. , 1992, Journal of immunology.

[26]  Colin B. Reese,et al.  3-Phosphoinositide-dependent protein kinase-1 (PDK1): structural and functional homology with the Drosophila DSTPK61 kinase , 1997, Current Biology.

[27]  N. Isakov.  ITIMs and ITAMs , 1997, Immunologic research.

[28]  T. Yamamoto,et al.  Association of B cell antigen receptor with protein tyrosine kinase Lyn. , 1991, Science.

[29]  T. Yamamoto,et al.  Impaired proliferation of peripheral B cells and indication of autoimmune disease in lyn-deficient mice. , 1995, Immunity.

[30]  Tony Pawson,et al.  Syk tyrosine kinase required for mouse viability and B-cell development , 1995, Nature.

[31]  S. R. Datta,et al.  Akt Phosphorylation of BAD Couples Survival Signals to the Cell-Intrinsic Death Machinery , 1997, Cell.

[32]  B. B. Mishell,et al.  Selected Methods in Cellular Immunology , 1980 .

[33]  J. Testa,et al.  A retroviral oncogene, akt, encoding a serine-threonine kinase containing an SH2-like region. , 1991, Science.

[34]  J. Cyster,et al.  Polygenic autoimmune traits: Lyn, CD22, and SHP-1 are limiting elements of a biochemical pathway regulating BCR signaling and selection. , 1998, Immunity.

[35]  A. Burkhardt,et al.  Anti-immunoglobulin stimulation of B lymphocytes activates src-related protein-tyrosine kinases. , 1991, Proceedings of the National Academy of Sciences of the United States of America.