Tyrosine residues in phospholipase C gamma 2 essential for the enzyme function in B-cell signaling

Institute of Cancer Research, Londinium, England, United Kingdom
Journal of Biological Chemistry (Impact Factor: 4.6). 01/2002; 276(51):47982-92. DOI: 10.1074/jbc.M107577200
Source: PubMed

ABSTRACT Phospholipase Cgamma (PLCgamma) isoforms are regulated through activation of tyrosine kinase-linked receptors. The importance of growth factor-stimulated phosphorylation of specific tyrosine residues has been documented for PLCgamma1; however, despite the critical importance of PLCgamma2 in B-cell signal transduction, neither the tyrosine kinase(s) that directly phosphorylate PLCgamma2 nor the sites in PLCgamma2 that become phosphorylated after stimulation are known. By measuring the ability of human PLCgamma2 to restore calcium responses to the B-cell receptor stimulation or oxidative stress in a B-cell line (DT40) deficient in PLCgamma2, we have demonstrated that two tyrosine residues, Tyr(753) and Tyr(759), were important for the PLCgamma2 signaling function. Furthermore, the double mutation Y753F/Y759F in PLCgamma2 resulted in a loss of tyrosine phosphorylation in stimulated DT40 cells. Of the two kinases that previously have been proposed to phosphorylate PLCgamma2, Btk, and Syk, purified Btk had much greater ability to phosphorylate recombinant PLCgamma2 in vitro, whereas Syk efficiently phosphorylated adapter protein BLNK. Using purified proteins to analyze the formation of complexes, we suggest that function of Syk is to phosphorylate BLNK, providing binding sites for PLCgamma2. Further analysis of PLCgamma2 tyrosine residues phosphorylated by Btk and several kinases from the Src family has suggested multiple sites of phosphorylation and, in the context of a peptide incorporating residues Tyr(753) and Tyr(759), shown preferential phosphorylation of Tyr(753).

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Small molecule inhibitors targeting dysregulated pathways (RAS/RAF/MEK, PI3K/AKT/mTOR, JAK/STAT) have significantly improved clinical outcomes in cancer patients. Recently Bruton's tyrosine kinase (BTK), a crucial terminal kinase enzyme in the B-cell antigen receptor (BCR) signaling pathway, has emerged as an attractive target for therapeutic intervention in human malignancies and autoimmune disorders. Ibrutinib, a novel first-in-human BTK-inhibitor, has demonstrated clinical effectiveness and tolerability in early clinical trials and has progressed into phase III trials. However, additional research is necessary to identify the optimal dosing schedule, as well as patients most likely to benefit from BTK inhibition. This review summarizes preclinical and clinical development of ibrutinib and other novel BTK inhibitors (GDC-0834, CGI-560, CGI-1746, HM-71224, CC-292, and ONO-4059, CNX-774, LFM-A13) in the treatment of B-cell malignancies and autoimmune disorders.
    Journal of Hematology & Oncology 08/2013; 6(1):59. DOI:10.1186/1756-8722-6-59 · 4.93 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Majority of patients with indolent B-cell lymphoma fail to achieve complete remission with current approaches and invariably relapse. During the last decade, innovative chemoimmunotherapy strategies have substantially improved disease control rates but not survival thus providing the rationale for development of novel agents targeting dysregulated pathways that are operable in these hematological malignancies. Ibrutinib, a novel first-in-human BTK inhibitor, has progressed into phase III trials after early phase clinical studies demonstrated effective target inhibition, increased tumor response rates, and significant improvement in survival particularly in patients with indolent B-cell lymphomas. Recently, the compound was designated a ‘breakthrough therapy’ by the FDA for the treatment of patients with relapsed/refractory MCL and WM. This review summarizes recent achievements of ibrutinib, with a focus on its emerging role in the treatment of patients with indolent B-cell lymphoid malignancies.
    Clinical lymphoma, myeloma & leukemia 01/2013; DOI:10.1016/j.clml.2013.11.005 · 1.93 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.
    Physiological Reviews 07/2013; 93(3):1019-137. DOI:10.1152/physrev.00028.2012 · 29.04 Impact Factor