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).
"Activated BTK can interact with adapter protein BLNK/SLP65 through its SH2 domain. The complex can then activate phospholipase C (PLC)-γ2 , triggering a cascade of events that culminates in sustained intracellular calcium influx and indirect activation of downstream transcriptional signaling such as MEK/ERK, p38 MAPK, and JNK/SAPK pathways (Figure 2) [27,28,33-35]. Other downstream substrates of BTK include transcription factors BAP-135/TFII-I, NFκB, ARID3A, STAT3 and NFAT, where BTK plays a critical role in direct transcription regulation and the expression of hundreds of genes [29,31,34,36]. "
[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.
"It has been proposed that the negatively charged XY-linkers of these PLCs prevent PtdIns(4,5)P2 gaining access to the active site, by a combination of steric exclusion and electrostatic repulsion of negatively charged membranes (Hicks et al., 2008). The PLCγ XY-linker possesses additional regulatory domains: a PH domain, two SH2 domains and an SH3 domain, and this enzyme is activated by tyrosine phosphorylation within the XY-linker region (Rodriguez et al., 2001; Ozdener et al., 2002; Sekiya et al., 2004). A recent study suggested that the general mechanism of PLC auto-inhibition mediated by the XY-linker region also applies to PLCγ isozymes and the crucial determinant for the auto-inhibition is the C-terminal SH2 domain (Gresset et al., 2010). "
[Show abstract][Hide abstract] ABSTRACT: Phospholipase C-zeta (PLCζ) is a strong candidate for the mammalian sperm-derived factor that triggers the Ca(2+) oscillations required for egg activation at fertilization. PLCζ lacks a PH domain, which targets PLCδ1 to the phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)) substrate in the plasma membrane. Previous studies failed to detect PLCζ in the plasma membrane, hence the means of PLCζ binding to PtdIns(4,5)P(2) is unclear. We find that the PLCζ XY linker, but not the C2 domain, exhibits robust binding to PtdIns(4,5)P(2) or to liposomes containing near-physiological levels of PtdIns(4,5)P(2). The role of positively charged residues within the XY linker was addressed by sequentially substituting alanines for three lysine residues, K374, K375 and K377. Microinjection of these mutants into mouse eggs enabled their Ca(2+) oscillation-inducing activities to be compared with wild-type PLCζ. The XY-linker mutant proteins were purified and the in vitro PtdIns(4,5)P(2) hydrolysis and binding properties were monitored. Successive reduction of net positive charge within the PLCζ XY linker significantly affects both in vivo Ca(2+)-oscillation-inducing activity and in vitro PtdIns(4,5)P(2) interaction of mouse PLCζ. Our data suggest that positively charged residues within the XY linker play an important role in the PLCζ interaction with PtdIns(4,5)P(2), a crucial step in generating the Ca(2+) activation signal that is essential for fertilization in mammals.
"tibody were greatly reduced . The interaction of GIT1 with PLCγ1 also appeared to be dependent upon integrin engagement . The data in Fig . 4A , B suggest that PLCγ1 is placed downstream of Src kinases . In addition , it has been reported that PLCγ isoforms can be phosphorylated directly by several members of the Src family ( Liao et al . , 1993 ; Rodriguez et al . , 2001 ) . In agreement with these previous observations , we found that purified Src , Fyn and Lck can phosphorylate PLCγ1 in vitro . Furthermore , unlike Syk tyrosine kinase , they were capable of phosphorylating the tyrosine residue critical for activation , Y783 ( Fig . 4D ) ; this residue was also phosphorylated in BE cells attached to Ma"
[Show abstract][Hide abstract] ABSTRACT: Cell motility is a critical event in many processes and is underlined by complex signalling interactions. Although many components have been implicated in different forms of cell migration, identification of early key mediators of these events has proved difficult. One potential signalling intermediate, PLCgamma1, has previously been implicated in growth-factor-mediated chemotaxis but its position and roles in more-complex motility events remain poorly understood. This study links PLCgamma1 to early, integrin-regulated changes leading to cell motility. The key role of PLCgamma1 was supported by findings that specific depletion of PLCgamma1 by small interfering (si)RNA, or by pharmacological inhibition, or the absence of this isoform in PLCgamma1(-/-) cells resulted in the failure to form cell protrusions and undergo cell spreading and elongation in response to integrin engagement. This integrin-PLCgamma1 pathway was shown to underlie motility processes involved in morphogenesis of endothelial cells on basement membranes and invasion of cancer cells into such three-dimensional matrices. By combining cellular and biochemical approaches, we have further characterized this signalling pathway. Upstream of PLCgamma1 activity, beta1 integrin and Src kinase are demonstrated to be essential for phosphorylation of PLCgamma1, formation of protein complexes and accumulation of intracellular calcium. Cancer cell invasion and the early morphological changes associated with cell motility were abolished by inhibition of beta1 integrin or Src. Our findings establish PLCgamma1 as a key player in integrin-mediated cell motility processes and identify other critical components of the signalling pathway involved in establishing a motile phenotype. This suggests a more general role for PLCgamma1 in cell motility, functioning as a mediator of both growth factor and integrin-initiated signals.
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