Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several mammalian mutant cell lines are deficient in the biosynthesis of glycophosphatidylinositol anchors for membrane proteins. When metabolically labeled with [3H]myo-inositol or [3H]mannose, two out of five mutant lines (SIA-b and EL4-f) accumulated abnormal lipids which remained undetectable in the corresponding parental cell lines. The most abundant glycolipid of SIA-b cells (named lipid X) was isolated and partially characterized using hydrofluoric acid, nitrous acid deamination, acetolysis, and exoglycosidase treatments alone or in combination. The partial structure for the carbohydrate moiety of lipid X is Man alpha-(X----)Man alpha-GlcN-inositol, X being a charged, HF-sensitive substituent (possibly phosphoethanolamine). Lipid X is largely resistant to phosphatidylinositol-specific phospholipase C treatment but can be rendered sensitive to the enzyme by treatment with methanolic NH3, which suggests the presence of an acyl chain on the inositol moiety. The lipid moieties of lipid X are heterogenous in that about 50% of headgroups remain bound to a lipid moiety after mild alkaline hydrolysis. Similarly, about 50% of the lipid moieties of Thy-1, a glycophosphatidylinositol-anchored surface glycoprotein, isolated from SIA, the parent of SIA-b cells or from EL4 lymphoma cells, are resistant to mild alkaline hydrolysis. Altogether the data suggest that the SIA-b mutant line lacks an enzyme acting late in the anchor glycolipid biosynthesis pathway.
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PMID:Characterization of glycophospholipid intermediate in the biosynthesis of glycophosphatidylinositol anchors accumulating in the Thy-1-negative lymphoma line SIA-b. 168 15

The glycosyl phosphatidylinositol (GPI) anchors that attach certain proteins to membranes are preassembled by sequential addition of glycan components to phosphatidylinositol (PI) before being transferred to nascent polypeptide. A cell-free system consisting of trypanosome membranes has been reported to catalyze GPI biosynthesis (Masterson, W. J., Doering, T. L., Hart, G. W., and Englund, P. T. (1989) Cell 56, 793-800; Menon, A. K., Schwarz, R. T., Mayor, S., and Cross, G. A. M. (1990) J. Biol. Chem. 265, 9033-9042). We now describe conditions for studying the initial steps of GPI biosynthesis in extracts of murine lymphoma cells. Two chloroform-soluble products, tentatively identified as [6-3H]GlcNAc-PI and [6-3H]GlcN-PI were generated during incubations of EL4 cell lysates with UDP-[6-3H]GlcNAc. The involvement of PI in the reaction was established by the sensitivity of the products to hydrolysis by PI-specific phospholipase C and the finding that the addition of exogenous PI to the incubation stimulated the reaction. The minor, more polar product was sensitive to nitrous acid cleavage and was converted to the major product, as judged by TLC, after treatment with acetic anhydride. The glycolipids generated in lymphoma extracts appeared to be the same as the products produced in parallel incubations with trypanosome membranes. Analysis of available lymphoma mutants deficient in Thy-1 surface expression revealed that extracts of the class A, C, and H mutants are completely defective in synthesizing GlcNAc-PI and GlcN-PI.
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PMID:Defective glycosyl phosphatidylinositol biosynthesis in extracts of three Thy-1 negative lymphoma cell mutants. 182 68

The transforming protein of mouse polyomavirus, the mouse middle T antigen (MomT), and its counterpart in the hamster polyomavirus, the hamster middle T antigen (HamT), interact with a number of cellular proteins. Among these are members of the Src family of tyrosine kinases, the phosphatidylinositol 3-kinase, the serine/threonine phosphatase PP2A and the adaptor protein Shc (in the case of MomT). However, both the relative affinity of these antigens for the members of the Src family and the tumor profile induced by their respective viruses are quite distinct. Particularly noteworthy are the preferential binding of Fyn by HamT and the induction of lymphoid malignancies by the hamster polyomavirus. Here we report that, when expressed in fibroblasts, HamT also associated with phospholipase C gamma (PLC gamma), which led to an increased intracellular concentration of inositol-1, 4, 5-trisphosphate. We also show that expression of HamT in the mouse T cell line EL4 was sufficient to induce transcription from interleukin-2 (IL-2), NFAT and NF kappa B reporter constructs. The immunosuppressant FK506 as well as dominant negative alleles of Ras and Raf inhibited HamT-induced IL-2 transcription. This, together with the observation of NFAT responses, suggests that the action of HamT depended at least in part on the integrity of signal transduction pathways elicited by activated PLC gamma. Furthermore, dominant negative Fyn but not the equivalent allele of Lck blocked HamT activation of IL-2 transcription, while both Lck and Fyn dominant negative alleles blocked LT cell receptor-mediated IL-2 transcriptional activation. These results support the hypothesis that Fyn is involved in signal transduction events leading to IL-2 transcriptional activation in T cells. Finally, the activation of IL-2 transcription by HamT and not by MomT shown here parallels the ability of the hamster polyomavirus to induce lymphoid malignancies.
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PMID:Induction of interleukin-2 transcription by the hamster polyomavirus middle T antigen: a role for Fyn in T cell signal transduction. 787

In the present study we investigated the interleukin (IL)-1beta and transforming growth factor-beta1 (TGF-beta1)-mediated proliferation, and production of IL-2 and TGF-beta, in the murine T-cell line, EL4.NOB-1. This cell line is resistant to TGF-beta concerning growth arrest but not autoinduction or suppression of IL-1-induced IL-2 production. When cocultured with IL-1beta, TGF-beta showed growth-promoting activity that could be antagonized by adding the phosphatidyl choline-dependent phospholipase C (PC-PLC) inhibitor, D609. Using specific enzyme inhibitors of protein kinases (PK) C and A, mitogen-activated protein kinase (MAPK), phospholipase A2 (PLA2), phosphatidylinositol-dependent (PI)-PLC and PC-PLC, we showed that IL-1beta-induced IL-2 synthesis was dependent on all investigated kinases and phospholipases, except PC-PLC. TGF-beta1 was able to inhibit IL-2 synthesis by the activation of PKA and MAPK. The same kinases are involved in TGF-beta autoinduction that is accompanied by a secretion of the active but not the latent growth factor and is antagonized by IL-1beta. Addition of the PI-PLC inhibitor, ET 18OCH3, or the PLA2 inhibitor (quinacrine) alone, resulted in secretion of latent TGF-beta and, in the case of ET 18OCH3, active TGF-beta. These data implicate a role for PI-PLC and PLA2 in the control of latency and secretion. Analysis of specific tyrosine activity and c-Fos expression showed synergistic but no antagonistic effects. These events are therefore not involved in IL- and TGF-beta-regulated IL-2 and TGF-beta production, but might participate in IL-1/TGF-beta-induced growth promotion.
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PMID:Analysis of interleukin (IL)-1 beta and transforming growth factor (TGF)-beta-induced signal transduction pathways in IL-2 and TGF-beta secretion and proliferation in the thymoma cell line EL4.NOB-1. 1007 17