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)

We have recently generated a series of gamma/delta T cell clones able to kill, after in vitro immunization, an Epstein-Barr Virus-transformed B cell line (designated E418) in a non-major histocompatibility complex-requiring fashion. A monoclonal antibody, termed anti-10H3, produced against E418 was selected by its ability to block these cytotoxic interactions. Further analysis indicated that the inhibitory effects of anti-10H3 were highly selective (i.e., no blocking activity with multiple control clones used as effector cells; no alteration of the natural killer-like function mediated by the relevant gamma/delta clones against 10H3+ tumor cells such as Rex). The molecule immunoprecipitated by anti-10H3, termed TCT.1, was characterized as a 43-kD protein broadly distributed in the hematopoietic system. The TCT.1 molecule has been further studied here by protein microsequencing. Results show that the TCT.1-derived peptide sequences are virtually identical to corresponding regions of Blast-1, a previously described surface protein with unknown function. The likely identity of the two molecules has been strengthened by analyzing the susceptibility of TCT.1 to phosphatidylinositol-specific phospholipase C digestion in light of the known anchorage of Blast-1 to the cell membrane through a glycosyl-phosphatidylinositol-containing lipid. The TCT.1/Blast-1-encoding gene is well characterized; it belongs to the immunoglobulin gene superfamily and it is located in the same band of chromosome 1 as the CD1 gene cluster. Together, these data further support the view that proteins distinct from the conventional class I/II histocompatibility molecules are involved in specific T cell recognition.
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PMID:TCT.1, a target molecule for gamma/delta T cells, is encoded by an immunoglobulin superfamily gene (Blast-1) located in the CD1 region of human chromosome 1. 182 26

We have analyzed the induction and expression of Blast-1 at the mRNA and protein levels and demonstrated its identity with CD48. Blast-1/CD48 is expressed on a wider range of cell types, notably T cells and monocytes, than previously thought, but appears to be restricted to lymphoid and myeloid cells. Resting B and T cells express Blast-1/CD48 molecules at the cell surface; however, they lack the epitope recognized by the 17D6 mAb. Resting B cells express no detectable Blast-1/CD48 mRNA. Induction by EBV infection or stimulation with PMA, IL-4, or PHA results in increased levels of Blast-1/CD48 protein (both 6.28 and 17D6 epitopes) at the cell surface. Detailed analysis of EBV-induced expression revealed that it is due to increased steady-state levels of Blast-1/CD48 mRNA induced by transforming but not nontransforming strains of the virus. Induction by IL-1 beta, ionomycin, or suboptimal levels of PMA plus ionomycin results in increased expression of the 17D6 epitope only. In transfected Cos-7 cells Blast-1/CD48 at the cell surface expresses only the 6.28 epitope, whereas cytoplasmic molecules express both 17D6 and 6.28 epitopes. We suggest that these results are most consistent with the idea that Blast-1/CD48 molecules are complexed at the surface of resting cells and Cos-7 cells, resulting in masking of the 17D6 epitope. Activation causes dissociation of the complex, revealing the 17D6 epitope. The existence of 17D6+6.28- Blast-1/CD48 molecules was demonstrated by immunoprecipitation analysis, which also revealed that, unlike the rest of the molecules, this subset was resistant to digestion with glyosylphosphatidylinositol-specific phospholipase C.
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PMID:Expression of the Blast-1 activation/adhesion molecule and its identification as CD48. 184 79

Rat lymphocytes were found to aggregate in response to monoclonal antibodies to the glycosyl phosphatidylinositol (GPI)-anchored surface antigen CD48. This clustering required bivalent antibodies but was not Fc mediated. It was blocked by inhibitors of cellular metabolism and cytoskeletal function but not by antibodies to leucocyte function-associated antigen-1 (LFA-1) or intracellular adhesion molecule-1 (ICAM-1). The clusters were found to be due to homotypic adhesion of B cells, with T cells showing no response despite expressing equal levels of CD48. In addition, thymocytes, which are known to cluster in response to cross-linking of Thy-1, another GPI-anchored molecule, were found not to respond to cross-linking of CD48. These results suggest that specific signalling through CD48 in B cells, but not T cells, and through Thy-1, but not CD48, in thymocytes, lead to cell adhesion events. This differential signalling is interesting as neither CD48 nor Thy-1 have transmembrane or intracellular domains. Levels of CD48-associated protein kinase activity were very low in both B and T cells, and no difference in the susceptibility to cleavage with phosphatidylinositol-specific phospholipase C was detected between B- and T-cell CD48.
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PMID:Homotypic adhesion of rat B cells, but not T cells, in response to cross-linking of CD48. 813 6

The alternative CD2-mediated pathway of T cell activation, which is independent of MHC/peptide recognition by the TCR/CD3 complex, is dependent upon two signals being received by the CD2 molecule. The natural ligand for CD2 is CD58, but controversy exists over alternative or additional ligands that could deliver the second signal in vivo. We have used rat retinal pigment epithelial cells (RPE), which lack temperature-insensitive ligands for CD2 adhesion, to study Ag-independent T cell activation. Rat RPE cells expressed high levels of CD59 and low levels of another potential CD2 ligand, CD48, both in vitro and in the in vivo model of experimental autoimmune uveoretinitis. When increasing numbers of syngeneic T cells were added to microwell cultures of rat RPE cells, the T cells, even in the absence of any exogenous stimulant in the cultures, underwent spontaneous proliferation. This effect required metabolically active RPE cells, and was IL-2 driven and enhanced in the presence of indomethacin. Proliferation was modulated by phosphatidylinositol-phospholipase C treatment of the RPE, and blocked by mAbs to CD59. Ab cross-linking of CD48 but not CD59 on the RPE was found to induce messenger RNA expression for IL-1 beta, which together with constitutively expressed IL-6 are required costimulatory factors for T cell activation through CD2. This is the first demonstration in a fully syngeneic system that bi-directional signaling involving CD59 and CD48 molecules expressed by physiologically normal, nonhematopoietic, cells can trigger T lymphocyte activation and proliferation through autocrine IL-2 production in the absence of Ag.
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PMID:CD59 and CD48 expressed by rat retinal pigment epithelial cells are major ligands for the CD2-mediated alternative pathway of T cell activation. 862 4

Mast cells are well known for their harmful role in IgE-mediated hypersensitivity reactions, but their physiological role remains a mystery. Several recent studies have reported that mast cells play a critical role in innate immunity in mice by releasing tumor necrosis factor alpha (TNF-alpha) to recruit neutrophils to sites of enterobacterial infection. In some cases, the mast cell TNF-alpha response was triggered when these cells directly bound FimH on the surface of Escherichia coli. We have identified CD48, a glycosylphosphatidylinositol-anchored molecule, to be the complementary FimH-binding moiety in rodent mast cell membrane fractions. We showed that (i) pretreatment of mast cell membranes with antibodies to CD48 or phospholipase C inhibited binding of FimH+ E. coli, (ii) FimH+ E. coli but not a FimH- derivative bound isolated CD48 in a mannose-inhibitable manner, (iii) binding of FimH+ bacteria to Chinese hamster ovary (CHO) cells was markedly increased when these cells were transfected with CD48 cDNA, and (iv) antibodies to CD48 specifically blocked the mast cell TNF-alpha response to FimH+ E. coli. Thus, CD48 is a functionally relevant microbial receptor on mast cells that plays a role in triggering inflammation.
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PMID:The mast cell tumor necrosis factor alpha response to FimH-expressing Escherichia coli is mediated by the glycosylphosphatidylinositol-anchored molecule CD48. 1039 56

Interleukin (IL)-18 induces T cells and natural killer cells to produce not only interferon-gamma but also other cytokines by binding to the IL-18 receptor (IL-18R) alpha and beta subunits. However, little is known about how IL-18, IL-18Ralpha, and IL-18Rbeta form a high-affinity complex on the cell surface and transduce the signal. We found that IL-18 and IL-18Ralpha bind to glycosylphosphatidylinositol (GPI) glycan via the third mannose 6-phosphate diester and the second beta-GlcNAc-deleted mannose 6-phosphate of GPI glycan, respectively. To determine which GPI-anchored glycoprotein is involved in the complex of IL-18 and IL-18Ralpha, IL-18Ralpha of IL-18-stimulated KG-1 cells was immunoprecipitated together with CD48 by anti-IL-18Ralpha antibody. More than 90% of CD48 was detected as beta-GlcNAc-deleted GPI-anchored glycoprotein, and soluble recombinant human CD48 without GPI glycan bound to IL-18Ralpha, indicating that CD48 is associated with IL-18Ralpha via both the peptide portion and the GPI glycan. To investigate whether the carbohydrate recognition of IL-18 is involved in physiological activities, KG-1 cells were digested with phosphatidylinositol-specific phospholipase C before IL-18 stimulation. Phosphatidylinositol-specific phospholipase C treatment inhibited the phosphorylation of tyrosine kinases and the following IL-18-dependent interferon-gamma production. These observations suggest that the complex formation of IL-18.IL-18Ralpha. CD48 via both the peptide portion and GPI glycan triggers the binding to IL-18Rbeta, and the IL-18.IL-18Ralpha.CD48.IL-18Rbeta complex induces cellular signaling.
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PMID:Functional role played by the glycosylphosphatidylinositol anchor glycan of CD48 in interleukin-18-induced interferon-gamma production. 1576 Sep 5

Regulation by the NK and T cell surface receptor CD244 in mice and humans depends both on engagement at the cell surface by CD48 and intracellular interactions with SAP and EAT-2. Relevance to human disease by manipulating CD244 in mouse models is complicated by rodent CD2 also binding CD48. We distinguish between contributions of mouse CD244 and CD2 on engagement of CD48 in a mouse T cell hybridoma. CD2 and CD244 both contribute positively to the immune response as mutation of proline-rich motifs or tyrosine motifs in the tails of CD2 and CD244, respectively, result in a decrease in antigen-specific interleukin-2 production. Inhibitory effects of mouse CD244 are accounted for by competition with CD2 at the cell surface for CD48. In humans CD2 and CD244 are engaged separately at the cell surface but biochemical data suggest a potential conserved intracellular link between the two receptors through FYN kinase. We identify a novel signaling mechanism for CD244 through its potential to recruit phospholipase C-gamma1 via the conserved phosphorylated tyrosine motif in the tail of the adaptor protein EAT-2, which we show is important for function.
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PMID:Inhibition and activation by CD244 depends on CD2 and phospholipase C-gamma1. 1958 19