Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Sam68 is a member of a growing family of proteins that contain a single KH domain embedded in a larger conserved domain of approximately 170 amino acids. Loops 1 and 4 of this KH domain family are longer than the corresponding loops in other KH domains and contain conserved residues. KH domains are protein motifs that are involved in RNA binding and are often present in multiple copies. Here we demonstrate by coimmunoprecipitation studies that Sam68 self-associated and that cellular RNA was required for the association. Deletion studies demonstrated that the Sam68 KH domain loops 1 and 4 were required for self-association. The Sam68 interaction was also observed in Saccharomyces cerevisiae by the two-hybrid system. In situ chemical cross-linking studies in mammalian cells demonstrated that Sam68 oligomerized in vivo. These Sam68 complexes bound homopolymeric RNA and the SH3 domains of p59fyn and phospholipase Cgamma1 in vitro, demonstrating that Sam68 associates with RNA and signaling molecules as a multimer. The formation of the Sam68 complex was inhibited by p59fyn, suggesting that tyrosine phosphorylation regulates Sam68 oligomerization. Other Sam68 family members including Artemia salina GRP33, Caenorhabditis elegans GLD-1, and mouse Qk1 also oligomerized. In addition, Sam68, GRP33, GLD-1, and Qk1 associated with other KH domain proteins such as Bicaudal C. These observations indicate that the single KH domain found in the Sam68 family, in addition to mediating protein-RNA interactions, mediates protein-protein interactions.
Mol Cell Biol 1997 Oct
PMID:Self-association of the single-KH-domain family members Sam68, GRP33, GLD-1, and Qk1: role of the KH domain. 931 29

In RBL-2H3 tumor mast cells, cross-linking the high affinity IgE receptor (FcepsilonRI) with antigen activates cytosolic tyrosine kinases and stimulates Ins(1,4,5)P3 production. Using immune complex phospholipase assays, we show that FcepsilonRI cross-linking activates both PLCgamma1 and PLCgamma2. Activation is accompanied by the increased phosphorylation of both PLCgamma isoforms on serine and tyrosine in antigen-treated cells. We also show that the two PLCgamma isoforms have distinct subcellular localizations. PLCgamma1 is primarily cytosolic in resting RBL-2H3 cells, with low levels of plasma membrane association. After antigen stimulation, PLCgamma1 translocates to the plasma membrane where it associates preferentially with membrane ruffles. In contrast, PLCgamma2 is concentrated in a perinuclear region near the Golgi and adjacent to the plasma membrane in resting cells and does not redistribute appreciably after FcepsilonRI cross-linking. The activation of PLCgamma1, but not of PLCgamma2, is blocked by wortmannin, a PI 3-kinase inhibitor previously shown to block antigen-stimulated ruffling and to inhibit Ins(1,4,5)P3 synthesis. In addition, wortmannin strongly inhibits the antigen-stimulated phosphorylation of both serine and tyrosine residues on PLCgamma1 with little inhibition of PLCgamma2 phosphorylation. Wortmannin also blocks the antigen-stimulated translocation of PLCgamma1 to the plasma membrane. Our results implicate PI 3-kinase in the phosphorylation, translocation, and activation of PLCgamma1. Although less abundant than PLCgamma2, activated PLCgamma1 may be responsible for the bulk of antigen-stimulated Ins(1,4,5)P3 production in RBL-2H3 cells.
Mol Biol Cell 1998 Feb
PMID:Wortmannin-sensitive phosphorylation, translocation, and activation of PLCgamma1, but not PLCgamma2, in antigen-stimulated RBL-2H3 mast cells. 945 Sep 69

BKS-2 is an immature B cell lymphoma that undergoes apoptotic cell death when signaled via its surface IgM receptor. To study the signaling components of surface IgM mediated apoptosis in B lymphoma cells, we generated mutants of BKS-2 that were resistant to anti-IgM induced apoptosis. One mutant cell line, 1.B5, did not undergo apoptotic cell death upon treatment with anti-IgM antibodies and also did not exhibit elevation of intracellular Ca2+ in response to cross-linking of surface IgM. This appeared to be due to a defect in protein tyrosine kinase (PTK) activity since fewer proteins were tyrosine phosphorylated in the mutant cells stimulated with anti-IgM when compared to wild type BKS-2. Subsequently, we showed that protein tyrosine kinases lyn and blk were inducibly tyrosine phosphorylated in the wild type BKS-2 but not in 1.B5 mutant cells in response to anti-IgM. Also the kinase activity of lyn was elevated in the wild type but not in mutant cells upon triggering through surface IgM. Furthermore, tyrosine phosphorylation of CD19, a known substrate of lyn, was inducible in anti-IgM stimulated BKS-2 cells but severely reduced in 1.B5 cells. In contrast, kinase activity of another src kinase, blk, was increased on anti-IgM stimulation in both wild type and mutant cells. Surprisingly, syk, a non-src protein tyrosine kinase important for surface IgM mediated signaling, was tyrosine phosphorylated in the lyn deficient mutant cells as well as in the wild type BKS-2 cells. Furthermore, anti-IgM induced increase in kinase activity of syk was similar in the mutant and wild type cells. Thus, in contrast to other studies that propose syk to be a downstream target of src family kinases, syk may act upstream of lyn in immature B cells. Consistent with a functional syk, its target, phospholipase gamma2 (PLC-gamma2) was normally tyrosine phosphorylated in mutant cells.
Mol Immunol
PMID:Activation of syk in an immature B cell line does not require lyn activity. 946 22

The secreted form of beta-amyloid precursor protein (sAPP) has been reported to exert various biological activities in cultured neurons. The signal transduction mechanisms underlying these physiological functions of sAPP remain unclear. We now report that treatment of neural cells with the secreted form of APP695 (sAPP695) leads to dose- and time-dependent increase in phosphorylation of the endogenous substrates with a molecular mass of 80, 57 and 43 kDa. Pretreatment of cells with protein kinase C (PKC) inhibitor H-7 reduced phosphorylation of the 80- and 43-kDa proteins in a dose-dependent manner. The effect of sAPP695 on the phosphorylation is mimicked by phorbol 12-myristate-13-acetate (PMA). Downregulation of PKC by prolonged treatment of cells with PMA abolished sAPP695-enhanced phosphorylation of the 80- and 43-kDa proteins, indicating PKC is involved in the sAPP695-enhanced phosphorylation of these proteins in the cells. We also suggest that the 80- and 43-kDa proteins phosphorylated by sAPP695-stimulation are the major PKC substrates myristoylated alanine-rich C-kinase substrate and growth-associated protein-43. Furthermore, we demonstrate that tyrosine phosphorylation of phospholipase Cgamma1 and formation of inositol 1,4,5-trisphosphate were increased by sAPP695-stimulation. These observations suggest that sAPP695 induces the activation of the signaling pathways through a stimulation of phosphoinositide-PKC cascade.
Brain Res Mol Brain Res 1998 Jan
PMID:Secreted form of beta-amyloid precursor protein activates protein kinase C and phospholipase Cgamma1 in cultured embryonic rat neocortical cells. 947 70

Platelet-activating factor acetylhydrolases (PAF-AHs, EC 3.1.1.47) constitute a unique and biologically important family of phospholipase A2s. They are related to neither the well-characterized secretory nor cytosolic PLA2s, and unlike them do not require Ca2+ for catalytic activity. The distinguishing property of PAF-AHs is their unique substrate specificity: they act on the phospholipid platelet-activating factor (PAF), and in some cases on proinflammatory polar phospholipids, from which they remove a short acyl moiety--acetyl in the case of PAF--located at the sn-2 position. Because PAF is found both in the plasma and in the cytosol of many tissues, PAF-acetylhydrolases are equally widely distributed in an animal organism. Recent crystallographic studies shed new light on the complex structure-function relationships in PAF-AHs.
Cell Mol Life Sci 1998 May
PMID:The structure and function of platelet-activating factor acetylhydrolases. 964 24

The amino-terminal, 138 amino acid C2 domain of cytosolic phospholipase A2 (cPLA2-C2) mediates an initial step in the production of lipid mediators of inflammation: the Ca2+-dependent translocation of the enzyme to intracellular membranes with subsequent liberation of arachidonic acid. The high resolution solution structure of this Ca2+-dependent, lipid-binding domain (CaLB) has been determined using heteronuclear three-dimensional NMR spectroscopy. Secondary structure analysis, derived from several sets of spectroscopic data, shows that the domain is composed of eight antiparallel beta-strands with six interconnecting loops that fits the "type II" topology for C2 domains. Using a total of 2370 distance and torsional restraints, the structure was found to be a beta-sandwich in the "Greek key" motif. The solution structure of cPLA2-C2 domain is very similar to the X-ray crystal structure of the C2 domain of phospholipase-C-delta and phylogenetic analysis clarifies the structural role of highly conserved residues. Calorimetric studies further demonstrate that cPLA2-C2 binds two Ca2+ with observed Kds of approximately 2 microM in an entropically assisted process. Moreover, regions on cPLA2-C2 interacting with membranes were identified by 15N-HSQC-spectroscopy of cPLA2-C2 in the presence of low molecular weight lipid micelles. An extended binding site was identified that binds the phosphocholine headgroup in a Ca2+-dependent manner and also interacts with proximal regions of the membrane surface. Based upon these results, a structural model is presented for the mechanism of association of cPLA2 with its membrane substrate.
J Mol Biol 1998 Jul 17
PMID:Solution structure and membrane interactions of the C2 domain of cytosolic phospholipase A2. 966 51

The expression of luteinizing hormone-releasing hormone (LHRH) and its receptors has been demonstrated in a number of human malignant tumors, including cancers of the breast, ovary, endometrium and prostate. These findings suggest the presence of an autocrine regulatory system based on LHRH. Recent studies in our laboratory have demonstrated that the function of LHRH produced by ovarian cancer cells is the inhibition of their proliferation. Dose-dependent antiproliferative effects of LHRH-agonists have been observed by several laboratories in cell lines derived from the above cancers. Interestingly, also LHRH-antagonists have marked antiproliferative activity in most of the ovarian, breast and endometrial cancer cell lines tested so far, indicating that the dichotomy of LHRH-agonists/LHRH-antagonists is not valid for the LHRH-system in cancer cells. In addition, our data suggest that the classical LHRH receptor signal transduction mechanisms known from the pituitary (phospholipase-C, protein kinase C, adenylyl cyclase) are not involved in the mediation of LHRH effects in cancer cells. Data obtained by several groups, including ours, rather suggest that LHRH analogs interfere with the signal transduction of growth-factor receptors and related oncogene products associated with tyrosine-kinase activity. The mechanism of action is probably an LHRH-induced activation of a phosphotyrosine phosphatase, counteracting the effects of receptor associated tyrosine kinase. In our hands, LHRH analogs virtually blocked the EGF-induced MAP-kinase activity of ovarian and endometrial cancer cells. The pharmacological exploitation of this mechanism might provide promising new therapies for these cancers.
J Steroid Biochem Mol Biol 1998 Apr
PMID:Effects of LHRH-analogues on mitogenic signal transduction in cancer cells. 969 74

As part of a cDNA library screen for clones that induce transformation of NIH 3T3 fibroblasts, we have isolated a cDNA encoding the murine homolog of the guanine nucleotide exchange factor RasGRP. A point mutation predicted to prevent interaction with Ras abolished the ability of murine RasGRP (mRasGRP) to transform fibroblasts and to activate mitogen-activated protein kinases (MAP kinases). MAP kinase activation via mRasGRP was enhanced by coexpression of H-, K-, and N-Ras and was partially suppressed by coexpression of dominant negative forms of H- and K-Ras. The C terminus of mRasGRP contains a pair of EF hands and a C1 domain which is very similar to the phorbol ester- and diacylglycerol-binding C1 domains of protein kinase Cs. The EF hands could be deleted without affecting the ability of mRasGRP to transform NIH 3T3 cells. In contrast, deletion of the C1 domain or an adjacent cluster of basic amino acids eliminated the transforming activity of mRasGRP. Transformation and MAP kinase activation via mRasGRP were restored if the deleted C1 domain was replaced either by a membrane-localizing prenylation signal or by a diacylglycerol- and phorbol ester-binding C1 domain of protein kinase C. The transforming activity of mRasGRP could be regulated by phorbol ester when serum concentrations were low, and this effect of phorbol ester was dependent on the C1 domain of mRasGRP. The C1 domain could also confer phorbol myristate acetate-regulated transforming activity on a prenylation-defective mutant of K-Ras. The C1 domain mediated the translocation of mRasGRP to cell membranes in response to either phorbol ester or serum stimulation. These results suggest that the primary mechanism of activation of mRasGRP in fibroblasts is through its recruitment to diacylglycerol-enriched membranes. mRasGRP is expressed in lymphoid tissues and the brain, as well as in some lymphoid cell lines. In these cells, RasGRP has the potential to serve as a direct link between receptors which stimulate diacylglycerol-generating phospholipase Cs and the activation of Ras.
Mol Cell Biol 1998 Dec
PMID:Regulation of RasGRP via a phorbol ester-responsive C1 domain. 981 87

Several studies have indicated that patients with bipolar disorder (BD) who respond well to lithium prophylaxis constitute a biologically distinct subgroup. Lithium is thought to stabilize mood by acting at the phosphoinositide cycle. We have investigated a polymorphism located in the gene (PLCG1) that codes for a gamma-1 isozyme of phospholipase (PLC), an enzyme that plays an important role in the phosphoinositide second messenger system. A population-based association study and a family-based linkage study were carried out on patients who were considered excellent responders to lithium prophylaxis. Response to lithium was evaluated prospectively with an average follow-up of 14.4 +/- 6.8 years. The PLCG1 polymorphism was investigated in 136 excellent lithium responders and 163 controls. In addition, the segregation of this marker was studied in 32 families ascertained through lithium-responsive bipolar probands. The allele distributions between lithium-responsive bipolar patients and controls were different, with a higher frequency of one of the PLCG1 polymorphisms in patients (chi2 = 8.09; empirical P = 0.033). This polymorphism, however, confers only a small risk (OR = 1.88, CI 1.19-3.00). Linkage studies with the same marker yielded modest support for the involvement of this gene in the pathogenesis of BD when unilineal families were considered (Max LOD = 1.45; empirical P = 0.004), but not in the whole sample. Our results provide preliminary evidence that a PLC isozyme may confer susceptibility to bipolar disorder, probably accounting for a fraction of the total genetic variance. Whether this polymorphism is implicated in the pathogenesis of BD or in the mechanism of lithium response remains to be determined.
Mol Psychiatry 1998 Nov
PMID:Evidence for a role of phospholipase C-gamma1 in the pathogenesis of bipolar disorder. 985 80

Activation of protein kinase A (PKA) in B lymphocytes prior to the ligation of the B cell antigen receptor (BCR) results in a profound inhibition of BCR induced proliferation. The major effect of increased PKA activity in B lymphocytes was the induction of apoptosis leading to a reduced BCR induced growth response. The growth promoting cytokine IL-4 rescued B lymphocytes from PKA mediated negative effects. IL-4 protected BCR stimulated cells from PKA mediated inhibition primarily by preventing apoptosis and growth arrest. PKA-activation caused a downregulation of anti-IgM induced expression of Bcl-xL protein, that was restored by IL-4. Previous studies have shown that PKA-activation blocks BCR induced phospholipase Cgamma-activation and calcium mobilization. IL-4 was unable to overcome the block in anti-IgM mediated calcium mobilization due to PKA-activation. B cell apoptosis induced by PKA-activation was also seen in CD72 stimulated cells, although CD72 mediated B-lymphocyte proliferation was not affected. PKA mediated block in phospholipase gamma-activation and calcium mobilization were not due to alterations in the activation of tyrosine kinases lyn, blk and syk. Moreover, BCR mediated tyrosine phosphorylation of PLC gamma2 and CD19 were also unaffected by cAMP accumulation. These observations are in contrast to the ability of PKA to drastically reduce the activity of ZAP-70 and syk in T lymphocytes and neutrophils, respectively. The IL-4 mediated protection appears to be due to a change in late events in BCR signaling, which are important for Bcl-xL expression.
Mol Immunol 1998 Oct
PMID:Interleukin-4 overcomes the negative influence of cyclic AMP accumulation on antigen receptor stimulated B lymphocytes. 988 95


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