Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.2.1.7 (BAL)
 1,977 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of Ag binding on B cell development and activation are mediated by intracellular signals initiated by the B cell AgR. In this report, we show that the B cell AgR regulates the production of inositol phospholipids involved in two different signal transduction pathways, the phosphatidylinositol 3-kinase (PtdIns 3-kinase) pathway and the phospholipase C (PLC) pathway. Phosphatidylinositol 3-phosphate (PtdIns3P), phosphatidylinositol 3,4-bisphosphate [PtdIns(3,4)P2], and phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] are produced by PtdIns 3-kinase, an enzyme that appears to be an essential component of tyrosine kinase-mediated signaling. Both PtdIns(3,4)P2 and PtdIns(3,4,5)P3 are likely to function as second messengers in vivo because they can activate the zeta isoform of protein kinase C (PKC) in vitro. We show that cross-linking of the B cell AgR with anti-Ig antibodies caused a five- to sixfold increase in the levels of PtdIns(3,4)P2 in both the mature B cell line BAL 17 and the immature B cell line WEHI-231. PtdIns(3,4)P2 levels increased within 15 s of anti-Ig addition and remained elevated for at least 5 min. AgR cross-linking also caused a slower increase in PtdIns3P levels (approximately 50% over control) and a small, transient increase in PtdIns(3,4,5)P3 levels. Thus, the B cell AgR activates the PtdIns 3-kinase pathway. The other inositol phospholipid signaling pathway involves PLC, which cleaves phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], yielding second messengers that increase intracellular calcium and activate other isoforms of PKC. We analyzed the effects of AgR signaling on PtdIns(4,5)P2 and its precursor, phosphatidylinositol 4-phosphate (PtdIns4P). Consistent with its ability to activate PLC, AgR ligation decreased the levels of PtdIns(4,5)P2. In contrast, AgR cross-linking increased the levels of PtdIns4P. Increased synthesis of PtdIns4P followed by phosphorylation at the D-5 position may prevent depletion of PtdIns(4,5)P2. Thus, signaling by the B cell AgR increases the levels of PtdIns 4-kinase products and PtdIns 3-kinase products. The simplest interpretation of our results is that the B cell AgR activates both PtdIns 3-kinase and PtdIns 4-kinase.
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PMID:Both phosphatidylinositol 3-kinase and phosphatidylinositol 4-kinase products are increased by antigen receptor signaling in B cells. 825 4

Cross-linking membrane Ig (mIg) on B cells stimulates tyrosine phosphorylation of proteins involved in signal transduction including the mIg-associated proteins Ig-alpha and Ig-beta, the tyrosine kinases p53/p56lyn, p55blk, p59fyn, and PTK72, phosphatidylinositol 3-kinase, phospholipase C gamma 1 and gamma 2, and the mitogen-activated protein kinase. We now show that the p21ras GTPase-activating protein (GAP) is also a substrate for mIg-activated tyrosine kinases. p21ras is a key regulator of cell growth and GAP may act as both a regulator of p21ras activity and as a downstream effector of p21ras. We found that mIg cross-linking caused a rapid increase in tyrosine phosphorylation of GAP in the immature B cell line WEHI-231, the mature B cell lines BAL 17 and Daudi, and the IgG-bearing B cell line A20. In fibroblasts, tyrosine kinase activation causes GAP to associate with two other tyrosine-phosphorylated proteins, p62 and p190, which have homologies to an RNA-binding protein and a transcriptional repressor, respectively. Similarly, mlg cross-linking induced the association of GAP with a 62-kDa tyrosine-phosphorylated protein in BAL 17, WEHI-231, and Daudi cells. Anti-Ig treatment also increased the amount of a 190-kDa tyrosine-phosphorylated protein associated with GAP in WEHI-231 and Daudi cells. After separation by SDS-PAGE and transfer to nitrocellulose, the tyrosine-phosphorylated p62 and p190 present in anti-GAP immunoprecipitates from B cells were capable of binding radiolabeled recombinant GAP, as previously reported for the GAP-associated p62 and p190 from fibroblasts. The amount of p62 that could be detected in this way after immunoprecipitation with antiphosphotyrosine antibodies was much greater from anti-IgM-treated BAL 17 cells than from unstimulated BAL 17 cells. This probably reflects anti-Ig-induced tyrosine phosphorylation of p62. In any case, GAP, p62, and/or p190 may be involved in signal transduction by mIg in B cells.
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PMID:Targets of B lymphocyte antigen receptor signal transduction include the p21ras GTPase-activating protein (GAP) and two GAP-associated proteins. 841 71