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 report here that a synthetic peptide of the effector domain of the small-molecular-weight GTP-binding protein Rab3A (EDRab3AL) is a potent stimulator of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production and amylase secretion in digitonin-permeabilized pancreatic acini. Moreover, the Rab3A effector domain peptide caused phosphatidylinositol 4,5-bisphosphate breakdown, indicating that the observed increase in Ins(1,4,5)P3 is due to stimulation of a phosphoinositide-specific phospholipase C (PLC). The dose-response curve for EDRab3AL-induced amylase release was biphasic, showing a maximum at 0.3 nM EDRab3AL and a decline at higher peptide concentrations. By contrast, the dose-response curve for EDRab3AL-induced Ins(1,4,5)P3 production was monophasic, showing stimulation with increasing EDRab3AL concentrations. A peptide of the effector domain of Rab1A, EDRab1AL, had no effect, indicating that the response to EDRab3AL is specific. Cholecystokinin octapeptide (CCK-8) and EDRab3AL had additive effects on the acinar Ins(1,4,5)P3 level. Epidermal growth factor (EGF), which has recently been shown to inhibit CCK-8-induced Ins(1,4,5)P3 production in pancreatic acinar cells, also decreased EDRab3AL-induced Ins(1,4,5)P3 production. These results suggest that EDRab3AL and CCK-8 act on the same EGF-inhibitable PLC by independent mechanisms. CCK-8 increased and EGF decreased amylase release in response to submaximal EDRab3AL concentrations. By contrast, at supramaximal EDRab3AL concentrations EGF increased and CCK-8 decreased EDRab3AL-stimulated amylase release. EDRab3AL had no effect in intact acini, indicating that the site of action of EDRab3AL is intracellular. We conclude that EDRab3AL regulates phosphoinositide-specific PLC activity and thereby amylase secretion in an analogous fashion to CCK-8, but from within the cell.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effect of a Rab3A effector domain-related peptide, CCK, and EGF in permeabilized pancreatic acini. 752 41

Rab3 proteins are localized on secretory vesicles and appear to be involved in regulated exocytosis. We have previously shown that a modified peptide corresponding to the effector domain of the small molecular mass GTP-binding protein Rab3A, Rab3AAL, stimulates inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] production and amylase release in digitonin-permeabilized pancreatic acini. Experiments using monoclonal antibodies reveal that the Rab3-like protein present in pancreatic acini is not the Rab3A isoform. However, since the putative effector domains of the four as yet known Rab3 proteins (A, B, C and D) differ only in the C-terminal four amino acid residues, Rab3A effector domain peptide could mimic the action of the pancreas-specific Rab3 isoform. In the present study we report that peptides corresponding to the different Rab3 isoforms stimulate both Ins(1,4,5)P3 production and amylase secretion with an order of potency Rab3B/D > Rab3AAL > Rab3A = Rab3C. For Rab3A, B/D and C effector domain peptides the concentrations causing half-maximal response (EC50) were 3, 0.2 and 3 nM for Ins(1,4,5)P3 accumulation and 0.3, 0.02 and 0.3 nM for amylase release, respectively. A Rab1A effector domain peptide, Rab1AAL, and a scrambled peptide of Rab3AAL were less potent by several orders of magnitude in eliciting these responses compared with native Rab3 effector domain peptides. None of the peptides influenced Ins(1,4,5)P3 production and amylase release in intact acini. Cross-linking of 125I-Rab3B/D peptide to pancreatic acinar membranes showed a band at 70 to 75 kDa with maximum intensity at 75 kDa. Radiolabelling of the substrates could be displaced by unlabelled Rab3B/D peptide, and to a lesser extend by Rab3A peptide, whereas the scrambled peptide of Rab3AAL had no effect. These data suggest that phospholipase C and exocytosis might be regulated by Rab3B-or Rab3D-like proteins in pancreatic acinar cells. A 75 kDa protein that preferentially cross-linked to 125I-Rab3B/D effector domain peptide is a potential candidate as an effector protein of Rab3 effector domain peptides.
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PMID:Stimulation of inositol 1,4,5-trisphosphate production by peptides corresponding to the effector domain of different Rab3 isoforms and cross-linking of an effector domain peptide target. 762 28

Synthetic peptides corresponding to the effector domain of the small molecular weight GTP-binding protein Rab3A are known to stimulate exocytosis in various secretory cells. In the present study, we report that Rab3A effector domain peptide (33-48) causes accumulation of inositol 1,4,5-trisphosphate (1,4,5-IP3) in permeabilized pancreatic acinar cells, hepatocytes, 3T3 fibroblasts, and SH-SY5Y neuroblastoma cells. A scrambled peptide of Rab3A had no effect showing specificity of the Rab3A peptide response. No effect was observed in intact cells indicating that the target of the peptide is located intracellularly. We conclude that Rab3 effector domain peptide-induced accumulation of 1,4,5-IP3 is a wide-spread phenomenon, suggesting regulation of phosphoinositide-specific phospholipase C by Rab3-like proteins.
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PMID:Synthetic Rab3A effector domain peptide stimulates inositol 1,4,5-trisphosphate production in various permeabilized cells. 809 53