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)

The functional and biochemical responses evoked by the addition of platelet-activating factor (PAF) to a suspension of rabbit neutrophils have been characterized in an effort to define the mode of action of this lipid mediator. PAF was found to elicit a secretory response and to stimulate a rapid breakdown of the polyphosphoinositides, an increase in the cytoplasmic level of free calcium (as monitored by quin2), a decrease in the fluorescence of cell-associated chlortetracycline, an enhanced activity of the sodium/hydrogen antiport, a transient depolarization, and an increase in the level of cytoskeletal actin. The quin2 response to PAF was found to be detectable at concentrations as low as 0.01 nM, to be very dependent on the presence of extracellular calcium, and to be sensitive to inhibition by phorbol esters. On the other hand, the increase in free calcium induced by PAF in the presence of extracellular calcium was essentially unaffected by pertussis toxin. PAF-induced neutrophil degranulation was similarly extracellular calcium dependent and phorbol ester sensitive. The secretory activity of PAF was evident only at concentrations in excess of 1 nM. All of the other effects of PAF were found to be independent of the presence of external calcium and to be demonstrable only at concentrations larger than 1 nM. In addition, all neutrophil responses to PAF (with the above noted exception of quin2) were potently inhibited by pertussis toxin. These results are interpreted in terms of the possible existence of two functionally distinct populations of receptors. The occupation of one set (of apparent high affinity) induces an increase in permeability to calcium in a phorbol-ester-, but not pertussis-toxin-, sensitive manner. The activation of the other set of receptors at higher concentrations of PAF stimulates the polyphosphoinositide-specific phospholipase C and induces the attendant biochemical responses. These latter responses appear to be mediated by a guanine-nucleotide-binding regulatory protein.
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PMID:Biochemical events associated with the stimulation of rabbit neutrophils by platelet-activating factor. 302 82

The PACAP receptor (PACAP I receptor, selective for PACAP) and the PACAP II VIP1 receptor (recognizing PACAP and VIP with the same high affinity) were stably expressed in Chinese Hamster Ovary (CHO) cells. Cell lines expressing different receptor densities, as measured by binding saturation curves, were selected. Inositol phosphate production was stimulated dose dependently in all the cell lines by PACAP and VIP, and the order of potency of the agonists was identical to that of high affinity receptor occupancy. The stimulatory effect of a saturating peptide concentration was proportional to the total receptor density. At similar receptor densities, however, the PACAP receptor mediated stimulation was higher than the VIP receptor-mediated stimulation. Pretreatment of the cells with pertussis toxin for 8 h had no effect on receptor densities, did not alter the PACAP stimulated inositol phosphate synthesis by the cells expressing the PACAP I receptor but markedly inhibited the response of the cells expressing the PACAP II VIP1 receptor. Thus, the present results indicate that the two G(s)-coupled PACAP I and PACAP II VIP1 receptors may stimulate IP production. The maximal stimulation depended on the number of receptor expressed; the PACAP I and PACAP II VIP1 receptors probably activated the phospholipase C through G proteins of the G(q), and of the G(i)/G(o) families, respectively.
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PMID:The pituitary adenylate cyclase activating polypeptide (PACAP I) and VIP (PACAP II VIP1) receptors stimulate inositol phosphate synthesis in transfected CHO cells through interaction with different G proteins. 922 29

Pleckstrin homology (PH) domains are small protein modules involved in recruitment of signaling molecules to cellular membranes, in some cases by binding specific phosphoinositides. We describe use of a convenient "dot-blot" approach to screen 10 different PH domains for those that recognize particular phosphoinositides. Each PH domain bound phosphoinositides in the assay, but only two (from phospholipase C-delta1 and Grp1) showed clear specificity for a single species. Using soluble inositol phosphates, we show that the Grp1 PH domain (originally cloned on the basis of its phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) binding) binds specifically to D-myo-inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4) (the PtdIns(3,4,5)P3 headgroup) with KD = 27.3 nM, but binds D-myo-inositol 1,3,4-trisphosphate (Ins(1,3,4)P3) or D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) over 80-fold more weakly. We show that this specificity allows localization of the Grp1 PH domain to the plasma membrane of mammalian cells only when phosphatidylinositol 3-kinase (PI 3-K) is activated. The presence of three adjacent equatorial phosphate groups was critical for inositol phosphate binding by the Grp1 PH domain. By contrast, another PH domain capable of PI 3-K-dependent membrane recruitment (encoded by EST684797) does not distinguish Ins(1,3,4)P3 from Ins(1,3,4,5)P3 (binding both with very high affinity), despite selecting strongly against Ins(1,4,5)P3. The remaining PH domains tested appear significantly less specific for particular phosphoinositides. Together with data presented in the literature, our results suggest that many PH domains bind similarly to multiple phosphoinositides (and in some cases phosphatidylserine), and are likely to be regulated in vivo by the most abundant species to which they bind. Thus, using the same simple approach to study several PH domains simultaneously, our studies suggest that highly specific phosphoinositide binding is a characteristic of relatively few cases.
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PMID:Specificity and promiscuity in phosphoinositide binding by pleckstrin homology domains. 980 18