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)

Mucin secretion by airway goblet cells is under the control of apical P2Y2, phospholipase C-coupled purinergic receptors. In SPOC1 cells, the mobilization of intracellular Ca2+ by ionomycin or the activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate (PMA) stimulates mucin secretion in a fully additive fashion [L. H. Abdullah, J. D. Conway, J. A. Cohn, and C. W. Davis. Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17): L201-L210, 1997]. This apparent independence between PKC and Ca2+ in the stimulation of mucin secretion was tested in streptolysin O-permeabilized SPOC1 cells. These cells were fully competent to secrete mucin when Ca2+ was elevated from 100 nM to 3.1 microM for 2 min following permeabilization; the Ca2+ EC50 was 2.29 +/- 0.07 microM. Permeabilized SPOC1 cells were exposed to PMA or 4alpha-phorbol at Ca2+ activities ranging from 10 nM to 10 microM. PMA, but not 4alpha-phorbol, increased mucin release at all Ca2+ activities tested: at 10 nM Ca2+ mucin release was 2.1-fold greater than control and at 4.7 microM Ca2+ mucin release was maximal (3.6-fold increase). PMA stimulated 27% more mucin release at 4.7 microM than at 10 nM Ca2+. Hence, SPOC1 cells possess Ca2+-insensitive, PKC-dependent, and Ca2+-dependent PKC-potentiated pathways for mucin granule exocytosis.
 ...
PMID:Ca2+ and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells. 968 60

Conceptually, in vitro models for airway mucin secretion may provide useful information pertinent to many aspects of goblet cell biology/physiology. Such models may be especially useful in identifying potential secretagogues, probing the distribution of receptors between goblet cell apical and basolateral membrane domains, and revealing intracellular messenger pathways underlying receptor activation. We have focused most recently on human bronchial epithelial cell cultures grown as tracheal xenografts and SPOC1 cell cultures. These two models are remarkably similar with respect to the regulation of mucin secretion: luminal challenges with the P2Y2 purinoceptor agonists ATP or UTP elicit mucin secretion with EC50s of about 3 microM and archetypal agonists to other purinoceptors test negative. P2Y2 purinoceptors typically couple via Gq to phospholipase C, suggesting that intracellular Ca2+ and protein kinase C (PKC) are important in activating intracellular pathways leading to goblet cell mucin release. Consistent with this notion, phorbol myristate acetate and ionomycin elicit mucin secretion from SPOC1 cells and HBE xenografts, whereas cyclic nucleotides do not. Delineation of the molecules comprising these receptor/messenger interactions and their supporting pathways remains an important challenge for the development of drugs effective in therapeutic interventions in mucin hypersecretory airway diseases; with these models we have initiated the process.
 ...
PMID:Regulation of mucin secretion from in vitro cellular models. 1256 91

SPOC1 airway goblet cells secrete mucin in response to P2Y2 receptor agonists and to secretagogues, phorbol 12-myristate 13-acetate (PMA) and ionomycin, which mobilize elements of the phospholipase C pathway, PKC and Ca2+, respectively. Previous studies demonstrated that mucin secretion from SLO-permeabilized, EGTA-buffered SPOC1 cells was stimulated by PMA at low Ca2+ levels (< 0.1 microm), consistent with the notion that regulated exocytosis may occur by Ca2+-independent pathways. We tested the alternative hypothesis that PMA-induced mucin secretion is, in fact, a Ca2+-dependent process under the conditions of low bulk Ca2+, one that is permitted in the typical SLO-permeabilized cell model by the slow binding kinetics of EGTA. Both IP3 and elevated bulk Ca2+ activated mucin secretion in SPOC1 cells buffered by EGTA, suggesting that IP3 generates a local Ca2+ gradient in the vicinity of the secretory granules to the degree necessary to trigger exocytosis. BAPTA, which binds Ca2+ approximately 100-fold faster than EGTA, diminished IP3-induced mucin release over a range of concentrations by > or = 69%, yet maintained an essentially normal mucin secretory response to elevated bulk Ca2+ in permeabilized SPOC1 cells. BAPTA also diminished the mucin secretory response of permeabilized cells to PMA, relative to the EGTA-buffered control: at PMA below 30 nm, BAPTA abolished the secretory response, and at higher concentrations it was reduced significantly relative to the EGTA-buffered controls. PMA-induced secretion in EGTA was insensitive to heparin. These results suggest that Ca2+ is released locally during PMA-induced exocytosis, by an IP3-independent mechanism.
 ...
PMID:Ca2+ dependency of 'Ca2+-independent' exocytosis in SPOC1 airway goblet cells. 1521 74

Airway goblet cells secrete mucin onto mucosal surfaces under the regulation of an apical, phospholipase C/G(q)-coupled P2Y(2) receptor. We tested whether cortical actin filaments negatively regulate exocytosis in goblet cells by forming a barrier between secretory granules and plasma membrane docking sites as postulated for other secretory cells. Immunostaining of human lung tissues and SPOC1 cells (an epithelial, mucin-secreting cell line) revealed an apical distribution of beta- and gamma-actin in ciliated and goblet cells. In goblet cells, actin appeared as a prominent subplasmalemmal sheet lying between granules and the apical membrane, and it disappeared from SPOC1 cells activated by purinergic agonist. Disruption of actin filaments with latrunculin A stimulated SPOC1 cell mucin secretion under basal and agonist-activated conditions, whereas stabilization with jasplakinolide or overexpression of beta- or gamma-actin conjugated to yellow fluorescent protein (YFP) inhibited secretion. Myristoylated alanine-rich C kinase substrate, a PKC-activated actin-plasma membrane tethering protein, was phosphorylated after agonist stimulation, suggesting a translocation to the cytosol. Scinderin (or adseverin), a Ca(2+)-activated actin filament severing and capping protein was cloned from human airway and SPOC1 cells, and synthetic peptides corresponding to its actin-binding domains inhibited mucin secretion. We conclude that actin filaments negatively regulate mucin secretion basally in airway goblet cells and are dynamically remodeled in agonist-stimulated cells to promote exocytosis.
 ...
PMID:Barrier role of actin filaments in regulated mucin secretion from airway goblet cells. 1534 43

Mucus hyperproduction in pulmonary obstructive diseases results from increased goblet cell numbers and possibly increased cellular mucin synthesis, occurring in response to inflammatory mediators acting via receptor tyrosine kinases (RYK) and tyrosine phosphorylation (Y-Pi) signaling pathways. Yet, increased mucin synthesis does not lead necessarily to increased secretion, as mucins are stored in secretory granules and secreted in response to extracellular signals, commonly assumed to be mediated by G protein-coupled receptors (GPCRs). We asked whether activation 1) of Y-Pi signaling pathways, in principal, and 2) of the novel PKC isoform, nPKCdelta, by Y-Pi, specifically, might lead to regulated mucin secretion. nPKCdelta in SPOC1 cells was tyrosine phosphorylated by exposure to purinergic agonist (ATPgammaS) or PMA, actions that were blocked by the Src kinase inhibitor, PP1. Mucin secretion, however, was not affected by PP1. Hence, activation of nPKCdelta by Y-Pi is unlikely to participate in GPCR-related mucin secretion. Mucin secretion from both SPOC1 and normal human bronchial epithelial (NHBE) cells was stimulated by generalized protein Y-Pi induced by the tyrosine phosphatase inhibitor, pervanadate (PV). PV-induced SPOC1 cell mucin secretion was not affected by inhibition of Src kinases (genistein or PP1), or of PI3 kinase (LY-294002). MAP kinase pathway inhibitors, RAF1 kinase inhibitor-I and U0126 (MEK), inhibited SPOC1 cell PV-induced secretion by approximately 50%. Significantly, the phospholipase C (PLC) inhibitor, U-73122, essentially abolished PV- and ATPgammaS-induced mucin secretion from both SPOC1 and NHBE cells. Hence, PLC signaling may play a key role in regulated mucin secretion, whether the event is initiated by mediators interacting with GPCRs or RYKs.
 ...
PMID:Regulation of airway goblet cell mucin secretion by tyrosine phosphorylation signaling pathways. 1761 47