EGF inhibits muscarinic receptor-mediated calcium signaling in a human salivary cell line.
The effects of epidermal growth factor (EGF) on intracellular calcium ([Ca(2+)](i)) responses to the muscarinic agonist carbachol were studied in a human salivary cell line (HSY). Carbachol (10(-4) M)-stimulated [Ca(2+)](i) mobilization was inhibited by 40% after 48-h treatment with 5 x 10(-10) M EGF. EGF also reduced carbachol-induced [Ca(2+)](i) in Ca(2+)-free medium and Ca(2+) influx following repletion of extracellular Ca(2+). Under Ca(2+)-free conditions, thapsigargin, an inhibitor of Ca(2+) uptake to internal stores, induced similar [Ca(2+)](i) signals in control and EGF-treated cells, indicating that internal Ca(2+) stores were unaffected by EGF; however, in cells exposed to thapsigargin, Ca(2+) influx following Ca(2+) repletion was reduced by EGF. Muscarinic receptor density, assessed by binding of the muscarinic receptor antagonist L-[benzilic-4,4'-(3)HCN]quinuclidinyl benzilate ([(3)H]QNB), was decreased by 20% after EGF treatment. Inhibition of the carbachol response by EGF was not altered by phorbol ester-induced downregulation of protein kinase C (PKC) but was enhanced upon PKC activation by a diacylglycerol analog. Phosphorylation of mitogen-activated protein kinase (MAP kinase) and inhibition of the carbachol response by EGF were both blocked by the MAP kinase pathway inhibitor PD-98059. The results suggest that EGF decreases carbachol-induced Ca(2+) release from internal stores and also exerts a direct inhibitory action on Ca(2+) influx. A decline in muscarinic receptor density may contribute to EGF inhibition of carbachol responsiveness. The inhibitory effect of EGF is mediated by the MAP kinase pathway and is potentiated by a distinct modulatory cascade involving activation of PKC. EGF may play a physiological role in regulating muscarinic receptor-stimulated salivary secretion.
Zhang
B X
BX
Medical Research Service, Texas 78284, USA.
Yeh
C K
CK
Hymer
T K
TK
Lifschitz
M D
MD
Katz
M S
MS
D001667:Binding, Competitive / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D004075:Diglycerides / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012469:Salivary Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D004075:Diglycerides; D004791:Enzyme Inhibitors; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; C044295:1,2-dioctanoylglycerol; D004815:Epidermal Growth Factor; D011813:Quinuclidinyl Benzilate; D019284:Thapsigargin; D002217:Carbachol; D011493:Protein Kinase C; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium