Mucin secretion by T84 cells: stimulation by PKC, Ca2+, and a protein kinase activated by Ca2+ ionophore.
T84 adenocarcinoma cells were stimulated to secrete mucin by the phorbol ester phorbol 12-myristate 13-acetate (PMA) and Ca2+ ionophores A23187 and ionomycin. In Ca(2+)-containing media, maximal stimulation by PMA was significantly inhibited by staurosporine, but maximal A23187-stimulated secretion was not affected. Downregulation of protein kinase C (PKC) reduced maximal PMA-stimulated secretion without affecting the response to A23187. Thus PKC activation is not required for maximal Ca(2+)-mediated mucin secretion. PMA stimulated secretion in low-Ca2+ media, with and without intracellular chelation of Ca2+ by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. Surprisingly, Ca2+ ionophores also stimulated secretion under the same circumstances. Persistent A23187-stimulated secretion was strongly inhibited by the protein kinase inhibitors staurosporine and H-7. Secretion in Ca(2+)-containing media was also inhibited at submaximal levels of Ca(2+)-ionophore stimulation. These results indicate that PKC and Ca2+ stimulate mucin exocytosis independently. Ca2+ ionophores also stimulate secretion via a protein-kinase dependent pathway. Enhancement of protein kinase inhibition at lower Ca2+ concentrations suggests that the response could be mediated by a Ca2+ ionophore-induced depletion of an intracellular Ca2+ pool.
Forstner
G
G
Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
Zhang
Y
Y
McCool
D
D
Forstner
J
J
D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D000470:Alkaloids / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D003470:Culture Media; D015536:Down-Regulation; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D009077:Mucins / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000494:pharmacology*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000470:Alkaloids; D003470:Culture Media; D009077:Mucins; D047428:Protein Kinase Inhibitors; D000001:Calcimycin; D004533:Egtazic Acid; D011494:Protein Kinases; D011493:Protein Kinase C; D019311:Staurosporine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium