PROTEIN-KINASE-C AND CA2+ ACTIVATION OF MUCIN SECRETION IN AIRWAY GOBLET CELLS

Airway goblet cells secrete mucin in response to ATP and uridine 5'-tr iphosphate (UTP), but the underlying signal transduction pathways are poorly understood. Cultures of SPOC1 cells (L. H. Abdullah, S. W. Davi s, L. Burch, M. Yamauchi, S. H. Randell, P. Nettesheim, and C. W. Davi s. Biochem. J. 316: 943-951, 1996) secreted mucin on exposure to phorb ol 12-myristate 13-acetate (PMA) [apparent affinity (K-0.5) similar to 100 nM] and ionomycin (K-0.5 similar to 5 mu M) almost fivefold over baseline. Thapsigargin also elicited secretion (K-0.5 similar to 20 nM ). Ionomycin and PMA together elicited approximately twice the secreti on of either agent alone. Overnight exposure to half-maximal PMA aboli shed the response to maximal doses of UTP and PMA, whereas ionomycin w as fully effective. Protein kinase C (PKC) activity in the membrane fr action was increased by maximal doses of PMA and UTP, whereas ionomyci n had no effect. PKC inhibitors were relatively ineffective against PM A- and UTP-induced mucin secretion. Human and canine goblet cells in e pithelial explants, by video microscopy, underwent exocytosis with ion omycin (1 mu M) and PMA (0.1 or 1 mu M). SPOC1 cell mucin secretion wa s not stimulated by forskolin, 8-(4-chlorophenylthio)-adenosine 3',5'- cyclic monophosphate, or 8-bromoguanosine 3',5'-cyclic monophosphate. Cystic fibrosis transmembrane conductance regulator was not detected i n SPOC1 cells by Western blotting, and its mRNA was detected by revers e transcriptase polymerase chain reaction (PCR) only as a very weak ba nd and after 55 PCR cycles. Multidrug resistance (MDR1), however, was readily detected by Western blotting, and its mRNA was detected as a m ajor band after 35 PCR cycles. Thus airway goblet cell mucin secretion , distal to receptor activation, may be regulated independently by Ca2 +- and PKC-dependent pathways. Cystic fibrosis transmembrane conductan ce regulator and cyclic nucleotides, however, may not play a major rol e in this secretion.