Protein kinase-A-mediated secretion of mucin from human colonic epithelialcells

Both Ca2+- and cAMP-mediated second messenger cascades acutely regulate muc in secretion from human colonic epithelial cells. To better understand the cAMP-dependent regulation of mucin secretion we have characterized the comp lement of cAMP-dependent protein kinase (PKA) isoforms in mucus-secreting T 84 cells, and determined which of these isoforms is responsible for agonist -stimulated mucin secretion. Our results show the presence of both type I a nd type II PKA in cells that also contain large mucin granules. Forskolin c aused a rapid and sustained increase in PKA activity that reached a maximum 5-10 min following its addition. Secretion of mucin was detected 15 min fo llowing exposure to forskolin, and continued to increase for a further 15 m in before reaching a plateau. Mucin secretion was also measured in the pres ence of combinations of site-selective cAMP analog pairs, which preferentia lly activate either type I or type II PKA. Similar levels of mucin secretio n were observed for both type I and type II PKA-selective analog pairs. Sub sequent addition of forskolin was unable to further increase mucin secretio n. Thus, activation of either type I or type II PKA is able to maximally st imulate secretion of mucins from T84 human colonic epithelial cells. J. Cel l. Physiol. 185:408-415, 2000. (C) 2000 Wiley-Liss, Inc.