Cyclic AMP and chloride-dependent regulation of the apical constitutive secretory pathway in colonic epithelial cells.
Epithelial cells of the colonic crypt engage in cAMP-mediated fluid and electrolyte secretion. In addition to participating in electrolyte transport, colonic crypt cells also synthesize and secrete a number of proteins and peptides that play a crucial role in mucosal homeostasis. In the present study we show that cAMP regulates not only electrolyte secretion but also polarized protein secretion in a tissue culture model of colonic crypt cells. We found that apical but not basolateral protein secretion was stimulated by a physiological activator of the cAMP pathway, vasoactive intestinal peptide, as well as by a cell-permeant analogue of cAMP (8-(4-chlorophenylthio)cAMP) at concentrations as low as 12.5 microM. Based on several criteria, we determined that the regulation of protein secretion by cAMP in HT29-CL19A cells occurs via stimulation of constitutive membrane traffic from the trans-Golgi network (TGN) to the apical cell surface. In addition, the regulation of apical protein secretion by cAMP was Cl--dependent with cAMP inhibiting rather than stimulating secretion in Cl--depleted cells. The locus of cAMP action on the secretory pathway is at least in part at the level of the TGN, where it stimulates the sialylation of alpha1-antitrypsin (i.e. one of the identified secretory proteins) in addition to the traffic of secretory proteins from the TGN to the apical cell surface. We propose that a cyclic AMP and Cl--dependent regulation of TGN acidification could modulate both sialylation and secretory vesicle budding at the TGN.
Jilling
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Department of Physiology and Biophysics, Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, 35294-0005, USA.
Kirk
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D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D002999:Clone Cells; D003110:Colonic Neoplasms; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004848:Epithelium / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008565:Membrane Proteins / Q000096:biosynthesis*; D012794:Sialic Acids / Q000378:metabolism; D013873:Thionucleotides / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D002712:Chlorides; D008565:Membrane Proteins; D012794:Sialic Acids; D013873:Thionucleotides; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000242:Cyclic AMP