TGF-beta effects on epithelial ion transport and barrier: reduced Cl- secretion blocked by a p38 MAPK inhibitor.
Growth factors affect a variety of epithelial functions. We examined the ability of TGF-beta to modulate epithelial ion transport and permeability. Filter-grown monolayers of human colonic epithelia, T84 and HT-29 cells, were treated with TGF-beta (0.1-100 ng/ml, 15 min-72 h) or infected with an adenoviral vector encoding TGF-beta (Ad-TGF beta) for 144 h. Ion transport (i.e., short-circuit current, I(sc)) and transepithelial resistance (TER) were assessed in Ussing chambers. Neither recombinant TGF-beta nor Ad-TGF beta infection affected baseline I(sc); however, exposure to > or = 1 ng/ml TGF-beta led to a significant (30-50%) reduction in the I(sc) responses to forskolin, vasoactive intestinal peptide, and cholera toxin (agents that evoke Cl(-) secretion via cAMP mobilization) and to the cell-permeant dibutyryl cAMP. Pharmacological analysis of signaling pathways revealed that the inhibition of cAMP-driven epithelial Cl(-) secretion by TGF-beta was blocked by pretreatment with SB-203580, a specific inhibitor of p38 MAPK, but not by inhibitors of JNK, ERK1/2 MAPK, or phosphatidylinositol 3'-kinase. TGF-beta enhanced the barrier function of the treated monolayers by up to threefold as assessed by TER; however, this event was temporally displaced from the altered I(sc) response, being statistically significant only at 72 h posttreatment. Thus, in addition to TGF-beta promotion of epithelial barrier function, we show that this growth factor also reduces responsiveness to cAMP-dependent secretagogues in a chronic manner and speculate that this serves as a braking mechanism to limit secretory enteropathies.
Howe
Kathryn
K
Intestinal Disease Research Program, Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada L8N 3Z5.
Gauldie
Jack
J
McKay
Derek M
DM
D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000378:metabolism* / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018014:Gene Transfer Techniques; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000502:physiology; D007477:Ions; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*; D010539:Permeability / Q000187:drug effects; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011725:Pyridines / Q000494:pharmacology*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases
D002712:Chlorides; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007477:Ions; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011725:Pyridines; D016212:Transforming Growth Factor beta; D005576:Colforsin; D000242:Cyclic AMP; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580