TGF-β effects on epithelial ion transport and barrier: reduced Cl⁻ secretion blocked by a p38 MAPK inhibitor

Abstract

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.

Transforming Growth Factor β1 Inhibits Cystic Fibrosis Transmembrane Conductance Regulator-dependent cAMP-stimulated Alveolar Epithelial Fluid Transport via a Phosphatidylinositol 3-Kinase-dependent Mechanism

“…First, for example, TGF-␤1 down-regulated CFTR expression and cAMP-dependent current across epithelial cell monolayers from nasal polyps (45). Second, TGF-␤1 decreased cAMP-dependent current across colonic epithelia via a decrease in CFTR mRNA and protein expression (46,47). Third, TGF-␤1 decreased adenylylcyclase mRNA expression in pulmonary artery smooth muscle cells (48).…”

Role for TGF-β in Cyclosporine-Induced Modulation of Renal Epithelial Barrier Function

“…The MEK inhibitor U0126 prevented residual ERK phosphorylation and abrogated the synergistic responses to TGF-␤1 and EGF. TGF-␤ enhanced epithelial barrier function of T84 and HT-29 monolayers up to three-fold (16). The barrier function could be restored by treatment with SB203580, an inhibitor of the p38 MAPK pathway, but not by inhibitors of c-Jun N-terminal kinase, ERK1/2 MAPK, or phosphatidylinositol 3-kinase (16).…”

“…TGF-␤ enhanced epithelial barrier function of T84 and HT-29 monolayers up to three-fold (16). The barrier function could be restored by treatment with SB203580, an inhibitor of the p38 MAPK pathway, but not by inhibitors of c-Jun N-terminal kinase, ERK1/2 MAPK, or phosphatidylinositol 3-kinase (16). In contrast, TGF-␤3 reduced Sertoli cell tight junction function (20).…”

“…TGF-␤ has been implicated in the modulation of paracel-lular permeability. TGF-␤1 enhanced the barrier function of intestinal epithelial monolayers and promoted intestinal epithelial restitution (12)(13)(14)(15)(16). A recent study demonstrated that TGF-␤ lowered endothelial permeability in mouse brain capillary endothelial cells, suggesting that cellular constituents that produce TGF-␤ in the brain may keep the blood-brain barrier functioning (17).…”

Transforming growth factor-β1 impairs CFTR-mediated anion secretion across cultured porcine vas deferens epithelial monolayer via the p38 MAPK pathway

“…the effect of TGF-␤1 on vas deferens epithelia (18,19,38,39). TGF-␤1 exposure led to a significant reduction in the magnitude of the response to forskolin or a cAMP analog in colonic epithelia, T84 and HT-29 cells, and in kidney epithelia, MadinDarby canine kidney cells, by changing the expression and distribution of CFTR (18,19).…”