Proceedings of The Physiological Society

University College Dublin (2009) Proc Physiol Soc 15, PC185

Poster Communications

Epidermal growth factor enhances colonic epithelial secretory capacity through activation of phosphatidylinositol 3-kinase, mitogen-activated protein kinase and upregulation of multiple transport proteins.

M. S. Mroz1, F. Toumi1, F. O'Mahony1, S. Keely1

1. Molecular Medicine, RCSI, Dublin, Ireland.

  • Table1. Isc responses to CCh and FSK were measured 24 hrs after pretreatment with EGF (100 ng/ml for 15 min). Data are expressed as % control response to CCh (n = 6) or FSK (n = 5) alone (**p<0.01; ***p<0.001).

Background: There is increasing evidence that growth factors, such as epidermal growth factor (EGF), are important regulators of epithelial transport function. Previous work from our laboratory has shown that EGF chronically enhances colonic epithelial secretory function through a mechanism involving increases in NKCC1 expression. Aim: Here we set out to further investigate molecular mechanisms underlying EGF potentiation of colonic epithelial secretory capacity. Methods: Monolayers of T84 cells, grown on permeable supports, were mounted in Ussing chambers and Cl- secretion measured as changes in short-circuit current (Isc). Transport protein mRNA expression was measured by RT-PCR. Results are expressed as mean ± standard error of the mean for a series of n experiments. Statistical analyses were made by one way ANOVA with the Newman-Keuls post test. P values < 0.05 were considered to be significant. Results: In addition to NKCC1, acute treatment with EGF (100 ng/ml for 15 min) induced increases in the mRNA levels of CFTR (270 ± 20 % of controls; n = 3; p < 0.01), KCNN4 (150 ± 20 of controls; n = 5; p < 0.05) and Na/K-ATPase β1 subunit (370 ± 100 % of controls; n = 4; p < 0.01) but did not alter expression of the α1 subunit of Na/K ATPase (130 ± 30 % of controls; n=4). To determine signaling pathways involved in mediating the effects of EGF, we examined the effects of PI3-K (LY294002), ERK (PD98059) and p38 MAPK (SB203580;) inhibitors on the ability of EGF to enhance Isc responses to either the Ca2+ or cAMP-dependent secretagogues, carbachol (CCh) and forskolin (FSK) (Table 1). Conclusions: EGF chronically increases colonic epithelial secretory function through upregulation of key transport proteins that comprise the Cl- secretory pathway. PI3-K and ERK MAPK are important in mediating EGF potentiation of both Ca2+ and cAMP-dependent responses, while p38 MAPK is involved only in enhancing cAMP-dependent responses. The precise roles of these effector pathways in mediating EGF-induced increases in transport protein expression are currently under study. Our data suggest that agents targeting EGFR-dependent signaling pathways may be useful in therapy of intestinal disorders associated with dysregulated epithelial transport.

Where applicable, experiments conform with Society ethical requirements