Abstract
CFTR is a cAMP-regulated chloride channel, whose mutations produce cystic fibrosis. The impairment of CFTR activity increases the intracellular Cl- concentration, which in turn produces an increased interleukin-1β (IL-1β) secretion. The secreted IL-1β then induces an autocrine positive feedback loop, further stimulating IL-1β priming and secretion. Since IL-1β can transactivate the epidermal growth factor receptor (EGFR), we study here the levels of expression for different EGFR ligands in Caco-2/pRS26 cells (expressing shRNA against CFTR resulting in a reduced CFTR expression and activity). The epiregulin (EREG), amphiregulin (AREG), and heparin binding EGF like growth factor (HBEGF) mRNAs, were found overexpressed in Caco-2/pRS26 cells. The EREG mRNA had the highest differential expression and was further characterized. In agreement with its mRNA levels, Western blots (WB) showed increased EREG levels in CFTR-impaired cells. In addition, EREG mRNA and protein levels were stimulated by incubation with exogenous IL-1β and inhibited by the Interleukin 1 receptor type I (IL1R1) antagonist IL1RN, suggesting that the overexpression of EREG is a consequence of the autocrine IL-1β loop previously described for these cells. In addition, the JNK inhibitor SP600125, and the EGFR inhibitors AG1478 and PD168393, also had an inhibitory effect on EREG expression, suggesting that EGFR, activated in Caco-2/pRS26 cells, is involved in the observed EREG upregulation. In conclusion, in Caco-2 CFTR-shRNA cells, the EGFR ligand EREG is overexpressed due to an active IL-1β autocrine loop that indirectly activates EGFR, constituting new signaling effectors for the CFTR signaling pathway, downstream of CFTR, Cl- , and IL-1β.