IMMEDIATE-EARLY GENE-EXPRESSION IN EGF-STIMULATED INTESTINAL EPITHELIAL-CELLS

The mammalian small intestinal epithelium is a continuously renewable population of cells which arise from a proliferative zone of undifferentiated stem cells within the crypts. Epidermal growth factor (EGF) is thought to play a role in the maintenance and proliferative response of the intestinal epithelium. In order to investigate the early changes in intestinal gene expression which occur in response to a mitogenic stimulus, we performed studies in two different cell lines (IEC-6 and HT-29), both of which have characteristics of intestinal crypt cells. Cells were grown in DMEM + 10% FCS at 37 degrees C/5% CO2 and treated with either EGF (10 ng/ml) and/or cycloheximide (CHx) (10 mu g/ml) for various times. Northern blot analyses were performed on total RNA using P-32-labeled cDNA probes corresponding to various protooncogenes. Our results showed that EGF treatment caused rapid increases in c-fos, c-jun, and junB expression (P < 0.001) in both cell lines. c-fos and c-jun followed similar time courses, peaking at 30 min, whereas junB levels plateaued at 1 hr. The magnitude and time course of protooncogene induction by EGF were similar in the two cell lines. A dose-response experiment indicated peak EGF effects at 10 ng/ml. CHx treatment resulted in greater and more prolonged increases in protooncogene expression when compared to EGF alone, indicating that protein synthesis is not required for protooncogene induction. These results suggest that c-fos, c-jun, and junB are all part of the ''immediate-early'' genomic response to EGF within the intestine, and that both IEC-6 and HT-29 cells may be suitable models to study the molecular mechanisms underlying intestinal epithelial growth.