Epithelial cell-derived components induce transforming growth factor-alpha mRNA expression and epithelial cell proliferation in vitro.

Abstract

Epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha protect the gastrointestinal mucosa against injury. In response to mucosal injury TGF-alpha, but not EGF, is locally increasingly expressed in the mucosa of the rat colon and stomach 4-8 h after injury. The aim of our present study was to characterize the possible signal for the induction of TGF-alpha expression. Monolayers of the non-transformed intestinal epithelial cell (IEC)-6 and IEC-18 lines were harvested, homogenized and shock-frozen at -80 degrees C for 1 h. Cell cultures of intact IEC-6 or IEC-18 cells were exposed to these cell homogenates and modulation of epithelial cell migration and proliferation was evaluated using standardized procedures as described previously. TGF-alpha mRNA expression in the exposed epithelial cell monolayers was assessed using reverse transcriptase-polymerase chain reaction (RT-PCR) and normalized to the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The proliferation of IEC-6 and IEC-18 epithelial cell monolayers was significantly inhibited if epithelial cell homogenates of 2000 cells/ml or more, and significantly induced if homogenates of less than 2000 cells/ml, were applied to the medium of the monolayers in vitro. In proliferating epithelial cells, a significant two-fold increase in TGF-alpha mRNA expression was obtained at 48 h and 72 h after application of the cell homogenates. The homogenate-induced epithelial cell proliferation was completely abolished after preincubation of the epithelial cell homogenates with neutralizing monoclonal anti-TGF-alpha antibodies. No effect on epithelial cell migration was noticed after application of epithelial-cell homogenates to the cell cultures. Epithelial cell-derived components induce TGF-alpha mRNA expression and TGF-alpha-dependent cell proliferation of intact epithelial cells. We hypothesize that epithelial cell interaction bears one of the possible signals for the increased TGF-alpha mRNA expression after mucosal injury.