Epidermal growth factor regulation of system L alanine transport in undifferentiated and differentiated intestinal Caco-2 cells

Epidermal growth factor (EGF) in intestinal lumen regulates many gut epithelial cell functions. Influenced by growth factors at various differentiation stages, enterocytes execute the major task of absorbing nutrient amino acids. The purpose of this study was to investigate the effects of EGF on Na+-independent L-alanine transport in intestinal epithelial cells. Na+-independent [3H]-L-alanine transport was measured in the differentiating Caco-2 cells. In both the undifferentiated and differentiated states, L-alanine uptake occurred via a single saturable Na+-independent system L plus simple passive diffusion. System L activity decreased as the cells progressed from the undifferentiated to the differentiated state. Prolonged incubation with EGF (>30 hours) resulted in a 70% increase in system L activity in both undifferentiated and differentiated cells. EGF stimulated the system L Vmax without affecting Km. System L activity stimulation was inhibited by chelerythrine chloride, cycloheximide, or actinomycin D. These data suggest that intestinal epithelial cell differentiation is associated with a decrease in system L transport capacity. EGF activates system L transport activity through a signaling mechanism involving protein kinase C, independent of cell differentiation state. Both cell differentiation and EGF regulation of system L activity occur via alteration of functional copies of the system L transporter.