INTERNALIZATION OF ESCHERICHIA-COLI ST MEDIATED BY GUANYLYL CYCLASE-CIN T84 HUMAN COLON-CARCINOMA CELLS

Internalization of Escherichia coli heat-stable enterotoxin (ST) media ted by guanylyl cyclase C was examined in T84 human colon carcinoma ce lls. Surface-associated, receptor-bound ST was quantitatively separate d from intracellular ligand employing acidic guanidine-HCl. ST was int ernalized in a time-, temperature-, and ligand concentration-dependent fashion only by cells specifically expressing guanylyl cyclase C. Onl y receptors which bound reversibly to ST appeared to mediate endocytos is. The rate of internalization of ST empirically determined in these studies was 0.23 min(-1). The density of surface receptors for ST was similar at 4 degrees C and 37 degrees C, suggesting that these recepto rs recycle back to the cell surface following internalization of ligan d. Similarly, internalized ST was rapidly cleared from the intracellul ar compartment following endocytosis. These studies demonstrate that S T undergoes ligand-dependent receptor-mediated endocytosis in human co lon carcinoma cells.