RECEPTORS FOR ESCHERICHIA-COLI HEAT-STABLE ENTEROTOXIN IN HUMAN INTESTINE AND IN A HUMAN INTESTINAL-CELL LINE (CACO-2)

Escherichia coli heat stable enterotoxin (ST(a)) and the newly identif ied endogenous ligand guanylin bind to an intestinal receptor and acti vate membrane bound guanylate cyclase. We compared ST(a) binding and a ffinity crosslinking of ST(a) receptors in human small intestine to th ose in the Caco-2 human colon carcinoma cell line. ST(a) had similar k inetics of binding in human intestinal and Caco-2 brush border membran es. In both human intestine and Caco-2 brush border membranes, multipl e specifically radiolabeled bands, including a 140-165 kDa band, were identified by affinity crosslinking. However, in human intestine the m ost prominent autoradiographic species was a 60 kDa band. A 60 kDa pro tein was also specifically immunoprecipitated from solubilized human b rush border membranes using antisera raised against a cloned ST(a) rec eptor fusion protein. Our observations of multiple crosslinked protein s in human intestine and Caco-2 cells could be explained by the existe nce of several members of a family of ST(a) receptors and/or the exist ence of smaller ST(a) binding proteins generated by the protease cleav age of a larger complete ST(a) receptor. (C) 1993 Wiley-Liss, Inc.