AJP - Gastrointestinal and Liver Physiology, Vol 247, Issue 6 623-G631, Copyright © 1984 by American Physiological Society

ARTICLES

Interaction of cholera toxin and Escherichia coli enterotoxin with isolated intestinal epithelial cells

C. S. Hyun and G. A. Kimmich

The interaction of biologically active 125I-labeled cholera toxin with isolated chick intestinal epithelial cells involves a large number (approx 1.7 10(6)/cell) of high-affinity (Kd = 8-9 X 10(-9) M) binding sites that belong to a single class. Binding of iodotoxin to the cells occurs rapidly, is half-maximal within 1 min, and is complete in 3-7 min (at 37 degrees C) depending on the toxin concentration. Toxin binding is saturable and includes only a small contribution from nonspecific sites. Ligand competition studies suggest that the isolated B subunit of choleragen (CT-B) behaves in an almost identical fashion to the holotoxin (CT), whereas the A subunit shows no detectable activity in competitive binding. Assays for cAMP indicate that neither that A nor the B subunits of CT contain any activity for increasing the level of intracellular cAMP. B subunit, when incubated with CT, inhibits CT-induced elevation of cAMP in a dose-dependent manner. Preincubation of 125I-CT with various concentrations of ganglioside GM1 also shows a dose-dependent inhibitory effect on the binding activity of the toxin. Pretreatment of CT with increasing concentrations of GM1 results in a progressive decrease in toxin-induced formation of cAMP. Escherichia coli heat-labile enterotoxin, which is known to alter intestinal function via a mechanism similar to that of CT, has binding and biological effects very similar to those of CT.

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				P.-H. Kim, L. Eckmann, W. J. Lee, W. Han, and M. F. Kagnoff Cholera Toxin and Cholera Toxin B Subunit Induce IgA Switching Through the Action of TGF-{beta}1 J. Immunol., February 1, 1998; 160(3): 1198 - 1203. [Abstract] [Full Text] [PDF]