Binding of cholera toxin B subunit to intestinal epithelial cells.

We have preparedI-labeled cholera toxin B subunit (I-labeled CT-B, a specific activity of 98Ci/mmol) and found that it binds to rat IEC-6 and human Caco-2 intestinal epithelial cells with high affinity (K3.6 and 3.7nM, respectively). The binding of labeled protein was completely inhibited by unlabeled thymosin-α(TM-α), interferon-α(IFN-α), and the synthetic peptide LKEKK that corresponds to residues 16-20 in TM-αand 131-135 in IFN-α, but was not inhibited by the synthetic peptide KKEKL with inverted amino acid sequence (K>10μM). Thus, TM-α, IFN-α, and the peptide: LKEKK bind with high affinity and specificity to the cholera toxin receptor on IEC-6 and Caco-2 cells. It was found that CT-B and the peptide: LKEKK at concentrations of 10-1000nM increased in a dose-dependent manner the nitric oxide production and the soluble guanylate cyclase activity in IEC-6 and Caco-2 cells.