Interaction of Cholera Toxin B Subunit with Rat Intestinal Epithelial Cells

We prepared 125I-labeled cholera toxin B subunit (125I-labeled CT-B, specific activity 98 Ci/mmol) and found that its binding to rat IEC-6 intestinal epithelial cells was high-affinity (Kd 1.9 nM). The binding of labeled protein was completely inhibited by unlabeled thymosin-α1 (TM-α1), interferon-α2 (IFN-α2), and synthetic peptide LKEKK, which corresponds to residues 16–20 in TM-α1 and 131–135 in IFN-α2 (Ki 1.2, 0.9, and 1.6 nM, respectively), but was not inhibited by synthetic peptide KKEKL with inverted amino acid sequence (Ki > 10 μM). Thus, TM-α1, IFN-α2, and the LKEKK peptide bind with high affinity and specificity to CT-B receptor on rIEC-6 cells. It was found that CT-B and the LKEKK peptide at concentrations of 10–1000 nM increased nitric oxide production and soluble guanylate cyclase activity in the cells in a dose-dependent manner.