INSULIN-DEGRADING ENZYME IN A HUMAN COLON ADENOCARCINOMA CELL-LINE (CACO-2)

The activity of insulin-degrading enzyme (IDE), a thiol metalloproteas e degrading insulin in many insulin target cells, was determined in hu man colon adenocarcinoma (Caco-2) cells. Insulin-degrading activity wa s localized in the cytosol of Caco-2 cells, accounting for 88% of tota l activity. Western blots and immunoprecipitation showed that IDE was present in the cytosol of Caco-2 cells and contributed to more than 93 % cytosolic insulin-degrading activity. Cytosolic insulin degradation was strongly inhibited by IDE inhibitors, including N-ethylmaleimide, 1,10-phenanthroline, p-chloro-mericuribenzoate, and EDTA, but was not significantly or not as extensively inhibited by strong inhibitors of proteasome, i.e., chymostatin, soybean trypsin inhibitor, leupeptin, a nd Dip-F. These results suggest that IDE is present in Caco-2 cells, t hat Caco-2 IDE has properties similar to those of its counterparts in insulin-target tissues, and that it significantly contributes to intra cellular insulin degradation.