title: Receptor-mediated degradation and internalization of insulin in the adenocarcinoma cell line HT-29 from human colon.
abstract: In the adenocarcinoma cell line HT-29 receptor-bound insulin is substrate for a proteolytic process leading to the release of about half of the cell-associated [125I]monoiodoinsulin in the form of [125I]iodide and [125I]monoiodotyrosine. Classical lysosomal inhibitors (NH+4, methylamine, leupeptin) did not inhibit this proteolysis. Inhibitors of membrane traffic (chloroquine and monensin) and of metabolism (CN-) inhibited the fractional receptor-mediated degradation. The former led to an increased cell-associated 125I activity whereas the latter reduced the uptake. Sulphydryl reagents inhibited the receptor-mediated degradation. The data are not compatible with a quantitatively major role of lysosomes in the receptor-mediated insulin degradation. However, since the process requires energy it is suggested that the receptor-mediated degradation takes place in vesicles other than secondary lysosomes. The responsible enzyme(s) may belong to the thiol group of proteases. Both insulin and the insulin receptor are internalized as a consequence of incubation of HT-29 cells with insulin.
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D003110:Colonic Neoplasms / Q000378:metabolism*; D003208:Concanavalin A / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008214:Lymphocytes / Q000378:metabolism; D051381:Rats; D011972:Receptor, Insulin / Q000502:physiology*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013696:Temperature
chemical_list: D007328:Insulin; D007457:Iodine Radioisotopes; D013439:Sulfhydryl Reagents; D003208:Concanavalin A; D011972:Receptor, Insulin