title: Cytosolic insulin-degrading activity in islet-derived tumor cell lines and in normal rat islets.
abstract: RIN-m cells, cultured from a rat insulinoma, not only bind and secrete but also degrade insulin (Diabetes 1982; 31:521-31). The insulin-degrading activity resides in the cytosol and is similar to the insulin-specific proteases previously described in muscle and other tissues. It has an apparent Km of 0.15 microM for porcine insulin in crude cell-free extracts, a competitive inhibition constant for proinsulin that is close to the Km, and a lower but measurable affinity for glucagon. The enzyme is inactive at pHs below 6.0, indicating that it is not lysosomal, is completely inhibited by N-ethylmaleimide, and exhibits apparent competitive inhibition constants (microM) for the following peptides: desoctapeptide insulin, 0.043; guinea pig insulin, 0.048; proinsulin, 0.64; insulin B-chain, 1.17; glucagon, 7.0; and cyclic somatostatin, 8.6. Highly active insulin-degrading activity was found using cell suspensions of 22 cloned and 8 subcloned cell lines derived from RIN-m as well as 11 other continuous cell lines derived from a variety of nonislet tissues of rat, mouse, and human origin. Homogenates of the original rat islet tumor and cytosol of normal rat islets also contained insulin-degrading activity. Although insulin protease is present in a variety of tissues, it may have an additional regulatory function in cells that are actively synthesizing, storing, and secreting insulin.
authors.forename: S J
authors.initials: SJ
authors.lastname: Bhathena
authors.forename: K I
authors.initials: KI
authors.lastname: Timmers
authors.forename: H K
authors.initials: HK
authors.lastname: Oie
authors.forename: N R
authors.initials: NR
authors.lastname: Voyles
authors.forename: L
authors.initials: L
authors.lastname: Recant
mesh_terms: D007516:Adenoma, Islet Cell / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D005978:Glutathione / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism*; D007340:Insulinoma / Q000378:metabolism* / Q000473:pathology; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D007328:Insulin; D011480:Protease Inhibitors; D011972:Receptor, Insulin; D005978:Glutathione