title: Regulation of a thyrotropin-releasing hormone-degrading enzyme in GH3 cells: induction of pyroglutamyl peptidase I by 3,5,3'-triiodothyronine.
abstract: The effect of exposure of GH3 cells to T3 on the TRH-degrading enzymes pyroglutamyl peptidase I (EC 3.4.19.3) and prolyl endopeptidase (EC 3.4.21.26) was studied. T3 produced a dose-dependent increase in the specific activity of pyroglutamyl peptidase I after 3 days of exposure. The EC50 for T3 was 5 X 10(-10) M. The specific activity of prolyl endopeptidase was unaffected by exposure to T3. The increase in pyroglutamyl peptidase I activity was dependent upon the time of exposure of the cells to this hormone. A maximal effect occurred at 72 h. The stimulation of pyroglutamyl peptidase I by T3 was totally blocked by cycloheximide, indicating that this enzyme is induced in GH3 cells by T3. The effect of T3 on the two TRH-degrading enzymes was also studied in the ACTH-secreting cell line AtT20. T3 had no effect on these enzymes in the AtT20 cell, suggesting that the effect of T3 on pyroglutamyl peptidase I may be cell specific. These studies indicate that the induction of pyroglutamyl peptidase I by T3 may contribute to the negative feedback regulation of T3 levels.
mesh_terms: D000626:Aminopeptidases / Q000096:biosynthesis*; D000818:Animals; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D010450:Endopeptidases / Q000096:biosynthesis*; D004790:Enzyme Induction / Q000187:drug effects; D006868:Hydrolysis; D007700:Kinetics; D010911:Pituitary Neoplasms / Q000201:enzymology*; D000085822:Prolyl Oligopeptidases; D011751:Pyroglutamyl-Peptidase I / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D012697:Serine Endopeptidases; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D014284:Triiodothyronine; C046251:pyroglutamyl diazomethyl ketone; D003513:Cycloheximide; D010450:Endopeptidases; D000626:Aminopeptidases; D011751:Pyroglutamyl-Peptidase I; D012697:Serine Endopeptidases; D000085822:Prolyl Oligopeptidases; D011761:Pyrrolidonecarboxylic Acid