Inhibition of pyroglutamyl peptidase II synthesis by phorbol ester in the Y-79 retinoblastoma cell.
Pyroglutamyl peptidase II (EC 3.4.19.-), a highly specific membrane-bound TRH-degrading enzyme, is inactivated in Y-79 human retinoblastoma cells by exposure to 12-O-tetradecanoyl phorbol-13-acetate (TPA) in a biphasic manner. We have previously demonstrated a rapid decrease in pyroglutamyl peptidase II activity to 10% of the control level within 15 min, which returns to 70% of the control level by 1 h. This decrease results from enzyme phosphorylation by TPA-activated protein kinase-C. We now report a second phase of inactivation after longer exposure of cells to TPA. After 1 h, enzymatic activity slowly and progressively declined. By 7 h, only 15% of control activity remained. Cotreatment of cells with H-7, a protein kinase-C inhibitor, prevented this second phase of inactivation. Immunoblot experiments demonstrated a reduction in the amount of pyroglutamyl peptidase II in Y-79 membranes after long term exposure to TPA. Y-79 cells were labeled with [35S]methionine, and pyroglutamyl peptidase II was immunoprecipitated. A decreased incorporation of [35S]methionine paralleled the decrease in enzyme activity. These studies demonstrate that the second phase of inactivation after exposure to TPA is due to an inhibition of enzyme synthesis.
Suen
C S
CS
Department of Pharmacology, Mount Sinai School of Medicine, City University of New York, New York 10029.
Wilk
S
S
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D002462:Cell Membrane / Q000201:enzymology; D006801:Humans; D015151:Immunoblotting; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011751:Pyroglutamyl-Peptidase I / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D012175:Retinoblastoma / Q000201:enzymology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D007546:Isoquinolines; D010879:Piperazines; D015240:Phorbol 12,13-Dibutyrate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D011751:Pyroglutamyl-Peptidase I; D013755:Tetradecanoylphorbol Acetate