title: Protein kinase C-dependent inhibition of the lysosomal degradation of endocytosed proteins in rat hepatocytes.
abstract: We studied the role of protein kinase C (PKC) in the lysosomal processing of endocytosed proteins in isolated rat hepatocytes. We used [14C]sucrose-labeled horseradish peroxidase ([14C]S-HRP) to simultaneously evaluate endocytosis and lysosomal proteolysis. The PKC activator phorbol 12-myristate 13-acetate (PMA) inhibited the lysosomal degradation of [14C]S-HRP (1 microM PMA: 40% inhibition, P<.05), without affecting either the endocytic uptake or the delivery to lysosomes. However, PMA was not able to affect the lysosomal processing of the beta-galactosidase substrate dextran galactosyl umbelliferone. The PKC inhibitors, chelerytrine (Che), staurosporine (St) and Gö 6976, prevented PMA inhibitory effect on lysosomal proteolysis. Nevertheless, purified PKC failed to alter proteolysis in [14C]S-HRP-loaded isolated lysosomes, suggesting that intracellular intermediates are required. PMA induced phosphorylation and hepatocyte membrane-to-lysosome redistribution of the myristoylated alanine-rich C kinase substrate (MARCKS) protein, raising the possibility that MARCKS mediates the PKC-induced inhibition of lysosomal proteolysis.
authors.affiliation: Instituto de Fisiología Experimental-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 570, 2000 Rosario, Santa Fe, Argentina.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Larocca
authors.forename: Elena J
authors.initials: EJ
authors.lastname: Ochoa
authors.forename: Emilio A
authors.initials: EA
authors.lastname: Rodriguez Garay
authors.forename: Raúl A
authors.initials: RA
authors.lastname: Marinelli
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004705:Endocytosis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005959:Glucosidases; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D006735:Horseradish Peroxidase / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008247:Lysosomes / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D021381:Protein Transport; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D014468:Umbelliferones / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; C000619712:Marcks protein, rat; D008565:Membrane Proteins; D010750:Phosphoproteins; C512948:Prkcsh protein, rat; D011506:Proteins; D014468:Umbelliferones; C028501:galactosylumbelliferone; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D006735:Horseradish Peroxidase; D011493:Protein Kinase C; D005959:Glucosidases; D013755:Tetradecanoylphorbol Acetate