title: Taurocholate-induced inhibition of hepatic lysosomal degradation of horseradish peroxidase.
abstract: Endocytosed proteins in hepatocytes are transported to lysosomes for degradation. Metabolites accumulating in these organelles are released into bile by exocytosis, a process that seems to be regulated by the bile salt taurocholate (TC). In this study we examined if TC is also involved in the control of the lysosomal degradation of endocytosed proteins. We used [(14)C]sucrose-labeled horseradish peroxidase ([(14)C]S-HRP), a probe suitable to evaluate lysosomal proteolysis. TC-infused rats as well as isolated rat hepatocytes exposed to TC showed a significant inhibition in the lysosomal degradation of [(14)C]S-HRP (approximately 30%), with no change in either the uptake or the amount of protein reaching lysosomes. Under these conditions, the in vitro assay of lysosomal cathepsins B, L, H, and D revealed no change in their activities, suggesting that a reversible inhibition (lysosomal alkalinization?) was taking place in hepatocytes. Nevertheless, lysosomal pH measured using fluorescein isothiocyanate-dextran was shown not to be altered by TC. In addition, TC was unable to inhibit proteolysis in [(14)C]S-HRP loaded lysosomes or interfere in cathepsin assays. The results suggest that TC inhibits the lysosomal degradation of endocytosed proteins in hepatocytes and that the mechanism does not involve an effect of the bile salt per se or a rise in lysosomal pH.
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, Argentin.
authors.forename: M C
authors.initials: MC
authors.lastname: Larocca
authors.forename: J M
authors.initials: JM
authors.lastname: Pellegrino
authors.forename: E A
authors.initials: EA
authors.lastname: Rodriguez Garay
authors.forename: R A
authors.initials: RA
authors.lastname: Marinelli
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes; D002403:Cathepsins / Q000378:metabolism; D002474:Cell-Free System; D002756:Cholagogues and Choleretics / Q000494:pharmacology*; D006735:Horseradish Peroxidase / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013656:Taurocholic Acid / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D002250:Carbon Radioisotopes; D002756:Cholagogues and Choleretics; D013656:Taurocholic Acid; D006735:Horseradish Peroxidase; D002403:Cathepsins