title: Distinctive inhibition of the lysosomal targeting of lysozyme and cathepsin D by drugs affecting pH gradients and protein kinase C.
abstract: Morphological and biochemical evidence indicates that in several cell types, lysozyme is found in both lysosomes and the medium. Here we report that in calcitriol-treated human promonocytes U937, in which approx. two-thirds of the synthesized lysozyme is secreted, most of the intracellular lysozyme co-localizes with cathepsin D in lysosomal organelles. In the presence of NH4Cl the lysosomal targeting of procathepsin D, but not that of lysozyme, is inhibited. In the presence of 4 beta-phorbol 12-myristate 13-acetate (4 beta-PMA; 'TPA'), the lysosomal packaging of lysozyme is almost completely inhibited, while that of procathepsin D is only partially so. However, the inhibition of the lysosomal targeting of procathepsin D by NH4Cl and 4 beta-PMA is additive. The targeting of lysozyme is partially inhibited in the presence of R-59022, an inhibitor of diacylglycerol kinase, whereas it is not affected by 4 alpha-phorbol 12-myristate 13-acetate, an isomer of 4 beta-PMA that does not activate protein kinase C. It is concluded that in U937 cells both carbohydrate-dependent and -independent recognition contributes to the lysosomal targeting of soluble proteins. We suggest that the carbohydrate-independent traffic of proteins to lysosomal compartments is controlled by a signalling pathway involving protein kinase C.
authors.affiliation: Institut für Physiologische Chemie und Pathobiochemie, Universität Münster, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Radons
authors.forename: U
authors.initials: U
authors.lastname: Biewusch
authors.forename: S
authors.initials: S
authors.lastname: Grässel
authors.forename: H J
authors.initials: HJ
authors.lastname: Geuze
authors.forename: A
authors.initials: A
authors.lastname: Hasilik
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002402:Cathepsin D / Q000378:metabolism*; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D005966:Glucuronidase / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000187:drug effects* / Q000201:enzymology; D008854:Microscopy, Electron; D009000:Monocytes / Q000187:drug effects; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
chemical_list: D000643:Ammonium Chloride; D011493:Protein Kinase C; D005966:Glucuronidase; D001619:beta-N-Acetylhexosaminidases; D002402:Cathepsin D; D013755:Tetradecanoylphorbol Acetate