Inhibitor studies indicate that active cathepsin L is probably essential to its own processing in cultured fibroblasts.
The lysosomal cysteine proteinase cathepsin L is synthesized in cultured mouse NIH 3T3 cells as a 39 kDa precursor and processed intracellularly into active 29 kDa and 20 kDa + 5 kDa lysosomal forms. Addition to culture media of the peptidyl aldehyde leupeptin, a non-covalent inhibitor of cathepsin L, results in the accumulation of the 20 kDa mature form of the enzyme, resulting in increased activity of cathepsin L as measured in an in vitro assay system in the absence of leupeptin. The more potent irreversible cathepsin L inhibitors benzyloxycarbonyl-Phe-Ala-diazomethane and L-transepoxysuccinyl-L-leucylamino-(4-guanidino)butane, when added to living cells at low concentrations, result in accumulation of all partially processed forms of cathepsin L, especially the 29 kDa form, suggesting that cathepsin L is responsible for its own processing. Exogenous procathepsin L introduced into CHO cells by endocytosis via the mannose 6-phosphate receptor is processed in a manner similar to endogenous procathepsin L. We conclude that the major intracellular pathway for processing of procathepsin L, either endogenous or exogenous, probably requires active cathepsin L.
Salminen
A
A
Laboratory of Cell Biology, National Cancer Institute, Bethesda, MD 20892.
Gottesman
M M
MM
D000818:Animals; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000302:isolation & purification; D002460:Cell Line; D003546:Cysteine Endopeptidases; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases; D005347:Fibroblasts / Q000201:enzymology; D007700:Kinetics; D007976:Leupeptins / Q000494:pharmacology; D008715:Methionine / Q000378:metabolism; D051379:Mice; D008970:Molecular Weight
D007976:Leupeptins; D008715:Methionine; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D056668:Cathepsin L; C534278:Ctsl protein, mouse; C032854:leupeptin