© 2006 The Japanese Biochemical Society.
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Processing of Human Cathepsin D Is Independent of Its Catalytic Function and Auto-Activation: Involvement of Cathepsins L and B
1 Inserm, U540, Montpellier, F-34000 France; 2 Univ Montpellier 1, Montpellier, F-34000 France; and 3 Institute of Health Sciences, Tokushima Bunri University, Yamashiro, Tokushima 770-8514, Japan
To whom correspondence should be addressed. E Liaudet-Coopman, Inserm U540, ‘Molecular and Cellular Endocrinology of Cancers,’ 60 rue de Navacelles, 34090 Montpellier, France. Tel: +33 4 67 04 30 80, Fax: +33 4 67 54 05 98, E-mail:liaudet{at}montp.inserm.fr
The current mechanism proposed for the processing and activation of the 52 kDa lysosomal aspartic protease cathepsin D (cath-D) is a combination of partial auto-activation generating a 51 kDa pseudo-cath-D, followed by enzyme-assisted maturation involving cysteine and/or aspartic proteases and yielding successively a 48 kDa intermediate and then 34 + 14 kDa cath-D mature species. Here we have investigated the in vivo processing of human cath-D in a cath-D–deficient fibroblast cell line in order to determine whether its maturation occurs through already active cath-D and/or other proteases. We demonstrate that cellular cath-D is processed in a manner independent of its catalytic function and that auto-activation is not a required step. Moreover, the cysteine protease inhibitor E-64 partially blocks processing, leading to accumulation of 52-48 kDa cath-D intermediates. Furthermore, two inhibitors, CLICK148 and CA-074Met, specific for the lysosomal cath-L and cath-B cysteine proteases induce accumulation of 48 kDa intermediate cath-D. Finally, maturation of endocytosed pro-cath-D is also independent of its catalytic function and requires cysteine proteases. We therefore conclude that the mechanism of cath-D maturation involves a fully-assisted processing similar to that of pro-renin.
* Present address: Inserm, U583, Montpellier, F-34000 France.
Authors contributed equally to the work.
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