Non-redundant Roles of Cathepsins L, B and S in CD1a+ Dendritic Cells Knocked-down for Cathepsin S by RNA Interference

Aim. The ability to modulate the functional properties of dendritic cells (DCs) with chemical drugs or via RNAbased technologies may lead to significant therapeutic applications. In light of their relevance to the biology of DCs, particularly within the antigen-presentation pathway, cysteine cathepsins L, B and S were investigated with the long-term objective of assessing their value as molecular target. Methods. Cathepsin expression was monitored via a cell-based model in which human, CD34+hematopoietic stem cells (HSCs) were induced to differentiate into CD1a+DCs. Time-course analyses were performed via Real time RT-PCR and Western blotting. The same experiments were conducted, in parallel, using HSCs subjected to cathepsin S knockdown by RNA interference. Results. Processing of cathepsins L, B and S is subjected to temporal patterns of expression throughout DC differentiation (a 14 day process). The mature form of cathepsin S appeared in the lysosomal fraction on day 7, while mature cathepsin L and B proteins displayed such localization only upon completion of differentiation (day 14). The non-redundant roles of these cathepsins were evident on day 7, as CatS-RNAi-mediated knockdown cells were found to show a marked decrease of HLA-DR expression. Conclusion. Cathepsins L, B and S are subjected to a temporal regulation of expression that is apparently associated with the progress of the differentiation process. CD1a+DCs knocked-down for cathepsin S show the nonredundant roles of cathepsin L, B and S within the DC maturation pathway and highlight the potential of cathepsin S as a molecular target for drug discovery research.