Perforin is synthesized as an inactive precursor in natural killer (NK) cells and it becomes active only when a glycosylated C-terminal peptide is cleaved within the lytic granules. The cleavage is pH dependent and can be prevented by E-64d, a cysteine cathepsin inhibitor. In vitro, cathepsin L processes the C-terminal part of perforin. The addition of cysteine proteinase inhibitors (E-64d or L1) reduced perforin processing in NK cells and consequently decreased K562 target cell killing.
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COBISS.SI-ID: 22116903Upon the activation of macrophages we have observed almost complete localization of cathepsin S and only partial localization of cathepsin L to the multivesicular body (MVB). The activities of endosomal / lysosomal cysteine proteinases were determined with activity-based probes (ABP) in cell lysates as well as in living cells. In activated macrophages most of the cathepsin activity dermined by ABP is co localised with cathepsin S.
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COBISS.SI-ID: 22065447