We recently demonstrated that TLCK and TPCK could act as potent but nonspecific inhibitors of mature caspases [Frydrych and Mlejnek [2008] J Cell Biochem 103:1646-1656]. The question whether TLCK and TPCK inhibit simultaneously caspase activation and/or processing remained, however, open. In this article, we demonstrated that TPCK even enhanced caspase-3 and caspase-7 processing although it substantially inhibited caspase-3 and caspase-7 enzymatic (DEVDase) activity in HL-60 cells exposed to various cell death inducing stimuli. Under the same conditions, TLCK had no effect or affected caspase-3 and caspase-7 processing marginally depending on cell treatment used. Importantly, TLCK substantially inhibited caspase-3 and caspase-7 enzymatic (DEVDase) activity irrespectively to the treatment used. Interestingly, treatment of cells with toxic concentrations of TPCK alone was accompanied by full caspase-3 and -7 processing even if it induced necrosis. In contrast, treatment of cells with concentrations of TLCK that caused necrosis was accompanied by only partial caspase-3 and caspase-7 processing. Our results clearly indicated that TPCK and TLCK did not inhibit caspase-3 and -7 enzymatic activity by prevention of their activation and/or processing.

Faculty of Medicine and Dentistry Department of Biology Palacky University Olomouc Hnevotinska 3 Olomouc 77515 Czech Republic