Caspase I-related protease inhibition retards the execution of okadaic acid- and camptothecin-induced apoptosis and PAI-2 cleavage, but not commitment to cell death in HL-60 cells

Abstract

We have previously reported that the putative cytoprotective protease inhibitor, plasminogen activator inhibitor type 2 (PAI-2), is specifically cleaved during okadaic acid-induced apoptosis in a myeloid leukaemic cell line ( Br J Cancer (1994) 70 : 834–840). HL-60 cells exposed to okadaic acid and camptothecin underwent morphological and biochemical changes typical of apoptosis, including internucleosomal DNA fragmentation and PAI-2 cleavage. Significant endogenous PAI-2 cleavage was observed 9 h after exposure to okadaic acid; thus correlating with other signs of macromolecular degradation, like internucleosomal DNA fragmentation. In camptothecin-treated cells, PAI-2 cleavage was an early event, detectable after 2 h of treatment, and preceding internucleosomal DNA fragmentation. The caspase I selective protease inhibitor, YVAD-cmk, inhibited internucleosomal DNA fragmentation and PAI-2 cleavage of okadaic acid and camptothecin-induced apoptotic cells. YVAD-cmk rather sensitively and non-toxically inhibited camptothecin-induced morphology, but not okadaic acid-induced morphology. In in vitro experiments recombinant PAI-2 was not found to be a substrate for caspase I. The results suggest that caspase I selective protease inhibition could antagonize parameters coupled to the execution phase of okadaic acid- and camptothecin-induced apoptosis, but not the commitment to cell death. © 1999 Cancer Research Campaign

Khat (Catha edulis)-induced apoptosis is inhibited by antagonists of caspase-1 and -8 in human leukaemia cells

“…Our results showed that khat had to be present for 0.5 -0.75 h to be fully active (Figure 6). This suggested that khat-induced cell deaths were partly dependent on a commitment phase for induction of apoptosis as has also been reported previously during apoptotic cell death in acute myeloid leukaemia cells (Wyllie et al, 1980;Jensen et al, 1999). This is probably related to induction of specific genes during the cell death process although this is not a prerequisite for cell death by apoptosis (Wang and El-Deiry, 2003).…”

“…death suggesting a role for caspase-1 in the execution of apoptosis (Jensen et al, 1999). The observed 50% inhibition constant (IC 50 ) of khat-induced apoptosis by Z-YVAD-fmk was 8 Â 10 À7 M as compared to 2 Â 10 À8 and 9 Â 10 À8 M, respectively, for Z-VAD and Z-IETD ( Figure 8B).…”

“…The cells were exposed to 63.2 or 200 mg ml À1 khat for short periods of time and then washed and replenished with conditioned medium. Cells with condensed nuclear chromatin were considered to be irreversibly committed to cell death, whereas cells with normal nuclear features were healthy (Jensen et al, 1999). In cells treated with 63.2 mg ml À1 khat for 0.75 h, the effect of khat could be abolished ( Figure 6A), whereas in cells exposed for 1 or 2 h the effect of khat was only partially abolished (data not shown).…”

Actions of PP2A on the MAP kinase pathway and apoptosis are mediated by distinct regulatory subunits

“…Treatment with okadaic acid activates apoptosis in many cell types (14)(15)(16)(17)(18)(19)(20). Although these observations suggest PP2A plays a role in preventing apoptosis, they are not conclusive because other phosphatases, including PP1, PP4, PP5, and PP6, are also inhibited by okadaic acid.…”

39 Structure function relationships of plasminogen activator inhibitor type-2 (PAI-2)

“…T N F a , cycloheximide, okadaic acid, campothecin, and infection by Mycobacterium avium) (Kumar & Baglioni 1991;Gan et al 1995;Dickinson et al 1995;Jensen et al 1999) (refer sections 1.4.6.4 and 4.1). The mechanism by which PAI-2 protects cells from apoptosis is unclear, with the various studies cited above presenting often conflicting data concerning the fate of PAI-2 in apoptotic cells.…”