Modulation of apoptosis by procaspase-2 short isoform: selective inhibition of chromatin condensation, apoptotic body formation and phosphatidylserine externalization

Abstract

Procaspase-2 is one of the cysteine aspartate proteases involved in apoptotic cell death. Alternative splicing of CASP-2 messenger RNA generates a long isoform, procaspase-2L, whose overexpression induces cell death and a truncated isoform, procaspase-2S, whose function remains poorly de®ned. The present study explored the consequences of procaspase-2S overexpression in U937 human leukemic cells exposed to the topoisomerase II inhibitor etoposide as an apoptotic stimulus. Overexpression of procaspase-2S in U937 cells partially prevented nuclear changes associated with etoposideinduced cell death, as determined by Hoechst 33342 staining of nuclear chromatin and electron microscopy studies. Procaspase-2S also prevented the maturation of apoptotic bodies, delayed phosphatidylserine externalization on the plasma membrane and prevented the cleavage and activation of procaspase-2L. These e ects were not observed when the cysteine 289 in the consensus QACRG motif was mutated into a serine. Wild-type procaspase-2S overexpression did not in¯uence the cleavage of procaspase-3, procaspase-7 and poly(ADPribose)polymerase nor the fragmentation of nuclear DNA into nucleosome-sized fragments. Altogether, these results indicate that the short isoform of procaspase-2 negatively interferes with selective features of apoptosis, an activity that is suppressed by mutation of the cysteine 289. Oncogene (2001) 20, 260 ± 269.

Caspase-independent death of meiotic and postmeiotic cells overexpressing p53: calpain involvement

“…One can argue that the overexpressed shorter caspase-2 isoform may interfere and inhibit death signal transduction, as previously observed in leukemic cells. 35 On the other hand, we have detected in germ cells and in somatic tissue a third alternative transcript, caspase-2SL, whose putative protein does not include the catalytic domain and has a shorter Cterminal than caspase-2S. This isoform as a CARD protein could be involved in protein recruitment.…”

The human caspase-2 gene: alternative promoters, pre-mRNA splicing and AUG usage direct isoform-specific expression

“…Overexpression of the long isoform caspase-2L was shown to induce programmed cell death (Kumar et al, 1994), whereas its decreased expression by antisense technology delayed apoptosis in response to various stimuli (Kumar, 1995;Troy et al, 2000;Droin et al, 2001a). Conversely, overexpression of the short isoform, caspase-2S, could suppress mammalian cell death (Wang et al, 1994;Kumar, 1995;Droin et al, 2001b). Experiments using caspase-2-knockout mice showed that oocytes were resistant to cell death induced by cytotoxic drugs and that B lymphoblasts were resistant to perforin-and granzyme B-induced apoptosis whereas cell death was accelerated in some neuronal populations (Bergeron et al, 1998;Morita et al, 2001).…”

“…Upon activation, the 48-kDa procaspase-2 is processed in two subunits of 18 and 14 kDa (Li et al, 1997;Colussi et al, 1998a;Paroni et al, 2001). This activation occurs in many cell types in response to various apoptotic stimuli, including growth factor withdrawal, cytotoxic drug or death receptor ligand treatment, and antigen receptor ligation (Harvey et al, 1996;Stefanis et al, 1998;Droin et al, 2001b). Golgin-160 has been identified as a true caspase-2 substrate (Mancini et al, 2000).…”

Nonsense-mediated mRNA decay among human caspases: the caspase-2S putative protein is encoded by an extremely short-lived mRNA

“…5 From some of these in vitro results, accelerated death of facial motor neurons observed in vivo during the development of…”

“…The long isoform, caspase-2L, is an ubiquitously expressed 48 kDa protein that appears to be instrumental in the triggering of apoptosis, whereas the short isoform, caspase-2S, is a predicted 34 kDa protein that can antagonize cell death when overexpressed. 5 Synthesis of these proteins depends in part on an alternative mRNA splicing event occurring in the 3 0 portion of the pre-mRNA. 6 Exon 9, a 61 bp sequence, is specifically inserted into caspase-2S mRNA, which leads to a premature stop codon at the very beginning of exon 10.…”