Signal transduction pathway involving caspase-2, -4 and -12

Abstract

The signal transduction pathway of caspase-2 has not been known well. In this report, cell permeable Tat-reverse-caspase-2 was employed to induce caspase-2-specific cell death with high efficiency. Cell death occurred as early as 2 hr, and caspase-2-specific VDVADase activity was detected but not other caspase activities including DEVDase and IETDase. Interestingly, nuclear DNA fragmentation occurred without activation of caspase-3. Consistently, DFF45/ICAD was cleaved inside the cell and also in vitro by caspase-2, suggesting that the caspase could transduce the apoptotic signal to the downstream through nuclear DNA fragmentation without involvement of caspase-3. Caspase-12 is endoplasmic reticulum (ER)-specific caspase in Rodent. In human, however, caspase-4 appeared to play the similar roles. This study was carried out to compare the enzymatic characteristics of caspase-4 and caspase-12. Ac-WEHD-AMC is found to be the best caspase-4 substrate in terms of kcat/KM, followed by Ac-LEHD-AMC, Ac-LEVD-AMC, Ac-IETD-AMC, Ac-VEID-AMC and Ac-DEVD-AMC while caspase-12 showed no activity with any of these substrates. Caspase-4 could induce DEVDase activity in SK-N-BE (2) cell extract and could cleave downstream caspases such as caspases-3 and -7. Caspase-4 could also induce DNA fragmentation upon incubation with ICAD/CAD and cleave proapoptotic Bcl-2 family protein Bid, although they were weak. None of the above proteins, however, were cleaved by caspase-12. These results suggest that caspases-4 and -12 transduce the apoptotic signal to the downstream pathway through different pathway in spite of their similar physiological role in ER stress-mediated apoptosis.