An Anti-apoptotic Protein Human Survivin Is a Direct Inhibitor of Caspase-3 and -7

Abstract

Survivin, an apoptosis inhibitor/cell-cycle regulator, is critically required for suppression of apoptosis and ensuring normal cell division in the G2/M phase of the cell cycle. It is highly expressed in a cell cycle-regulated manner and localizes together with caspase-3 on microtubules within centrosomes. Whether survivin is a physiologically relevant caspase inhibitor has been unclear due to the difficulties with obtaining correctly folded survivin and finding the right conditions for inhibition assay. In this study, recombinant, active human survivin was expressed in Escherichia coli and purified to homogeneity. The protein, existing as a homodimer in solution, binds caspase-3 and -7 tightly with dissociation constants of 20.9 and 11.5 nM, respectively, when evaluated by surface plasmon resonance spectroscopy. Consistently, survivin potently inhibits the cleavage of a physiological substrate poly(ADP-ribose) polymerase and an artificial tetrapeptide by caspase-3 and -7 in vitro with apparent inhibition constants of 36.0 and 16.5 nM, respectively. The data suggest that sequestering caspase-3 and -7 in inhibited states on microtubules is at least one mechanism of survivin in the suppression of default apoptosis in the G2/M phase. The localization of survivin on microtubules, which is essential for its function, should increase the protective activity at the action site.

Knockdown of survivin expression by small interfering RNA reduces the clonogenic survival of human sarcoma cell lines independently of p53

“…44 A direct association between survivin and the effector caspase-3, caspase-7, or both has been reported. [45][46][47][48] Furthermore, caspase-independent induction of apoptosis of nervous system tumor cells after survivin inhibition has been described. 36 However, other colleagues 44,49 believe that survivin does not inhibit caspase-3 activity.…”

Expression of IAP-family proteins in adult acute mixed lineage leukemia (AMLL)

“…Although the biochemical mechanism by which IAP-family members suppress apoptosis is under debate, survivin is known to bind directly to and inhibit caspase-3 and -7, which act as terminal effectors in apoptotic protease cascades [15,16]. The expression of survivin is ubiquitous in fetal tissues but is restricted during development and is negligible in the majority of terminally differentiated adult tissues [17,18].…”

N-(4-hydroxyphenyl) retinamide (4HPR) enhances TRAIL-mediated apoptosis through enhancement of a mitochondrial-dependent amplification loop in ovarian cancer cell lines

“…8,9 Several mechanisms have been described that regulate sensitivity to TRAIL-mediated apoptosis. These include the expression of decoy receptors that bind to TRAIL but do not activate the caspase cascade, 3 the expression of inhibitory downstream molecules such as survivin, 10 FADD-like ICE inhibitory proteins (FLIP), 11,12 and inhibitors of apoptosis (IAPs), 13 and the activation of antiapoptotic transcription factors such as NF-kB. 14,15 Studies in breast and ovarian cancer cell lines have failed to identify the major determinants of TRAIL sensitivity.…”