Acute Ablation of Survivin Uncovers p53-dependent Mitotic Checkpoint Functions and Control of Mitochondrial Apoptosis

Elena Beltrami,Janet Plescia,John C Wilkinson,Colin S Duckett,Dario C Altieri

doi:10.1074/jbc.m309479200

Abstract

Survivin is a member of the Inhibitor of Apoptosis gene family that has been implicated in cell division and suppression of apoptosis. Here, we show that preferential ablation of the nuclear pool of survivin by RNA interference produces a mitotic arrest followed by re-entry into the cell cycle and polyploidy. Survivin ablation causes multiple centrosomal defects, aberrant multipolar spindle formation, and chromatin missegregation, and these phenotypes are exacerbated by loss of the cell cycle regulator, p21(Waf1/Cip1) in p21(-/-) cells. The mitotic checkpoint activated by loss of survivin is mediated by induction of p53 and associated with increased expression of its downstream target, p21(Waf1/Cip1). Accordingly, p53(-/-) cells exhibit reduced mitotic arrest and enhanced polyploidy upon survivin ablation as compared with their p53(+/+) counterparts. Partial reduction of the cytosolic pool of survivin by RNA interference sensitizes cells to ultraviolet B-mediated apoptosis and results in enhanced caspase-9 proteolytic cleavage, whereas complete ablation of cytosolic survivin causes loss of mitochondrial membrane potential and spontaneous apoptosis. These data demonstrate that survivin has separable checkpoint functions at multiple phases of mitosis and in the control of mitochondrial-dependent apoptosis.

Highlights

Survivin is a member of the Inhibitor of Apoptosis gene family that has been implicated in cell division and suppression of apoptosis
We have positioned survivin in a p53-dependent pathway [3] that surveys the progression through multiple phases of mitosis, and we have linked its second function in cytoprotection to the upstream regulation of mitochondrial-dependent apoptosis [26]
The first conclusion that can be drawn from these studies is that a reduction in the nuclear pool of survivin [18] was sufficient to cause a composite deregulation of cell division, in which mitotic arrest and polyploidy was one but several defects involving centrosome replication, microtubule nucleation, and mitotic spindle assembly/stability

Summary

Introduction

Survivin is a member of the Inhibitor of Apoptosis gene family that has been implicated in cell division and suppression of apoptosis. Partial reduction of the cytosolic pool of survivin by RNA interference sensitizes cells to ultraviolet B-mediated apoptosis and results in enhanced caspase-9 proteolytic cleavage, whereas complete ablation of cytosolic survivin causes loss of mitochondrial membrane potential and spontaneous apoptosis. These data demonstrate that survivin has separable checkpoint functions at multiple phases of mitosis and in the control of mitochondrial-dependent apoptosis. Programmed cell death, or apoptosis, is essential for embryonic development and the homeostasis of adult organisms [1] This involves a dynamic coupling of apoptotic pathways to checkpoint mechanisms that survey cell cycle transitions and eliminate potentially dangerous cells before they progress through mitosis [2]. We obtained clear evidence that survivin is embedded in a p53-dependent mitotic checkpoint [3] that affects multiple phases of mitosis and directly couples to upstream events in mitochondrialdependent cell death

Methods

Results

Conclusion