1. ¹Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin, Ireland
2. ²Experimental Neurosurgery, Centre for Neurology and Neurosurgery, Johann Wolfgang Goethe University Clinics, Theodor-Stern-Kai 7, Frankfurt/Main, Germany
3. ³Division of Experimental Pathophysiology and Immunology, Biocenter, Innsbruck Medical University, Innsbruck, Austria
4. ⁴The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia

Correspondence: Professor JHM Prehn, Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, 123 St Stephen's Green, Dublin 2, Ireland. E-mail: prehn@rcsi.ie

⁵These authors share equal senior authorship.

Received 29 March 2006; Revised 27 July 2006; Accepted 1 August 2006; Published online 18 September 2006.

Abstract

The proteasome has emerged as a novel target for antineoplastic treatment of hematological malignancies and solid tumors, including those of the central nervous system. To identify cell death pathways activated in response to inhibition of the proteasome system in cancer cells, we treated human SH-SY5Y neuroblastoma cells with the selective proteasome inhibitor (PI) epoxomicin (Epoxo). Prolonged exposure to Epoxo was associated with increased levels of poly-ubiquitinylated proteins and p53, release of cytochrome c from the mitochondria, and activation of caspases. Analysis of global gene expression using high-density oligonucleotide microarrays revealed that Epoxo triggered transcriptional activation of the two Bcl-2-homology domain-3-only (BH3-only) genes p53 upregulated modulator of apoptosis (PUMA) and Bim. Subsequent studies in PUMA- and Bim-deficient cells indicated that Epoxo-induced caspase activation and apoptosis was predominantly PUMA-dependent. Further characterization of the transcriptional response to Epoxo in HCT116 human colon cancer cells demonstrated that PUMA induction was p53-dependent; with deficiency in either p53 or PUMA significantly protected HCT116 cells against Epoxo-induced apoptosis. Our data suggest that p53 activation and the transcriptional induction of its target gene PUMA play an important role in the sensitivity of cancer cells to apoptosis induced by proteasome inhibition, and imply that antineoplastic therapies with PIs might be especially useful in cancers with functional p53.