This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Vaziri, S. A.J. Articles by Ganapathi, R. Search for Related Content PubMed PubMed Citation Articles by Vaziri, S. A.J. Articles by Ganapathi, R.

Experimental Therapeutics Program, Taussig Cancer Center, Cleveland Clinic Foundation, Cleveland, Ohio

Requests for reprints: Ram Ganapathi, Experimental Therapeutics Program, Taussig Cancer Center, Cleveland Clinic Foundation, R40, 9500 Euclid Avenue, Cleveland, OH 44195. Phone: 216-444-2085; Fax: 216-444-7115. E-mail: ganapar{at}ccf.org

Proteasome inhibition following DNA damage results in the synergistic induction of apoptosis via a nuclear factor-B–independent mechanism. In this study, we identify the role of p53 in mediating apoptosis by the sequence-specific treatment involving the DNA-damaging, topoisomerase I–targeting drug SN-38 followed by the proteasome inhibitor PS-341 (SN-38PS-341). The p53-dependent sensitization of DNA damage–induced apoptosis by PS-341 is accompanied by persistent inhibition of proteasome activity and increased cytosolic accumulation of p53, including higher molecular weight forms likely representing ubiquitinated species. In contrast, pretreatment with PS-341 followed by treatment with SN-38 (PS-341SN-38), which leads to an antagonistic interaction, results in transient inhibition of proteasome activity and accumulation of significantly lower levels of p53 localized primarily to the nucleus. Whereas cells treated with PS-341SN-38 undergo G₂ + M cell cycle arrest, cells treated with SN-38PS-341 exhibit a decreased G₂ + M block with a concomitant increase in the sub-G₁ population. Decreased accumulation of cells in the G₂ + M phase of the cell cycle in SN-38PS-341–treated cells compared with PS-341SN-38–treated cells correlates with enhanced apoptosis and reduced expression of two p53-modulated proteins, 14-3-3 and survivin, both of which play critical roles in regulating G₂ + M progression and apoptosis. The functional role of 14-3-3 or survivin in regulating the divergent function of p53 in response to SN-38PS-341 and PS-341SN-38 treatment in inducing apoptosis versus G₂ + M arrest/DNA repair, respectively, was confirmed by targeted down-regulation of these proteins. These results provide insights into the mechanisms by which inhibition of proteasome activity modulates DNA damage–induced apoptosis via a p53-dependent pathway. [Mol Cancer Ther 2005;4(12):1880–90]

Received 7/ 5/05; revised 9/30/05; accepted 10/19/05.