Proteasome inhibitors abolish cell death downstream of caspase activation during anti-microtubule drug-induced apoptosis in leukemia cells

Katalin Nagy, Istvan Petak, Gergely Imre, Gabor Barna, Maria Gezane-Csorba, Anna Sebestyen, Janet A. Houghton, Rudolf Mihalik, Laszlo Kopper

Research output: Contribution to journalArticle

3 Citations (Scopus)


Purpose: Anti-microtubule drugs and proteasome inhibitors are currently among the most intensively studied anti-tumor agents, however little is known about their pharmacological interactions at the cellular level. Materials and Methods: The human promyelocytic leukemia cell line, HL-60, was exposed to nocodazole or etoposide in combination with proteasome or caspase inhibitors. Apoptotic cell death was detected by flow cytometry as sub-G1 population. Caspase and proteasome activities were monitored by the fluorogenic substrates Ac-DEVD-AMC and Suc-LLVY-AMC, respectively, in cell lysate. Heat shock protein 70 (HSP70) expression was determined by Western blotting. Results: Nocodazole, a microtubule inhibitor, induced caspase-dependent apoptosis in the HL-60 cell line. At sub-cytotoxic concentrations, proteasome inhibitors, including MG-132 or clasto-β-lactone, decreased nocodazole-induced apoptotic DNA fragmentation without affecting the induction of caspase-3 activity. In contrast, MG-132 decreased both DNA fragmentation and caspase activation induced by etoposide, a topoisomerase-II inhibitor. HSP70 had previously been found to inhibit apoptosis independently from caspase activation. In this study, MG-132 up-regulated HSP70 protein expression, both in the presence or absence of nocodazole. Conclusion: Proteasome inhibitors decreased anti-microtubule agent-induced apoptotic DNA fragmentation downstream of caspase-3 activation, possibly due to increased HSP70 expression. The results indicate that combination treatment with these novel anti-tumor agents in leukemia requires careful evaluation of their molecular interaction at the level of apoptosis induction.

Original languageEnglish
Pages (from-to)3321-3326
Number of pages6
JournalAnticancer research
Issue number5
Publication statusPublished - Sep 1 2005


  • Clasto-β-lactone
  • Etoposide
  • HSP70
  • MG-132
  • Nocodazole

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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