Bcl-2 blocks 2-methoxyestradiol induced leukemia cell apoptosis by a p27Kip1-dependent G1/S cell cycle arrest in conjunction with NF-κB activation

Christina Batsi, Soultana Markopoulou, Evangelos Kontargiris, Christiana Charalambous, Christoforos Thomas, Savvas Christoforidis, Panagiotis Kanavaros, Andreas I. Constantinou, Kenneth B. Marcu, Evangelos Kolettas

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

2-Methoxyestradiol (2-ME2) induces leukemia cells to undergo apoptosis in association with Bcl-2 inactivation but the mechanisms whereby Bcl-2 contributes to protection against programmed cell death in this context remain unclear. Here we showed that 2-ME2 inhibited the proliferation of Jurkat leukemia cells by markedly suppressing the levels of cyclins D3 and E, E2F1 and p21Cip1/Waf1 and up-regulating p16INK4A. Further, 2-ME2 induced apoptosis of Jurkat cells in association with down-regulation and phosphorylation of Bcl-2 (as mediated by JNK), up-regulation of Bak, activation of caspases-9 and -3 and PARP-1 cleavage. To determine the importance and mechanistic role of Bcl-2 in this process, we enforced its expression in Jurkat cells by retroviral transduction. Enforcing Bcl-2 expression in Jurkat cells abolished 2-ME2-induced apoptosis and instead produced a G1/S phase cell cycle arrest in association with markedly increased levels of p27Kip1. Bcl-2 and p27Kip1 were localized mainly in the nucleus in these apoptotic resistant cells. Interestingly, NF-κB activity and p50 levels were increased by 2-ME2 and suppression of NF-κB signaling reduced p27Kip1 expression and sensitized cells to 2-ME2-induced apoptosis. Importantly, knocking-down p27Kip1 in Jurkat Bcl-2 cells sensitized them to spontaneous and 2-ME2-induced apoptosis. Thus, Bcl-2 prevented the 2-ME2-induced apoptotic response by orchestrating a p27Kip1-dependent G1/S phase arrest in conjunction with activating NF-κB. Thus, we achieved a much better understanding of the penetrance and mechanistic complexity of Bcl-2 dependent anti-apoptotic pathways in cancer cells and why Bcl-2 inactivation is so critical for the efficacy of apoptosis and anti-proliferative inducing drugs like 2-ME2.

Original languageEnglish (US)
Pages (from-to)33-44
Number of pages12
JournalBiochemical pharmacology
Volume78
Issue number1
DOIs
StatePublished - Jul 1 2009

Keywords

  • 2-Methoxyestradiol (2-ME2)
  • Apoptosis
  • Bcl-2
  • Cell cycle
  • NF-κB
  • p27

ASJC Scopus subject areas

  • Biochemistry
  • Pharmacology

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