• Journal of Microbiology and Biotechnology
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• v.24 no.12
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• pp.1654-1663
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• 2014

To examine the effect of tumor suppressor protein p53 on the antitumor activity of 2-methoxyestradiol (2-MeO-$E_2$), 2-MeO-$E_2$-induced cell cycle changes and apoptotic events were compared between the human colon carcinoma cell lines HCT116 ($p53^{+/+}$) and HCT116 ($p53^{-/-}$). When both cell types were exposed to 2-MeO-$E_2$, a reduction in the cell viability and an enhancement in the proportions of $G_2/M$ cells and apoptotic sub-$G_1$ cells commonly occurred dose-dependently. These 2-MeO-$E_2$-induced cellular changes, except for $G_2/M$ arrest, appeared to be more apparent in the presence of p53. Immunofluorescence microscopic analysis using anti-${\alpha}$-tubulin and anti-lamin B2 antibodies revealed that after 2-MeO-$E_2$ treatment, impaired mitotic spindle network and prometaphase arrest occurred similarly in both cell types. Following 2-MeO-$E_2$ treatment, only HCT116 ($p53^{+/+}$) cells exhibited an enhancement in the levels of p53, p-p53 (Ser-15), $p21^{WAF1/CIP1}$, and Bax; however, the Bak level remained relatively constant in both cell types, and the Bcl-2 level decreased only in HCT116 ($p53^{+/+}$) cells. Additionally, mitochondrial apoptotic events, including the activation of Bak and Bax, loss of ${\Delta}{\psi}m$, activation of caspase-9 and -3, and cleavage of lamin A/C, were more dominantly induced in the presence of p53. The Bak-specific and Bax-specific siRNA approaches confirmed the necessity of both Bak and Bax activations for the 2-MeO-$E_2$-induced apoptosis in HCT116 cells. These results show that among 2-MeO-$E_2$-induced apoptotic events, including prometaphase arrest, up-regulation of Bax level, down-regulation of Bcl-2 level, activation of both Bak and Bax, and mitochondria-dependent caspase activation, the modulation of Bax and Bcl-2 levels is the target of the pro-apoptotic action of p53.

• Journal of Life Science
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• v.26 no.3
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• pp.376-386
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• 2016

Apoptosis induction has been proposed as an efficient mechanism by which malignant tumor cells can be removed following chemotherapy. The intrinsic mitochondria-dependent apoptotic pathway is frequently implicated in chemotherapy-induced tumor cell apoptosis. Since DNA-damaging agent (DDA)-induced apoptosis is mainly regulated by the tumor suppressor protein p53, and since more than half of clinical cancers possess inactive p53 mutants, microtubule-damaging agents (MDAs), of which apoptotic effect is mainly exerted via p53-independent routes, can be promising choice for cancer chemotherapy. Recently, we found that the apoptotic signaling pathway induced by MDAs (nocodazole, 17α-estradiol, or 2-methoxyestradiol) commonly proceeded through mitotic spindle defect-mediated prometaphase arrest, prolonged Cdk1 activation, and subsequent phosphorylation of Bcl-2, Mcl-1, and Bim in human acute leukemia Jurkat T cells. These microtubule damage-mediated alterations could render the cellular context susceptible to the onset of mitochondria-dependent apoptosis by triggering Bak activation, Δψm loss, and resultant caspase cascade activation. In contrast, when the MDA-induced Bak activation was inhibited by overexpression of anti-apoptotic Bcl-2 family proteins (Bcl-2 or Bcl-xL), the cells in prometaphase arrest failed to induce apoptosis, and instead underwent mitotic slippage and endoreduplication cycle, leading to formation of populations with 8N and 16N DNA content. These data indicate that cellular apoptogenic mechanism is critical for preventing polyploid formation following MDA treatment. Since the formation of polyploid cells, which are genetically unstable, may cause acquisition of therapy resistance and disease relapse, there is a growing interest in developing new combination chemotherapies to prevent polyploidization in tumors after MDA treatment.