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Displacement of Bim by Bmf and Puma rather than increase in Bim level mediates paclitaxel-induced apoptosis in breast cancer cells.

Kutuk O, Letai A - Cell Death Differ. (2010)

Bottom Line: However, the signaling pathways that connect paclitaxel-induced microtubule perturbation to mitochondrial outer membrane permeabilization and cytochrome c release are not well characterized.Bim and either Puma or Bmf are required for paclitaxel toxicity.This novel mechanism suggests the potential usage of novel therapies targeted at altering BH3-only protein heterodimerization.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.

ABSTRACT
Taxanes exert their antitumor effect through stabilizing microtubule dynamics and initiating G2/M arrest in cancer cells followed by apoptotic cell death. However, the signaling pathways that connect paclitaxel-induced microtubule perturbation to mitochondrial outer membrane permeabilization and cytochrome c release are not well characterized. Here, we show that in breast cancer cells, paclitaxel induces a novel displacement mechanism: prodeath BH3-only proteins Bmf and Puma competitively displace prodeath BH3-only protein Bim from antiapoptotic proteins to activate Bax and Bak and commit the cell to apoptotic death. Bim and either Puma or Bmf are required for paclitaxel toxicity. Although prior mechanisms of apoptosis induced by taxol have focused on changes in Bim levels, we find that an increase is not required for paclitaxel killing of breast cancer cells. Rather, competitive displacement of Bim from antiapoptotic proteins is the important step committing the cell to death. This novel mechanism suggests the potential usage of novel therapies targeted at altering BH3-only protein heterodimerization.

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Bim is displaced from Bcl-2 and Bcl-xL following paclitaxel treatment. (a) T47D, (b) MDA-MB-468 and (c) BT20 cells were treated with paclitaxel (100 nM) for 12 h and the interaction of Bim with Bcl-2, Bcl-xL and Mcl-1 was detected by coimmunoprecipitation assays. Inputs for coimmunoprecipitations were also subjected to immunoblot analysis and actin was probed as a loading control.
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Figure 4: Bim is displaced from Bcl-2 and Bcl-xL following paclitaxel treatment. (a) T47D, (b) MDA-MB-468 and (c) BT20 cells were treated with paclitaxel (100 nM) for 12 h and the interaction of Bim with Bcl-2, Bcl-xL and Mcl-1 was detected by coimmunoprecipitation assays. Inputs for coimmunoprecipitations were also subjected to immunoblot analysis and actin was probed as a loading control.

Mentions: Since Bim displacement was so important in paclitaxel-mediated killing of MCF-7 cells, we also investigated the interaction of Bim with antiapoptotic Bcl-2 proteins Bcl-2, Bcl-xL and Mcl-1 in response to paclitaxel (100 nM) treatment for these other breast cancer cell lines. In Figure 4a, we show that Bim interacts with all three antiapoptotic proteins in untreated T47D cells, but the interaction with Bcl-xL is easiest to detect. Only Bim bound to Bcl-xL decreases following paclitaxel treatment in T47D cells. In MDA-MB-468 and BT20 cells, Bim was also found to be complexed to all three antiapoptotic Bcl-2 proteins. Paclitaxel treatment led to decreased levels of Bcl-2/Bim and Bcl-xL/Bim complexes in these two cell lines (Figure 4b and 4c). Similar to MCF-7 and T47D cells, the Mcl-1/Bim interaction did not change upon paclitaxel treatment in these cell lines (Figure 4b and 4c). In common with MCF-7 cells, displacement of Bim from anti-apoptotic proteins is a consistent event following paclitaxel treatment in all four breast cancer cell lines.


Displacement of Bim by Bmf and Puma rather than increase in Bim level mediates paclitaxel-induced apoptosis in breast cancer cells.

Kutuk O, Letai A - Cell Death Differ. (2010)

Bim is displaced from Bcl-2 and Bcl-xL following paclitaxel treatment. (a) T47D, (b) MDA-MB-468 and (c) BT20 cells were treated with paclitaxel (100 nM) for 12 h and the interaction of Bim with Bcl-2, Bcl-xL and Mcl-1 was detected by coimmunoprecipitation assays. Inputs for coimmunoprecipitations were also subjected to immunoblot analysis and actin was probed as a loading control.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2914832&req=5

Figure 4: Bim is displaced from Bcl-2 and Bcl-xL following paclitaxel treatment. (a) T47D, (b) MDA-MB-468 and (c) BT20 cells were treated with paclitaxel (100 nM) for 12 h and the interaction of Bim with Bcl-2, Bcl-xL and Mcl-1 was detected by coimmunoprecipitation assays. Inputs for coimmunoprecipitations were also subjected to immunoblot analysis and actin was probed as a loading control.
Mentions: Since Bim displacement was so important in paclitaxel-mediated killing of MCF-7 cells, we also investigated the interaction of Bim with antiapoptotic Bcl-2 proteins Bcl-2, Bcl-xL and Mcl-1 in response to paclitaxel (100 nM) treatment for these other breast cancer cell lines. In Figure 4a, we show that Bim interacts with all three antiapoptotic proteins in untreated T47D cells, but the interaction with Bcl-xL is easiest to detect. Only Bim bound to Bcl-xL decreases following paclitaxel treatment in T47D cells. In MDA-MB-468 and BT20 cells, Bim was also found to be complexed to all three antiapoptotic Bcl-2 proteins. Paclitaxel treatment led to decreased levels of Bcl-2/Bim and Bcl-xL/Bim complexes in these two cell lines (Figure 4b and 4c). Similar to MCF-7 and T47D cells, the Mcl-1/Bim interaction did not change upon paclitaxel treatment in these cell lines (Figure 4b and 4c). In common with MCF-7 cells, displacement of Bim from anti-apoptotic proteins is a consistent event following paclitaxel treatment in all four breast cancer cell lines.

Bottom Line: However, the signaling pathways that connect paclitaxel-induced microtubule perturbation to mitochondrial outer membrane permeabilization and cytochrome c release are not well characterized.Bim and either Puma or Bmf are required for paclitaxel toxicity.This novel mechanism suggests the potential usage of novel therapies targeted at altering BH3-only protein heterodimerization.

View Article: PubMed Central - PubMed

Affiliation: Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA.

ABSTRACT
Taxanes exert their antitumor effect through stabilizing microtubule dynamics and initiating G2/M arrest in cancer cells followed by apoptotic cell death. However, the signaling pathways that connect paclitaxel-induced microtubule perturbation to mitochondrial outer membrane permeabilization and cytochrome c release are not well characterized. Here, we show that in breast cancer cells, paclitaxel induces a novel displacement mechanism: prodeath BH3-only proteins Bmf and Puma competitively displace prodeath BH3-only protein Bim from antiapoptotic proteins to activate Bax and Bak and commit the cell to apoptotic death. Bim and either Puma or Bmf are required for paclitaxel toxicity. Although prior mechanisms of apoptosis induced by taxol have focused on changes in Bim levels, we find that an increase is not required for paclitaxel killing of breast cancer cells. Rather, competitive displacement of Bim from antiapoptotic proteins is the important step committing the cell to death. This novel mechanism suggests the potential usage of novel therapies targeted at altering BH3-only protein heterodimerization.

Show MeSH
Related in: MedlinePlus