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Open Access Research article

PMA synergistically enhances apicularen A-induced cytotoxicity by disrupting microtubule networks in HeLa cells

Kang-Sik Seo1, Jong-Seok Kim1, Ji-Hoon Park1, Kyoung-Sub Song1, Eun-Jin Yun1, Jong-Il Park1, Gi Ryang Kweon13, Wan-Hee Yoon1, Kyu Lim123* and Byung-Doo Hwang1*

Author Affiliations

1 Department of Biochemistry, College of Medicine, Chungnam National University, Daejeon, Korea

2 Cancer Research Institute, Chungnam National University, Daejeon, Korea

3 Infection Signaling Network Research Center, Chungnam National University, Daejeon, Korea

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BMC Cancer 2014, 14:36  doi:10.1186/1471-2407-14-36

Published: 22 January 2014

Abstract

Background

Combination therapy is key to improving cancer treatment efficacy. Phorbol 12-myristate 13-acetate (PMA), a well-known PKC activator, increases the cytotoxicity of several anticancer drugs. Apicularen A induces cytotoxicity in tumor cells through disrupting microtubule networks by tubulin down-regulation. In this study, we examined whether PMA increases apicularen A-induced cytotoxicity in HeLa cells.

Methods

Cell viability was examined by thiazolyl blue tetrazolium (MTT) assays. To investigate apoptotic potential of apicularen A, DNA fragmentation assays were performed followed by extracting genomic DNA, and caspase-3 activity assays were performed by fluorescence assays using fluorogenic substrate. The cell cycle distribution induced by combination with PMA and apicularen A was examined by flow cytometry after staining with propidium iodide (PI). The expression levels of target proteins were measured by Western blotting analysis using specific antibodies, and α-tubulin mRNA levels were assessed by reverse transcription polymerase chain reaction (RT-PCR). To examine the effect of combination of PMA and apicularen A on the microtubule architecture, α-tubulin protein and nuclei were visualized by immunofluorescence staining using an anti-α-tubulin antibody and PI, respectively.

Results

We found that apicularen A induced caspase-dependent apoptosis in HeLa cells. PMA synergistically increased cytotoxicity and apoptotic sub-G1 population induced by apicularen A. These effects were completely blocked by the PKC inhibitors Ro31-8220 and Go6983, while caspase inhibition by Z-VAD-fmk did not prevent cytotoxicity. RNA interference using siRNA against PKCα, but not PKCβ and PKCγ, inhibited cytotoxicity induced by combination PMA and apicularen A. PMA increased the apicularen A-induced disruption of microtubule networks by further decreasing α- and β-tubulin protein levels in a PKC-dependent manner.

Conclusions

These results suggest that the synergy between PMA and apicularen A is involved by PKCα activation and microtubule disruption, and that may inform the development of novel approaches to treat cancer.

Keywords:
PMA; Apicularen A; PKCα; Cell death; Microtubule disruption