PMA synergistically enhances apicularen A-induced cytotoxicity by disrupting microtubule networks in HeLa cells.
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.
Kang-Sik
KS
Seo
Jong-Seok
JS
Kim
Ji-Hoon
JH
Park
Kyoung-Sub
KS
Song
Eun-Jin
EJ
Yun
Jong-Il
JI
Park
Gi Ryang
GR
Kweon
Wan-Hee
WH
Yoon
Department of Biochemistry, College of Medicine, Chungnam National University, Daejeon, Korea. kyulim@cnu.ac.kr.
Kyu
K
Lim
Byung-Doo
BD
Hwang
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D059447:Cell Cycle Checkpoints; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008870:Microtubules / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051571:Protein Kinase C-alpha / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D014404:Tubulin / Q000235:genetics / Q000378:metabolism; D050257:Tubulin Modulators / Q000494:pharmacology; D002583:Uterine Cervical Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
D019086:Bridged Bicyclo Compounds, Heterocyclic; D047428:Protein Kinase Inhibitors; D014404:Tubulin; D050257:Tubulin Modulators; C117813:apicularen A; C496628:PRKCA protein, human; D051571:Protein Kinase C-alpha; C505407:CASP3 protein, human; D053148:Caspase 3; D013755:Tetradecanoylphorbol Acetate