Combination of cytokinin and auxin induces apoptosis, cell cycle progression arrest and blockage of the Akt pathway in HeLa cells.
Plant cytokinins and auxins have recently been proposed as novel cancer therapies, which proceed via different mechanisms; however, their combined use has not been investigated. To the best of our knowledge, the present study was the first to show that the cytokinin ortho-methoxytopolin-riboside (MeoTR) strongly inhibited the proliferation of HeLa cells, the effect of which was synergistically enhanced by auxin indole-3-acetic acid (IAA), while IAA demonstrated to have no cytotoxic effects on cells. MeoTR was found to activate intrinsic and extrinsic caspase-dependent pathways, and IAA potentiated this activation. In addition, these effects were blocked by Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK), a pan-specific-caspase-inhibitor. IAA increased the MeoTR- induced inhibition of B cell lymphoma 2 (Bcl-2) and survivin, whereas IAA-only decreased Bcl-2 expression. MeoTR downregulated phosphorylated (p)-pyruvate dehydrogenase kinase 1, p-Akt and p-glycogen synthase kinase 3β, the effect of which was more potent in combination with IAA, despite the weak effect of IAA alone. LY294002, an Akt-inhibitor, was able to increase the inhibition of p-Akt through MeoTR and combination treatment. IAA and MeoTR increased the proportion of cells in S phase independently. However, the combination treatment induced a further increase. In addition, IAA and MeoTR treatment downregulated protein levels of cyclin A, cyclin-dependent kinase 2 (CDK2) and p-CDK2, and upregulated protein levels of p21 and p27. Furthermore, the combination treatment enhanced these effects, indicating that IAA potentiated the inhibitory effect of MeoTR on HeLa cells via cell cycle progression arrest and accumulation in S phase, coupled with the negative regulation of Bcl-2. In conclusion, the results of the present study suggested that treatment with these two phytohormones in combination, may offer a novel therapeutic strategy for the treatment of malignant cervical cancer.
Department of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, P.R. China.
Liwei
L
Zhao
Department of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, P.R. China.
Peng
P
Liu
Department of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, P.R. China.
Guangqin
G
Guo
Department of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, P.R. China.
Li
L
Wang
D000241:Adenosine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D017209:Apoptosis / Q000187:drug effects*; D059447:Cell Cycle Checkpoints / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects; D051357:Cyclin-Dependent Kinase 2 / Q000096:biosynthesis; D003583:Cytokinins / Q000008:administration & dosage*; D004357:Drug Synergism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D007210:Indoleacetic Acids / Q000008:administration & dosage*; D009363:Neoplasm Proteins / Q000096:biosynthesis; D051058:Oncogene Protein v-akt / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy* / Q000235:genetics
D003583:Cytokinins; D007210:Indoleacetic Acids; D009363:Neoplasm Proteins; C000604145:ortho-methoxytopolin-riboside; C030737:indoleacetic acid; D051058:Oncogene Protein v-akt; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D000241:Adenosine