Administration sequence-dependent antitumor effects of paclitaxel and 5-fluorouracil in the human gastric cancer cell line MKN45.

Toiyama Y, Tanaka K, Konishi N, Mohri Y, Tonouchi H, Miki C, Kusunoki M.

The Second Department of Surgery, Mie University School of Medicine, 2-174 Edobashi, Tsu, Mie, 514-8507, Japan.

Background: The clinical outcome of gastric cancer patients has been improved by combination of 5-fluorouracil (5-FU) and paclitaxel (PXL). However, the optimal schedule of this combination has not been determined. Methods: The efficacies of sequential administrations of 5-FU and PXL on the gastric cancer cell line MKN45 were investigated using a WST-8 colorimetric assay. The cell cycle distribution of each drug was evaluated by flow-cytometry. Furthermore, the mechanism of antitumor activity enhancement by the administration sequence was investigated by western blotting. Results: MKN45 cell growth was significantly inhibited by each drug in a dose- and time-dependent manner. The cytotoxicities of PXL followed by 5-FU were significantly greater than those of 5-FU followed by PXL. The flow-cytometric analysis revealed that PXL exposure caused viable cell accumulation in G2/M phase in a dose-dependent manner. Western blotting showed that PXL exposure followed by 5-FU up-regulated Chk1 and Wee1 protein expressions until PXL removal and 5-FU exposure, when these expressions gradually decreased to their basal levels. 14-3-3sigma protein expression was significantly up-regulated upon PXL treatment followed by 5-FU. Interestingly, Mad2 protein expression with PXL treatment followed by 5-FU gradually increased after the PXL removal and 5-FU exposure. Conclusions: PXL followed by 5-FU administration may be the optimal sequence for treatment of gastric cancer. The enhanced viable cell accumulation after PXL pretreatment may be related to G2 arrest. After PXL removal and 5-FU exposure, the cells progressing to M phase may undergo cell death by mitotic catastrophe due to DNA damage caused by 5-FU exposure.

Targeted proteomic analysis of 14-3-3 sigma, a p53 effector commonly silenced in cancer.

Benzinger A, Muster N, Koch HB, Yates JR 3rd, Hermeking H.

Molecular Oncology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried/Munich, Germany.

To comprehensively identify proteins interacting with 14-3-3 sigma in vivo, tandem affinity purification and the multidimensional protein identification technology were combined to characterize 117 proteins associated with 14-3-3 sigma in human cells. The majority of identified proteins contained one or several phosphorylatable 14-3-3-binding sites indicating a potential direct interaction with 14-3-3 sigma. 25 proteins were not previously assigned to any function and were named SIP2-26 (for 14-3-3 sigma-interacting protein). Among the 92 interactors with known function were a number of proteins previously implicated in oncogenic signaling (APC, A-RAF, B-RAF, and c-RAF) and cell cycle regulation (AJUBA, c-TAK, PTOV-1, and WEE1). The largest functional classes comprised proteins involved in the regulation of cytoskeletal dynamics, polarity, adhesion, mitogenic signaling, and motility. Accordingly ectopic 14-3-3 sigma expression prevented cellular migration in a wounding assay and enhanced mitogen-activated protein kinase signaling. The functional diversity of the identified proteins indicates that induction of 14-3-3 sigma could allow p53 to affect numerous processes in addition to the previously characterized inhibitory effect on G2/M progression. The data suggest that the cancer-specific loss of 14-3-3 sigma expression by epigenetic silencing or p53 mutations contributes to cancer formation by multiple routes.

















Text Box: Chk1

Text Box: Wee1Text Box: 5-Fu







Flowchart: Preparation: Wee1