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sMEK1 enhances gemcitabine anti-cancer activity through inhibition of phosphorylation of Akt/mTOR

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Abstract

Recently, we reported that sMEK1 is down-regulated in cancer cells and tissues, and that it enhances the pro-proliferative effect as a novel pro-apoptotic protein. However, the biological mechanism of the sMEK1 tumor suppressor in the cellular signal pathway has not been well understood. In our current work, we examined whether sMEK1 could promote the cytotoxic activity of gemcitabine in the human ovarian carcinoma system. Initially, we attempted to use a treatment of gemcitabine traditional chemotherapeutic agent and over-expression of sMEK1 in OVCAR-3 cancer cells. The combined treatment of sMEK1 and gemcitabine was more effective at inhibiting cell proliferation than either chemotherapeutic agent treatment alone. In addition, sMEK1 actively contributes to cell migration through its ability to promote gemcitabine-inhibited cell migration in tumorigenesis. Cell cycle-related proteins are highly associated with the down-regulation of cyclin D1 and CDK4, and the promotion of p16 and p27 as a cyclin-dependent kinase inhibitor. At the same time, sMEK1 arrests cell cycle progression in the G1–G0 phase, and activates p53 and p21 expression, whereas Bcl-2 and Bcl-xL protein expression is reduced. Additionally, sMEK1 and gemcitabine suppresses the phosphorylation of signaling modulators downstream of PI3K, such as PDK1 and Akt. The p53 and p21 promoter luciferase activities were promoted by either sMEK1 or gemcitabine, and sMEK1 and gemcitabine combined additively activated the promoter further. Furthermore, as expected, sMEK1 plus gemcitabine markedly reduced the phosphorylation of p70S6K and the phosphorylation of 4E-BP1, which is one of the best characterized targets of the mTOR complex cascade. Taken together, these results provide evidence that sMEK1 can effectively regulate the pro-apoptotic activity of gemcitabine through the up-regulation of p53 expression.

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Abbreviations

sMEK1:

Suppressor of MEK null 1

PP4R3:

Protein phosphatase 4 regulatory subunit 3

Gemcitabine:

2′deoxy-2′2′-difluorocytidine monohydrochloride

MDR:

Multidrug resistance

FITC:

Fluorescein isothiocyanate

PI:

Propidium iodide

MTT:

3-(4,5-dimethylthiazol-2-yl)-2.5-diphenyl-2H-tetrazolium bromide

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Acknowledgments

This work was supported by a grant from the National Cancer Center, Korea (NCC-1210470-1). We thank Dr. S.A. Martinis (Department of Biochemistry, University of Illinois at Urbana-Champaign, IL, USA) for critical reading of the manuscript.

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Authors and Affiliations

  1. Research Institute, National Cancer Center, 323, Ilsan-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do, 410-769, Republic of Korea

    Hyun-Jung Byun, Boh-Ram Kim & Seung Bae Rho

  2. Department of Biochemistry, University of Washington, Seattle, WA, 98195, USA

    Richard Yoo

  3. Center for Uterine Cancer, Research Institute and Hospital, National Cancer Center, 323, Ilsan-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do, 410-769, Republic of Korea

    Sang-Yoon Park

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  1. Hyun-Jung Byun
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  2. Boh-Ram Kim
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  5. Seung Bae Rho
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Correspondence to Seung Bae Rho.

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Byun, HJ., Kim, BR., Yoo, R. et al. sMEK1 enhances gemcitabine anti-cancer activity through inhibition of phosphorylation of Akt/mTOR. Apoptosis 17, 1095–1103 (2012). https://doi.org/10.1007/s10495-012-0751-0

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