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Upregulation of connexin43 contributes to PX-12-induced oxidative cell death

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Tumor Biology

Abstract

Thioredoxin (Trx) is a small redox protein that underlies aggressive tumor growth and resistance to chemotherapy. Inhibition of Trx with the chemical inhibitor PX-12 suppresses tumor growth and induces cell apoptosis. Currently, the mechanism underlying the therapeutic actions of PX-12 and the molecules influencing cell susceptibility to PX-12 are incompletely understood. Given that connexin43 (Cx43), a tumor suppressor, regulates tumor cell susceptibility to chemotherapy, we examined the possible involvement of Cx43 in PX-12-induced cell death. Exposure of cells to PX-12 led to a loss of cell viability, which was associated with the activation of oxidative sensitive c-Jun N-terminal kinase (JNK). Inhibition of JNK or supplement of cells with anti-oxidants prevented the cell-killing action of PX-12. The forced expression of Cx43 in normal and tumor cells increased cell sensitivity to PX-12-induced JNK activation and cell death. In contrast, the downregulation of Cx43 with siRNA or the suppression of gap junctions with chemical inhibitors attenuated JNK activation and enhanced cell resistance to PX-12. Further analysis revealed that PX-12 at low concentrations induced a JNK-dependent elevation in the Cx43 protein, which was also preventable by supplementing the cells with anti-oxidants. Our results thus indicate that Cx43 is a determinant in the regulation of cell susceptibility to PX-12 and that the upregulation of Cx43 may be an additional mechanism by which PX-12 exerts its anti-tumor actions.

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Abbreviations

NAC:

N-Acetyl-1-cysteine

CA:

Carbenoxolone

Cx:

Connexin

EGFP:

Enhanced green fluorescent protein

GJ:

Gap junction

GSH:

Glutathione reduced ethyl ester

α-GA:

α-Glycyrrhetinic acid

LDH:

Lactate dehydrogenase

PI:

Propidium iodide

ROS:

Reactive oxygen species

Trx:

Thioredoxin

WT:

Wild type

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Acknowledgments

This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science, and Technology, Japan (to 26461219 to J.Y.) and by a grant from the National Natural Science Foundation of China (Grant 81302918 to K.G.).

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Author notes

  1. Gang Li

    Present address: Department of Urology, Liaoning Cancer Hospital and Institute, Cancer Hospital of China Medical University, Shenyang, China

Authors and Affiliations

  1. Department of Molecular Signaling, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, 409-3898, Japan

    Gang Li, Kun Gao, Yuan Chi, Xiling Zhang & Jian Yao

  2. Department of Urology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Yamanashi, Japan

    Gang Li, Takahiko Mitsui & Masayuki Takeda

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  1. Gang Li
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Correspondence to Jian Yao.

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Gang Li and Kun Gao contributed equally to this work.

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Li, G., Gao, K., Chi, Y. et al. Upregulation of connexin43 contributes to PX-12-induced oxidative cell death. Tumor Biol. 37, 7535–7546 (2016). https://doi.org/10.1007/s13277-015-4620-7

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