Proteasome inhibition sensitizes hepatocellular carcinoma cells, but not human hepatocytes, to TRAIL

Authors

  • Tom M. Ganten,

    1. Division of Apoptosis Regulation, German Cancer Research Center (DKFZ), Heidelberg, Germany
    2. Department of Internal Medicine, University of Heidelberg, Heidelberg, Germany
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    • T.M.G. and R.K. contributed equally to this work.

  • Ronald Koschny,

    1. Division of Apoptosis Regulation, German Cancer Research Center (DKFZ), Heidelberg, Germany
    2. Department of Internal Medicine, University of Heidelberg, Heidelberg, Germany
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    • T.M.G. and R.K. contributed equally to this work.

  • Tobias L. Haas,

    1. Division of Apoptosis Regulation, German Cancer Research Center (DKFZ), Heidelberg, Germany
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  • Jaromir Sykora,

    1. Division of Apoptosis Regulation, German Cancer Research Center (DKFZ), Heidelberg, Germany
    2. Department of Internal Medicine, University of Heidelberg, Heidelberg, Germany
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  • Min Li-Weber,

    1. Division of Immunogenetics, German Cancer Research Center (DKFZ), Heidelberg, Germany
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  • Kerstin Herzer,

    1. Division of Immunogenetics, German Cancer Research Center (DKFZ), Heidelberg, Germany
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  • Henning Walczak

    Corresponding author
    1. Division of Apoptosis Regulation, German Cancer Research Center (DKFZ), Heidelberg, Germany
    • Division of Apoptosis Regulation, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany
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    • fax: (49) 6221-423699


  • Potential conflict of interest: Nothing to report.

Abstract

TRAIL exhibits potent anti-tumor activity on systemic administration in mice. Because of its proven in vivo efficacy, TRAIL may serve as a novel anti-neoplastic drug. However, approximately half of the tumor cell lines tested so far are TRAIL resistant, and potential toxic side effects of certain recombinant forms of TRAIL on human hepatocytes have been described. Pretreatment with the proteasome inhibitor MG132 and PS-341 rendered TRAIL-resistant hepatocellular carcinoma (HCC) cell lines but not primary human hepatocytes sensitive for TRAIL-induced apoptosis. We investigated the different levels of possible MG132-induced interference with resistance to apoptotic signal transduction. Although proteasome inhibition efficiently suppressed nuclear factor-kappaB (NF-κB) activity, specific suppression of NF-κB by mutIκBα failed to sensitize TRAIL-resistant cell lines for TRAIL-induced apoptosis. In contrast to the previously reported mechanism of sensitization by 5-fluorouracil (5-FU), cellular FLICE-inhibitory protein (cFLIP)L and cFLIPS were markedly upregulated in the TRAIL death inducing signaling complex (DISC) by proteasome inhibitor pretreatment. Compared with 5-FU pretreatment, caspase-8 was more efficiently recruited to the DISC in MG132 pretreated cells despite the presence of fewer death receptors and more cFLIP in the DISC. But downregulation of cFLIP by short interference RNA (siRNA) further sensitized the HCC cell lines. In conclusion, these results show that otherwise chemotherapy-resistant tumor cells can be sensitized for TRAIL-induced apoptosis at the DISC level in the presence of high levels of cFLIP, which suggests the existence of an additional factor that modulates the interaction of FADD and the TRAIL death receptors. Of clinical relevance, proteasome inhibitors sensitize HCC cells but not primary human hepatocytes for TRAIL-induced apoptosis. (HEPATOLOGY 2005.)

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