The Ca2+ concentration of the endoplasmic reticulum is a key determinant of ceramide-induced apoptosis: significance for the molecular mechanism of Bcl-2 action

Authors

  • Paolo Pinton,

    1. Department of Biomedical Sciences and CNR Center for the Study of Biomembranes, University of Padova, Via Colombo 3, Padova, Italy
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  • Davide Ferrari,

    1. Department of Experimental and Diagnostic Medicine, Section of General Pathology and Center for the Study of Inflammatory Diseases, Via Borsari 46, Ferrara, Italy
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  • Elena Rapizzi,

    1. Department of Experimental and Diagnostic Medicine, Section of General Pathology and Center for the Study of Inflammatory Diseases, Via Borsari 46, Ferrara, Italy
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  • Francesco Di Virgilio,

    1. Department of Experimental and Diagnostic Medicine, Section of General Pathology and Center for the Study of Inflammatory Diseases, Via Borsari 46, Ferrara, Italy
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  • Tullio Pozzan,

    1. Department of Biomedical Sciences and CNR Center for the Study of Biomembranes, University of Padova, Via Colombo 3, Padova, Italy
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  • Rosario Rizzuto

    Corresponding author
    1. Department of Experimental and Diagnostic Medicine, Section of General Pathology and Center for the Study of Inflammatory Diseases, Via Borsari 46, Ferrara, Italy
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  • P.Pinton and D.Ferrari contributed equally to this work

Abstract

The mechanism of action of the anti-apoptotic oncogene Bcl-2 is still largely obscure. We have recently shown that the overexpression of Bcl-2 in HeLa cells reduces the Ca2+ concentration in the endoplasmic reticulum ([Ca2+]er) by increasing the passive Ca2+ leak from the organelle. To investigate whether this Ca2+ depletion is part of the mechanism of action of Bcl-2, we mimicked the Bcl-2 effect on [Ca2+]er by different pharmacological and molecular approaches. All conditions that lowered [Ca2+]er protected HeLa cells from ceramide, a Bcl-2-sensitive apoptotic stimulus, while treatments that increased [Ca2+]er had the opposite effect. Surprisingly, ceramide itself caused the release of Ca2+ from the endoplasmic reticulum and thus [Ca2+] increased both in the cytosol and in the mitochondrial matrix, paralleled by marked alterations in mitochondria morphology. The reduction of [Ca2+]er levels, as well as the buffering of cytoplasmic [Ca2+] changes, prevented mitochondrial damage and protected cells from apoptosis. It is therefore concluded that the Bcl-2-dependent reduction of [Ca2+]er is an important component of the anti-apoptotic program controlled by this oncogene.

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