Phosphorylation of BCL-2 regulates ER Ca2+ homeostasis and apoptosis

Authors

  • Michael C Bassik,

    1. Department of Pathology and Medicine, Howard Hughes Medical Institute, Dana Farber Cancer Institute, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
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  • Luca Scorrano,

    1. Department of Pathology and Medicine, Howard Hughes Medical Institute, Dana Farber Cancer Institute, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
    2. Dulbecco-Telethon Institute, Venetian Institute of Molecular Medicine, Padova, Italy
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  • Scott A Oakes,

    1. Department of Pathology and Medicine, Howard Hughes Medical Institute, Dana Farber Cancer Institute, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
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  • Tullio Pozzan,

    1. Dulbecco-Telethon Institute, Venetian Institute of Molecular Medicine, Padova, Italy
    2. Department of Biomedical Sciences, University of Padova, Padova, Italy
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  • Stanley J Korsmeyer

    Corresponding author
    1. Department of Pathology and Medicine, Howard Hughes Medical Institute, Dana Farber Cancer Institute, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
    • Corresponding author. Department of Pathology and Medicine, Howard Hughes Medical Institute, Dana Farber Cancer Institute, Brigham and Women's Hospital, Harvard Medical School, 44 Binney Street, Boston, MA 02115, USA. Tel.: +1 617 632 6402; Fax: +1 617 632 6401; E-mail: stanley_korsmeyer@dfci.harvard.edu

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Abstract

Phosphorylation of BCL-2 within an unstructured loop inhibits its antiapoptotic effect. We found that phosphorylated BCL-2 predominantly localized to the endoplasmic reticulum (ER) and tested whether phosphorylation would control its activity at this organelle, where Ca2+ dynamics serve as a critical control point for apoptosis. Phosphorylation greatly inhibits the ability of BCL-2 to lower [Ca2+]er and protect against Ca2+-dependent death stimuli. Cells expressing nonphosphorylatable BCL-2AAA exhibited increased leak of Ca2+ from the ER and further diminished steady-state [Ca2+]er stores when compared to cells expressing BCL-2wt. Consequently, when BCL-2 is phosphorylated, Ca2+ discharge from the ER is increased, with a secondary increase in mitochondrial Ca2+ uptake. We also demonstrate that phosphorylation of BCL-2 inhibits its binding to proapoptotic family members. This inhibitory mechanism manifested at the ER, where phosphorylated BCL-2 was unable to bind proapoptotic members. [Ca2+]er proved coordinate with the capacity of BCL-2 to bind proapoptotic BH3-only members, further integrating the apoptotic pathway and Ca2+ modulation. Unexpectedly, the regulation of ER Ca2+ dynamics is a principal avenue whereby BCL-2 phosphorylation alters susceptibility to apoptosis.

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