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First published online 27 July 2004
doi: 10.1242/jcs.01274

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Ribosome-translocon complex mediates calcium leakage from endoplasmic reticulum stores

Fabien Van Coppenolle^1,*,, Fabien Vanden Abeele^1,*, Christian Slomianny¹, Matthieu Flourakis¹, John Hesketh², Etienne Dewailly¹ and Natalia Prevarskaya¹

¹ Laboratoire de Physiologie Cellulaire, INSERM EMI 0228, Université de Lille 1, Bâtiment SN3, 59655 Villeneuve d'Ascq CEDEX, France
² School of Cellular and Molecular Biosciences, University of Newcastle, Agriculture Building, Kings Road, Newcastle-upon-Tyne, NE1 7RU, UK

Author for correspondence (e-mail: fvancopp{at}pop.univ-lille1.fr)

Accepted 19 April 2004

Under resting conditions, the endoplasmic reticulum (ER) intraluminal free calcium concentration ([Ca²⁺]_ER) reflects a balance between active uptake by Ca²⁺-ATPases and passive efflux via `leak channels'. Despite their physiological importance and ubiquitous leak pathway mechanism, very little is known about the molecular nature of these channels. As it has been suggested that the open translocon pore complex of the ER is permeable to ions and neutral molecules, we hypothesized that the ribosome-bound translocon would be permeable to calcium after treatment with puromycin, a translation inhibitor that specifically releases polypeptide chains. At this time, the translocon channel is left open. We measured the fluctuations in cytoplasmic and luminal calcium concentrations using fluorescent dyes (fura-2 and magfura-2, respectively). The calcium release induced by thapsigargin (a Ca²⁺-ATPase inhibitor) was lower after puromycin treatment. Puromycin also reduced the [Ca²⁺]_ER level when perfused into the medium, but was ineffective after anisomycin pre-treatment (an inhibitor of the peptidyl transferase). Puromycin had a similar effect in the presence of heparin and ryanodine. This puromycin-evoked [Ca²⁺]_ER decrease was specific to the translocon. We conclude that the translocon complex is a major calcium leak channel. This work reveals a new role for the translocon which is involved in the control of the [Ca²⁺]_ER and could therefore supervise many physiological processes, including gene expression and apoptosis.

Key words: Prostate cancer, Translocon, Puromycin, Calcium leak, Endoplasmic reticulum, LNCaP cells

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