Ribosome-translocon complex mediates calcium leakage from endoplasmic reticulum stores.
Under resting conditions, the endoplasmic reticulum (ER) intraluminal free calcium concentration ([Ca(2+)](ER)) reflects a balance between active uptake by Ca(2+)-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 Ca(2+)-ATPase inhibitor) was lower after puromycin treatment. Puromycin also reduced the [Ca(2+)](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 [Ca(2+)](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 [Ca(2+)](ER) and could therefore supervise many physiological processes, including gene expression and apoptosis.
Laboratoire de Physiologie Cellulaire, INSERM EMI 0228, Université de Lille 1, Bâtiment SN3, 59655 Villeneuve d'Ascq CEDEX, France. fvancopp@pop.univ-lille1.fr
Fabien
F
Van Coppenolle
Fabien
F
Vanden Abeele
Christian
C
Slomianny
Matthieu
M
Flourakis
John
J
Hesketh
Etienne
E
Dewailly
Natalia
N
Prevarskaya
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016257:Fura-2; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D046911:Macromolecular Substances / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport / Q000502:physiology; D011691:Puromycin / Q000494:pharmacology; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure; D012433:Ryanodine / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D046911:Macromolecular Substances; D011500:Protein Synthesis Inhibitors; D012433:Ryanodine; D011691:Puromycin; D006493:Heparin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2