Calcium-signaling microdomains during early phase of Endoplasmic Reticulum Stress

FELIZIANI C; HOLSTEIN D; PATON AW; PATON JC; BOLLO M, CHEN Y, PAREDES R.M, HOLSTEIN D, AIMÉ S AND LECHLEITER JD.; BOLLO, M

Congreso; 51 Reunion Anual de la Sociedad Bioquimica y de Biologia Celular?; 2015

The Endoplasmic Reticulum (ER) is a multi-functional organelle that plays a critical role in a variety of processes, where the ER Ca2+ acts as a key player. Under resting conditions, the luminal Ca2+ concentration reflects a balance between active uptake by Ca2+-ATPases and passive efflux pathways, of which can play a prominent role the translocon. This is an aqueous pore, primarily formed by the Sec61α complex spanning the ER lipid bilayer, that is blocked by the ribosome on the cytosolic side and by the ER chaperone, BiP, on the luminal side. We hypothesize that during the acute phase of the UPR (Unfolded Protein Response), the Ca2+ ER eflux through the translocon is increased. To test this mechanism of action, we performed cytosolic Ca2+ measurements in primary cultures astrocytes, expressing the Ca2+ indicator GCaMP6 tethered to the ER membrane, after induction of the UPR by Tunicamycin (Tm). We observed focal release of Ca2+ in stressed astrocytes that was significantly inhibited by translocon blockers (emetine or anisomycin). In addition, pre-treatment with AB5 toxine, which specifically hydrolyses BiP, amplified the Tm-induced Ca2+ signal. Finally, co-immunoprecipitation studies showed that Tm treatments disrupted the interaction between Sec61α and BiP. Overall these data, strongly suggest that the chaperone is dissociated from the translocon increasing Ca2+ permeability.