MECHANISM OF CALCIUM RELEASE DURING UNFOLDED PROTEIN RESPOSE

FELIZIANI C; HOLSTEIN D; FERNÁNDEZ M; QUASOLLO G, ; PATON A W; PATON J C; LECHLEITER J; BOLLO M

Congreso; XXXIII Reunión Anual de la Sociedad Argentina de Investigación en Neurociencias; 2018

SOCIEDAD ARGENTINA de Neurociencias (SAN)

MECHANISM OF CALCIUM RELEASE DURING UNFOLDED PROTEIN RESPOSE. The Endoplasmic Reticulum (ER) plays a critical role in different processes, where the ER Ca2+ acts as a key messenger. Under resting conditions, the luminal Ca2+ concentration reflects a balance between uptake by Ca2+-ATPases and efflux pathways of which the translocon can play a prominent role. The translocon is an aqueous pore, formed by the Sec61α core spanning the ER lipid bilayer, blocked by the ribosome (cytosolic side) and by BiP (luminal side). During the acute phase of the UPR (Unfolded Protein Response), immediately after unfolded protein are accumulated in the lumen, the Ca2+ ER eflux through the translocon would increase. We performed cytosolic Ca2+ measurements in primary human astrocytes, expressing the Ca2+ indicator GCaMP6 tethered to the ER membrane, after UPR induction with Tunicamycin. We observed focal release of Ca2+ in stressed astrocytes that was significantly inhibited by translocon blockers (emetine or anisomycin). The Tm-induced Ca2+ signal was amplified by pre-treatment either with AB5 cytotoxine (hydrolyzes BiP) or with the translocon opener puromycin. This effect was corroborated by co-immunoprecipitations. The likelihood of obtained Tm-induce local Ca2+ events, increase by using either the slow Ca2+ chelator EGTA-AM or Xestospongin C and Ryanodine, InsP3 and Ry Receptors inhibitors, respectively. Finally, InsP3 Receptor null HEK-293 cell line exhibited Tm-evoked Ca2+ release near ER microdomain, which is inhibited by BiP over-expression.