Calcineurin B-mediated Ca2+ sensing translates stress signal intensity into the assembly of phase-separated condensates at PERK complexes.

Bairo, S. M.; Fernandez, M.; Quassollo, G.; Pellegrini, A.; de Battista, J. C.; Asis, S.; Martin, M. G.; Holstein, D.; Lechleiter, J. D.; Gomez, G. E.; Bisbal, M.; Bollo, M.

doi:10.64898/2026.08.03.742535

bioRxiv · 10.64898/2026.08.03.742535

Calcineurin B-mediated Ca2+ sensing translates stress signal intensity into the assembly of phase-separated condensates at PERK complexes.

Bairo, S. M.·Fernandez, M.·Quassollo, G.·Pellegrini, A.·de Battista, J. C.·Asis, S.·Martin, M. G.·Holstein, D.·Lechleiter, J. D.·Gomez, G. E.·Bisbal, M.·Bollo, M.

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Abstract

Endoplasmic reticulum (ER) stress activates protein kinase RNA-like ER kinase (PERK), which initially promotes adaptive responses but remains the only active UPR branch during prolonged stress, mediating both early cytoprotective and chronic pro-apoptotic signaling. Recently, we identified translocon-generated Ca2+ microdomains that promote PERK phosphorylation during early UPR, revealing a mechanism by which local Ca2+ signals regulate UPR activation. However, the molecular mechanism linking these Ca2+ microdomains to PERK activation remains elusive. Previously, we showed that calcineurin (CN), a Ca2+ -dependent heterodimer composed of catalytic (CNA) and regulatory (CNB) subunits, exerts a non-canonical pro-survival function by promoting PERK autophosphorylation. Here, using super-resolution microscopy, CRISPR-Cas9 editing, in silico analyses, and optogenetic droplet assays, we identify CNB as a local Ca2+ sensor that couples translocon-generated Ca2+ signals to liquid condensate assembly, thereby promoting adaptive PERK phosphorylation. These findings establish CNB-mediated condensate assembly as a mechanism that translates local Ca2+ signals into spatially organized early adaptive PERK signaling.

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Bairo, S. M., Fernandez, M., Quassollo, G., Pellegrini, A., de Battista, J. C., Asis, S., Martin, M. G., Holstein, D., Lechleiter, J. D., Gomez, G. E., Bisbal, M., Bollo, M.. 2026-08-04. Calcineurin B-mediated Ca2+ sensing translates stress signal intensity into the assembly of phase-separated condensates at PERK complexes.. https://doi.org/10.64898/2026.08.03.742535

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