Calcineurin regulates PERK autophosphorylation in astrocytes during oxygen glucose deprivation (OGD)

BOLLO M, CHEN Y, PAREDES R.M, HOLSTEIN D, AIMÉ S AND LECHLEITER JD.

Congreso; GORDON CONFERENCE, Calcium Signaling; 2011

The accumulation of unfolded proteins into the Endoplasmic Reticulum (ER) activates a signal transduction cascade called Unfolding Protein Response (UPR), which attempts to restore homeostasis in the organelle. (PKR)-like ER kinase (PERK) is an early stress response transmembranes proteins that is generally inactive due to its association with the chaperone BIP (Bertolotti et al Nat Cell Biol 2: 326, 2000). During ER stress, BIP is titrated by the excess of unfolded protein, which leads to PERK dimerization and autophosphorylation. This in turn, increases phosphorylation level of eukaryotic initiation factor-2 alpha (eIF2alpha), which attenuates protein synthesis. We recently demonstrated that calcineurin (CN) associates with PERK during ER stress, increasing its auto-phosphorylation and significantly enhancing inhibition of protein translation in Xenopus oocytes. Here, we report that the interaction of CN-A/B and PERK is significantly increased after 30 minutes of Oxygen and Glucose Deprivation (OGD) treatment in astrocytes. These cells express two CN-A isoforms, CN-Aalpha and CN-Abeta. Astrocytes deficient in CN-Abeta isoform exhibited constitutively active UPR. OGD treatment did not further increase cell death or eIF2alpha phosphorylation, in CN-Abeta-/- cells, but did so in both CN-Aalpha -/- and wild-type controls. These results are consistent with data obtained from in vitro kinase assays using both recombinant CN-A isoforms. CN-Abeta was more effective and Ca2+ sensitive at promoting PERK auto-phosphorylation. Preliminary experiments suggest that the CN/PERK association may involve the regulatory subunit B of CN, although its interaction appears much weaker than when CN-A is present. Taking together, these results indicate that CN plays a key role in initiating the early UPR during ER stress induced by OGD in astrocytes. Notably, this new function of CN is neuroprotective, which could lead to novel therapeutic treatments for cerebral brain ischemia.