Resveratrol-induced autophagy is dependent on IPRs and on cytosolic Ca.

Previous work revealed that intracellular Ca signals and the inositol 1,4,5-trisphosphate (IP) receptors (IPR) are essential to increase autophagic flux in response to mTOR inhibition, induced by either nutrient starvation or rapamycin treatment. Here, we investigated whether autophagy induced by resveratrol, a polyphenolic phytochemical reported to trigger autophagy in a non-canonical way, also requires IPRs and Ca signaling. Resveratrol augmented autophagic flux in a time-dependent manner in HeLa cells. Importantly, autophagy induced by resveratrol (80μM, 2h) was completely abolished in the presence of 10μM BAPTA-AM, an intracellular Ca-chelating agent. To elucidate the IPR's role in this process, we employed the recently established HEK 3KO cells lacking all three IPR isoforms. In contrast to the HEK293 wt cells and to HEK 3KO cells re-expressing IPR1, autophagic responses in HEK 3KO cells exposed to resveratrol were severely impaired. These altered autophagic responses could not be attributed to alterations in the mTOR/p70S6K pathway, since resveratrol-induced inhibition of S6 phosphorylation was not abrogated by chelating cytosolic Ca or by knocking out IPRs. Finally, we investigated whether resveratrol by itself induced Ca release. In permeabilized HeLa cells, resveratrol neither affected the sarco- and endoplasmic reticulum Ca ATPase (SERCA) activity nor the IP-induced Ca release nor the basal Ca leak from the ER. Also, prolonged (4 h) treatment with 100μM resveratrol did not affect subsequent IP-induced Ca release. However, in intact HeLa cells, although resveratrol did not elicit cytosolic Ca signals by itself, it acutely decreased the ER Ca-store content irrespective of the presence or absence of IPRs, leading to a dampened agonist-induced Ca signaling. In conclusion, these results reveal that IPRs and cytosolic Ca signaling are fundamentally important for driving autophagic flux, not only in response to mTOR inhibition but also in response to non-canonical autophagy inducers like resveratrol. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.