Calreticulin promotes EMT in pancreatic cancer by enhancing endoplasmic reticulum stress-induced autophagy

Abstract

Abstract Background Our previous study showed that Calreticulin (CRT) promoted EMT in pancreatic cancer (PC) via mediating endoplasmic reticulum stress (ERS). Methods In current study, we further investigate the association of CRT with ERS-induced autophagy in regulating malignant behavior of PC in vitro and vivo. Results We first found thapsigargin (TG)-stimulated ERS and subsequent UPR signaling specifically induced the late stage of autophagy in vitro following the activation of ATG5/ATG12/LC3II signaling, and the increase of autophagosome formation and autophagic flux. However, CRISPR/Cas9 mediated CRT silencing reversed ERS-induced autophagy via specifically inhibiting TG-stimulated PERK/eIF2a axis. Similarly, TG-stimulated ERS promoted cell mobility and Gemcitabine resistance in vitro via promoting autophagy, which was significantly reversed by CRT silencing and autophagy inhibitor Chloroquine (CQ). In vivo, CRT silencing and CQ treatment profoundly inhibited TG-induced pancreatic tumor size in situ and the number of distant liver metastasis following the same change of UPR and autophagy signaling as shown in vitro. Mechanistically, CRT was co-localized and co-immunoprecipitated with LC3 under TG treatment. GST pulldown showed a conserved but critical LC3-interacting region (LIR: WDFL) for the interaction between CRT and LC3, which is required for CRT-mediated augmentation of ERS-induced autophagy. The subsequent augmentation of ERS-induced autophagy profoundly promoted EMT in vitro, which was reversed by CRT silencing and CQ. Finally, a close relationship between CRT with critical markers of UPR and autophagy signaling was also observed in clinical PC samples, which coordinately promoted poor prognosis of PC patients. Conclusions CRT promotes EMT in PC via enhancing ERS-induced autophagy.