Endoplasmic Reticulum Stress‐Induced Membrane Exposure of Calreticulin Serves as a Guide for Phagocytic Removal of Stressed‐But‐Viable Cytotrophoblasts

Calreticulin (CRT), a protein in the endoplasmic reticulum (ER), plays critical roles in protein quality control and homeostasis of cytosolic and ER calcium levels. We previously reported that ER stress, a risk factor for poor placentation and preeclampsia, induced extracellular release of CRT in a cytotrophoblast (CTB) BeWo cell model; extracellular CRT impaired CTB syncytialization. Several stresses, including ER stress, reportedly exposed CRT on membranes, but the roles of membrane‐exposed CRT in CTBs have remained unclear.