Calreticulin

Calreticulin was first identified as a calcium binding protein, but it also appears to be a multifunctional protein found predominately in the endoplasmic reticulum (ER). Calreticulin appears to buffer ER Ca²⁺ levels in the ER, which affects intracellular calcium signaling. It also functions as an autophagy receptor and may also act as a molecular chaperone. Calreticulin was found to localize to intracellular, cell surface, and extracellular compartments, from which calreticulin regulates a variety of important biological processes such as cell proliferation, cell adhesion, migration and cell anoikis. Calreticulin on the cell surface may mediate phagocytosis of apoptotic or dying tumor cells by triggering immune responses and allowing the immune system to remove tumor cells.