Calreticulin (CRT) is a multifunctional protein found in the endoplasmic reticulum (ER) of cells. It was initially identified as a calcium-binding protein in skeletal muscle sarcoplasmic reticulum, but it is now known to be abundant in non-muscle tissues as well and plays a variety of roles in cellular processes. As a chaperone, calreticulin helps in the folding of proteins and prevents the premature export of misfolded proteins from the ER. It works in conjunction with other chaperones like calnexin and ERp57. And it buffers calcium ions, which are essential for various cellular signaling pathways. Calreticulin also plays a role in integrin-mediated cell adhesion and calcium signaling. On the surface of cells undergoing immunogenic cell death (ICD), calreticulin can expose and enhance the uptake of cell corpses by phagocytes, thereby supporting anticancer immunity. Moreover, it is part of the peptide-loading complex, which ensures the proper loading of cellular antigens onto MHC Class I molecules. Calreticulin has been implicated in the enhancement of wound healing through multiple biological effects, including the modulation of extracellular matrix components and the promotion of cell proliferation. It also interacts with various components of the immune system, such as C1q and mannan-binding protein, which suggests its involvement in the clearance of apoptotic cells and inflammation resolution.
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