1. Calreticulin—From the Endoplasmic Reticulum to the Plasma Membrane—Adventures of a Wandering Protein.
- Author
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Okura, Gillian C., Bharadwaj, Alamelu G., and Waisman, David M.
- Subjects
CELL membranes ,HOMEOSTASIS ,CALCIUM-binding proteins ,ENDOPLASMIC reticulum ,IMMUNE system ,CELL death ,TUMORS ,DRUG discovery - Abstract
Simple Summary: This review examines the chronological timeline of studies identifying and characterizing calreticulin (CRT) from its origin as an endoplasmic reticulum (ER) protein to an important cell surface signaling molecule. A detailed literature analysis shows that CRT was initially discovered as the Ca
2+ -binding ER protein, called calregulin, and not as the SR protein(s), called the high-affinity calcium-binding protein (HACBP). We further elucidate the critical functions of CRT in calcium homeostasis, protein folding, immunogenic cell death (ICD), and antigen presentation. The roles of CRT in the regulation of the destruction of cancer cells by the immune system and as a causative factor in certain blood cancers are also discussed. Overall, this review critically and comprehensively identifies the original studies that revealed CRT's discovery, structure, and functions in the ER and at the cell surface. Calreticulin (CRT) is a 46 kDa highly conserved protein initially identified as calregulin, a prominent Ca2+ -binding protein of the endoplasmic reticulum (ER). Subsequent studies have established that CRT functions in the ER's protein folding response and Ca2+ homeostatic mechanisms. An ER retention signal on the carboxyl terminus of CRT suggested that CRT was restricted to the ER. However, the identification of CRT in the nucleus and cytosol has established that CRT is a multi-compartmental, multifunctional protein. CRT also plays an important role in cancer progression. Most recently, CRT was identified on the cell surface and shown to be a potent 'eat-me' signal that plays a key role in the uptake of apoptotic and viable cancer cells by phagocytes. Elevated CRT exposure on the outer leaflet of cancer cells has been linked with anticancer immunity and superior therapeutic outcomes in patients with non-small cell lung carcinoma, colorectal carcinoma, acute myeloid leukemia, ovarian cancer, and high-grade serous carcinomas. Mutations in the CRT gene have been identified in a subset of patients with myeloproliferative neoplasms. The most recent studies from our laboratory have revealed a new and significant function for extracellular CRT as a plasminogen receptor. This discovery has profound implications for our understanding of the role of CRT in myeloproliferative neoplasms, specifically, essential thrombocythemia. [ABSTRACT FROM AUTHOR]- Published
- 2025
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