[Endoplasmic Reticulum Chaperones at the Tumor Cell Surface and in the Extracellular Space]

Endoplasmic reticulum chaperones are stress induced proteins capable of translocation into cytosol, cell membrane or extracellular space. The chaperones are transported from the endoplasmic reticulum particularly under endoplasmic reticulum stress conditions, while their constitutive extracellular expression was found in many cancers. Cell surface or extracellular endoplasmic reticulum chaperones take up distinct functions compared to their endoplasmic reticulum resident variants because they act like multifunctional receptors and thus affect cell signaling and proliferation.

The presented review focuses primarily on endoplasmic reticulum chaperones expression on the cell surface of cancer cells and into extracellular space. The work describes possible mechanisms of chaperones translocation to the cancer cell surface, including KDEL transport mechanism and retrotranslocation and the influence of chaperone posttranslation modifications on their localization within the cell. Well described cancer cell surface endoplasmic reticulum chaperones include GRP78, GRP94, calreticulin and calnexin that are involved in cancer cell signaling in different ways. The attention is also paid to immunogenic properties of membrane-localized chaperones for their ability to participate in immune reactions. They can take part in innate and adaptive immune response through their interaction with toll-like receptors or during the antigen presentation as well as in tumor-specific immunity. The expression of endoplasmic reticulum chaperones on the cancer cells surface is potentially exploitable in specific antitumor therapy as well as vaccine therapy, thus the final part of this review is dedicated to this topic.Key words: endoplasmic reticulum - glucose-regulated proteins - molecular chaperones - KDEL sequence - immunobiologyThis work was supported by the project MEYS - NPS I - LO1413.The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study.The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers.Submitted: 17. 5. 2016Accepted: 20. 7. 2016.