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Chapter category: Cell Metabolism

Calreticulin-Mediated Nuclear Protein Export

This chapter appears in the following book:

Calreticulin
Second Edition

Edited by: Paul Eggleton and Marek Michalak
ISBN: 0-306-47845-5
» Get more information about this book at landesbioscience.com «

Chapter authors:
Ben E. Black and Bryce M. Paschal


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The role of calreticulin (CRT) as a molecular chaperone that functions in the endoplasmic reticulum (ER) is well established. This involves transient binding of CRT to hydrophobic residues and carbohydrate chains in polypeptides undergoing folding reactions in the lumen of the ER. The issue of CRT distribution and function outside of the ER, though controversial for several years, has now been addressed by rigorous biochemical fractionation and cell biological analysis. Cytosolic CRT, which refers to the non-ER form of the protein that shuttles between the cytoplasm and nucleus, can function as a receptor that mediates nuclear export of the glucocorticoid receptor (GR). The signal recognized by CRT is contained within the DNA binding domain (DBD) of GR. In this chapter, we introduce the topic of nuclear export and summarize the characterization of cytosolic CRT as an export receptor. We also review the evidence that the DBD functions as a signal for export of GR. The DBD is likely to function as the export signal for other members of the nuclear receptor (NR) superfamily, which is the largest family of transcription factors in higher eukaryotes. Our working model is that the non-ER form of CRT contributes to the regulation of multiple cellular pathways through a nuclear export-based mechanism.

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