Role of Molecular Chaperones in the Biosynthesis of Anion Exchanger 1

• Main Author: Patterson, Sian T.
• Other Authors: Reithmeier, Reinhart A. F.
• Language: en_ca
• Published: 2011
• Subjects: membrane; glycoprotein; transporter; chaperones; biosynthesis; anion exchanger 1; disease; treatment; 0306; 0379; 0307
• Online Access: http://hdl.handle.net/1807/29838

Mutations in the SLC4A1 gene result in misfolding and trafficking defects of the human erythroid (AE1) and kidney (kAE1) forms of the anion exchanger 1 glycoprotein. This affects the amount of functional protein at the cell surface, resulting in hematological and renal diseases. In this thesis, the role of the quality control system of molecular chaperones (cytosolic and ER) was examined during the biosynthesis of wild type and mutant AE1 in different cellular models. The hypothesis to be tested is that molecular chaperones are responsible for the intracellular retention of AE1 mutants. Chaperones were found to interact with AE1 and kAE1 in vitro and in vivo (HEK-293, K562, MDCK cells). Disruption of the calnexin-AE1 interaction in K562 cells did not affect the cell surface levels of wild type or mutant erythroid AE1. AE1 also trafficked to the cell surface in mouse embryonic fibroblasts completely deficient in calnexin or calreticulin. In contrast, in MDCK cells, disruption of the calnexin-kAE1 interaction allowed functional dominant (R589H, R901stop), but not misfolded kAE1 mutants (kSAO, G701D), to escape the ER and traffic to the cell surface. Calnexin is therefore not required for the cell surface expression of erythroid AE1, but can be responsible for the intracellular retention of certain kAE1 mutants in cells with the complete complement of molecular chaperones. Components involved in membrane glycoprotein folding and quality control (calnexin, ERp57, Hsc70, Hsp70), were lost at later stages during the differentiation of CD34+ erythroid progenitor cells. This suggests that the loss of molecular chaperones may facilitate the massive production of red cell glycoproteins, allowing erythroid AE1 mutants to escape quality control, traffic to the plasma membrane, and be present in mature red blood cells. These studies demonstrate that the role chaperones play varies, depending on cellular context. By understanding the cellular context and factors involved, therapeutic strategies may be tailored to deal with protein misfolding diseases, and in the case of kAE1, rescue the cell surface trafficking of misfolded, but functional, transport protein using pharmacological modulators.