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First published online 22 March 2005
doi: 10.1242/jcs.02294

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Protein synthesis inhibitors and the chemical chaperone TMAO reverse endoplasmic reticulum perturbation induced by overexpression of the iodide transporter pendrin

¹ Department of Pathology, Sackler School of Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel
² Johns Hopkins Bay View Medical Center, Johns Hopkins University, Baltimore, MD 21224, USA
³ Department of Internal Medicine E, Meir Hospital Sapir Medical Center, Kfar-Sava, Israel

^* Author for correspondence (e-mail: koty{at}post.tau.ac.il)

Accepted 28 January 2005

An outcome of overloading of the endoplasmic reticulum (ER) folding machinery is a perturbation in ER function and the formation of intracellular aggregates. The latter is a key pathogenic factor in numerous diseases known as ER storage diseases. Here, we report that heterologous overexpression of the green fluorescent protein-tagged iodide transporter pendrin (GFP-PDS) perturbs folding and degradation processes in the ER. Pendrin (PDS) is a chloride-iodide transporter found in thyroid cells. Mutations in PDS can cause its retention in the ER and are associated with Pendred syndrome. Biochemical and live-cell analyses demonstrated that wild-type GFP-PDS is predominantly retained in perinuclear aggregates and in ER membranes, causing their collapse and vesiculation. Inhibition of protein synthesis by cycloheximide (CHX) or puromycin caused dissociation of the GFP-PDS aggregates and returned the ER to its normal reticular morphology. Blocking protein synthesis promoted folding and export of ER-retained GFP-PDS, as demonstrated by surface-biotinylation analysis and by CHX- or puromycin-induced accumulation of YFP-PDS in the Golgi apparatus during a 20°C temperature-block experiment. The chemical chaperone trimethylamine-N-oxide (TMAO) also reversed the GFP-PDS-mediated ER collapse and vesiculation, suggesting that exposed hydrophobic stretches of misfolded or aggregated GFP-PDS may contribute to ER retention. These data suggest that GFP-PDS is a slow-folding protein with a propensity to form aggregates when overexpressed. Thus, we describe a system for the reversible induction of ER stress that is based entirely on the heterologous overexpression of GFP-PDS.

Key words: Pendrin, Green fluorescent protein, Endoplasmic reticulum, Aggregation, Folding, ERAD

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