Protein disulfide isomerase–like proteins play opposing roles during retrotranslocation

Harvard University, Cambridge, Massachusetts, United States
The Journal of Cell Biology (Impact Factor: 9.83). 07/2006; 173(6):853-9. DOI: 10.1083/jcb.200602046
Source: PubMed


Misfolded proteins in the endoplasmic reticulum (ER) are retained in the organelle or retrotranslocated to the cytosol for proteasomal degradation. ER chaperones that guide these opposing processes are largely unknown. We developed a semipermeabilized cell system to study the retrotranslocation of cholera toxin (CT), a toxic agent that crosses the ER membrane to reach the cytosol during intoxication. We found that protein disulfide isomerase (PDI) facilitates CT retrotranslocation, whereas ERp72, a PDI-like protein, mediates its ER retention. In vitro analysis revealed that PDI and ERp72 alter CT's conformation in a manner consistent with their roles in retrotranslocation and ER retention. Moreover, we found that PDI's and ERp72's opposing functions operate on endogenous ER misfolded proteins. Thus, our data identify PDI family proteins that play opposing roles in ER quality control and establish an assay to further delineate the mechanism of CT retrotranslocation.

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    • "In the current analysis, MG132 treatment led also to the accumulation of a protein disulfide isomerase-like (PDI). PDI facilitates the retrotranslocation of some misfolded proteins from the ER to the proteasome in yeast and animal cells [50], [51]. Immunogold labeling with anti-ubiquitin antibody has provided direct proof of UbP accumulation in ER membranes upon MG132 treatment, leading to significant ER stress [13]. "
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    • "As noted above, retrotranslocation of ERAD substrates is preceded by a recognition step. The chaperone BiP, which is known to be involved in identification of non-glycosylated ERAD substrates, and an ER-resident ATPase (Torsin A) promote CTA1 retrotranslocation (Tsai et al., 2001; Winkeler et al., 2003; Forster et al., 2006; Moore et al., 2010). Sel1L and ERdj5, a co-chaperone of BiP, also facilitate CTA1 retrotranslocation, where the J domain of ERdj5 is required (Williams et al., 2013). "
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    • "To additionally test whether in vitro release of CTA1 resembles release in vivo, we examined an uncleavable mutant form of CTA, R192G CTA, that is not released into the cytosol in vivo [21], [29]. The R192 cleavage site is flanked by C187 and C199 that form the lone disulfide bond. "
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