Cell Biology

Stress Testing the ER

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Science  04 Dec 2009:
Vol. 326, Issue 5958, pp. 1323
DOI: 10.1126/science.326.5958.1323-c

The antibody-producing cells of our immune system are able to secrete their own weight in antibodies each day. This prodigious feat relies on the endoplasmic reticulum (ER), which is a network of internal membranes in eukaryotic cells and which ensures that secreted proteins are folded and packaged correctly. Misfolded proteins are horrifically sticky and potentially harmful; luckily, the ER detects, via the unfolded protein response (UPR), when it is full up and boosts its handling capacity by, for example, increasing the expression of ER-resident chaperone proteins that untangle protein aggregates.

Schuck et al. find that a dramatic expansion of the area and volume of the ER during the UPR helps to alleviate the refolding bottleneck. The UPR drives ER expansion through increased synthesis of membrane lipids, which are incorporated into the peripheral ER. The shape of the ER enlargements, be they sheets or tubules, does not seem critical; rather, it is the increase in volume, which facilitates protein refolding and reduces the chance of aggregation, and the increase in surface area, which promotes membrane-associated degradation processes.

J. Cell Biol. 187, 525 (2009).

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