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Vol. 19, Issue 5, 1825-1836, May 2008

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Bap31 Is an Itinerant Protein That Moves between the Peripheral Endoplasmic Reticulum (ER) and a Juxtanuclear Compartment Related to ER-associated Degradation

Yuichi Wakana^*,, Sawako Takai^*, Ken-ichi Nakajima^*,, Katsuko Tani^*, Akitsugu Yamamoto, Peter Watson^||, David J. Stephens^||, Hans-Peter Hauri^¶, and Mitsuo Tagaya^*

*School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan; Department of Cell Biology, Nagahama Institute of Bio-Science and Technology, Nagahama, Shiga 526-0829, Japan; ^||Department of Biochemistry, University of Bristol, School of Medical Sciences, Bristol BS8 1TD, United Kingdom; and ^¶Department of Pharmacology and Neurobiology, University of Basel, Basel CH-4056, Switzerland

Submitted August 14, 2007; Revised February 5, 2008; Accepted February 8, 2008
Monitoring Editor: Adam Linstedt

Certain endoplasmic reticulum (ER)-associated degradation (ERAD) substrates with transmembrane domains are segregated from other ER proteins and sorted into a juxtanuclear subcompartment, known as the ER quality control compartment. Bap31 is an ER protein with three transmembrane domains, and it is assumed to be a cargo receptor for ER export of some transmembrane proteins, especially those prone to ERAD. Here, we show that Bap31 is a component of the ER quality control compartment and that it moves between the peripheral ER and a juxtanuclear ER or ER-related compartment distinct from the conventional ER–Golgi intermediate compartment. The third and second transmembrane domains of Bap31 are principally responsible for the movement to and recycling from the juxtanuclear region, respectively. This cycling was blocked by depolymerization of microtubules and disruption of dynein–dynactin function. Overexpression of Sar1p and Arf1 mutants affected Bap31 cycling, suggesting that this cycling pathway is related to the conventional vesicular transport pathways.

Present addresses: Cell and Developmental Biology, Centre for Genomic Regulation, Barcelona Biomedical Research Park, c/o Dr. Aiguader, 88, 08003 Barcelona, Spain;

Department of Molecular Cell Physiology, Graduate School of Medicine, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan.

Address correspondence to: Mitsuo Tagaya (tagaya{at}ls.toyaku.ac.jp)

Abbreviations used: BFA, brefeldin A; CB5, cytochrome b₅; CFTR, cystic fibrosis transmembrane conductance regulator; ER, endoplasmic reticulum; ERAD, endoplasmic reticulum-associated degradation; ERGIC, endoplasmic reticulum-Golgi intermediate compartment; GFP, green fluorescent protein; mRFP, monomeric red fluorescent protein; Noc, nocodazole; TMD, transmembrane domain; WT, wild type.

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