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Vol. 17, Issue 1, 525-538, January 2006

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Cis-Golgi Matrix Proteins Move Directly to Endoplasmic Reticulum Exit Sites by Association with Tubules

Gonzalo A. Mardones ^*, Christopher M. Snyder , and Kathryn E. Howell

Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO 80045

Submitted May 23, 2005; Revised September 30, 2005; Accepted October 14, 2005
Monitoring Editor: Benjamin Glick

The role of cis-medial Golgi matrix proteins in retrograde traffic is poorly understood. We have used imaging techniques to understand the relationship between the cis-medial Golgi matrix and transmembrane proteins during retrograde traffic in control and brefeldin A (BFA)-treated cells. All five of the cis-medial matrix proteins tested were associated with retrograde tubules within 2-3 min of initiation of tubule formation. Then, at later time points (3-10 min), transmembrane proteins are apparent in the same tubules. Strikingly, both the matrix proteins and the transmembrane proteins moved directly to endoplasmic reticulum (ER) exit sites labeled with p58 and Sec13, and there seemed to be a specific interaction between the ER exit sites and the tips or branch points of the tubules enriched for the matrix proteins. After the initial interaction, Golgi matrix proteins accumulated rapidly (5-10 min) at ER exit sites, and Golgi transmembrane proteins accumulated at the same sites 2 h later. Our data suggest that Golgi cis-medial matrix proteins participate in Golgi-to-ER traffic and play a novel role in tubule formation and targeting.

Abbreviations used: BFA, brefeldin A; GalT, galactosyltransferase; Man-II, mannosidase II.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

^* Present address: Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892

Present address: Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, OR 97239.

Address correspondence to: Kathryn E. Howell (kathryn.howell{at}uchsc.edu).