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Vol. 19, Issue 2, 523-535, February 2008

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Distinct Functions for Arf Guanine Nucleotide Exchange Factors at the Golgi Complex: GBF1 and BIGs Are Required for Assembly and Maintenance of the Golgi Stack and trans-Golgi Network, Respectively

Florin Manolea^*, Alejandro Claude, Justin Chun^*, Javier Rosas, and Paul Melançon^*

*Department of Cell Biology, University of Alberta, Edmonton, AB, T6G 2H7 Canada; and Instituto de Bioquímica, Universidad Austral de Chile, Campus Isla Teja, Casilla 567, Valdivia, Chile

Submitted May 1, 2007; Revised October 31, 2007; Accepted November 6, 2007
Monitoring Editor: Benjamin Glick

We examined the relative function of the two classes of guanine nucleotide exchange factors (GEFs) for ADP-ribosylation factors that regulate recruitment of coat proteins on the Golgi complex. Complementary overexpression and RNA-based knockdown approaches established that GBF1 regulates COPI recruitment on cis-Golgi compartments, whereas BIGs appear specialized for adaptor proteins on the trans-Golgi. Knockdown of GBF1 and/or COPI did not prevent export of VSVGtsO45 from the endoplasmic reticulum (ER), but caused its accumulation into peripheral vesiculotubular clusters. In contrast, knockdown of BIG1 and BIG2 caused loss of clathrin adaptor proteins and redistribution of several TGN markers, but had no impact on COPI and several Golgi markers. Surprisingly, brefeldin A–inhibited guanine nucleotide exchange factors (BIGs) knockdown prevented neither traffic of VSVGtsO45 to the plasma membrane nor assembly of a polarized Golgi stack. Our observations indicate that COPII is the only coat required for sorting and export from the ER exit sites, whereas GBF1 but not BIGs, is required for COPI recruitment, Golgi subcompartmentalization, and cargo progression to the cell surface.

Address correspondence to: Paul Melançon (Paul.Melancon{at}UAlberta.ca)

Abbreviations used: AP, adaptor protein; Arf, ADP-ribosylation factor; BFA, brefeldin A; BIG, brefeldin A–inhibited guanine nucleotide exchange factor; COP, coat protein; ERES, ER exit sites; ERGIC, ER-Golgi intermediate compartment; GBF, Golgi-specific brefeldin A resistance factor; GEF, guanine nucleotide exchange factor; GGA, gamma ear Golgi-localized Arf-binding protein; IF, immunofluorescence; ManII, mannosidase II; KD, knockdown; PM, plasma membrane; shRNA, short hairpin RNA; siRNA, small inhibitory RNA; TGN, trans-Golgi Network; VSVG, vesicular stomatitis virus glycoprotein; VTC, vesiculotubular cluster.

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