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© The Rockefeller University Press, 0021-9525/1998//391 $5.00
The Journal of Cell Biology, Volume 142, Number 2, , 1998 391-402


Articles

ADP-Ribosylation Factor 1 (ARF1) Regulates Recruitment of the AP-3 Adaptor Complex to Membranes



Chean Eng Ooi, Esteban C. Dell'Angelica, and Juan S. Bonifacino

Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health (NIH), Bethesda, Maryland 20892

Small GTP-binding proteins such as ADP- ribosylation factor 1 (ARF1) and Sar1p regulate the membrane association of coat proteins involved in intracellular membrane trafficking. ARF1 controls the clathrin coat adaptor AP-1 and the nonclathrin coat COPI, whereas Sar1p controls the nonclathrin coat COPII. In this study, we demonstrate that membrane association of the recently described AP-3 adaptor is regulated by ARF1. Association of AP-3 with membranes in vitro was enhanced by GTP{gamma}S and inhibited by brefeldin A (BFA), an inhibitor of ARF1 guanine nucleotide exchange. In addition, recombinant myristoylated ARF1 promoted association of AP-3 with membranes. The role of ARF1 in vivo was examined by assessing AP-3 subcellular localization when the intracellular level of ARF1-GTP was altered through overexpression of dominant ARF1 mutants or ARF1- GTPase-activating protein (GAP). Lowering ARF1-GTP levels resulted in redistribution of AP-3 from punctate membrane-bound structures to the cytosol as seen by immunofluorescence microscopy. In contrast, increasing ARF1-GTP levels prevented redistribution of AP-3 to the cytosol induced by BFA or energy depletion. Similar experiments with mutants of ARF5 and ARF6 showed that these other ARF family members had little or no effect on AP-3. Taken together, our results indicate that membrane recruitment of AP-3 is promoted by ARF1-GTP. This finding suggests that ARF1 is not a regulator of specific coat proteins, but rather is a ubiquitous molecular switch that acts as a transducer of diverse signals influencing coat assembly.

Key Words: ARF • adaptin • coat • endosomes • BFA



Abbreviations used in this paper: AP, adaptor protein; ARF, ADP-ribosylation factor; BFA, brefeldin A; CB, coat-binding; DOG, 2-deoxyglucose; GAP, GTPase-activating protein; GEF, guanine nucleotide exchange factor; HA, hemagglutinin; HB, homogenization buffer; HMW, high molecular weight.

Address all correspondence to Juan S. Bonifacino, Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, Building 18T/Room 101, National Institutes of Health (NIH), Bethesda, MD 20892. Tel.: (301) 496-6368. Fax: (301) 402-0078. E-mail: juan{at}helix.nih.gov

2. The ARF antibody used (clone 1D9) recognizes all five known human ARF proteins, but ARF1 and/or ARF3 is by far the most abundant ARF species in cells, comprising >90% of total cellular ARF.



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