The TBC (Tre-2/Bub2/Cdc16) Domain Protein TRE17 Regulates Plasma Membrane-Endosomal Trafficking through Activation of Arf6

Abstract

TBC (Tre-2/Bub2/Cdc16) domains are predicted to encode GTPase-activating proteins (GAPs) for Rab family G proteins. While approximately 50 TBC proteins are predicted to exist in humans, little is known about their substrate specificity. Here we show that TRE17 (also called Tre-2 and USP6), a founding member of the TBC family, targets the Arf family GTPase Arf6, which regulates plasma membrane-endosome trafficking. Surprisingly, TRE17 does not function as a GAP for Arf6 but rather promotes its activation in vivo. TRE17 associates directly with Arf6 in its GDP- but not GTP-bound state. Mapping experiments pinpoint the site of interaction to the TBC domain of TRE17. Forced expression of TRE17 promotes the localization of Arf6 to the plasma membrane, leading to Arf6 activation, presumably due to facilitated access to membrane-associated guanine nucleotide exchange factors (GEFs). Furthermore, TRE17 cooperates with Arf6 GEFs to induce GTP loading of Arf6 in vivo. Finally, short interfering RNA-mediated loss of TRE17 leads to attenuated Arf6 activation. These studies identify TRE17 as a novel regulator of the Arf6-regulated plasma membrane recycling system and reveal an unexpected function for TBC domains.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org.

We thank Gerd Blobel, Michael Marks, Christopher Burd, and Erfei Bi for critical comments on the manuscript. Special thanks to Clara Franzini-Armstrong and Nosta Glaser for assistance with immunoelectron microscopy. We also thank Jonathan Fletcher and Andre Oliveira for discussing data prior to publication.

This work was supported by Public Health Service grant CA-81415 from the National Cancer Institute and the Abramson Cancer Center of the University of Pennsylvania Pilot Projects Program.