The Arf6 clathrin-independent endosomal trafficking pathway is regulated by the TRE17 proto-oncogene and the Erk signaling pathway

Endocytosis, the uptake of substances from the extracellular environment and plasma membrane, is important for processes such as receptor recycling, cellular adhesion and immune surveillance. Multiple endocytic pathways have been described, largely distinguished by their dependence or independence on clathrin. However, little is known about the mechanisms of cargo sorting and the machinery required for any but the clathrin-dependent pathway. One of these other pathways is regulated by the small GTPase, ADP-ribosylation factor 6 (Arf6). Work presented here identifies two novel regulators of the Arf6 pathway, TRE17 and extracellular signal-regulated kinase (Erk).; Multiple splice variants have been described for the TRE17 proto-oncogene, which give rise to isoforms variably encoding a TBC (GTPase-activating protein homology domain) and a de-ubiquitination (DUB) domain. We further show that TRE17 promotes the activation of Arf6 in vivo. TRE17 binds directly to Arf6 via its TBC domain and promotes its recruitment to the plasma membrane. We further show that the activity of TRE17 as a de-ubiquitinating enzyme modulates its ability to promote Arf6 activation in vivo.; The Erk kinase cascade is one of the best characterized signaling pathways. Erk has been shown to signal from multiple locations in the cell, including endosomal compartments. No role for Erk in regulating endosomal trafficking has been demonstrated. We show that components of the Erk pathway localize to the recycling compartment of the Arf6 pathway, the tubular endosome. Furthermore, inhibition of Erk activity leads to expansion of the tubular endosome and the accumulation of Arf6 pathway-specific cargo, such as class I major histocompatibility complex (MHCI), at this site. The MEK inhibitor U0126 causes a reduction in cell surface levels of MHCI without affecting the rate of endocytosis, suggesting that Erk inactivation perturbs recycling through this pathway. In contrast, no effects on trafficking of clathrin pathway cargo were observed.; In summary, this work identifies two novel regulators of the Arf6-regulated plasma membrane-endosomal system. Our studies on TRE17 provide the first indication that regulated ubiquitination modulates trafficking through this pathway. They further reveal a previously unappreciated role for Erk in recycling of Arf6 pathway cargo, but not of classical clathrin-dependent pathway cargo.