TOM1 is a PI5P effector involved in the regulation of endosomal maturation

Abstract

Phosphoinositides represent a major class of lipids specifically involved in the organization of signaling cascades, maintenance of the identity of organelles and regulation of multiple intracellular trafficking steps. We previously reported that phosphatidylinositol 5-monophosphate (PI5P), produced by the Shigella flexneri phosphatase IpgD, is implicated in the endosomal sorting of the epidermal growth factor receptor (EGFR). Here, we show that the adaptor protein TOM1 is a new direct binding partner of PI5P. We identify the domain of TOM1 involved in this interaction and characterize the binding motif. Finally, we demonstrate that the recruitment of TOM1 by PI5P on signaling endosomes is responsible for the delay in EGFR degradation and fluid-phase bulk endocytosis. Taken together, our data strongly suggest that PI5P enrichment in signaling endosomes prevents endosomal maturation through the recruitment of TOM1, and point to a new function of PI5P in regulating discrete maturation steps in the endosomal system.

Tom1 Modulates Binding of Tollip to Phosphatidylinositol 3-Phosphate via a Coupled Folding and Binding Mechanism

“…Interestingly, the GAT domain-perturbed region in TBD represents the most conserved among Tollip proteins ( Figure S1A). The effect of the Tom1 GAT domain was specific, since the Tollip TBD HSQC spectrum was not perturbed by ubiquitin ( Figure S1C), a ligand of the Tollip C2 and CUE domains (Mitra et al, 2013), nor by PtdIns(3)P ( Figure S1D), a ligand of the C2 (Ankem et al, 2011) and GAT domains (see Figures S6B and S6D) (Boal et al, 2015).…”

“…Tom1 has recently been reported to weakly bind phosphatidylinositol monophosphates (Boal et al, 2015) and does so under conditions whereby Shigella flexneri inositol phosphate phosphatase increases endosomal levels of PtdIns(5)P (Ramel et al, 2011). The lipid-binding function of Tom1 is particularly relevant in higher plants, since neither Tollip nor ESCRT-0 proteins are encoded by these organisms (Blanc et al, 2009;Schellmann and Pimpl, 2009).…”

“…By using a lipid-protein overlay assay, Tollip, but not Tom1, bound PtdIns(3)P ( Figures 5A and S6A). Using the same assay, but with 3-fold higher protein concentration, Tronchere and colleagues recently reported that the Tom1 GAT domain binds monophosphate phosphoinositides, although the association seems to lack specificity (Boal et al, 2015). To shed light on these conflicting data, we further explored lipid association of the Tom1 GAT domain using more highly sensitive methods such as NMR spectroscopy.…”

The Central Polybasic Region of the Soluble SNARE (Soluble N-Ethylmaleimide-sensitive Factor Attachment Protein Receptor) Vam7 Affects Binding to Phosphatidylinositol 3-Phosphate by the PX (Phox Homology) Domain

“…The role of PI5P in membrane trafficking is not well understood. That said, Boal et al (37) showed that the endosomal protein TOM1 interacts with PI5P to regulate endosomal maturation. Thus it is possible that Vam7 interactions with other phosphoinositides could be part of its function.…”

Les phosphoinositides

“…Cette interaction conduit à l'activation de la GTPase Rac1 et à une forte dynamique membranaire associée à la perte des fibres de stress, pour induire la mobilité et l'invasion cellulaire [15]. Le PtdIns5P module également le trafic intracellulaire en empêchant la dégradation lysosomale, notamment par le recrutement de TOM1 (target of myb1) sur les endosomes [16], et en favorisant le recyclage vésiculaire. Il régule aussi l'autophagie indépendante de la voie canonique impliquant Vps34 et le PtdIns3P [17].…”