STARD3/STARD3NL and VAP make a novel molecular tether between late endosomes and the ER

Abstract

SummaryInter-organelle membrane contacts sites (MCSs) are specific subcellular regions favoring the exchange of metabolites and information. We investigated the potential role of the late-endosomal membrane-anchored proteins StAR related lipid transfer domain-3 (STARD3) and STARD3 N-terminal like (STARD3NL) in the formation of MCSs involving late-endosomes (LEs). We demonstrate that both STARD3 and STARD3NL create MCSs between LEs and the endoplasmic reticulum (ER). STARD3 and STARD3NL use a conserved two phenylalanines in an acidic tract (FFAT)-motif to interact with ER-anchored VAP proteins. Together, they form an LE-ER tethering complex allowing heterologous membrane apposition. This LE-ER tethering complex affects organelle dynamics by altering the formation of endosomal tubules. An in situ proximity ligation assay between STARD3, STARD3NL and VAP proteins identified endogenous LE-ER MCS. Thus, we report here the identification of proteins involved in inter-organellar interaction.

Phosphoregulation of the Ceramide Transport Protein CERT at Serine 315 in the Interaction with VAMP-associated Protein (VAP) for Inter-organelle Trafficking of Ceramide in Mammalian Cells

“…TFFSAN to EFFDAN) enabled the motif to weakly interact with VAP (21), which raised the possibility that the phosphorylation of FFAT-like motifs might affect the interaction of motif-containing proteins with VAP. FFAT-like motifs of STARD3/MNL64 and STARD3NL/MENTAL were recently found to be essential for association of these proteins with VAP to tether late endosomes and the ER (28). However, it remains unclear whether phosphorylation in or around FFAT-like motifs really occurs in cells.…”

Rab Proteins and the Compartmentalization of the Endosomal System

“…Rab7 endosome motility on microtubules is selectively regulated by protein interactions that are sensitive to cholesterol levels (Chen et al 2008;Rocha et al 2009). When cholesterol levels are low, the Rab7 effector oxysterol-binding protein-related protein 1 L (ORP1L) together with two integral membrane proteins (STARD3 and STARD3NL) induces late endosome interactions with the endoplasmic reticulum VAP protein, allowing dissociation of the p150/dynein motor complex (Alpy et al 2013). Early endosome contacts with the endoplasmic reticulum have also been observed but remain functionally undefined (Friedman et al 2013).…”

Role of cholesterol in SNARE-mediated trafficking on intracellular membranes

“…1B,C). In addition, membrane contact sites between late endosome or lysosomes and other compartments, such as the ER, appear to enable cholesterol transfer (Alpy et al, 2013;Chang et al, 2006;Ikonen, 2008;Rowland et al, 2014;van der Kant and Neefjes, 2014).…”