A SNX3-dependent retromer pathway mediates retrograde transport of the Wnt sorting receptor Wntless and is required for Wnt secretion

Abstract

Wnt proteins are lipid modified glycoproteins that play a central role in development, adult tissue homeostasis and disease. Secretion of Wnt proteins is mediated by the Wnt-binding protein Wntless (Wls), which transports Wnt from the Golgi network to the cell surface for release. It has recently been shown that recycling of Wls through a retromer-dependent endosome-to-Golgi trafficking pathway is required for efficient Wnt secretion, but the mechanism of this retrograde transport pathway is poorly understood. Here, we report that Wls recycling is mediated through a novel retromer pathway that is independent of the retromer sorting nexins SNX1-SNX2 and SNX5-SNX6. We found that the unrelated sorting nexin, SNX3, has an evolutionarily conserved function in Wls recycling and Wnt secretion and show that SNX3 interacts directly with the cargo-selective sub-complex of the retromer to sort Wls into a morphologically distinct retrieval pathway. These results demonstrate that SNX3 is part of an alternative retromer pathway that functionally separates the retrograde transport of Wls from other retromer cargo.

Re-mention of an old neurodegenerative disease: Alzheimer’s disease

“…Another line of evidence endorsing that Retromer activity is associated with AD pathogenesis came from the clinical epide-miological studies. It has been reported that the mutations of SNX3 [61,66], which has been shown as an essential component of Retromer in sorting wntless, is genetically associated with AD [67]. These data supported an association between Retromer deficiency and neurodegeneration, and suggested parallel increases in A generation.…”

A mechanism for retromer endosomal coat complex assembly with cargo

“…However, a formal test of this hypothesis is lacking. Retromer binds sorting nexin 3 [henceforth referred to as SNX3 (human) or Snx3 (yeast)] (12)(13)(14)(15), and in SNX3 knockdown cells, less retromer is associated with endosomes (14). In this study, we show that SNX3 and RAB7 are coordinately recognized by retromer and that these interactions are sufficient to recruit retromer to a membrane where they poise retromer to capture integral membrane retrograde cargo.…”

“…1A) (16) that we speculate serves as an interaction surface for binding other factors such as retromer and/or cargo proteins. Because both human and yeast SNX3 associate with retromer (12,13,17), we implemented a functional assay in yeast to determine whether residues on this surface are required for the function of yeast Snx3 in vivo, and then extended this information to human SNX3. Two or three codons encoding residues (depending on the length of the strand) with solvent-exposed side chains were changed to alanine (Fig.…”

BMP signaling requires retromer-dependent recycling of the type I receptor

“…Although a recent study failed to show a VPS35 RNAi effect in Madin-Darby canine kidney cells on TGFβR1(ALK5) (34), they did demonstrate that TGFβRII was mislocalized to both the basolateral and apical membrane, as opposed to its normal localization to the basolateral membrane. Examination of the role of the retromer complex on BMP signaling in Drosophila has been incongruent (27,35,36). On the basis of our genetic and cell biological data, as well as the preliminary data from the mammalian proteomic analysis, it is very likely that retromer-dependent regulation of type I BMP and Activin receptors is a conserved mechanism of TGFβ-receptor regulation.…”

“…To test directly whether type I receptor SMA-6 recycling is dependent on the retromer pathway, we analyzed receptor localization in mutants lacking the core retromer subunit VPS-35 (vacuolar protein sorting factor-35) and several sorting nexins (SNX-1, SNX-3, and SNX-27) that may be specific for particular subsets of retromer-dependent cargo (24)(25)(26)(27). Expression of the RAD-SMAD GFP reporter in wildtype, sma-6(wk7), and arf-6(tm1447) staged at L3 (n = 6).…”