SNX19 restricts endolysosome motility through contacts with the endoplasmic reticulum

AbstractThe ability of endolysosomal organelles to move within the cytoplasm is essential for the performance of their functions. Long-range movement involves coupling of the endolysosomes to motor proteins that carry them along microtubule tracks. This movement is influenced by interactions with other organelles, but the mechanisms involved are incompletely understood. Herein we show that the sorting nexin SNX19 tethers endolysosomes to the endoplasmic reticulum (ER), decreasing their motility and contributing to their concentration in the perinuclear area of the cell. Tethering depends on two N-terminal transmembrane domains that anchor SNX19 to the ER, and a PX domain that binds to phosphatidylinositol 3-phosphate on the endolysosomal membrane. Two other domains named PXA and PXC negatively regulate the interaction of SNX19 with endolysosomes. These studies thus identify a mechanism for controlling the motility and positioning of endolysosomes that involves tethering to the ER by a sorting nexin.

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Determinants of the Endosomal Localization of Sorting Nexin 1

Molecular Biology of the Cell ◽

10.1091/mbc.e04-06-0504 ◽

2005 ◽

Vol 16 (4) ◽

pp. 2049-2057 ◽

Cited By ~ 29

Author(s):

Qi Zhong ◽

Martin J. Watson ◽

Cheri S. Lazar ◽

Andrea M. Hounslow ◽

Jonathan P. Waltho ◽

...

Keyword(s):

Binding Pocket ◽

Early Endosome ◽

Nmr Structure ◽

Sorting Nexin ◽

High Affinity ◽

Terminal Domain ◽

Px Domain ◽

Phox Homology ◽

Phosphatidylinositol 3

The sorting nexin (SNX) family of proteins is characterized by sequence-related phox homology (PX) domains. A minority of PX domains bind with high affinity to phosphatidylinositol 3-phosphate [PI(3)P], whereas the majority of PX domains exhibit low affinity that is insufficient to target them to vesicles. SNX1 is located on endosomes, but its low affinity PX domain fails to localize in vivo. The NMR structure of the PX domain of SNX1 reveals an overall fold that is similar to high-affinity PX domains. However, the phosphatidylinositol (PI) binding pocket of the SNX1 PX domain is incomplete; regions of the pocket that are well defined in high-affinity PX domains are highly mobile in SNX1. Some of this mobility is lost upon binding PI(3)P. The C-terminal domain of SNX1 is a long helical dimer that localizes to vesicles but not to the early endosome antigen-1–containing vesicles where endogenous SNX1 resides. Thus, the obligate dimerization of SNX1 that is driven by the C-terminal domain creates a high-affinity PI binding species that properly targets the holo protein to endosomes.

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TMCC3 localizes at the three-way junctions for the proper tubular network of the endoplasmic reticulum

Biochemical Journal ◽

10.1042/bcj20190359 ◽

2019 ◽

Vol 476 (21) ◽

pp. 3241-3260

Author(s):

Sindhu Wisesa ◽

Yasunori Yamamoto ◽

Toshiaki Sakisaka

Keyword(s):

Endoplasmic Reticulum ◽

Membrane Proteins ◽

Membrane Protein ◽

Mammalian Cells ◽

Coiled Coil ◽

Transmembrane Domains ◽

Domain Family ◽

Coiled Coil Domain ◽

U2os Cells ◽

Er Membrane

The tubular network of the endoplasmic reticulum (ER) is formed by connecting ER tubules through three-way junctions. Two classes of the conserved ER membrane proteins, atlastins and lunapark, have been shown to reside at the three-way junctions so far and be involved in the generation and stabilization of the three-way junctions. In this study, we report TMCC3 (transmembrane and coiled-coil domain family 3), a member of the TEX28 family, as another ER membrane protein that resides at the three-way junctions in mammalian cells. When the TEX28 family members were transfected into U2OS cells, TMCC3 specifically localized at the three-way junctions in the peripheral ER. TMCC3 bound to atlastins through the C-terminal transmembrane domains. A TMCC3 mutant lacking the N-terminal coiled-coil domain abolished localization to the three-way junctions, suggesting that TMCC3 localized independently of binding to atlastins. TMCC3 knockdown caused a decrease in the number of three-way junctions and expansion of ER sheets, leading to a reduction of the tubular ER network in U2OS cells. The TMCC3 knockdown phenotype was partially rescued by the overexpression of atlastin-2, suggesting that TMCC3 knockdown would decrease the activity of atlastins. These results indicate that TMCC3 localizes at the three-way junctions for the proper tubular ER network.

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Faculty Opinions recommendation of The crystal structure of the PX domain from p40(phox) bound to phosphatidylinositol 3-phosphate.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1002584.16713 ◽

2001 ◽

Author(s):

David Lambright

Keyword(s):

Crystal Structure ◽

Px Domain ◽

Phosphatidylinositol 3

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Faculty Opinions recommendation of Autophagosome formation from membrane compartments enriched in phosphatidylinositol 3-phosphate and dynamically connected to the endoplasmic reticulum.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1119428.14740217 ◽

2011 ◽

Author(s):

Fulvio Reggiori ◽

Muriel Mari

Keyword(s):

Endoplasmic Reticulum ◽

Autophagosome Formation ◽

Membrane Compartments ◽

Phosphatidylinositol 3

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A Role for Sorting Nexin 2 in Epidermal Growth Factor Receptor Down-regulation: Evidence for Distinct Functions of Sorting Nexin 1 and 2 in Protein Trafficking

Molecular Biology of the Cell ◽

10.1091/mbc.e03-09-0711 ◽

2004 ◽

Vol 15 (5) ◽

pp. 2143-2155 ◽

Cited By ~ 74

Author(s):

Anuradha Gullapalli ◽

Tiana A. Garrett ◽

May M. Paing ◽

Courtney T. Griffin ◽

Yonghua Yang ◽

...

Keyword(s):

Epidermal Growth Factor Receptor ◽

Growth Factor ◽

Epidermal Growth Factor ◽

Protein Trafficking ◽

Growth Factor Receptor ◽

Down Regulation ◽

Sorting Nexin ◽

Px Domain ◽

Early Endosomes ◽

Epidermal Growth

Sorting nexin 1 (SNX1) and SNX2, homologues of the yeast vacuolar protein-sorting (Vps)5p, contain a phospholipid-binding motif termed the phox homology (PX) domain and a carboxyl terminal coiled-coil region. A role for SNX1 in trafficking of cell surface receptors from endosomes to lysosomes has been proposed; however, the function of SNX2 remains unknown. Toward understanding the function of SNX2, we first examined the distribution of endogenous protein in HeLa cells. We show that SNX2 resides primarily in early endosomes, whereas SNX1 is found partially in early endosomes and in tubulovesicular-like structures distributed throughout the cytoplasm. We also demonstrate that SNX1 interacts with the mammalian retromer complex through its amino terminal domain, whereas SNX2 does not. Moreover, activated endogenous epidermal growth factor receptor (EGFR) colocalizes markedly with SNX2-positive endosomes, but minimally with SNX1-containing vesicles. To assess SNX2 function, we examined the effect of a PX domain-mutated SNX2 that is defective in vesicle localization on EGFR trafficking. Mutant SNX2 markedly inhibited agonist-induced EGFR degradation, whereas internalization remained intact. In contrast, SNX1 PX domain mutants failed to effect EGFR degradation, whereas a SNX1 deletion mutant significantly inhibited receptor down-regulation. Interestingly, knockdown of SNX1 and SNX2 expression by RNA interference failed to alter agonist-induced EGFR down-regulation. Together, these findings suggest that both SNX1 and SNX2 are involved in regulating lysosomal sorting of internalized EGFR, but neither protein is essential for this process. These studies are the first to demonstrate a function for SNX2 in protein trafficking.

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