Tyrosine phosphorylation of a SNARE protein, Syntaxin 17: Implications for membrane trafficking in the early secretory pathway

The GPI (glycosylphosphatidylinositol) moiety is attached to newly synthesized proteins in the lumen of the ER (endoplasmic reticulum). The modified proteins are then directed to the PM (plasma membrane). Less well understood is how nascent mammalian GPI-anchored proteins are targeted from the ER to the PM. In the present study, we investigated mechanisms underlying membrane trafficking of the GPI-anchored proteins, focusing on the early secretory pathway. We first established a cell line that stably expresses inducible temperature-sensitive GPI-fused proteins as a reporter and examined roles of transport-vesicle constituents called p24 proteins in the traffic of the GPI-anchored proteins. We selectively suppressed one of the p24 proteins, namely p23, employing RNAi (RNA interference) techniques. The suppression resulted in pronounced delays of PM expression of the GPI-fused reporter proteins. Furthermore, maturation of DAF (decay-accelerating factor), one of the GPI-anchored proteins in mammals, was slowed by the suppression of p23, indicating delayed trafficking of DAF from the ER to the Golgi. Trafficking of non-GPI-linked cargo proteins was barely affected by p23 knockdown. This is the first to demonstrate direct evidence for the transport of mammalian GPI-anchored proteins being mediated by p24 proteins.

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Defects in early secretory pathway transport machinery components and neurodevelopmental disorders

Reviews in the Neurosciences ◽

10.1515/revneuro-2021-0020 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Bor Luen Tang

Keyword(s):

Membrane Trafficking ◽

Mammalian Cells ◽

Secretory Pathway ◽

Underlying Disease ◽

Membrane Dynamics ◽

Coat Proteins ◽

Disease Manifestation ◽

Vesicular Traffic ◽

Early Secretory Pathway ◽

Genes Encoding

Abstract The early secretory pathway, provisionally comprising of vesicular traffic between the endoplasmic reticulum (ER) and the Golgi apparatus, occurs constitutively in mammalian cells. Critical for a constant supply of secretory and plasma membrane (PM) materials, the pathway is presumably essential for general cellular function and survival. Neurons exhibit a high intensity in membrane dynamics and protein/lipid trafficking, with differential and polarized trafficking towards the somatodendritic and axonal PM domains. Mutations in genes encoding early secretory pathway membrane trafficking machinery components are known to result in neurodevelopmental or neurological disorders with disease manifestation in early life. Here, such rare disorders associated with autosomal recessive mutations in coat proteins, membrane tethering complexes and membrane fusion machineries responsible for trafficking in the early secretory pathway are summarily discussed. These mutations affected genes encoding subunits of coat protein complex I and II, subunits of transport protein particle (TRAPP) complexes, members of the YIP1 domain family (YIPF) and a SNAP receptor (SNARE) family member. Why the ubiquitously present and constitutively acting early secretory pathway machinery components could specifically affect neurodevelopment is addressed, with the plausible underlying disease etiologies and neuropathological mechanisms resulting from these mutations explored.

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Membrane-Bound Meet Membraneless in Health and Disease

Cells ◽

10.3390/cells8091000 ◽

2019 ◽

Vol 8 (9) ◽

pp. 1000 ◽

Cited By ~ 4

Author(s):

Chujun Zhang ◽

Catherine Rabouille

Keyword(s):

Phase Separation ◽

Membrane Trafficking ◽

Secretory Pathway ◽

Dependent Manner ◽

P Bodies ◽

Early Secretory Pathway ◽

Cell Organization ◽

Health And Disease ◽

Membrane Bound ◽

And Function

Membraneless organelles (MLOs) are defined as cellular structures that are not sealed by a lipidic membrane and are shown to form by phase separation. They exist in both the nucleus and the cytoplasm that is also heavily populated by numerous membrane-bound organelles. Even though the name membraneless suggests that MLOs are free of membrane, both membrane and factors regulating membrane trafficking steps are emerging as important components of MLO formation and function. As a result, we name them biocondensates. In this review, we examine the relationships between biocondensates and membrane. First, inhibition of membrane trafficking in the early secretory pathway leads to the formation of biocondensates (P-bodies and Sec bodies). In the same vein, stress granules have a complex relationship with the cyto-nuclear transport machinery. Second, membrane contributes to the regulated formation of phase separation in the cells and we will present examples including clustering at the plasma membrane and at the synapse. Finally, the whole cell appears to transit from an interphase phase-separated state to a mitotic diffuse state in a DYRK3 dependent manner. This firmly establishes a crosstalk between the two types of cell organization that will need to be further explored.

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The golgin GMAP-210 is required for efficient membrane trafficking in the early secretory pathway

Journal of Cell Science ◽

10.1242/jcs.166710 ◽

2015 ◽

Vol 128 (8) ◽

pp. 1595-1606 ◽

Cited By ~ 27

Author(s):

P. Roboti ◽

K. Sato ◽

M. Lowe

Keyword(s):

Membrane Trafficking ◽

Secretory Pathway ◽

Early Secretory Pathway

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The TRAPP complex mediates secretion arrest induced by stress granule assembly

10.1101/528380 ◽

2019 ◽

Author(s):

Francesca Zappa ◽

Cathal Wilson ◽

Giuseppe Di Tullio ◽

Michele Santoro ◽

Piero Pucci ◽

...

Keyword(s):

Membrane Trafficking ◽

Secretory Pathway ◽

Acute Stress ◽

Stress Exposure ◽

Proliferating Cells ◽

Early Secretory Pathway ◽

Er Exit Sites ◽

Protein Particle ◽

Mediate Cell ◽

Er Export

The TRAnsport-Protein-Particle (TRAPP) complex controls multiple membrane trafficking steps and is thus strategically positioned to mediate cell adaptation to diverse environmental conditions, including acute stress. We have identified TRAPP as a key component of a branch of the integrated stress response that impinges on the early secretory pathway. TRAPP associates with and drives the recruitment of the COPII coat to stress granules (SGs) leading to vesiculation of the Golgi complex and an arrest of ER export. Interestingly, the relocation of TRAPP and COPII to SGs only occurs in actively proliferating cells and is CDK1/2-dependent. We show that CDK1/2 activity controls the COPII cycle at ER exit sites (ERES) and that its inhibition prevents TRAPP/COPII relocation to SGs by stabilizing them at the ERES. Importantly, TRAPP is not just a passive constituent of SGs but controls their maturation since SGs that assemble in TRAPP-depleted cells are smaller and are no longer able to recruit RACK1 and Raptor, rendering the cells more prone to undergo apoptosis upon stress exposure.

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Conserved function of ether lipids and sphingolipids in the early secretory pathway

10.1101/2019.12.19.881094 ◽

2019 ◽

Author(s):

Noemi Jiménez-Rojo ◽

Manuel D. Leonetti ◽

Valeria Zoni ◽

Adai Colom ◽

Suihan Feng ◽

...

Keyword(s):

Membrane Trafficking ◽

Cell Biology ◽

Secretory Pathway ◽

Protein Transport ◽

Lipid Synthesis ◽

Chemical Properties ◽

Ether Lipid ◽

Ether Lipids ◽

Early Secretory Pathway ◽

A Genome

ABSTRACTSphingolipids have been shown to play important roles in physiology and cell biology, but a systematic examination of their functions is lacking. We performed a genome-wide CRISPRi screen in sphingolipid-depleted cells and identified hypersensitive mutants in genes of membrane trafficking and lipid biosynthesis, including ether lipid synthesis. Systematic lipidomic analysis showed a coordinate regulation of ether lipids with sphingolipids, where depletion of one of these lipid types resulted in increases in the other, suggesting an adaptation and functional compensation. Biophysical experiments on model membranes show common properties of these structurally diverse lipids that also share a known function as GPI anchors in different kingdoms of life. Molecular dynamics simulations show a selective enrichment of ether phosphatidylcholine around p24 proteins, which are receptors for the export of GPI-anchored proteins and have been shown to bind a specific sphingomyelin species. Our results support a model of convergent evolution of proteins and lipids, based on their physico-chemical properties, to regulate GPI-anchored protein transport and maintain homeostasis in the early secretory pathway.

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