Related Experiment Video
Updated: Jun 10, 2026

Cholesterol Efflux Assay
Published on: March 6, 2012
Cholesterol transfer proteins promote Atg-independent ER clearance by lysosomes
Ruoxi Wang1, Tina M Fortier2, Xiaofeng Sun3
1Department of Molecular, Cell and Cancer Biology, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA; Department of Neuroscience, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China.
Abstract:
Selective removal of endoplasmic reticulum (ER) is important for cell health. Macroautophagy is the primary mechanism for the removal of the ER, but the ER can be cleared in a macroautophagy-independent manner. However, the physiological relevance and mechanisms underlying macroautophagy-independent ER clearance remain largely unknown. Here we show that ER is cleared by lysosomes in a macroautophagy Atg gene-independent manner during development. This developmentally programmed Atg-independent ER clearance by lysosomes requires the ER protein Vap33 that promotes ER and lysosome contact. Oxysterol-binding protein (Osbp) is known to associate with Vap33, and Osbp lysosomal localization is required for ER clearance in cells lacking macroautophagy. Significantly, the cholesterol transport-associated protein Start1 regulates ER and lysosome contact, macroautophagy-independent ER clearance, and cholesterol transport from ER to the lysosome. These studies reveal that Vap33, Osbp, and Start1 promote ER clearance by lysosomes that is associated with cholesterol trafficking.
Related Concept Videos
Export of Misfolded Proteins out of the ER
Post-translational Translocation of Proteins to the RER
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...
ER Retrieval Pathway
The ER uses many checkpoints to prevent the entry of incorrectly folded or a resident protein as cargo onto a transport vesicle. These mechanisms...
Overview of Protein Sorting and Transport
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation. In gated transport, folded...
Role of ER in the Secretory Pathway
Components of the secretory pathway
About a third of proteins synthesized in the cell are sorted via the secretory route. They shuffle between different compartments in membrane-bound vesicles until they reach their final destination. The main intracellular compartments involved...
GPI Anchoring of Proteins in the ER Membrane
GPI-anchor structure
A sequence of 11 enzymatic reactions results in the synthesis of the complete GPI anchor consisting of a hydrophobic and a hydrophilic portion. The hydrophobic portion comprises phosphatidylinositol, while the hydrophilic part comprises polar groups like phosphoethanolamine,...

