Oxysterol-binding protein ORP3 rescues the Amyotrophic Lateral Sclerosis-linked mutant VAPB phenotype

• Co-overexpression of ORP3 rescues the mutant VAPB aggregation phenotype.
• It restores mutant VAPB-induced protein trafficking defect.
• VAPB and ORP3 collectively regulate intracellular PtdIns4P levels.
• PtdIns4P plays a pivotal role in this VAPB-mediated protein trafficking step.

A mutation in VAPB causes a familial form of Amyotrophic Lateral Sclerosis. The mutant protein (VAPB-P56S) is aggregate prone and blocks retrograde traffic from the endoplasmic reticulum (ER) Golgi intermediate compartment (ERGIC) including trafficking to the nuclear envelope (NE). Here we report a morphological screen where overexpression of oxysterol binding protein-related protein-3 (ORP3) rescued the mutant VAPB phenotype. It resolved the mutant VAPB-induced membrane expansions, restored solubility of the mutant protein in non-ionic detergent, and restored trafficking of Emerin to the NE. Knockdown of ORP3 or VAPB increased the intracellular level of phosphatidylinositol 4-phosphate (PtdIns4P). Decreasing PtdIns4P levels by inhibiting its synthesis reduced the severity of the mutant VAPB-induced membrane expansions and restored Emerin trafficking to the NE. Thus, VAPB and its interacting partners cooperatively regulate protein trafficking through the ERGIC by modulating PtdIns4P levels.

Overexpression of ORP3 rescues the mutant VAPB phenotype. It collectively regulates trafficking from the endoplasmic reticulum Golgi intermediate compartment (ERGIC) with VAPB and SAC1 by modulating intracellular levels of phosphatidylinositol 4-phosphate (PtdIns4P).Figure optionsDownload high-quality image (151 K)Download as PowerPoint slide