ERdj3 Is an Endoplasmic Reticulum Degradation Factor for Mutant Glucocerebrosidase Variants Linked to Gaucher’s Disease

• Immunoprecipitation and mass spectrometry identify ERdj3 as a GCase interactor
• ERdj3 depletion enhances mutant GCase folding, trafficking, and lysosomal function
• The ERdj3 degradation factor competes with profolding calnexin for mutant GCase
• ERdj3 depletion and increased calnexin function synergize to rescue mutant GCase

SummaryGaucher’s disease (GD) is caused by mutations that compromise β-glucocerebrosidase (GCase) folding in the endoplasmic reticulum (ER), leading to excessive degradation instead of trafficking, which results in insufficient lysosomal function. We hypothesized that ER GCase interacting proteins play critical roles in making quality control decisions, i.e., facilitating ER-associated degradation (ERAD) instead of folding and trafficking. Utilizing GCase immunoprecipitation followed by mass-spectrometry-based proteomics, we identified endogenous HeLa cell GCase protein interactors, including ERdj3, an ER resident Hsp40 not previously established to interact with GCase. Depleting ERdj3 reduced the rate of mutant GCase degradation in patient-derived fibroblasts, while increasing folding, trafficking, and function by directing GCase to the profolding ER calnexin pathway. Inhibiting ERdj3-mediated mutant GCase degradation while simultaneously enhancing calnexin-associated folding, by way of a diltiazem-mediated increase in ER Ca2+ levels, yields a synergistic rescue of L444P GCase lysosomal function. Our findings suggest a combination therapeutic strategy for ameliorating GD.