Inhibition of Endoplasmic Reticulum-associated Degradation Rescues Native Folding in Loss of Function Protein Misfolding Diseases

Abstract

Background: Lysosomal storage disorders are caused by ER-associated degradation (ERAD) of mutated unstable lysosomal enzymes. Results: ERAD inhibition enhances folding and activity of unstable lysosomal protein by prolonging ER retention. Conclusion: ERAD is the rate-limiting step in the folding of mutated lysosomal proteins. Significance: ERAD inhibition ameliorates the progression of multiple lysosomal storage disorders caused by protein misfolding and degradation.

Alteration of the proteostasis network of plant cells promotes the post-endoplasmic reticulum trafficking of recombinant mutant (L444P) human β-glucocerebrosidase

“…31 This modification renders the N-glycan resistant to Endo H; thus this characteristic has been used to follow the transport of secretory proteins through the Golgi complex in eukaryotic cells. 7,10,16,32 More specifically the N-glycans become resistant to cleavage by Endo H just prior to the addition of xylose and fucose in the Golgi complex, after they have undergone processing by the enzyme Golgi α-mannosidase II, a trimming enzyme that removes 2 mannose residues from the N-glycan GlcNAcMan 5 [GlcNAc] 2 . The wild-type (WT) GCase was largely resistant to Endo H digestion, indicative of its trafficking beyond the medial Golgi complex ( Fig.…”

“…5,6 One of the most prevalent disease-causing mutations in humans is a L444P missense mutation in the GCase protein, which is linked to the neuronopathic form of the disease in homozygous patients as there is a complete loss of GCase activity. 7 L444P GCase is severely destabilized due to its defective folding, and consequently it undergoes extensive ERAD. 8,9 The use of pharmacological agents to correct the impairment in lysosomal trafficking of the disease-causing mutant proteins has recently been studied.…”

“…16 Augmenting the pool of mutant GCase in the ER is critical to enable its folding and post-ER trafficking. 7 However, extensive ERAD and rapid clearance of mutant L444P GCase from the lumen of the ER reduces the pool of "restorable" GCase. ERAD inhibitors including kifunensine (Kif) and eeyarestatin I (EerI) increase the steady-state pool of L444P GCase in the ER lumen.…”

“…ERAD inhibitors including kifunensine (Kif) and eeyarestatin I (EerI) increase the steady-state pool of L444P GCase in the ER lumen. 7 Kif inhibits ER mannosidase I, a key component of the quality control mechanism that recognizes malfolded proteins; 17,18 EerI acts later in the pathway to inhibit the activity of p97 ATPase which plays a role in retro-translocation of misfolded substrates. 19,20 Treatment of patient-derived fibroblasts with EerI restored the folding and increased the lysosomal activity of the L444P GCase variant; however, the cells responded by inducing genes of the "unfolded protein response" (UPR), and exhibited cytotoxicity and apoptosis.…”

“…Kif on the other hand was less efficient at "salvaging" L444P GCase, but mediated minimal UPR activation and had no effect on apoptosis. 7 Similar to the modulation of ERAD by chemicals such as Kif and EerI, modulation of the proteostasis network by proteostasis regulators has been explored as a therapeutic approach for the treatment of a variety of protein conformational diseases including neuronopathic subtypes of Gaucher disease. 10,[21][22][23] Agents such as celastrol, an inducer of the heat-shock response (HSR) and an inhibitor of the chymotrypsin-like activity of the proteasome, 10,24 and MG-132, a well known inhibitor of 26S proteasome activity, have been used for this endeavor.…”