Modulating Protein Homeostasis to Rescue the Folding of Unstable, Degradation-Prone Secretory Proteins

Lysosomal Storage Disorders (LSD) are a group of more than 50 metabolic diseases caused by deficiency in hydrolytic enzymes and aberrant buildup of metabolites in lysosomes. Gaucher's disease, the most common LSD, is characterized by mutations in the gene encoding for lysosomal glucocerebrosidase (GC). Most mutations are single amino acid substitutions that do not directly impair the enzyme activity, but rather destabilize its native folding, leading to ER-associated degradation (ERAD). If mutated enzyme variants are forced to fold into their native structure, they regain catalytic activity. We previously reported evidence of this approach by culturing patient-derived fibroblasts with small molecules that enhance the cellular folding capacity (Wang, F. ACS Chem Biol. 2011 Feb 18;6(2):158-68). We demonstrated that the L-type Ca²⁺ channel blocker lacidipine remodels protein homeostasis by influencing the expression of ER chaperones and inducing modest activation of the unfolded protein response. Specifically, we reported that upregulation of the main ER chaperone BiP/GRP78 and enhanced expression of GC encoding gene induced by lacidipine treatment play a key role in rescuing the folding and trafficking of mutated GC (Wang, F. Chem Biol. 2011 In press). This suggests that prolonging ER retention facilitate folding of degradation-prone enzyme variants in need for higher chaperoning capacity than their wild type counterpart. Based on this finding, we attempted an alternative strategy to engineer the cellular folding capacity based on ERAD inhibition. We used small molecules that inhibit different steps of the ERAD pathway and conducted a series of mechanistic studies to further elucidate GC misfolding pathways. The results reported contribute to our fundamental understanding of cellular folding and provide insights for the development of molecular engineering strategies to rescue the folding of unstable, degradation-prone substrates.