(724a) 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.