Endoplasmic Reticulum and Lysosomal Quality Control of Four Nonsense Mutants of Iduronate 2-Sulfatase Linked to Hunter's Syndrome

Abstract

Hunter's syndrome (mucopolysaccharidosis type II) is a rare X-linked lysosomal storage disorder caused by mutations in the iduronate-2-sulfatase (IDS) gene. Motivated by the case of a child affected by this syndrome, we compared the intracellular fate of wild-type IDS (IDS WT ) and four nonsense mutations of IDS (IDS L482X , IDS Y452X , IDS R443X , and IDS W337X ) generating progressively shorter forms of IDS associated with mild to severe forms of the disease. Our analyses revealed formylation of all forms of IDS at cysteine 84, which is a prerequisite for enzymatic activity. After formylation, IDS WT was transported within lysosomes, where it was processed in the mature form of the enzyme. The length of disease-causing deletions correlated with gravity of the folding and transport phenotype, which was anticipated by molecular dynamics analyses. The shortest form of IDS, IDS W337X , was retained in the endoplasmic reticulum (ER) and degraded by the ubiquitin-proteasome system. IDS R443X , IDS Y452X , and IDS L482X passed ER quality control and were transported to the lysosomes, but failed lysosomal quality control, resulting in their rapid clearance and in loss-of-function phenotype. Failure of ER quality control inspection is an established cause of loss of function observed in protein misfolding diseases. Our data reveal that fulfillment of ER requirements might not be sufficient, highlight lysosomal quality control as the distal station to control lysosomal enzymes fitness and pave the way for alternative therapeutic interventions.

Proteasome Composition and Activity Changes in Cultured Fibroblasts Derived From Mucopolysaccharidoses Patients and Their Modulation by Genistein

“…These results are compatible with previous reports (describing results of studies on single MPS types) which indicated enhanced expression of genes coding for proteasomal proteins in MPS I (Khalid et al, 2016), rapid proteasomal degradation of mutant forms of iduronate-2-sulfatase in MPS II (Osaki et al, 2018;Marazza et al, 2020), rapid proteasomal degradation of mutant N-sulfoglucosamine sulfhydrolase (Muschol et al, 2011) and cysteine string protein α (CSPα) (Sambri et al, 2017), as well as elevated levels of the 19S proteasomal subunit (Beard et al, 2017) in MPS IIIA, and rapid proteasomal degradation of synaptophysin in MPS IIIB (Vitry et al, 2009). Nevertheless, results presented in this report provided global picture of proteasomal changes in all MPS types.…”

“…Since proteasome is a protein-degrading cellular machinery, it is unlikely that it might be involved directly in GAG metabolism. However, it was reported that defective lysosomal enzymes, the products of mutated genes which are primary causes of MPS, are misfolded and therefore intensively ubiquitinated and extensively degraded by proteasomes (Vitry et al, 2009;Muschol et al, 2011;Osaki et al, 2018;Marazza et al, 2020). Therefore, any residual activity of the defective enzyme may be further reduced due to low stability of this protein.…”

“…Moreover, inhibition of proteasomal activities caused normalization of levels of CSPα (a protein required for presynaptic functions) in MPS IIIA mouse neurons which were otherwise significantly reduced due to enhanced proteasomal degradation of this protein (Sambri et al, 2017). Hence, stabilization of lysosomal enzymes by impairing their proteasomal degradation has been proposed as a novel approach in treatment of MPS (Osaki et al, 2018;Marazza et al, 2020). In this light, inhibitory activity of genistein against proteasome functions may appear as another activity of this isoflavone (apart from reduction of GAG synthesis efficiency, enhancement of lysosomal biogenesis, and stimulation of autophagy) which can be beneficial for patients suffering from MPS due to modulation of biochemical pathways toward re-establishment of the metabolic balance and cellular homeostasis.…”

Loss of Function of Mutant IDS Due to Endoplasmic Reticulum-Associated Degradation: New Therapeutic Opportunities for Mucopolysaccharidosis Type II

“…Therefore, rescue of IDS mutants by the inhibition of ERAD may be sufficient to attenuate the pathology in patients with MPS II. One of the severe-type truncated mutants, W337X, was also reported to be degraded by the ERAD pathway, although the lysosomal localization and enzyme activity of the mutant under the inhibition of ERAD have not been determined [43]. Although further investigations are needed, other MPS II-related IDS mutants may also cause loss of function through degradation via the ERAD pathway.…”