Résumé :
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The majority of sarcoglycanopathies are associated with missense mutations in each of the four sarcoglycans (a, b, g and d) that mainly generate misfolded proteins.These are identified by the endoplasmic reticulum quality control system and eliminated through the ubiquitin proteasome system. Importantly, the absence or reduction ofone sarcoglycan deprives muscle fiber membrane of the whole sarcoglycan complex. We have recently shown that inhibition of proteasome activity significantly reducesthe degradation of a-sarcoglycan mutants with beneficial effects on the expression and localization of sarcoglycan complex (Gastaldello et al 2008). These resultsindicate that interfering with proteasome might be an ideal pharmacological therapy of sarcoglycanopathy. This project was thus aimed to identify novel proteasomeinhibitors suitable to treat sarcoglycanopathy.Potential inhibitors were selected both within a collection of TMC-95 linear mimics or molecules identified by in silico-invitro screening (Basse et al 2007; 2010). In contrast to bortezomib, the molecules tested do not form a covalent bond with the catalytic Thr1 residue of proteasomesince they are devoid of a reactive group, which are usually associated to critical drawbacks in therapeutics (Genin et al. 2010). To test the effects of novel proteasomeinhibitors on protein mutant recovery and cell viability consequences, we generated HEK-293 clones constitutively expressing the V247M a-sarcoglycan mutant. Thefollowing inhibitors, AP4, NR128, NR127-1, A2, and A3 were able to produce recovery of the expression of V247M protein mutant, with the A2 molecule being the mosteffective. Importantly, the recovery was usually associated to limited cytotoxic effects. Our results suggest a possible utilization of these novel proteasome inhibitors inthe treatment of sarcoglycanopathies. Funded by AFM (14999).
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