Abstract
Low density lipoprotein receptor (LDLR) family members are involved in signaling in the developing brain. Previously we have reported that missense mutations in the Very Low Density Lipoprotein Receptor gene (VLDLR), causing Dysequilibrium syndrome (DES), disrupt ligand-binding, due to endoplasmic reticulum (ER) retention of the mutants. We explored the degradation routes of these VLDLR mutants in cultured cells. Our results indicate that VLDLR mutants are retained in the ER for prolonged periods which could be facilitated by association with the ER-resident chaperone calnexin. The mutants were prone to aggregation and capable of eliciting ER stress. The VLDLR mutants were found to be degraded predominantly by the proteasomal pathway, since ubiquitinated VLDLR was found to accumulate in response to proteasomal inhibition. Further, the mutants were found to interact with the ER degradation adaptor protein SEL1L. The degradation of VLDLR wild type and mutant were delayed in CRISPR/Cas9 edited SEL1L knock-out cells which was reversed by exogenous expression of SEL1L. In summary, ER retention of pathogenic VLDLR mutants involves binding to calnexin, elevated ER stress, and delayed degradation which is dependent on SEL1L. Since core LDLR family members share common structural domains, common mechanisms may be involved in their ER processing.
Highlights
Low density lipoprotein receptor (LDLR) family members are important mediators of signaling events during brain development and defects in many of these receptors relate to distinct neurobehavioural phenotypes[1]
Our results indicated that Very Low Density Lipoprotein Receptor gene (VLDLR) mutants are not subjected to premature degradation in the endoplasmic reticulum (ER), but retained in the ER for long periods of time, which could be facilitated by interactions with the ER- resident chaperone calnexin
We have reported that missense mutants of the VLDLR (D487Y, D521H and C706F) receptor were transport deficient and dysfunctional[8]
Summary
Low density lipoprotein receptor (LDLR) family members are important mediators of signaling events during brain development and defects in many of these receptors relate to distinct neurobehavioural phenotypes[1]. Prolonged ER stress induced by misfolded proteins cause initiation of macroautophagy programs termed ER-activated autophagy (ERAA) pathway, which serves to www.nature.com/scientificreports/. Activated IRE1α catalyzes the unconventional splicing of the mRNA of the transcription factor X-box binding protein-1, which in turn targets the regulation of a class of UPR-related genes that are involved in protein folding, protein entry to the ER, and ER-associated degradation (ERAD)[14]. 50% of the LDLR mutations are class II mutations that cause the mutant protein to be retained in the endoplasmic reticulum (ER) and ER-associated proteasomal degradation (ERAD) has been reported to be the principal pathway of degradation of these mutants[16]. Chemical chaperones like glycerol and 4-PBA have been able to restore functionality of some of the LDLR class 2 receptors in a mutation-specific manner[18], which can be explored for manipulating the disease outcomes caused by similar mutations in other lipoprotein receptors, given their structural similarity
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
