title: Impaired trafficking of the very low density lipoprotein receptor caused by missense mutations associated with dysequilibrium syndrome.
abstract: Dysequilibrium syndrome (DES, OMIM 224050) is a genetically heterogeneous condition that combines autosomal recessive non-progressive cerebellar ataxia with mental retardation. The subclass dysequilibrium syndrome type 1 (CAMRQ1) has been attributed to mutations in the VLDLR gene encoding the very low density lipoprotein receptor (VLDLR). This receptor is involved in the Reelin signaling pathway that guides neuronal migration in the cerebral cortex and cerebellum. Three missense mutations (c.1459G>T; p.D487Y, c.1561G>C; p.D521H and c.2117G>T; p.C706F) have been previously identified in VLDLR gene in patients with DES. However, the functional implications of those mutations are not known and therefore we undertook detailed functional analysis to elucidate the cellular mechanisms underlying their pathogenicity. The mutations have been generated by site-directed mutagenesis and then expressed in cultured cell lines. Confocal microscopy and biochemical analysis have been employed to examine the subcellular localization and functional activities of the mutated proteins relative to wild type. Our results indicate that the three missense mutations lead to defective intracellular trafficking and ER retention of the mutant VLDLR protein. This trafficking impairment prevents the mutants from reaching the plasma membrane and binding exogenous Reelin, the initiating event in Reelin signaling. Collectively, our results provide evidence that ER quality control is involved in the functional inactivation and underlying pathogenicity of these DES-associated mutations in the VLDLR.
authors.affiliation: Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
authors.forename: Praseetha
authors.initials: P
authors.lastname: Kizhakkedath
authors.affiliation: Department of Medical Biochemistry, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Anke
authors.initials: A
authors.lastname: Loregger
authors.affiliation: Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
authors.forename: Anne
authors.initials: A
authors.lastname: John
authors.affiliation: Department of Medical Biochemistry, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Boris
authors.initials: B
authors.lastname: Bleijlevens
authors.affiliation: Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
authors.forename: Ali S
authors.initials: AS
authors.lastname: Al-Blooshi
authors.affiliation: Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
authors.forename: Ahmed H
authors.initials: AH
authors.lastname: Al-Hosani
authors.affiliation: Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: Al-Nuaimi
authors.affiliation: Department of Pediatrics, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.
authors.forename: Lihadh
authors.initials: L
authors.lastname: Al-Gazali
authors.affiliation: Department of Medical Biochemistry, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
authors.forename: Noam
authors.initials: N
authors.lastname: Zelcer
authors.affiliation: Department of Pathology, College of Medicine and Heath Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates. Electronic address: bassam.ali@uaeu.ac.ae.
authors.forename: Bassam R
authors.initials: BR
authors.lastname: Ali
keywords: Dysequilibrium syndrome; ERAD; Protein misfolding; Reelin; VLDLR