Intellectual-disability-associated mutations in the ceramide transport protein gene CERT1 lead to aberrant function and subcellular distribution

Norito Tamura,Shota Sakai,Loreto Martorell,Roser Colomé,Aya Mizuike,Asako Goto,Juan Darío Ortigoza-Escobar,Kentaro Hanada

doi:10.1016/j.jbc.2021.101338

Abstract

The lipid molecule ceramide is transported from the endoplasmic reticulum to the Golgi apparatus for sphingomyelin production via the ceramide transport protein (CERT), encoded by CERT1. Hyperphosphorylation of CERT’s serine-repeat motif (SRM) decreases its functionality. Some forms of inherited intellectual disability (ID) have been associated with a serine-to-leucine substitution in the SRM (S132L mutation) and a glycine-to-arginine substitution outside the SRM (G243R mutation) in CERT; however, it is unclear if mutations outside the SRM disrupt the control of CERT functionality. In the current investigation, we identified a new CERT1 variant (dupAA) in a patient with mild ID that resulted from a frameshift at the C-terminus of CERT1. However, familial analysis revealed that the dupAA variant was not associated with ID, allowing us to utilize it as a disease-matched negative control for CERT1 variants that are associated with ID. Biochemical analysis showed that G243R and S132L, but not dupAA, impair SRM hyperphosphorylation and render the CERT variants excessively active. Additionally, both S132L and G243R mutations but not dupAA caused the proteins to be distributed in a punctate subcellular manner. On the basis of these findings, we infer that the majority of ID-associated CERT variants may impair SRM phosphorylation-dependent repression, resulting in an increase in sphingomyelin production concurrent with CERT subcellular redistribution.

Highlights

Intellectual disability (ID) is a developmental disorder that includes intellectual and adaptive functioning deficits in conceptual, social, and practical domains [1]
He was referred for evaluation of intellectual disability (ID) to the Hospital Sant Joan de Déu, Barcelona, Journal Pre-proof Spain. He presented with psychomotor developmental delay at 2 years old. He walked without support and he presented with speech delay with a limited number of words and no phrasing
While the dupAA was not associated with ID, we considered that this ceramide transport protein (CERT) variant could serve as an invaluable negative control to ID-associated CERT variants

Summary

Introduction

Intellectual disability (ID) is a developmental disorder that includes intellectual and adaptive functioning deficits in conceptual, social, and practical domains [1]. In line with the Sanger sequence analysis, heterozygous and homozygous KI cell lines did not show any defects in CERT function in biochemical studies (Fig. S1). Human whole-exon sequencing studies have recently shown various examples of missense mutations (e.g., S132L, S135C, S135P, and S138C) that generate amino acid replacements in the SRM of CERT are associated with inherited ID disorders [2,3,4,5,6,7].

Results

Conclusion