PIGN prevents protein aggregation in the endoplasmic reticulum independently of its function in the GPI synthesis

Abstract

Quality control of proteins in the endoplasmic reticulum (ER) is essential for ensuring the integrity of secretory proteins before their release into the extracellular space. Secretory proteins that fail to pass quality control form aggregates. Here we show the PIGN-1/PIGN is required for quality control in Caenorhabditis elegans and in mammalian cells. In C. elegans pign-1 mutants, several proteins fail to be secreted and instead form abnormal aggregation. PIGNknockout HEK293 cells also showed similar protein aggregation. Although PIGN-1/PIGN is responsible for glycosylphosphatidylinositol (GPI)-anchor biosynthesis in the ER, certain mutations in C. elegans pign-1 caused protein aggregation in the ER without affecting GPIanchor biosynthesis. These results show that PIGN-1/PIGN has a conserved and non-canonical function to prevent deleterious protein aggregation in the ER independently of the GPI-anchor biosynthesis. PIGN is a causative gene for some human diseases including multiple congenital seizure-related syndrome (MCAHS1). Two pign-1 mutations created by CRISPR/Cas9 that correspond to MCAHS1 also cause protein aggregation in the ER, implying that the dysfunction of the PIGN non-canonical function might affect symptoms of MCAHS1 and potentially those of other diseases.

Characterization of glycosylphosphatidylinositol biosynthesis defects by clinical features, flow cytometry, and automated image analysis

“…The craniofacial characteristics of many Mendelian disorders are highly informative for clinical geneticists and have also been used to delineate gene-specific phenotypes of several GPIBDs [ 3 – 5 , 10 , 12 , 19 , 28 – 30 , 32 , 39 , 40 , 43 , 44 , 60 , 61 ]. However, our medical terminology is often not capable of describing subtle differences in the facial gestalt.…”

Characterization of Glycosylphosphatidylinositol Biosynthesis Defects by Clinical Features, Flow Cytometry, and Automated Image Analysis

“…The craniofacial characteristics of many Mendelian disorders are highly informative for clinical geneticists and have also been used to delineate gene-specific phenotypes of several GPIBDs [3-5, 10, 19, 27-29, 31, 38, 39, 43, 44, 59-61]. However, our medical terminology is often not capable of describing subtle differences in the facial gestalt.…”

Complexity of the eukaryotic dolichol-linked oligosaccharide scramblase suggested by activity correlation profiling mass spectrometry

“…ATP secretion 24 . In addition, Mcd4 was shown to have a non-canonical role in protein quality control 25 . These intriguing moonlighting functions attributed to the GPI P-EtN transferases raised the possibility that these three proteins could potentially each, independently, contribute to M5-DLO scramblase activity.…”

“…Thus, over-expression of any of the three proteins in yeast unexpectedly results in enhanced secretion of ATP, consistent with the possibility that each of these proteins is involved in the transport of ATP into the lumen of secretory compartments 24 . Also, the Mcd4 ortholog in C. elegans and human was demonstrated to have a non-canonical role in ER protein quality control, distinct from its role in GPI anchoring 25 . Based on these indicators, we considered the possibility that the three GPI P-EtN transferases may each (redundantly) have M5-DLO scramblase activity.…”