A CRISPR Screen Identifies LAPTM4A and TM9SF Proteins as Glycolipid-Regulating Factors

Summary Glycosphingolipids (GSLs) are produced by various GSL-synthesizing enzymes, but post-translational regulation of these enzymes is incompletely understood. To address this knowledge disparity, we focused on biosynthesis of globotriaosylceramide (Gb3), the Shiga toxin (STx) receptor, and performed a genome-wide CRISPR/CAS9 knockout screen in HeLa cells using STx1-mediated cytotoxicity. We identified various genes including sphingolipid-related genes and membrane-trafficking genes. In addition, we found two proteins, LAPTM4A and TM9SF2, for which physiological roles remain elusive. Disruption of either LAPTM4A or TM9SF2 genes reduced Gb3 biosynthesis, resulting in accumulation of its precursor, lactosylceramide. Loss of LAPTM4A decreased endogenous Gb3 synthase activity in a post-transcriptional mechanism, whereas loss of TM9SF2 did not affect Gb3 synthase activity but instead disrupted localization of Gb3 synthase. Furthermore, the Gb3-regulating activity of TM9SF2 was conserved in the TM9SF family. These results provide mechanistic insight into the post-translational regulation of the activity and localization of Gb3 synthase.
Graphical Abstract
Highlights • Genome-wide CRISPR knockout screening using Shiga toxin-induced cell death • Both LAPTM4A and TM9SF2 are required for Gb3 biosynthesis • Loss of LAPTM4A reduces Gb3 synthase activity post-transcriptionally • TM9SF2 regulates the subcellular localization of Gb3 synthase
Molecular Biology; Molecular Mechanism of Behavior; Cell Biology; Functional Aspects of Cell Biology