The C10orf76–PI4KB axis orchestrates CERT-mediated ceramide trafficking to the distal Golgi

Abstract

Phosphatidylinositol 4-monophosphate [PtdIns(4)P] is a precursor for various phosphoinositides but also a membrane-embedded component crucial for membrane contact sites (MCSs). Several lipid transfer proteins are recruited to MCSs by recognizing PtdIns(4)P; however, it remains poorly elucidated how the production of PtdIns(4)P for lipid transport at MCSs is regulated. Following human genome-wide screening, we discovered that the PtdIns(4)P-related genes PI4KB, ACBD3, and C10orf76 are involved in endoplasmic reticulum-to-Golgi trafficking of ceramide by the ceramide transport protein CERT. CERT preferentially utilizes PtdIns(4)P generated by PI4KB recruited to the Golgi by C10orf76 rather than by ACBD3. Super-resolution microscopy observation revealed that C10orf76 predominantly localizes at distal Golgi regions, where sphingomyelin (SM) synthesis primarily occurs, while the majority of ACBD3 localizes at more proximal regions. This study provides a proof-of-concept that distinct pools of PtdIns(4)P are generated in different subregions, even within the same organelle, to facilitate interorganelle metabolic channeling for the ceramide-to-SM conversion.

Mechanisms of Nonvesicular Ceramide Transport

“…The ceramide transport protein (CERT) plays a critical role in the intracellular transportation of ceramides from the ER to the Golgi in mammals. This cytosolic protein, with a size of 68 kDa, functions by collecting newly synthesized ceramides at the ER and facilitating their transfer to the trans-Golgi ( Hanada et al, 2003 ; Kawano et al, 2006 ; Mizuike et al, 2023 ). CERT encompasses various functional domains and motifs, similar to other lipid transfer proteins (LTPs).…”

DGARM/C10orf76/ARMH3 for Ceramide Transfer Zone at the Endoplasmic Reticulum–Distal Golgi Contacts

“…A pool of PtdIns(4)P generated by the DGARM–PI4KB axis was shown to be important for defining the site at which CERT works to provide ceramide for sphingomyelin synthesis ( Mizuike et al, 2023 ), as discussed above. In this study, ACBD3 was also indicated to partially compensate for this function.…”

“…Phosphatidylinositol 4-monophosphate (PtdIns(4)P) is a well-studied membrane component for its role in specifying various contact sites. We recently found that C10orf76 (alias ARMH3), a PtdIns 4-kinase-binding protein, is recruited to the distal Golgi and plays a pivotal role in the ER-to-distal Golgi trafficking of ceramide for the synthesis of sphingomyelin ( Mizuike et al, 2023 ). Together with the predicted structure of C10orf76 as an armadillo (ARM)-like fold ( Figure 1 ), consisting of α-helices arranged into a characteristic superhelix ( Tewari et al, 2010 ), we proposed to rename it to DGARM after a d istal G olgi arm adillo repeat protein.…”

“…On the other hand, PI4KB is mostly dispersed in the cytosol and only a portion is recruited to the Golgi membrane ( Blomen et al, 2015 ; McPhail et al, 2020 ). PI4KB adopts several types of Golgi-localization machinery in mammalian cells; that is, via interaction with ACBD3, DGARM (or C10orf76, ARMH3), or GGA2 ( Sasaki et al, 2012 ; Mizuike et al, 2023 ; Daboussi et al, 2017 ). This allows PI4KB to localize at various regions within the Golgi complex ( Figure 2B ): since ACDB3 predominantly localize at the proximal regions ( Tie et al, 2018 ; Mizuike et al, 2023 ), DGARM at the distal regions ( Mizuike et al, 2023 ), and GGA2 at the TGN ( Doray et al, 2002 ).…”

“…PI4KB adopts several types of Golgi-localization machinery in mammalian cells; that is, via interaction with ACBD3, DGARM (or C10orf76, ARMH3), or GGA2 ( Sasaki et al, 2012 ; Mizuike et al, 2023 ; Daboussi et al, 2017 ). This allows PI4KB to localize at various regions within the Golgi complex ( Figure 2B ): since ACDB3 predominantly localize at the proximal regions ( Tie et al, 2018 ; Mizuike et al, 2023 ), DGARM at the distal regions ( Mizuike et al, 2023 ), and GGA2 at the TGN ( Doray et al, 2002 ). Although further observation of PI4KB using a super-resolution microscopy is demanded to prove this model.…”