Nonvesicular Trafficking of Ceramide-1-Phosphate by a Lipid Transfer Protein that Regulates Eicosanoid Production

Abstract

Phosphorylated sphingolipids such as ceramide-1-phosphate (C1P) and sphingosine-1-phosphate (S1P) have emerged as key regulators of cell growth, survival, migration, and inflammation. C1P produced by ceramide kinase is an activator of group IVA cytosolic phospholipase A2α (cPLA2α), the rate-limiting releaser of arachidonic acid used for pro-inflammatory eicosanoid production. To modulate eicosanoid action and avoid the damaging effects of chronic inflammation, cells require efficient targeting, trafficking, and presentation of C1P to specific cellular sites. Vesicular trafficking is likely but nonvesicular mechanisms for C1P sensing, transfer, and presentation remain unexplored. We have identified a ubiquitously-expressed lipid transfer protein (CPTP) that can specifically transfer C1P between membranes. Crystal structures establish C1P binding via a novel surface-localized, phosphate headgroup recognition center connected to an interior hydrophobic pocket that adaptively expands to ensheath differing-length lipid chains using a cleft-like gating mechanism. The two-layered, α helically-dominated 'sandwich' topology identifies CPTP as the prototype for a new GLTP-fold subfamily. CPTP resides in the cell cytosol but associates with the trans-Golgi/TGN, nucleus, and plasma membrane. RNAi-induced CPTP depletion elevates C1P steady-state levels and alters Golgi cisternae stack morphology. The resulting C1P decrease in plasma membranes and increase in the Golgi complex stimulate cPLA2α release of arachidonic acid, triggering pro-inflammatory eicosanoid generation. [Support: NCI CA121493 (DJP & REB), NIGMS GM45928 (REB), NIGMS GM072754 (EHH), NCI CA154314 (CEC), VA Merit Award (CEC), VA Research Career Scientist Award (CEC), VA Career Devel. Award (DSW), NRS-T32/NIGMS 008695 (DSW), Spanish Ministerio de Ciencia e Innovacion BFU2010-17711 (LM), Russian Fnd. for Basic Research #12-04-00168 (JGM), Abby Rockefeller Mauze Trust (DJP), Maloris Fnd. (DJP), and Hormel Fnd. (REB); Equal contributors to the work: DKS, RKK, & DSW; Corresponding authors: REB, EHH, CEC, DJP]