Phosphorylated sphingolipids 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 A 2 α (cPLA 2 α), the rate-limiting releaser of arachidonic acid used for pro-inflammatory eicosanoid production, which contributes to disease pathogenesis in asthma or airway hyper-responsiveness, cancer, atherosclerosis and thrombosis. 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 non-vesicular mechanisms for C1P sensing, transfer and presentation remain unexplored. Moreover, the molecular basis for selective recognition and binding among signalling lipids with phosphate headgroups, namely C1P, phosphatidic acid or their lyso-derivatives, remains unclear. Here, a ubiquitously expressed lipid transfer protein, human GLTPD1, named here CPTP, is shown to specifically transfer C1P between membranes. Crystal structures establish C1P binding through a novel surface-localized, phosphate headgroup recognition centre connected to an interior hydrophobic pocket that adaptively expands to ensheath differing-length lipid chains using a cleft-like gating mechanism. The two-layer, α-helically-dominated 'sandwich' topology identifies CPTP as the prototype for a new glycolipid transfer protein fold subfamily. CPTP resides in the cell cytosol but associates with the trans-Golgi network, nucleus and plasma membrane. RNA interference-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 stimulates cPLA 2 α release of arachidonic acid, triggering pro-inflammatory eicosanoid generation.
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Acknowledgements This research was supported by NIH/NCI CA121493 (D.J.P. & R.E.B.), NIH/NIGMS GM45928 (R.E.B.), NIH/NIGMS GM072754 (E.H.H.), NIH/ CA154314 (C.E.C.), VA Merit Award (C.E.C.), VA Research Career Scientist Award (C.E.C.), VA Career Devel. Award (D.S.W.), NRS-T32/NIGMS 008695 (D.S.W.), Spanish Ministerio de Ciencia e Innovacion BFU2010-17711 (L.M.), Russian Foundation for Basic Research #12-04-00168 (J.G.M.), Hormel Foundation. (R.E.B.), Abby Rockefeller Mauze Trust (D.J.P.) and Maloris Foundation (D.J.P.). We thank H. Pike for expressing and purifying protein used for transfer activity analyses, K. Karanjeet for preparing cells for confocal and epifluorescence microscopy, and the staff of X-29 beamline at the National Synchrotron Light Source and ID-24-C/E beamlines at the Advanced Photon Source for help.