Sphingosine and Sphingosine Kinase 1 Involvement in Endocytic Membrane Trafficking

Abstract

The balance between cholesterol and sphingolipids within the plasma membrane has long been implicated in endocytic membrane trafficking. However, in contrast to cholesterol functions, little is still known about the roles of sphingolipids and their metabolites. Perturbing the cholesterol/sphingomyelin balance was shown to induce narrow tubular plasma membrane invaginations enriched with sphingosine kinase 1 (SphK1), the enzyme that converts the bioactive sphingolipid metabolite sphingosine to sphingosine-1-phosphate, and suggested a role for sphingosine phosphorylation in endocytic membrane trafficking. Here we show that sphingosine and sphingosine-like SphK1 inhibitors induced rapid and massive formation of vesicles in diverse cell types that accumulated as dilated late endosomes. However, much smaller vesicles were formed in SphK1-deficient cells. Moreover, inhibition or deletion of SphK1 prolonged the lifetime of sphingosine-induced vesicles. Perturbing the plasma membrane cholesterol/sphingomyelin balance abrogated vesicle formation. This massive endosomal influx was accompanied by dramatic recruitment of the intracellular SphK1 and Bin/Amphiphysin/Rvs domain-containing proteins endophilin-A2 and endophilin-B1 to enlarged endosomes and formation of highly dynamic filamentous networks containing endophilin-B1 and SphK1. Together, our results highlight the importance of sphingosine and its conversion to sphingosine-1-phosphate by SphK1 in endocytic membrane trafficking.

Regulatory role of SphK1 in TLR7/9‐dependent type I interferon response and autoimmunity

“…Hence, our work describes an unexpected function of SphK1 in pDCs and the intracellular conversion of sphingosine to S1P in regulation of TLR7/9 uptake that is independent of the extracellular actions of S1P as a ligand of S1PRs. This is consistent with recent studies describing a new role for SphK1 and the conversion of sphingosine to S1P in endocytic trafficking independent of S1PRs . SphK1 is recruited to nascent endosomes and knockdown of SphKs results in endocytic recycling defects .…”

“…This is likely due to expression of TLR7/9 by CAL‐1 cells as reported previously, but not TLR3. As previous studies have suggested that SphK1 is also localized to endosomes, it was of interest to examine whether TLR7/9 co‐localized or interacted with SphK1. Confocal fluorescence microscopy revealed a high co‐localization of SphK1 and TLR9 (Figure A).…”

“…Similar results were obtained in three independent experiments. Statistical significance for difference between two groups for each indicated gene was determined by Student's t-test (B, D), *P < .05, **P < .005, ***P < .001 studies have suggested that SphK1 is also localized to endosomes, [44][45][46] it was of interest to examine whether TLR7/9 co-localized or interacted with SphK1. Confocal fluorescence microscopy revealed a high co-localization of SphK1 and TLR9 ( Figure 4A).…”

Novel Sphingolipid-Based Cancer Therapeutics in the Personalized Medicine Era

“…It has been hypothesized that vinblastine and other microtubule destabilizers such as chloroquine and vincristine synergize with C 6 ceramide by reducing autophagosome formation and switching ceramide-induced autophagy into ceramide-induced cell death (Adiseshaiah et al, 2013; Lima, Milstien, & Spiegel, 2017; Young et al, 2016). A recent study showed that the use of CNL combined with adoptive T cell transfer immunotherapy in mice bearing liver tumors was able to reduce the number of tumor-associated macrophages and decreased the ability of these immune cells to suppress the anti-tumor properties (Li et al, 2018).…”

Lipidomics in translational research and the clinical significance of lipid-based biomarkers

“…They postulated that this could be due ceramide turnover in early AD. More recently, the Spiegel laboratory reported that S1P, and the anabolic enzyme for S1P production, sphingosine kinase 1, regulated endocytic trafficking, which plays significant roles in AD, cancer and diseases associated with lipid storage (79). …”