Sphingosine kinases are not required for inflammatory responses in macrophages

The Tumorigenic Effect of Sphingosine Kinase 1 and Its Potential Therapeutic Target

Sphingosine kinase 1 (SPHK1) regulates cell proliferation and survival by converting sphingosine to the signaling mediator sphingosine 1-phosphate (S1P). SPHK1 is widely overexpressed in most cancers, promoting tumor progression and is associated with clinical prognosis. Numerous studies have explored SPHK1 as a promising target for cancer therapy. However, due to insufficient knowledge of SPHK1 oncogenic mechanisms, its inhibitors’ therapeutic potential in preventing and treating cancer still needs further investigation. In this review, we summarized the metabolic balance regulated by the SPHK1/S1P signaling pathway and highlighted the oncogenic mechanisms of SPHK1 via the upregulation of autophagy, proliferation, and survival, migration, angiogenesis and inflammation, and inhibition of apoptosis. Drug candidates targeting SPHK1 were also discussed at the end. This review provides new insights into the oncogenic effect of SPHK1 and sheds light on the future direction for targeting SPHK1 as cancer therapy.

Sphingosine kinases protect murine embryonic stem cells from sphingosine-induced cell cycle arrest

Sphingosine‐1‐phosphate (S1P) is a bioactive lipid molecule regulating organogenesis, angiogenesis, cell proliferation, and apoptosis. S1P is generated by sphingosine kinases (SPHK1 and SPHK2) through the phosphorylation of ceramide‐derived sphingosine. Phenotypes caused by manipulating S1P metabolic enzymes and receptors suggested several possible functions for S1P in embryonic stem cells (ESCs), yet the mechanisms by which S1P and related sphingolipids act in ESCs are controversial. We designed a rigorous test to evaluate the requirement of S1P in murine ESCs by knocking out both Sphk1 and Sphk2 to create cells incapable of generating S1P. To accomplish this, we created lines mutant for Sphk2 and conditionally mutant (floxed) for Sphk1, allowing evaluation of ESCs that transition to double‐null state. The Sphk1/2‐null ESCs lack S1P and accumulate the precursor sphingosine. The double‐mutant cells fail to grow due to a marked cell cycle arrest at G2/M. Mutant cells activate expression of telomere elongation factor genes Zscan4, Tcstv1, and Tcstv3 and display longer telomeric repeats. Adding exogenous S1P to the medium had no impact, but the cell cycle arrest is partially alleviated by the expression of a ceramide synthase 2, which converts excess sphingosine into ceramide. The results indicate that sphingosine kinase activity is essential in mouse ESCs for limiting the accumulation of sphingosine that otherwise drives cell cycle arrest.

Sphingolipids and their metabolism in physiology and disease

Studies of bioactive lipids in general and sphingolipids in particular have intensified over the past several years, revealing an unprecedented and unanticipated complexity of the lipidome and its many functions, which rivals, if not exceeds, that of the genome or proteome. These results highlight critical roles for bioactive sphingolipids in most, if not all, major cell biological responses, including all major cell signalling pathways, and they link sphingolipid metabolism to key human diseases. Nevertheless, the fairly nascent field of bioactive sphingolipids still faces challenges in its biochemical and molecular underpinnings, including defining the molecular mechanisms of pathway and enzyme regulation, the study of lipid-protein interactions and the development of cellular probes, suitable biomarkers and therapeutic approaches.