Lipidomics Shared Resource
Featured Research Project
Sphingosine Kinases Generate the Pro-survival Lipid Sphingosine-1-Phosphate
Dr. Charles D. Smith’s laboratory specializes in cancer pharmacology with a focus on molecular mechanisms of action of established and experimental anticancer drugs and on designing and developing new drugs against novel molecular targets, especially sphingosine kinases that generate the pro-survival lipid sphingosine-1-phosphate (S1P). One of his novel small molecule inhibitors of sphingosine kinase 2 (SK-2), ABC294640, is now in a Phase I clinical trial to treat patients with advanced solid tumors at the HCC. His research has shown that sphingosine kinases (SK) regulate the balance between proapoptotic ceramides and mitogenic S1P; however, the functions of the two isoenzymes (SK1 and SK2) in tumor cells are not well defined.
In a recent study using the Lipidomics Shared Resource, RNA interference was used to assess the individual roles of SK1 and SK2 in tumor cell sphingolipid metabolism, proliferation, and migration/invasion as shown in the Figure. Treatment of A498, Caki-1 or MDA-MB-231 cells with siRNAs specific for SK1 or SK2 effectively suppressed the expression of the target mRNA and protein. Ablation of SK1 did not affect mRNA or protein levels of SK2 and reduced intracellular levels of S1P while elevating ceramide levels. In contrast, ablation of SK2 elevated mRNA, protein and activity levels of SK1, and increased cellular S1P levels. Interestingly, cell proliferation and migration/invasion were suppressed more by SK2-selective ablation than by SK1-selective ablation, showing that the increased S1P does not rescue these phenotypes. Similarly, exogenous S1P did not rescue the cells from the anti-proliferative or anti-migratory effects of the siRNAs. Consistent with these results, differential effects of SK1- and SK2-selective siRNAs on signaling proteins, including p53, p21, ERK1, ERK2, FAK, and VCAM1, indicate that SK1 and SK2 have only partially overlapping functions in tumor cells. Overall, these data indicate that loss of SK2 has stronger anticancer effects than does suppression of SK1. Consequently, selective inhibitors of SK2 may provide optimal targeting of this pathway in cancer chemotherapy.