Abstract: Sphingolipid metabolites are critical to the regulation of a number of fundamental biological processes including cancer. Whereas ceramide and sphingosine mediate and trigger apoptosis or cell growth arrest, sphingosine 1-phosphate promotes proliferation, cell survival and angiogenesis. The delicate equilibrium between the intracellular levels of each of these sphingolipids is controlled by the enzymes that either produce or degrade these metabolites. Sphingosine kinase-1 is a crucial regulator of this two-pan balance, because its produces the pro-survival and pro-angiogenic sphingosine 1-phosphate and decreases the amount of both ceramide and sphingosine, the pro-apoptotic sphingolipids. Moreover, its gene is oncogenic, its mRNA is overproduced in several solid tumors, its overexpression protects cells from apoptosis, and its activity is down-regulated by anti-cancer treatments. Therefore, the sphingosine kinase-1/sphingosine 1-phosphate signaling pathway appears to be a target of interest for therapeutic manipulation.
Abstract: Here, we provide the first evidence that sphingosine kinase 1 (SphK1), an oncogenic lipid kinase balancing the intracellular level of key signaling sphingolipids, modulates the transcription factor hypoxia inducible factor 1alpha (HIF-1alpha), master regulator of hypoxia. SphK1 activity is stimulated under low oxygen conditions and regulated by reactive oxygen species. The SphK1-dependent stabilization of HIF-1alpha levels is mediated by the Akt/glycogen synthase kinase-3beta signaling pathway that prevents its von Hippel-Lindau protein-mediated degradation by the proteasome. The pharmacologic and RNA silencing inhibition of SphK1 activity prevents the accumulation of HIF-1alpha and its transcriptional activity in several human cancer cell lineages (prostate, brain, breast, kidney, and lung), suggesting a canonical pathway. Therefore, we propose that SphK1 can act as a master regulator for hypoxia, giving support to its inhibition as a valid strategy to control tumor hypoxia and its molecular consequences.
