Sphingosine Kinases are Involved in Macrophage NLRP3 Inflammasome Transcriptional Induction.

Recent studies suggested an important contribution of sphingosine-1-phospate (S1P) signaling via its specific receptors (S1PRs) in the production of pro-inflammatory mediators such as Interleukin (IL)-1 beta in cancer and inflammation. In an inflammation-driven cancer setting, we previously reported that myeloid S1PR1 signaling induces IL-1 beta production by enhancing NLRP3 (NOD-, LRR- and Pyrin Domain-Containing Protein 3) inflammasome activity. However, the autocrine role of S1P and enzymes acting on the S1P rheostat in myeloid cells are unknown. Using human and mouse macrophages with pharmacological or genetic intervention we explored the relative contribution of sphingosine kinases (SPHKs) in NLRP3 inflammasome activity regulation. We noticed redundancy in SPHK1 and SPHK2 activities towards macrophage NLRP3 inflammasome transcriptional induction and IL-1 beta secretion. However, pharmacological blockade of both kinases in unison completely abrogated NLRP3 inflammasome induction and IL-1 beta secretion. Interestingly, human and mouse macrophages demonstrate varied responses towards SPHKs inhibition and IL-1 beta secretion. Clinical datasets of renal cell carcinoma and psoriasis patients showed a positive correlation between enzymes affecting the S1P rheostat with NLRP3 inflammasome components expression, which corroborates our finding. Our data provide a better understanding on the role of SPHKs and de novo synthesized S1P in macrophage NLRP3 inflammasome activation.