Sphingosine-1-phosphate (S1P), a ligand for five specific receptors, is a potent lipid mediator that plays important roles in cancer cell proliferation, migration, and cancer-induced angiogenesis/lymphangiogenesis. S1P is produced inside cells and therefore must be secreted in order to exert its effects through these receptors. We have reported that E2-induced export of S1P mediated by ABCC1 and ABCG2 transporters and consequent activation of S1P receptors may contribute to nongenomic signaling of E2 important for breast cancer pathophysiology. Spinster 2 (Spns2) is one of the cell surface transporters thought to secrete S1P, thus it is important to elucidate its physiological role. Although lymphatic endothelial cells contribute to regulation of S1P levels in lymph, little is known how S1P levels are maintained in the lymphatic system. Spinster 2 knockout mice were used, and the lymphatic system was examined by flow cytometry and immunofluorescent staining. Sphingolipids in the blood, lymph, and organs were determined by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). We found that S1P secreted by breast cancer cells promotes tumor progression in a syngeneic model by stimulating angiogenesis and lymphangiogenesis. Interestingly, suppression of tumor S1P production resulted in less lymph node metastasis. Further, we found that serum S1P levels are elevated in breast cancer patients with lymph node metastasis. We confirmed that Spns2 can export endogenous S1P from cells and also dihydro-S1P, which is active at all cell surface S1P receptors. Moreover, Spns2-/- mice have decreased levels of both of these phosphorylated sphingoid bases in blood, accompanied by increases in very long chain ceramide species, and have defective lymphocyte trafficking. Surprisingly, levels of S1P and dihydro-S1P were increased in lymph from Spns2-/- mice as well as in specific tissues, including lymph nodes, and interstitial fluid. Moreover, lymph nodes from Spns2-/- mice have aberrant lymphatic sinuses, which appear collapsed, with reduced numbers of lymphocytes. Our data suggest that Spns2 is a S1P transporter in vivo that regulate not only of blood S1P but also lymph node and lymph S1P levels, which may implicate a role in lymph node metastasis.
M.N. is a Japan Society for the Promotion of Science Postdoctoral Fellow. S.S. is supported by NIH R37GM043880, and K.T. by NIH R01CA160688 and Susan G. Komen for the Cure Investigator Initiated Research Grant.
Citation Format: Masayuki Nagahashi, Eugene Y. Kim, Akimitsu Yamada, Subramaniam Ramachandran, Jeremy C. Allegood, Nitai Hait, Michael Maceyka, Sheldon Milstien, Sarah Spiegel, Kazuaki Takabe. Spinster 2 exports S1P, an important player in lymph node metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5000. doi:10.1158/1538-7445.AM2013-5000