Effects of sphingosine 1-phosphate on calcium signaling, proliferation and S1P2 receptor expression in PC Cl3 rat thyroid cells

Sphingosine 1-phosphate (S1P) regulates diverse biological processes, including mitosis, by binding to the S1P family of G-protein coupled receptors. The aim of the study was to determine the pattern of S1P receptor expression and to investigate the effects of S1P on intracellular calcium levels and proliferation in the rat thyroid cell line PC Cl3. S1P2 and S1P3 mRNA and proteins were detected in PC Cl3 cells, as well as in FRTL-5 rat thyroid cells. In addition, S1P5 mRNA was present at low levels, but not S1P1 or S1P4. In PC Cl3 cells, S1P invoked calcium release from intracellular stores, but not calcium entry. The Ca2+ release was mediated by phospholipase C and inositol 1,4,5-trisphosphate. S1P attenuated the TSH-evoked cAMP increase in a pertussis toxin-sensitive manner. S1P per se did not affect the proliferation of the cells, but attenuated the proliferation evoked by a combination of insulin and TSH. Furthermore, S1P attenuated the PMA-evoked proliferation. S1P2 expression was positively regulated by insulin and PMA. S1P itself transiently upregulated S1P2 receptor mRNA, while TSH had a net downregulating effect on S1P2 expression. In summary, S1P modulates central intracellular signaling cascades and is antiproliferative in PC Cl3 cells. S1P2 receptor expression is modulated by insulin and TSH, two central growth factors in thyroid cell regulation.