Sphingosine 1-phosphate activates Erk-1/-2 by transactivating epidermal growth factor receptor in rat-2 cells

We investigated a signaling pathway leading to activation of extracellular signal-regulated protein kinase (Erk) 1 and 2 in Rat-2 cells stimulated wit h sphingosine 1-phosphate (S1P), S1P treatment transiently activated Erk-1/ -2 in a dose-dependent manner, and its activation was blocked by pertussis toxin, expression of RasN17, or inhibition of Raf or MEK-1/-2, S1P-induced activation of Erk-l/-2 was also suppressed by the inhibition of epidermal g rowth factor (EGF) receptor tyrosine kinase with the specific inhibitor AG1 478, suggesting that activation of EGF receptor tyrosine kinase was involve d in the signaling pathway. S1P-induced Erk-1/-2 activation was enhanced up to 2-fold by inhibiting protein kinase C (PKC) with GF109203X, and PKC inh ibition in the absence of S1P treatment also activated Erk-1/-2, The stimul atory effects of Erk-1/-2 activation by PKC inhibition was blocked by treat ing cells with AG1478, suggesting the involvement of PKC in the regulation of EGF receptor tyrosine kinase activation that leads to Erk-1/-2 activatio n. Together, these results suggest that S1P activates the EGF receptor thro ugh a PKC-dependent pathway that links Ras signaling to the activation of E rk-1/-2 in Rat-2 cells.