Phosphocholine and sphingosine-1-phosphate synergistically stimulate DNA synthesis by a MAP kinase-dependent mechanism.

We have previously shown that in NIH 3T3 fibroblasts phosphocholine (PCho) potentiates sphingosine-1-phosphate (S1P)-induced mitogenesis. Here we report that PCho and S1P also synergistically stimulate DNA synthesis in mouse Swiss 3T3 fibroblasts and in mouse JB6 epidermal cells. The combined actions of PCho and S1P on DNA synthesis were associated with synergistic activation of the p42/p44 mitogen-activated protein (MAP) kinases. Ethanolamine (50-100 microM) further enhanced the synergistic effects of PCho and SIP on DNA synthesis but not on MAP kinase activity. The results indicate that the synergistic mitogenic effects of PCho and S1P (i) are not restricted to NIH 3T3 fibroblasts, (ii) are predominantly mediated by the MAP kinase-dependent signal transduction pathway, and (iii) are enhanced by ethanolamine via a MAP kinase-independent mechanism.