Structural requirements of sphingosylphosphocholine and sphingosine-1-phosphate for stimulation of activator protein-1 activity.

The sphingolipids sphingosine-1-phosphate (SPP) and sphingosylphosphocholine (SPC) stimulate mitogenesis in Swiss 3T3 fibroblasts and stimulate DNA binding activity of activator protein-1 (AP-1). We show that SPP and SPC were more potent agents than nonphosphorylated sphingosines and N-acyl-sphingolipids (ceramides) with respect to DNA synthesis, AP-1 DNA binding activity, and AP-1 trans-activation, illustrating the importance of the terminal phosphate group. The free 2-amino group and the 4E double bond of SPC and SPP were found to be important for these activities. Although the combination of decreasing the sphingoid backbone chain length of SPC by two carbons and hydrogenating the 4E bond only slightly reduced its effects, in contrast, the same modifications in SPP significantly decreased its mitogenic and AP-1 trans-activation effects. Furthermore, substitution of the 3-hydroxyl group in SPP with hydrogen decreased its ability to stimulate DNA synthesis and to stimulate AP-1 transcriptional activity. Thus, critical sphingolipid structural components for AP-1 activation and mitogenic stimulation include the free 2-amino group, the free 3-hydroxyl group, the 4,5-trans double bond, and terminal phosphorylation. These observations may be relevant for clinical uses of these compounds in applications such as wound healing and inhibition of metastasis.