MBTPS1 and astrocytic tumor: From cellular the lower affinity S1P receptor ligands dihydro-sphingosine and sphingosylphosphorylcholine in the high nanomolar to low micromolar range, Van Brocklyn et al. (2002) concluded that the proproliferative effects of S1P on astrocytic tumor cell lines are mediated by the S1P1 receptor involving PI3K and ERK1/2 activation rather than by intracellular effects of S1P.