DIFFERENTIAL STIMULATION OF PROLINE-RICH TYROSINE-KINASE-2 AND MITOGEN-ACTIVATED PROTEIN-KINASE BY SPHINGOSINE 1-PHOSPHATE

Sphingosine l-phosphate (SphP), a metabolite of cellular sphingolipids , has been shown to induce cell proliferation by activating the mitoge n-activated protein kinase (MAPK) pathway. Proline-rich tyrosine kinas e 2 (Pyk2) is a novel cytosolic tyrosine kinase which mediates activat ion of the MAPK or c-Jun N-terminal kinase (JNK) signaling pathways in response to a variety of stimuli that elevate intracellular calcium. In this report, we show that SphP stimulates both tyrosine phosphoryla tion of Pyk2 and MAPK activation in a transient and dose-dependent man ner in rat aortic smooth muscle cells. Further studies indicate that P yk2 phosphorylation, but not MAPK activation, is dependent on a pertus sis toxin-sensitive G-protein-coupled receptor as well as partially on actin cytoskeleton. In addition, both intracellular calcium mobilizat ion and protein kinase C (PKC) are required for optimal Pyk2 phosphory lation while either calcium increase or PKC activation is sufficient f or MAPK activation in response to SphP. Finally, we show that a tyrosi ne kinase(s) other than Pyk2 is necessary for MAPK activation by SphP. Together, these results suggest that SphP stimulates tyrosine phospho rylation of Pyk2 through a G-protein coupled receptor, which is dissoc iated from its activation of the MAPK pathway in these cells.