The endogenous phospholipids, lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are both known to generate a Vvide variety of effects in various cell systems by the endothelial differentiation gene (Edg) receptor family, including 7 different G-protein coupled Edg receptors.
In this study, expression of LPA- and SlP Edg receptors was examined, and so was the effect with respect to proliferation on cultured BPH smooth muscle cells smc. Mmeover, theresponse on cAMP levels was examined. Finally, a potential link between activation of the MAP kinase cascade and the LPA stimulated proliferation was investigated.
First, the RT-PCR analysis of the Edg receptors in BPH smc, demonstrated a heterogeneous expression including all receptors except the Edg6 subtype. Further, in contrast to LPA, the mitogen effect of SIP, demonstrated a concentration-dependent biphasic response, including stimulation below 1μM, whereas inhibition was obtained at higher concentrations. Forskolin induced a rapid and transient cAMP response in LPA stimulated cells, with a peak-value after 3 minutes. After 15 minutes the cAMP level had retmned to base-line level. However a gradual increase to 15% of maximum value was obtained after additional 30 minutes, and thereafter a gradual reduction was observed. The mentioned antiproliferative response generated by SIP could not be conelated to an intracellular cAMP increase. Finally, when the LPA treated smc was co-incubated with the MAPK kinase inhibitor PD98059 (10 μM) the mitogen response was eliminated.
The cAIVIP increase, which was induced by forskolin, corresponds with mentioned antiproliferative effect whereas a similar con-elation was not obtained regarding SIP. The intracellular signal mechanisms triggered by LPA and S1P in BPH smc remain to be further investigated.