G-protein-coupled receptor stimulation of the p42/p44 mitogen-activated protein kinase pathway is attenuated by lipid phosphate phosphatases 1, 1a, and 2 in human embryonic kidney 293 cells

Sphingosine l-phosphate, lysophosphatidic acid, and phosphatidic acid bind to G-protein-coupled receptors to stimulate intracellular signaling in mamm alian cells. Lipid phosphate phosphatases (1, la, 2, and 3) are a group of enzymes that catalyze de-phosphorylation of these lipid agonists. It has be en proposed that the lipid phosphate phosphatases exhibit ecto activity tha t may function to limit bioavailability of these lipid agonists at their re ceptors, In this study, we show that the stimulation of the p42/p44 mitogen -activated protein kinase pathway by sphingosine l-phosphate, lysophosphati dic acid, and phosphatidic acid, all of which bind to G(i/o)-coupled recept ors, is substantially reduced in human embyronic kidney 293 cells transfect ed with lipid phosphate phosphatases 1, la, and 2 but not 3. This was corre lated with reduced basal intracellular phosphatidic acid and not ecto lipid phosphate phosphatase activity. These findings were supported by results s howing that lipid phosphate phosphatases 1, la, and 2 also abrogate the sti mulation of p42/p44 mitogen-activated protein kinase by thrombin, a peptide G(i/o)-coupled receptor agonist whose bioavailability at its receptor is n ot subject to regulation by the phosphatases, Furthermore, the lipid phosph ate phosphatases have no effect on the stimulation of p42/p44 mitogen-activ ated protein kinase by other agents that do not use G-proteins to signal, s uch as serum factors and phorbol ester, Therefore, these findings show that the lipid phosphate phosphatases 1, la, and 2 may function to perturb G-pr otein-coupled receptor signaling per se rather than limiting bioavailabilit y of lipid agonists at their respective receptors.