Microsomal prostaglandin E synthase-1 regulates human glioma cell growth via prostaglandin E(2)-dependent activation of type II protein kinase A.

Dysregulation of enzymes involved in prostaglandin biosynthesis plays a critical role in influencing the biological behavior and clinical outcome of several tumors. In human gliomas, overexpression of cyclooxygenase-2 has been linked to increased aggressiveness and poor prognosis. In contrast, the role of prostaglandin E synthase in influencing the biological behavior of human gliomas has not been established. We report that constitutive expression of the microsomal prostaglandin E synthase-1 (mPGES-1) is associated with increased prostaglandin E(2) (PGE(2)) production and stimulation of growth in the human astroglioma cell line U87-MG compared with human primary astrocytes. Consistently, pharmacologic and genetic inhibition of mPGES-1 activity and expression blocked the release of PGE(2) from U87-MG cells and decreased their proliferation. Conversely, exogenous PGE(2) partially overcame the antiproliferative effects of mPGES-1 inhibition and stimulated U87-MG cell proliferation in the absence of mPGES-1 inhibitors. The EP2/EP4 subtype PGE(2) receptors, which are linked to stimulation of adenylate cyclase, were expressed in U87-MG cells to a greater extent than in human astrocytes. PGE(2) increased cyclic AMP levels and stimulated protein kinase A (PKA) activity in U87-MG cells. Treatment with a selective type II PKA inhibitor decreased PGE(2)-induced U87-MG cell proliferation, whereas a selective type I PKA inhibitor had no effect. Taken together, these results are consistent with the hypothesis that mPGES-1 plays a critical role in promoting astroglioma cell growth via PGE(2)-dependent activation of type II PKA.