Prostanoid EP1 receptors mediate up-regulation of the orphan nuclear receptor Nurr1 by cAMP-independent activation of protein kinase A, CREB and NF-κB.

BACKGROUND AND PURPOSE Prostaglandin E₂ (PGE₂) stimulation of the G protein-coupled prostanoid EP₁ receptor was found to up-regulate the expression of Nur-related factor 1 (Nurr1) (NR4A2), a transcription factor in the NR4A subfamily of nuclear receptors. The present studies characterize the molecular mechanism of this up-regulation. EXPERIMENTAL APPROACH The expression of Nurr1 was examined by immunoblot analysis, the polymerase chain reaction and reporter gene assays in human embryonic kidney (HEK) cells stably expressing the recombinant EP₁ receptor and in SH-SY5Y neuroblastoma cells expressing endogenous EP₁ receptors. Signalling pathway inhibitors were used to examine the roles of Rho, PKA, the cAMP response element binding protein (CREB) and NF-κB on the PGE₂ stimulated up-regulation of Nurr1. CREB and NF-κB signalling were also examined by immunoblot analysis and reporter gene assays. KEY RESULTS The EP₁ receptor mediated up-regulation of Nurr1 was blocked with inhibitors of Rho, PKA, NF-κB and CREB; but PGE₂ failed to significantly stimulate intracellular cAMP formation. PGE₂ stimulation of the EP1 receptor induced the phosphorylation and activation of CREB and NF-κB, which could be blocked by inhibition of PKA. CONCLUSIONS AND IMPLICATIONS PGE₂ stimulation of the human EP₁ receptor up-regulates the expression of Nurr1 by a mechanism involving the sequential activation of the Rho, PKA, CREB and NF-κB signalling pathways. EP₁ receptors are implicated in tumorigenesis and the up-regulation of Nurr1 may underlie the anti-apoptotic effects of PGE₂. [ABSTRACT FROM AUTHOR]