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 E(2) (PGE(2)) stimulation of the G protein-coupled prostanoid EP(1) 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 EP(1) receptor and in SH-SY5Y neuroblastoma cells expressing endogenous EP(1) 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 PGE(2) stimulated up-regulation of Nurr1. CREB and NF-κB signalling were also examined by immunoblot analysis and reporter gene assays.

KEY RESULTS

The EP(1) receptor mediated up-regulation of Nurr1 was blocked with inhibitors of Rho, PKA, NF-κB and CREB; but PGE(2) failed to significantly stimulate intracellular cAMP formation. PGE(2) 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

PGE(2) stimulation of the human EP(1) receptor up-regulates the expression of Nurr1 by a mechanism involving the sequential activation of the Rho, PKA, CREB and NF-κB signalling pathways. EP(1) receptors are implicated in tumorigenesis and the up-regulation of Nurr1 may underlie the anti-apoptotic effects of PGE(2) .

The spike protein of transmissible gastroenteritis coronavirus controls the tropism of pseudorecombinant virions engineered using synthetic minigenomes

The minimum sequence required for the replication and packaging of transmissible gastroenteritis virus (TGEV)-derived minigenomes has been determined. To this end, cDNAs encoding defective RNAs have been cloned and used to express heterologous spike proteins, to determine the influence of the peplomer protein in the control of TGEV tropism. A TGEV defective interfering RNA of 9.7 kb (DI-C) was isolated, and a cDNA complementary to DI-C RNA was cloned under the control of T7 promoter. In vitro transcribed DI-C RNA was replicated in trans upon transfection of helper virus-infected cells. A collection of DI-C deletion mutants (TGEV minigenomes) was generated and tested for their ability to be replicated and packaged. The size of the smallest minigenome replicated in trans was 3.3 kb. The rescue system was used to express the spike protein of an enteric TGEV isolate (C11) using as helper virus a TGEV strain (C8) that replicates very little in the gut. A mixture of two pseudorecombinant viruses containing either the helper virus genome or the minigenome was obtained. These pseudorecombinants display in the surface the S proteins from the enteric and the attenuated virus, and showed 10(4)-fold increase in their gut replication levels as compared to the helper isolate (C8). In addition, the pseudorecombinant virus increased its enteric pathogenicity as compared to the C8 isolate.