Localization of functional prostaglandin E-2 receptors EP3 and EP4 in the nuclear envelope

The effects of prostaglandin E-2 are thought to be mediated via G protein-c oupled plasma membrane receptors, termed EP. However recent data implied th at prostanoids may also act intracellularly. We investigated if the ubiquit ous EP3 and the EP4 receptors are localized in nuclear membranes. Radioliga nd binding studies on isolated nuclear membrane fractions of neonatal porci ne brain and adult rat liver revealed the presence of EP3 and EP4. A perinu clear localization of EP3 alpha and EP4 receptors was visualized by indirec t immunocytofluorescence and confocal microscopy in porcine cerebral microv ascular endothelial cells and in transfected HEK 293 cells that stably over express these receptors. Immunoelectron microscopy clearly revealed EP3 alp ha and EP4 receptors localization in the nuclear envelope of endothelial ce lls; this is the first demonstration of the nuclear localization of these r eceptors. Data also reveal that nuclear EP receptors are functional as they affect transcription of genes such as inducible nitric-oxide synthase and intranuclear calcium transients; this appears to involve pertussis toxin-se nsitive G proteins. These results define a possible molecular mechanism of action of nuclear EP3 receptors.