Fatty acids and prostaglandins, function not only through their cell membrane receptors but also through nuclear receptors to regulate gene expression. PGI₂ can interact with G protein-coupled receptor IP on the surface of cell membrane and nuclear receptor PPARs. Recently it was found that PGE₂ receptors localized not only on the cell membrane but also on the envelope of the nucleus. There exists difference in the signaling pathway and in regulation mechanism between nuclear receptor and membrane receptors.