Lysophosphatidic acid (LPA) is a bioactive molecule involved in inflammation, immunity, wound healing, and neoplasia. Its pleiotropic actions arise presumably by interaction with their cell surface G protein-coupled receptors. Herein, the presence of the specific nuclear lysophosphatidic acid receptor-1 (LPA 1 R) was revealed in unstimulated porcine cerebral microvascular endothelial cells (pCMVECs), LPA 1 R stably transfected HTC4 rat hepatoma cells, and rat liver tissue using complementary approaches, including radioligand binding experiments, electron-and cryomicroscopy, cell fractionation, and immunoblotting with three distinct antibodies. Coimmunoprecipitation studies in enriched plasmalemmal fractions of unstimulated pCMVEC showed that LPA 1 Rs are dually sequestrated in caveolin-1 and clathrin subcompartments, whereas in nuclear fractions LPA 1 R appeared primarily in caveolae. Immunofluorescent assays using a cell-free isolated nuclear system confirmed LPA 1 R and caveolin-1 co-localization. In pCMVEC, LPA-stimulated increases in cyclooxygenase-2 and inducible nitricoxide synthase RNA and protein expression were insensitive to caveolea-disrupting agents but sensitive to LPAgenerating phospholipase A 2 enzyme and tyrosine kinase inhibitors. Moreover, LPA-induced increases in Ca 2؉ transients and/or iNOS expression in highly purified rat liver nuclei were prevented by pertussis toxin, phosphoinositide 3-kinase/Akt inhibitor wortmannin and Ca 2؉ chelator and channel blockers EGTA and SK&F96365, respectively. This study describes for the first time the nucleus as a potential organelle for LPA intracrine signaling in the regulation of pro-inflammatory gene expression.In the mammalian system, LPA 1 signaling cascades regulate important cellular processes, including gene expression, cell proliferation and growth, cell survival and death, and cell motility and secretion (1-3). These plethora of activities are characteristic features of inflammation that occur in various physiological as well as pathological states (e.g. ontogenic change, wound healing, cancer, etc.) (1-3). In humans, physiological responses induced by LPA arise from specific interactions with at least three genetically identified receptors designated LPA 1 , LPA 2 , and LPA 3 (formerly referred to as EDG 2 , EDG 4 , and EDG 7 receptors, respectively), which belong to the heptahelical transmembrane-spanning G protein-coupled receptor (GPCR) superfamily (4). These receptors show a broad, virtually distinct distribution and may couple in a cell-dependent manner to numerous heterotrimeric G proteins. In this context, LPA 1 and LPA 2 receptors have been shown to interact with G i/o , G q/11/14 , and G 12/13 proteins, whereas the LPA 3 receptor combines with G i/o and G q/11/14 proteins (5). Although many responses induced by extracellular LPA can result from its interaction with plasma membrane GPCRs, there is circumstantial evidence for an intracrine mode of action of LPA. For instance, putative biogenesis (e.g. secretory and cytosolic calcium-depen...

Abstract-We reported upregulation of endothelial nitric oxide synthase (eNOS) by PGE 2 in tissues and presence of perinuclear PGE 2 receptors (EP). We presently studied mechanisms by which PGE 2 induces eNOS expression in cerebral microvessel endothelial cells (ECs). 16,16-Dimethyl PGE 2 and selective EP 3 receptor agonist M&B28767 increased eNOS expression in ECs and the NO-dependent vasorelaxant responses induced by substance P on cerebral microvessels. These effects could be prevented by prostaglandin transporter blocker bromcresol green and actinomycin D. EP 3 immunoreactivity was confirmed on plasma and perinuclear membrane of ECs. M&B28767 increased eNOS RNA expression in EC nuclei, and this effect was augmented by overexpression of EP 3 receptors. M&B28767 also induced increased phosphorylation of Erk-1/2 and Akt, as well as changes in membrane potential revealed by the potentiometric fluorescent dye RH421, which were prevented by iberiotoxin; perinuclear K Ca channels were detected, and their functionality corroborated by NS1619-induced Ca 2ϩ signals and nuclear membrane potential changes. Moreover, pertussis toxin, Ca 2ϩ chelator, and channel blockers EGTA, BAPTA, and SK&F96365, as well as K Ca channel blocker iberiotoxin, protein-kinase inhibitors wortmannin and PD 98059, and NF-B inhibitor pyrrolidine dithiocarbamate prevented M&B28767-induced increase in Ca 2ϩ transients and/or eNOS expression in EC nuclei. We describe for the first time that PGE 2 through its access into cell by prostaglandin transporters induces eNOS expression by activating perinuclear EP 3 receptors coupled to pertussis toxin-sensitive G proteins, a process that depends on nuclear envelope K Ca channels, protein kinases, and NF-B; the roles for nuclear EP 3 receptors seem different from those on plasma membrane. (Circ Res. 2002;90:682-689.)