The Prostacyclin Receptor Is Isoprenylated

Abstract

The prostacyclin receptor (IP), a G protein-coupled receptor, mediates the actions of the prostanoid prostacyclin and its mimetics. IPs from a number of species each contain identically conserved putative isoprenylation CAAX motifs, each with the sequence CSLC. Prostacyclin (prostaglandin (PG)1 I 2 ) is a labile metabolite of arachidonic acid, which is synthesized by the sequential actions of PGH 2 endoperoxide synthases 1 and 2 and prostacyclin synthase (1). The actions of prostacyclin generally counteract those of thromboxane A 2 , and thus the relative level of these two prostanoids in the circulation are important in the local control of vascular tone and platelet aggregation (2, 3). The main physiologic roles of thromboxane A 2 and prostacyclin are their contribution to the maintenance of vascular hemostasis: thromboxane A 2 , synthesized primarily by platelets, induces platelet shape change and aggregation and constriction of bronchial and vascular smooth muscle, whereas prostacyclin, mainly synthesized by the vascular endothelium, is a potent inhibitor of platelet aggregation and induces vasodilation (4 -7). Moreover, prostacyclin has been reported to confer a cytoprotective effect against tissue injury in acute myocardial ischemia or following hypoxic exposure of vascular endothelial cells (8). Imbalances in thromboxane A 2 or prostacyclin have been reported to be a major contributing factor in the development of a number of cardiovascular disorders including thrombosis, myocardial infarction, unstable angina, stroke, and atherosclerosis (9 -13). In addition to its central role in the cardiovascular system, prostacyclin may be important in the regulation of renal blood flow (14); it also acts as a negative feedback regulator of histamine secretion from mast cells (15) and acts as a lipolytic agent, antagonizing the antilipolytic effect of PGE 2 , in adipocytes (16).The actions of prostacyclin are mediated via interaction with a specific cell surface receptor, termed the prostacyclin receptor or IP (17). The major intracellular signaling pathway used is stimulation of adenylyl cyclase leading to increases in intracellular cAMP (18,19), a pathway thought to be relevant to inhibition of platelet aggregation and vascular smooth muscle relaxation (3). However, recent evidence indicates that IP agonists may couple to multiple signaling pathways including activation and inhibition of adenylyl cyclase, via G s and G i , respectively, stimulation of phosphoinositide metabolism, and changes in [Ca 2ϩ ] i concentrations (20,21). Evidence also exists to indicate that iloprost, a stable carbacyclin analogue of prostacyclin, can stimulate opening of ATP sensitive K ϩ channels resulting in hyperpolarization and relaxation of canine carotid artery (22).Molecular cloning of the human (23, 24), mouse (25), and rat

Interaction of the Human Prostacyclin Receptor with Rab11

“…The IP is somewhat unusual among GPCRs in that it undergoes both isoprenylation and palmitoylation within its carboxyl-terminal tail (C-tail) domain, modifications that are critical for its signaling and function (24 -30). More specifically, in the case of the human (hIP), it undergoes farnesylation at Cys 383 within an evolutionarily conserved -CAAX motif (24,25) and is dually palmitoylated at Cys 308 and Cys 311 , whereas an intervening Cys 309 was found not to be palmitoylated, at least under the experimental conditions used (27). Although neither lipidation affected its ligand binding properties, it is proposed that farnesylation in addition to palmitoylation of the hIP may confer a double loop structure within its C-tail domain to provide and/or orientate the critical structural domains for its G protein/effector(s) coupling and, possibly, for its interaction with components of the intracellular trafficking machinery to modulate its internalization after agonist activation (24,25,27).…”

“…More specifically, in the case of the human (hIP), it undergoes farnesylation at Cys 383 within an evolutionarily conserved -CAAX motif (24,25) and is dually palmitoylated at Cys 308 and Cys 311 , whereas an intervening Cys 309 was found not to be palmitoylated, at least under the experimental conditions used (27). Although neither lipidation affected its ligand binding properties, it is proposed that farnesylation in addition to palmitoylation of the hIP may confer a double loop structure within its C-tail domain to provide and/or orientate the critical structural domains for its G protein/effector(s) coupling and, possibly, for its interaction with components of the intracellular trafficking machinery to modulate its internalization after agonist activation (24,25,27). More specifically, although disruption of farnesylation effectively abolishes agonist-induced G s /adenylyl cyclase activation and cAMP generation by the hIP, palmitoylation at either Cys 308 or Cys 311 is sufficient to maintain functional G s coupling, whereas disruption of palmitoylation at both sites abolishes that signaling (24,25,27).…”

Conserved Cysteine and Tryptophan Residues of the Endothelin-converting Enzyme-1 CXAW Motif Are Critical for Protein Maturation and Enzyme Activity

“…Approximately 48 h after transfection, cells were preincubated with lovastatin at 40 M (a concentration known to inhibit hydroxymethylglutaryl-CoA reductase; Ref. 17) to deplete the intracellular pool of mevalonate and its metabolites. Cells were then incubated with [ 3 H]mevalonolactone for 16 h in the presence of lovastatin.…”

Thromboxane A2 Signalling in Humans: a ‘Tail’ of Two Receptors

“…Both TXA 2 and PGI 2 signal through their signature receptors, each members of the G protein coupled receptor (GPCR) superfamily [1,2,6,7]. TXA 2 interacts with the TXA 2 receptor, also termed TP or T Prostanoid receptor, whereas PGI 2 interacts with the PGI 2 receptor, also termed IP or I Prostanoid receptor [18,19]. Greater understanding of the molecular mechanisms governing the interaction between TXA 2 , PGI 2 and their receptors as well as a greater understanding of the interplay between their signal transduction pathways should lead to a greater appreciation of their involvement in vascular hemostasis under normal and patho-physiologic conditions.…”