Antagonizing effects of membrane-acting androgens on the eicosanoid receptor OXER1 in prostate cancer.

Accumulating evidence during the last decades revealed that androgen can exert membrane initiated actions that involve signaling via specific kinases and the modulation of significant cellular processes, important for prostate cancer cell growth and metastasis. Results of the present work clearly show that androgens can specifically act at the membrane level via the GPCR oxoeicosanoid receptor 1 (OXER1) in prostate cancer cells. In fact, OXER1 expression parallels that of membrane androgen binding in prostate cancer cell lines and tumor specimens, while in silico docking simulation of OXER1 showed that testosterone could bind to OXER1 within the same grove as 5-OxoETE, the natural ligand of OXER1. Interestingly, testosterone antagonizes the effects of 5-oxoETE on specific signaling pathways and rapid effects such as actin cytoskeleton reorganization that ultimately can modulate cell migration and metastasis. These findings verify that membrane-acting androgens exert specific effects through an antagonistic interaction with OXER1. Additionally, this interaction between androgen and OXER1, which is an arachidonic acid metabolite receptor expressed in prostate cancer, provides a novel link between steroid and lipid actions and renders OXER1 as new player in the disease. These findings should be taken into account in the design of novel therapeutic approaches in prostate cancer.

Identification of novel peptide agonists from a random peptide library for a 5-oxo-ETE receptor, a receptor for bioactive lipids.

A combinatorial peptide library contains an enormous combination of amino acid sequences and drug candidates, but an effective screening strategy to identify a variety of bioactive peptides has yet to be established. In this article, a random hexapeptide library was screened to identify novel peptide ligands for a 5-oxo-ETE receptor (OXER), which is a G-protein-coupled receptor for bioactive lipids, by using an OXER-Gi1alpha fusion protein. We successfully identified 2 hexapeptides-Ac-HMQLYF-NH2 and Ac-HMWLYF-NH(2)-that exhibited agonistic activity. Although the corresponding affinities were relatively low (EC50 values of 146 and 6.7 microM, respectively), the activities were confirmed by other independent cell-based assay methods, namely, intracellular calcium mobilization and cell chemotaxis. This study demonstrates that a combinatorial peptide library may be screened using a [35S]GTPgammaS binding assay with G-protein-coupled receptor (GPCR)-Galpha fusion proteins, in general, and that of peptide ligands can be obtained even for nonpeptide receptors.

Structural manipulation of eicosanoid receptors and cellular signaling.

Eicosanoids are lipid mediators derived from the metabolism of arachidonic acid. These agents are locally released and activate different cell membrane receptors, and the latter are part of the G-protein coupled receptor family. While activation of eicosanoid receptors is associated with a wide variety of actions, there is limited information concerning the structural components of the eicosanoid receptors. To date, our understanding of the eicosanoid ligand-receptor binding interaction has been based on the rhodopsin template model. While receptors in the same family do share a common architecture, there are amino acid residues in the membrane binding pocket that play a key role in ligand recognition as well as the diversity observed in the cellular signaling. In order to understand the eicosanoid receptor binding interaction, attention must be focused on both the nature of the endogenous ligands as well as the template G-protein model that has been proposed. The data derived from chemical alterations in the endogenous ligands, together with the mutagenesis studies involving the structural modifications of the eicosanoid receptors, have suggested a working model of the eicosanoid receptors. However, the data also document various nuances in the receptor structure associated with ligand binding as well as a number of differences that will require further investigation.

Targeted chiral lipidomics analysis.

Genomics, transcriptomics, and proteomics are proving to be very useful techniques, which have impacted significantly on our understanding mechanisms of human disease. However, this systems biology approach has several drawbacks than can be overcome by the integration of metabonomics and lipidomics. We have developed a targeted lipidomics approach that makes it possible to directly analyze chiral lipids generated in cellular systems. Bioactive lipids are usually present in trace amounts as enanatiomers and regioisomers that require separation before they can be analyzed by mass spectrometry. Normal phase chiral chromatography is generally used to resolve bioactive lipid enanatiomers. However, conventional electrospray and atmospheric pressure chemical ionization/tandem mass spectrometry have limited sensitivity when normal phase solvents are used, which makes it difficult to conduct studies when only trace amounts of the bioactive lipids are present. The use of electron capture atmospheric pressure chemical ionization/tandem mass spectrometry overcomes this problem. Enantiomers and regioisomers of targeted bioactive lipids can be quantified using stable isotope dilution methodology coupled with normal phase chiral chromatography and electron capture atmospheric chemical ionization/tandem mass spectrometry. A targeted lipidomics profile from rat epithelial cells transfected with cyclooxygenase-2 and maintained in culture was obtained. Inhibition with the non-selective cyclooxygenase inhibitor aspirin increased the formation of 15(R)-hydroxyeicosatetraenoic acid in the cells although it completely inhibited formation of the 15(S)-enantiomer and prostaglandin E2. New mass spectrometry instrumentation with an improved atmospheric pressure chemical ionization source was found to be an order of magnitude more sensitive than existing instruments for analysis of bioactive lipids using electron capture methodology. This type of mass spectrometer will permit a more detailed analysis of cellular bioactive lipid production than has been possible previously. It will also permit in vivo targeted lipidomics studies to be conducted using biological fluids derived from animal models and human subjects.

A short guide to the nomenclature of seven-transmembrane spanning receptors for lipid mediators.

The International Union of Pharmacology (IUPHAR) has established a Nomenclature Committee comprised of sub-committees of experts to evaluate types and subtypes of receptors and ion channels in an effort to establish universally accepted nomenclature [Vanhoutte, P.M., Barnard, E.A., Cosmides, G.J., Humphrey, P.P., Spedding, M., Godfraind, T., 1994. International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. Pharmacological Reviews 46, 111-116]. This overview cites the reports of the IUPHAR subcommittees and other prominent review articles in an effort to compile receptors for lipid mediators that bind to and evoke their pharmacological responses via seven-transmembrane spanning, G-protein-coupled receptors.

20-hydroxyeicosatetraenoic acid (20-HETE): structural determinants for renal vasoconstriction.

The effects of natural and synthetic eicosanoids on the diameter of rat interlobular arteries studied in vitro were compared to that of the potent, endogenous vasoconstrictor 20-HETE. Vasoconstrictor activity was optimum for chain lengths of 20-22 carbons with at least one olefin or epoxide between located between C(13)-C(15) and an oxygen substituent at C(20)-C(22). The presence of delta (Zou et al. Am. J. Physiol. 1996, 270, R228; Gebremedhin, D. et al. Am. J. Physiol. 1998, 507, 771)-, delta (Carroll et al. Am. J. Physiol. 1996, 271, R863; Vazquez et al. Life Sci. 1995, 56, 1455)-, or delta (Imig et al. Hypertension 2000, 35, 307; Lopez et al. Amer. J. Physiol. 2001, 281, F420)-olefins had no influence on the vasoconstrictor response whereas the introduction of a C(7)-thiomethylene enhanced potency. A sulfonamide or alcohol, but not a lactone, could replace the C(1)-carboxylate. These data were used to construct a putative binding domain map of the 20-HETE receptor consisting of: (i) a comparatively open, hydrophilic binding site accommodating the C(1)-functionality; (ii) a hydrophobic trough spanning the olefins; (iii) a shallow pocket containing a critical pi-pi binding site in the vicinity of the pi (Ito et al. Am. J. Physiol. 1998, 274, F395; Quigley, R.; Baum, M.; Reddy, K. M.; Griener, J. C.; Falck, J. R. Am. J. Physiol. 2000, 278, F949)-olefin; and (iv) an oxyphilic binding site proximate to the omega-terminus.

Structure-function analyses of eicosanoid receptors. Physiologic and therapeutic implications.

Prostaglandins (PGs) are ubiquitous lipid mediators derived from cyclooxygenase (COX) metabolism of arachidonic acid that exert a broad range of physiologic activities including modulation of inflammation, ovulation, and arterial blood pressure. The physiologic actions of PGs are mediated in part by their interaction with specific G-protein-coupled PG receptors. Eight PG receptors have been cloned, including four for the major COX metabolite, PGE2. The physiologic roles of the PGE2 receptors have been investigated utilizing subtype-selective agonists, localization of receptor mRNA expression, and creation of mice with targeted disruption of PG receptor genes. These analyses have delineated discrete roles for the various PG receptor subtypes. Recent studies on mice lacking the PGE2 EP2 receptor have implicated the PGE2 EP2 receptor subtype in arterial dilatation and salt-sensitive hypertension, and also indicate that this receptor plays a key role in female fertility. The EP2 receptor may thus prove to be a productive target for pharmacological intervention in the treatment of hypertension and infertility.

[Molecular structures of eicosanoid receptors].

Prostanoids exert versatile actions in diverse tissues and cells through specific cell surface receptors. Molecular biological studies have revealed the primary structure of eight types and subtypes of prostanoid receptors from various species. They are coupled to different signal transduction systems and show different tissue distribution. In addition, multiple isoforms of prostaglandin E receptor EP3 subtype have been identified in various species. They are produced through alternative RNA splicing from a single gene and differ only in their carboxyl-terminal tails. These isoforms differ in the efficiency of G protein activation, in the specificity of coupling to G proteins or in sensitivity to desensitization. This molecular characterization is useful for understanding the diverse physiological role of prostanoids.