Melatonin and retinoid orphan receptors: Demand for new interpretations after their exclusion as nuclear melatonin receptors

2018 ◽  
Vol 1 (1) ◽  
pp. 78-93 ◽  
Author(s):  
Ruediger Hardeland
Keyword(s):  
Nuclear Receptors ◽  
Retinoic Acid Receptor ◽  
Membrane Receptors ◽  
Melatonin Receptors ◽  
Sirtuin 1 ◽  
Orphan Receptor ◽  
Melatonin Receptor ◽  
Orphan Receptors ◽  
Synthetic Compound ◽  
Circadian Oscillators

The demonstrated incapability of the retinoic acid receptor-related orphan receptor-α (RORα) to bind melatonin inevitably requires consequences for interpreting numerous reports on actions of this protein as far as it was believed to be a nuclear melatonin receptor. While the synthetic compound CGP 52608 is, in fact, a ligand of RORα, effects obtained with this molecule can no longer be attributed to melatonin. Moreover, the sometimes assumed interplay between melatonin membrane receptors and RORα as nuclear receptors has to be dropped. Conclusions on melatonin’s actions via RORα that were based on a lack of demonstrable involvement of membrane receptors appear to have been precocious. Nevertheless, findings on melatonin uptake into the nucleus may still be taken as a hint for nuclear melatonin receptors, but this would require thorough characterization. Although RORα does not bind melatonin, it is interrelated to the latter in regulatory terms by involvement of cellular circadian oscillators. A mode of action seems to be the upregulation of sirtuin-1 by melatonin, deacetylation of poly ADP ribose polymerase-γ coactivator-1α (PGC-1α) by sirtuin-1, and facilitation of RORα binding to its response element by deacetylated PGC-1α, a route that had been shown to exist in circadian oscillators, thereby enhancing their amplitude. 

scholarly journals Efficient Lead Finding, Activity Enhancement and Preliminary Selectivity Control of Nuclear Receptor Ligands Bearing a Phenanthridinone Skeleton

2018 ◽  
Vol 19 (7) ◽  
pp. 2090 ◽  
Author(s):  
Yuko Nishiyama ◽  
Shinya Fujii ◽  
Makoto Makishima ◽  
Yuichi Hashimoto ◽  
Minoru Ishikawa
Keyword(s):  
Nuclear Receptors ◽  
Drug Targets ◽  
Retinoic Acid Receptor ◽  
Receptor Ligands ◽  
Orphan Receptors ◽  
Sar Studies ◽  
Activity Enhancement ◽  
X Receptors ◽  
Nuclear Receptor Ligands ◽  
Lead Finding

Background: Nuclear receptors (NRs) are considered as potential drug targets because they control diverse biological functions. However, steroidal ligands for NRs have the potential to cross-react with other nuclear receptors, so development of non-steroidal NR ligands is desirable to obtain safer agents for clinical use. We anticipated that efficient lead finding and enhancement of activity toward nuclear receptors recognizing endogenous steroidal ligands might be achieved by exhaustive evaluation of a steroid surrogate library coupled with examination of structure-activity relationships (SAR). Method: We evaluated our library of RORs (retinoic acid receptor-related orphan receptors) inverse agonists and/or PR (progesterone receptor) antagonists based on the phenanthridinone skeleton for antagonistic activities toward liver X receptors (LXRs), androgen receptor (AR) and glucocorticoid receptor (GR) and examined their SAR. Results: Potent LXRβ, AR, and GR antagonists were identified. SAR studies led to a potent AR antagonist (IC50: 0.059 μM). Conclusions: Our approach proved effective for efficient lead finding, activity enhancement and preliminary control of selectivity over other receptors. The phenanthridinone skeleton appears to be a promising steroid surrogate.

Mitochondria: the birth place, battle ground and the site of melatonin metabolism in cells

2019 ◽  
Vol 2 (1) ◽  
pp. 44-66 ◽  
Author(s):  
Dun-Xian Tan ◽  
Russel. J. Reiter
Keyword(s):  
Ischemia Reperfusion ◽  
Surface Membrane ◽  
Strong Association ◽  
Membrane Receptors ◽  
Melatonin Receptors ◽  
Metabolic Enzyme ◽  
Intermembrane Space ◽  
Antitumor Effects ◽  
The Matrix ◽  
Surprising Discovery

     It was a surprising discovery when mitochondria, as the power houses of cells, were also found to synthesize the potent mitochondrial targeted antioxidant, melatonin. The melatonin synthetic enzyme serotonin N-acetyltransferase (SNAT) was found in matrix and also in the intermembrane space of mitochondria. We hypothesize that the melatonin synthesis occurs in the matrix due to substrate (N-acetyl co-enzyme A) availability while the intermembrane space may serve as the recycling pool of SNAT to regulate the melatonin circadian rhythm. Another surprise was that the melatonin membrane receptors, including MT1 and MT2, were also present in mitochondria. The protective effects of melatonin against neuronal injury induced by brain ischemia/reperfusion were proven to be mainly mediated by mitochondrial melatonin receptors rather than the cell surface membrane receptors which is contrary to the classical principle. In addition, melatonin metabolic enzyme has also been identified in the mitochondria. This enzyme can convert melatonin to N-acetylserotonin to strengthen the antitumor effects of melatonin. Thus, mitochondria are the generator, battle ground and metabolic sites of melatonin. The biological significance of the strong association between mitochondria and melatonin should be intensively investigated. 

Mitochondria: the birth place, battle ground and the site of melatonin metabolism in cells

2019 ◽  
Vol 2 (1) ◽  
pp. 44-66 ◽  
Author(s):  
Dun-Xian Tan ◽  
Russel. J. Reiter
Keyword(s):  
Ischemia Reperfusion ◽  
Surface Membrane ◽  
Strong Association ◽  
Membrane Receptors ◽  
Melatonin Receptors ◽  
Metabolic Enzyme ◽  
Intermembrane Space ◽  
Antitumor Effects ◽  
The Matrix ◽  
Surprising Discovery

     It was a surprising discovery when mitochondria, as the power houses of cells, were also found to synthesize the potent mitochondrial targeted antioxidant, melatonin. The melatonin synthetic enzyme serotonin N-acetyltransferase (SNAT) was found in matrix and also in the intermembrane space of mitochondria. We hypothesize that the melatonin synthesis occurs in the matrix due to substrate (N-acetyl co-enzyme A) availability while the intermembrane space may serve as the recycling pool of SNAT to regulate the melatonin circadian rhythm. Another surprise was that the melatonin membrane receptors, including MT1 and MT2, were also present in mitochondria. The protective effects of melatonin against neuronal injury induced by brain ischemia/reperfusion were proven to be mainly mediated by mitochondrial melatonin receptors rather than the cell surface membrane receptors which is contrary to the classical principle. In addition, melatonin metabolic enzyme has also been identified in the mitochondria. This enzyme can convert melatonin to N-acetylserotonin to strengthen the antitumor effects of melatonin. Thus, mitochondria are the generator, battle ground and metabolic sites of melatonin. The biological significance of the strong association between mitochondria and melatonin should be intensively investigated. 

Molecular Modeling of an Orphan GPR18 Receptor

2019 ◽  
Vol 16 (10) ◽  
pp. 1167-1174 ◽  
Author(s):  
Kamil J. Kuder ◽  
Tadeusz Karcz ◽  
Maria Kaleta ◽  
Katarzyna Kiec-Kononowicz
Keyword(s):  
Cannabinoid Receptors ◽  
Cannabinoid Receptor ◽  
Glycine Receptor ◽  
Homology Model ◽  
Orphan Receptor ◽  
Receptor Ligands ◽  
Orphan Receptors ◽  
Inactive Form ◽  
Starting Point ◽  
Endogenous Cannabinoid

Background: : One of the best known to date GPCR class A (Rhodopsin) includes more than 100 orphan receptors for which the endogenous ligand is not known or is unclear. One of them is N-arachidonyl glycine receptor, named GPR18, a receptor that has been reported to be activated by Δ9-THC, endogenous cannabinoid receptors agonist anandamide and other cannabinoid receptor ligands suggesting it could be considered as third cannabinoid receptor. GPR18 activity, as well as its distribution might suggest usage of GPR18 ligands in treatment of endometriosis, cancer, and neurodegenerative disorders. Yet, so far only few GPR18 antagonists have been described, thus only ligand-based design approaches appear to be most useful to identify new ligands for this orphan receptor. Methods: : Main goal of this study, GPR18 inactive form homology model was built on the basis of the evolutionary closest homologous template: Human P2Y1 Receptor crystal structure. Results: : Obtained model was further evaluated and showed active/nonactive ligands differentiating properties with acceptable confidence. Moreover, it allowed for preliminary assessment of proteinligand interactions for a set of previously described ligands. Conclusion:: Thus collected data might serve as a starting point for a discovery of novel, active GPR18 blocking ligands.

scholarly journals High retinoic acid receptor-related orphan receptor A gene expression in peripheral blood leukocytes may be related to acute myocardial infarction

2021 ◽  
Vol 49 (6) ◽  
pp. 030006052110196
Author(s):  
Heyu Meng ◽  
Jianjun Ruan ◽  
Xiaomin Tian ◽  
Lihong Li ◽  
Weiwei Chen ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Coronary Artery Disease ◽  
Acute Myocardial Infarction ◽  
Coronary Artery ◽  
Peripheral Blood ◽  
Retinoic Acid Receptor ◽  
Stable Coronary Artery Disease ◽  
Orphan Receptor ◽  
Blood Leukocytes ◽  
Artery Disease

Objective This study aimed to investigate whether differential expression of the retinoic acid receptor-related orphan receptor A ( RORA) gene is related to occurrence of acute myocardial infarction (AMI). Methods This was a retrospective study. White blood cells of 93 patients with acute myocardial infarction and 74 patients with stable coronary artery disease were collected. Reverse transcription quantitative polymerase chain reaction and western blotting were used to measure RORA mRNA and protein expression, respectively. Results RORA mRNA expression levels in peripheral blood leukocytes in patients with AMI were 1.57 times higher than those in patients with stable coronary artery disease. Protein RORA levels in peripheral blood of patients with AMI were increased. Binary logistic regression analysis showed that high expression of RORA was an independent risk factor for AMI, and it increased the risk of AMI by 2.990 times. Conclusion RORA expression levels in patients with AMI is significantly higher than that in patients with stable coronary artery disease. High expression of RORA is related to AMI and it may be an independent risk factor for AMI.

scholarly journals Divergent Importance of Chronobiological Considerations in High- and Low-dose Melatonin Therapies

Diseases ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 18
Author(s):  
Rüdiger Hardeland
Keyword(s):  
Phase Response Curve ◽  
Sleep Onset ◽  
Melatonin Receptors ◽  
Duration Of Action ◽  
Circadian Oscillators ◽  
Protective Actions ◽  
Circadian Control ◽  
Dim Light ◽  
Poor Individual ◽  
Specific Phase

Melatonin has been used preclinically and clinically for different purposes. Some applications are related to readjustment of circadian oscillators, others use doses that exceed the saturation of melatonin receptors MT1 and MT2 and are unsuitable for chronobiological purposes. Conditions are outlined for appropriately applying melatonin as a chronobiotic or for protective actions at elevated levels. Circadian readjustments require doses in the lower mg range, according to receptor affinities. However, this needs consideration of the phase response curve, which contains a silent zone, a delay part, a transition point and an advance part. Notably, the dim light melatonin onset (DLMO) is found in the silent zone. In this specific phase, melatonin can induce sleep onset, but does not shift the circadian master clock. Although sleep onset is also under circadian control, sleep and circadian susceptibility are dissociated at this point. Other limits of soporific effects concern dose, duration of action and poor individual responses. The use of high melatonin doses, up to several hundred mg, for purposes of antioxidative and anti-inflammatory protection, especially in sepsis and viral diseases, have to be seen in the context of melatonin’s tissue levels, its formation in mitochondria, and detoxification of free radicals.

scholarly journals Hepatocyte nuclear factor-6 stimulates transcription of the alpha-fetoprotein gene and synergizes with the retinoic-acid-receptor-related orphan receptor alpha-4

2003 ◽  
Vol 369 (3) ◽  
pp. 583-591 ◽  
Author(s):  
Habib NACER-CHERIF ◽  
Brigitte BOIS-JOYEUX ◽  
Guy G. ROUSSEAU ◽  
Frédéric P. LEMAIGRE ◽  
Jean-Louis DANAN
Keyword(s):  
Retinoic Acid ◽  
Retinoic Acid Receptor ◽  
Orphan Receptor ◽  
Nuclear Factor ◽  
Hepatocyte Nuclear Factor ◽  
Acid Receptor ◽  
Splicing Isoforms ◽  
Liver Gene ◽  
A Site ◽  
Putative Binding Site

The rat α-fetoprotein (afp) gene is controlled by three enhancers whose function depends on their interaction with liver-enriched transcription factors. The afp enhancer III, located at −6kb, is composed of three regions that act in synergy. Two of these regions, called s1 and s2, contain a putative binding site for hepatocyte nuclear factor-6 (HNF-6). This factor is the prototype of the ONECUT family of cut-homoeodomain proteins and is a known regulator of liver gene expression in adults and during development. We show here that the two splicing isoforms of HNF-6 bind to a site in the s1 region and in the s2 region. The core sequence of the s1 site corresponds to none of the known HNF-6 binding sites. Nevertheless, the binding properties of the s1 site are identical with those of the s2 site and of previously characterized HNF-6 binding sequences. The HNF-6 consensus should therefore be rewritten as DRRTCVATND. Binding of HNF-6 to the s1 and s2 sites requires both the cut and the homoeo domains, is co-operative and induces DNA bending. HNF-6 strongly stimulates the activity of the afp enhancer III in transient transfection experiments. This effect requires the stereo-specific alignment of the two HNF-6 sites. Moreover, HNF-6 stimulates the enhancer in synergy with the retinoic-acid-receptor-related orphan receptor α (RORα), which binds to a neighbouring site in the s1 region. Thus expression of the afp gene requires functional interactions between HNF-6 molecules and between HNF-6 and RORα.

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