After decades of research, the sigma-1 receptor (Sig-1R)'s structure, and molecular functions are being unveiled. Sig-1R is an integral endoplasmic reticulum (ER) membrane protein which forms an ...oligomer and binds a variety of psychotropic drugs. It forms a complex with the ER chaperone BiP that controls specific signaling molecules' stability and function at the ER to regulate Ca
signaling, bioenergetics, and ER stress. Sig-1R is highly enriched in ER subdomains that are physically linked to outer mitochondrial membranes, reflecting its role in regulating ER-mitochondria communications. Thus, Sig-1R ligands are expected to serve as novel neuroprotective agents which treat certain psychiatric and neurodegenerative disorders. In this short review, the cell biological aspects of Sig-1R are discussed, with a particular focus on its role in fundamental ER functions.
Sigma-1 receptor ligands have been long expected to serve as drugs for treatment of human diseases such as neurodegenerative disorders, depression, idiopathic pain, drug abuse, and cancer. Recent ...research exploring the molecular function of the sigma-1 receptor started unveiling underlying mechanisms of the therapeutic activity of those ligands. Via the molecular chaperone activity, the sigma-1 receptor regulates protein folding/degradation, ER/oxidative stress, and cell survival. The chaperone activity is activated or inhibited by synthetic sigma-1 receptor ligands in an agonist-antagonist manner. Sigma-1 receptors are localized at the endoplasmic reticulum (ER) membranes that are physically associated with the mitochondria (MAM: mitochondria-associated ER membrane). In specific types of neurons (e.g., those at the spinal cord), sigma-1 receptors are also clustered at ER membranes that juxtapose postsynaptic plasma membranes. Recent studies indicate that sigma-1 receptors, partly in sake of its unique subcellular localization, regulate the mitochondria function that involves bioenergetics and free radical generation. The sigma-1 receptor may thus provide an intracellular drug target that enables controlling ER stress and free radical generation under pathological conditions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Psychiatrists empirically recognize that excessive or chronic psychological stress can result in long‐lasting impairments of brain functions that partly involve neuronal cell damage. Recent studies ...begin to elucidate the molecular pathways activated/inhibited by psychological stress. Activation of the hypothalamic–pituitary–adrenal axis under psychological stress causes inflammatory oxidative stresses in the brain, in part due to elevation of cytokines. Psychological stress or neuropathological conditions (e.g., accumulation of β‐amyloids) trigger ‘cellular stress responses’, which promote upregulation of molecular chaperones to protect macromolecules from degradation. The unfolded protein response, the endoplasmic reticulum (ER)‐specific cellular stress response, has been recently implicated in the pathophysiology of neuropsychiatric disorders and the pharmacology of certain clinically used drugs. The sigma‐1 receptor is an ER protein whose ligands are shown to exert antidepressant‐like and neuroprotective actions. Recent studies found that the sigma‐1 receptor is a novel ligand‐operated ER chaperone that regulates bioenergetics, free radical generation, oxidative stress, unfolded protein response and cytokine signaling. The sigma‐1 receptor also regulates morphogenesis of neuronal cells, such as neurite outgrowth, synaptogenesis, and myelination, which can be perturbed by cellular stress. The sigma‐1 receptor may thus contribute to a cellular defense system that protects nervous systems against chronic psychological stress. Findings from sigma receptor research imply that not only cell surface monoamine effectors but also intracellular molecules, especially those at the ER, may provide novel therapeutic targets for future drug developments.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
The membrane of the endoplasmic reticulum (ER) of a cell forms contacts directly with mitochondria whereby the contact is referred to as the mitochondrion-associated ER membrane or the MAM. Here we ...found that the MAM regulates cellular survival via an MAM-residing ER chaperone the sigma-1 receptor (Sig-1R) in that the Sig-1R chaperones the ER stress sensor IRE1 to facilitate inter-organelle signaling for survival. IRE1 is found in this study to be enriched at the MAM in CHO cells. We found that IRE1 is stabilized at the MAM by Sig-1Rs when cells are under ER stress. Sig-1Rs stabilize IRE1 and thus allow for conformationally correct IRE1 to dimerize into the long-lasting, activated endonuclease. The IRE1 at the MAM also responds to reactive oxygen species derived from mitochondria. Therefore, the ER-mitochondrion interface serves as an important subcellular entity in the regulation of cellular survival by enhancing the stress-responding signaling between mitochondria, ER, and nucleus.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Inter-organelle signaling plays important roles in many physiological functions. Endoplasmic reticulum (ER)–mitochondrion signaling affects intramitochondrial calcium (Ca2+ ) homeostasis and cellular ...bioenergetics. ER–nucleus signaling attenuates ER stress. ER–plasma membrane signaling regulates cytosolic Ca2+ homeostasis and ER–mitochondrion–plasma membrane signaling regulates hippocampal dendritic spine formation. Here, we propose that the sigma-1 receptor (Sig-1R), an ER chaperone protein, acts as an inter-organelle signaling modulator. Sig-1Rs normally reside at the ER–mitochondrion contact called the MAM ( m itochondrion- a ssociated ER m embrane), where Sig-1Rs regulate ER–mitochondrion signaling and ER–nucleus crosstalk. When cells are stimulated by ligands or undergo prolonged stress, Sig-1Rs translocate from the MAM to the ER reticular network and plasmalemma/plasma membrane to regulate a variety of functional proteins, including ion channels, receptors and kinases. Thus, the Sig-1R serves as an inter-organelle signaling modulator locally at the MAM and remotely at the plasmalemma/plasma membrane. Many pharmacological/physiological effects of Sig-1Rs might relate to this unique action of Sig-1Rs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The sigma-1 receptor (Sig-1R), an endoplasmic reticulum (ER) chaperone protein, is an interorganelle signaling modulator that potentially plays a role in drug-seeking behaviors. However, the brain ...site of action and underlying cellular mechanisms remain unidentified. We found that cocaine exposure triggers a Sig-1R-dependent upregulation of D-type K+ current in the nucleus accumbens (NAc) that results in neuronal hypoactivity and thereby enhances behavioral cocaine response. Combining ex vivo and in vitro studies, we demonstrated that this neuroadaptation is caused by a persistent protein-protein association between Sig-1Rs and Kv1.2 channels, a phenomenon that is associated to a redistribution of both proteins from intracellular compartments to the plasma membrane. In conclusion, the dynamic Sig-1R-Kv1.2 complex represents a mechanism that shapes neuronal and behavioral response to cocaine. Functional consequences of Sig-1R binding to K+ channels may have implications for other chronic diseases where maladaptive intrinsic plasticity and Sig-1Rs are engaged.
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► Sig-1R activity enhances sensitivity to cocaine by decreasing accumbal firing ► Cocaine decreases accumbal firing via Sig-1R-dependent increase of Kv1.2 current ► The Sig-1R forms a complex with Kv1.2 channel in the nucleus accumbens shell ► Cocaine triggers a long-lasting upregulation of the Sig-1R-Kv1.2 channel complex
Exposure to cocaine promotes a long-lasting interaction between the signaling modulator Sig-1R and a voltage-gated potassium channel, Kv1.2. The resulting change in potassium currents leads to neuronal hypoactivity that enhances the behavioral response to cocaine and may thus contribute to the addictive process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Introduction:
Current drugs for the treatment of psychiatric or neurodegenerative disorders have limitations. Psychotherapeutic drugs such as typical and atypical antipsychotics, tricyclic ...antidepressants and selective monoamine reuptake inhibitors, aim to normalize the hyper- or hypo-neurotransmission of monoaminergic systems. Despite their contribution to the outcomes of psychiatric patients, these agents often exert severe side effects and require chronic treatments to promote amelioration of symptoms. Drugs available for the treatment of neurodegenerative disorders are severely limited.
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Recent evidence that has shed light on sigma-1 receptor ligands, which may serve as a new class of antidepressants or neuroprotective agents. Sigma-1 receptors are novel ligand-operated molecular chaperones regulating signal transduction, ER stress, cellular redox, cellular survival and synaptogenesis. Selective sigma-1 receptor ligands exert rapid antidepressant-like, anxiolytic, antinociceptive and robust neuroprotective actions in preclinical studies. Recent studies that suggest that reactive oxygen species might play a role as signal integrators downstream of Sig-1Rs are also covered.
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The advances in sigma receptor research in the last decade have begun to elucidate the intracellular signal cascades upstream and downstream of sigma-1 receptors. The novel ligand-operated properties of the sigma-1 receptor chaperone may enable interventions by which stress-related cellular systems can be pharmacologically controlled.
Melanin is a secondary metabolite required for the infection of the rice blast fungus Pyricularia oryzae. Melanin biosynthesis enzymes are targets for controlling rice blast disease, and three types ...of commercial melanin biosynthesis inhibitors (MBIs) including MBI-R, MBI-D, and MBI-P have been developed. However, the occurrence of MBI-D-resistant strains containing scytalone dehydratase (SDH1/RSY1) with V75M mutations has been recently reported. In this study, we aimed to identify inhibitors of SDH1-V75M. We screened the RIKEN Natural Products Depository chemical library using chemical array technology and evaluated the inhibition of SDH1-V75M by candidate compounds. NPD13731 strongly inhibited the activity of wild-type and mutant SDH1. The structure–activity relationship data were used to create a more potent inhibitor 16, which controlled rice blast disease in rice plants infected with MBI-D-resistant P. oryzae. Compound 16, which we named melabiostin, may be used to develop fungicides for controlling rice blast infections.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
Actinomycetes bacteria produce diverse bioactive molecules that are useful as drug seeds. To improve their yield, researchers often optimize the fermentation medium. However, exactly how the ...extracellular chemicals present in the medium activate secondary metabolite gene clusters remains unresolved. BR-1, a β-carboline compound, was recently identified as a chemical signal that enhanced reveromycin A production in Streptomyces sp. SN-593. Here we show that BR-1 specifically bound to the transcriptional regulator protein RevU in the reveromycin A biosynthetic gene cluster, and enhanced RevU binding to its promoter. RevU belongs to the LuxR family regulator that is widely found in bacteria. Interestingly, BR-1 and its derivatives also enhanced the production of secondary metabolites in other Streptomyces species. Although LuxR-N-acyl homoserine lactone systems have been characterized in Gram-negative bacteria, we revealed LuxR-β-carboline system in Streptomyces sp. SN-593 for the production of secondary metabolites. This study might aid in understanding hidden chemical communication by β-carbolines.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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