Mechanisms of regulation and function of G-protein-coupled receptor kinases

Base Dependent Rearrangement of Dithiane and Dithiolane under Visible-light Photoredox catalysis

The rearrangement of dithiolanes and dithianes to access disulfide-linked-dithioesters under visible-light photoredox catalysis via controlled C-S bond cleavage has been disclosed. Unlike, the usual deprotection of dithioacetals to corresponding aldehydes under the oxidative conditions, we observed unique regioselective oxidative reactivity of five and six membered cyclic dithioacetals to form disulfide-linked-dithioesters by exchanging DMAP and imidazole bases. The generality of the protocol has been demonstrated by exploring a wide range of substrates. As an application, in situ generated thiyl radical has been trapped with disulfides to prepare hetero-disulfides of potential utility. The protocol proved to be practical on gram scale quantity and relied on clean energy source for the transformation. Based on the series of control experiments, cyclic voltammetry and Stern-Volmer studies the plausible mechanism has been proposed.

Direct Access to Thiocyano-Thioesters from Cyclic Thioacetals via Photoredox Catalysis: An Introduction of Two Functional Groups in One Pot

The cyanation of organic compounds is an important synthetic transformation and mainly relies on a toxic CN source. Undeniably, thiocyanate salt has emerged as a very mild and environmentally benign CN source, yet its synthetic utility for cyanation is highly limited to very few types of organic compounds. Herein, we report the direct cyanation of cyclic thioacetals for accessing compounds with two different functional groups (thiocyano-thioesters) in one pot using sodium thiocyanate via photoredox catalysis. The protocol has been further extended for the direct cyanation of disulfides and diselenide to access aryl thiocyanates and aryl selenocyanate. A plausible mechanism has been proposed based on a series of control experiments, cyclic voltammetry and Stern-Volmer studies.

Prolonged Morphine Treatment Alters Expression and Plasma Membrane Distribution of β-Adrenergic Receptors and Some Other Components of Their Signaling System in Rat Cerebral Cortex

β-Adrenergic signaling plays an important role in regulating diverse brain functions and alterations in this signaling have been observed in different neuropathological conditions. In this study, we investigated the effect of a 10-day treatment with high doses of morphine (10 mg/kg per day) on major components and functional state of the β-adrenergic receptor (β-AR) signaling system in the rat cerebral cortex. β-ARs were characterized by radioligand binding assays and amounts of various G protein subunits, adenylyl cyclase (AC) isoforms, G protein-coupled receptor kinases (GRKs), and β-arrestin were examined by Western blot analysis. AC activity was determined as a measure of functionality of the signaling system. We also assessed the partitioning of selected signaling proteins between the lipid raft and non-raft fractions prepared from cerebrocortical plasma membranes. Morphine treatment resulted in a significant upregulation of β-ARs, GRK3, and some AC isoforms (AC-I, -II, and -III). There was no change in quantity of G proteins and some other signaling molecules (AC-IV, AC-V/VI, GRK2, GRK5, GRK6, and β-arrestin) compared with controls. Interestingly, morphine exposure caused a partial redistribution of β-ARs, G_sα, G_oα, and GRK2 between lipid rafts and bulk plasma membranes. Spatial localization of other signaling molecules within the plasma membrane was not changed. Basal as well as fluoride- and forskolin-stimulated AC activities were not significantly different in membrane preparations from control and morphine-treated animals. However, AC activity stimulated by the beta-AR agonist isoprenaline was markedly increased. This is the first study to demonstrate lipid raft association of key components of the cortical β-AR system and its sensitivity to morphine.

Structural domains required for Caenorhabditis elegans G protein-coupled receptor kinase 2 (GRK-2) function in vivo

G protein-coupled receptor kinases (GRKs) are key regulators of signal transduction that specifically phosphorylate activated G protein-coupled receptors (GPCRs) to terminate signaling. Biochemical and crystallographic studies have provided great insight into mammalian GRK2/3 interactions and structure. However, despite extensive in vitro characterization, little is known about the in vivo contribution of these described GRK structural domains and interactions to proper GRK function in signal regulation. We took advantage of the disrupted chemosensory behavior characteristic of Caenorhabditis elegans grk-2 mutants to discern the interactions required for proper in vivo Ce-GRK-2 function. Informed by mammalian crystallographic and biochemical data, we introduced amino acid substitutions into the Ce-grk-2 coding sequence that are predicted to selectively disrupt GPCR phosphorylation, Gα(q/11) binding, Gβγ binding, or phospholipid binding. Changing the most amino-terminal residues, which have been shown in mammalian systems to be required specifically for GPCR phosphorylation but not phosphorylation of alternative substrates or recruitment to activated GPCRs, eliminated the ability of Ce-GRK-2 to restore chemosensory signaling. Disrupting interaction between the predicted Ce-GRK-2 amino-terminal α-helix and kinase domain, posited to stabilize GRKs in their active ATP- and GPCR-bound conformation, also eliminated Ce-GRK-2 chemosensory function. Finally, although changing residues within the RH domain, predicted to disrupt interaction with Gα(q/11), did not affect Ce-GRK-2 chemosensory function, disruption of the predicted PH domain-mediated interactions with Gβγ and phospholipids revealed that both contribute to Ce-GRK-2 function in vivo. Combined, we have demonstrated functional roles for broadly conserved GRK2/3 structural domains in the in vivo regulation of organismal behavior.

Na⁺,K⁺-ATPase as the Target Enzyme for Organic and Inorganic Compounds

This paper gives an overview of the literature data concerning specific and non specific inhibitors of Na⁺,K⁺-ATPase receptor. The immobilization approaches developed to improve the rather low time and temperature stability of Na⁺,K⁺-ATPase, as well to preserve the enzyme properties were overviewed. The functional immobilization of Na⁺,K⁺-ATPase receptor as the target, with preservation of the full functional protein activity and access of various substances to an optimum number of binding sites under controlled conditions in the combination with high sensitive technology for the detection of enzyme activity is the basis for application of this enzyme in medical, pharmaceutical and environmental research.

Involvement of kappa opioid receptors in the inhibition of receptor desensitization and PKC activation induced by repeated morphine treatment

Analgesic tolerance to morphine can develop from long-term use of this drug for the treatment of pain. Many reports have shown that stimulation of the kappa opioid receptor (KOR) suppresses development of analgesic tolerance to morphine. Here, we studied the KOR-mediated inhibition of morphine tolerance during repeated morphine treatment, with a focus on desensitization of the receptor. The development of analgesic tolerance to morphine during repeated morphine administration (10 mg kg(-1) s.c.) was completely suppressed by U-50488H (2 mg kg(-1) i.p.), a KOR agonist. The decrease in [35S] GTPgammaS binding activity stimulated by the mu opioid receptor (MOR) agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO) was also significantly inhibited by U-50488H. These results indicate that stimulation of KOR caused by repeated morphine treatment either inhibits MOR desensitization or accelerates recycling of MOR on the cell surface, thereby suppressing morphine tolerance. Furthermore, we found that activity of protein kinase C (PKC) was significantly decreased in mice treated with both U-50488H and morphine. These results suggest that the mechanisms underlying KOR-mediated inhibition of analgesic tolerance to morphine may be partly due to suppression of PKC activation and prevention of receptor desensitization.

Epinephrine increases DNA synthesis via ERK1/2s through cAMP, Ca(2+)/PKC, and PI3K/Akt signaling pathways in mouse embryonic stem cells

Epinephrine is a catecholamine that plays important roles in regulating a wide variety of physiological systems by acting through the adrenergic receptors (ARs). The cellular responses to AR stimulation are mediated through various signaling pathways. Therefore, this study examined the effects of epinephrine on DNA synthesis and related signaling molecules in mouse embryonic stem cells (ESCs). Epinephrine increased DNA synthesis in a dose- and time-dependent manner, as determined by the level of [(3)H]-thymidine incorporation. AR subtypes (alpha1(A), alpha2(A), beta1, beta2, and beta3) were expressed in mouse ESCs and their expression levels were increased by epinephrine. In this experiment, epinephrine increased cAMP levels, intracellular Ca(2+) concentration ([Ca(2+)](i)), and translocation of protein kinase C (PKC) from the cytosol to the membrane compartment. In addition, we observed Akt phosphorylation in response to epinephrine; this was stimulated by phosphorylation of the epidermal growth factor receptor (EGFR). Epinephrine also induced phosphorylation of ERK1/2 (p44/42 MAPKs), while inhibition of PKC or Akt blocked this phosphorylation. Epinephrine increased the mRNA levels of proto-oncogenes (c-fos, c-jun, c-myc), while inhibition of ERK1/2 decreased these mRNA levels. In experiments aimed at examining the involvement of cell cycle regulatory proteins, epinephrine increased the levels of cyclin E/cyclin-dependent kinase 2 (CDK2) and cyclin D1/cyclin-dependent kinase 4 (CDK4). In conclusion, epinephrine stimulates DNA synthesis via ERK1/2 through cAMP, Ca(2+)/PKC, and PI3K/Akt signaling pathways in mouse ESCs.