Isoform-specific enhancement of adenylyl cyclase activity by n-alkanols

Bi-directional modulation of hyperpolarization-activated cation currents (Ih) by ethanol in rat hippocampal CA3 pyramidal neurons

It is widely acknowledged that ethanol (EtOH) can alter many neuronal functions, including synaptic signaling, firing discharge, and membrane excitability, through its interaction with multiple membrane proteins and intracellular pathways. Previous work has demonstrated that EtOH enhances the firing rate of hippocampal GABAergic interneurons and thus the presynaptic GABA release at CA1 and CA3 inhibitory synapses through a positive modulation of the hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels. Activation of HCN channels produce an inward current, commonly called I_h, which plays an essential role in generating/regulating specific neuronal activities in GABAergic interneurons and principal glutamatergic pyramidal neurons such as those in the CA3 subregion. Since the direct effect of EtOH on HCN channels expressed in CA3 pyramidal neurons was not thoroughly elucidated, we investigated the possible interaction between EtOH and HCN channels and the impact on excitability and postsynaptic integration of these neurons. Patch-clamp recordings were performed in single CA3 pyramidal neurons from acute male rat coronal hippocampal slices. Our results show that EtOH modulates HCN-mediated I_h in a concentration-dependent and bi-directional manner, with a positive modulation at lower (20 mM) and an inhibitory action at higher (60-80 mM) concentrations. The modulation of I_h by EtOH was mimicked by forskolin, antagonized by different drugs that selectively interfere with the AC/cAMP/PKA intracellular pathway, as well as by the selective HCN inhibitor ZD7288. Altogether, these data further support the evidence that HCN channels may represent an important molecular target through which EtOH may regulate neuronal activity.

Role of Adenylyl Cyclase Type 7 in Functions of BV-2 Microglia

To assess the role of adenylyl cyclase type 7 (AC7) in microglia's immune function, we generated AC7 gene knockout (AC7 KO) clones from a mouse microglial cell line, BV-2, using the CRISPR-Cas9 gene editing system. The ability of BV-2 cells to generate cAMP and their innate immune functions were examined in the presence or absence of ethanol. The parental BV-2 cells showed robust cAMP production when stimulated with prostaglandin-E₁ (PGE₁) and ethanol increased cAMP production in a dose-dependent manner. AC7 KO clones of BV-2 cells showed diminished and ethanol-insensitive cAMP production. The phagocytic activity of the parental BV-2 cells was inhibited in the presence of PGE₁; AC7 KO BV-2 cells showed lower and PGE₁-insensitive phagocytic activity. Innate immune activities of the parental BV-2 cells, including bacterial killing, nitric oxide synthesis, and expression of arginase 1 and interleukin 10 were activated as expected with small effects of ethanol. However, the innate immune activities of AC7 KO cells were either drastically diminished or not detected. The data presented suggest that AC7 has an important role in the innate immune functions of microglial cells. AC7's involvement in ethanol's effects on immune functions remains unclear. Further studies are needed.

The effect of alcohol on recombinant proteins derived from mammalian adenylyl cyclase

The cyclic AMP (cAMP) signaling pathway is implicated in the development of alcohol use disorder. Previous studies have demonstrated that ethanol enhances the activity of adenylyl cyclase (AC) in an isoform specific manner; AC7 is most enhanced by ethanol, and regions responsible for enhancement by ethanol are located in the cytoplasmic domains of the AC7 protein. We hypothesize that ethanol modulates AC activity by directly interacting with the protein and that ethanol effects on AC can be studied using recombinant AC in vitro. AC recombinant proteins containing only the C_1a or C₂ domains of AC7 and AC9 individually were expressed in bacteria, and purified. The purified recombinant AC proteins retained enzymatic activity and isoform specific alcohol responsiveness. The combination of the C_1a or C₂ domains of AC7 maintained the same alcohol cutoff point as full-length AC7. We also find that the recombinant AC7 responds to alcohol differently in the presence of different combinations of activators including MnCl₂, forskolin, and Gsα. Through a series of concentration-response experiments and curve fitting, the values for maximum activities, Hill coefficients, and EC₅₀ were determined in the absence and presence of butanol as a surrogate of ethanol. The results suggest that alcohol modulates AC activity by directly interacting with the AC protein and that the alcohol interaction with the AC protein occurs at multiple sites with positive cooperativity. This study indicates that the recombinant AC proteins expressed in bacteria can provide a useful model system to investigate the mechanism of alcohol action on their activity.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

Adenylyl cyclases (ACs) generate the second messenger cAMP from ATP. Mammalian cells express nine transmembrane AC (mAC) isoforms (AC1-9) and a soluble AC (sAC, also referred to as AC10). This review will largely focus on mACs. mACs are activated by the G-protein Gαs and regulated by multiple mechanisms. mACs are differentially expressed in tissues and regulate numerous and diverse cell functions. mACs localize in distinct membrane compartments and form signaling complexes. sAC is activated by bicarbonate with physiologic roles first described in testis. Crystal structures of the catalytic core of a hybrid mAC and sAC are available. These structures provide detailed insights into the catalytic mechanism and constitute the basis for the development of isoform-selective activators and inhibitors. Although potent competitive and noncompetitive mAC inhibitors are available, it is challenging to obtain compounds with high isoform selectivity due to the conservation of the catalytic core. Accordingly, caution must be exerted with the interpretation of intact-cell studies. The development of isoform-selective activators, the plant diterpene forskolin being the starting compound, has been equally challenging. There is no known endogenous ligand for the forskolin binding site. Recently, development of selective sAC inhibitors was reported. An emerging field is the association of AC gene polymorphisms with human diseases. For example, mutations in the AC5 gene (ADCY5) cause hyperkinetic extrapyramidal motor disorders. Overall, in contrast to the guanylyl cyclase field, our understanding of the (patho)physiology of AC isoforms and the development of clinically useful drugs targeting ACs is still in its infancy.

Real-time monitoring of intracellular cAMP during acute ethanol exposure

BACKGROUND

In previous studies, we have shown that ethanol (EtOH) enhances the activity of stimulatory G protein (Gs)-stimulated membrane-bound adenylyl cyclase (AC). The effect is AC isoform specific, and the type 7 AC (AC7) is most responsive to EtOH. In this study, we employed a fluorescence resonance energy transfer (FRET)-based cyclic AMP (cAMP) sensor, Epac1-camps, to examine real-time temporal dynamics of EtOH effects on cAMP concentrations. To our knowledge, this is the first report on real-time detection of the EtOH effect on intracellular cAMP.

METHODS

Hela cells were transfected with Epac1-camps, dopamine (DA) receptor D1a , and 1 isoform of AC (AC7 or AC3). Fluorescent images were captured using a specific filter set for cyan fluorescent protein (CFP), yellow fluorescent protein (YFP), and FRET, respectively, and FRET intensity was calculated on a pixel-by-pixel basis to examine changes in cAMP.

RESULTS

During 2-minute stimulation with DA, the cytoplasmic cAMP level quickly increased and then decreased to a plateau, where the cAMP level was higher than the level prior to stimulation with DA. EtOH concentration dependently increased cytoplasmic cAMP in cells transfected with AC7, while EtOH did not have effect on cells transfected with AC3. Similar trends were observed for cAMP at the plasma membrane and in the nucleus during 2-minute stimulation with DA. Unexpectedly, when cells expressing AC7 were stimulated with DA or other Gs-coupled receptor's ligand plus EtOH for 5 seconds, EtOH reduced cAMP concentration.

CONCLUSIONS

These results suggest that EtOH has 2 opposing effects on the cAMP-generating system in an AC isoform-specific manner, the enhancing effect on AC activity and the short-lived inhibitory effect. Thus, EtOH may have a different effect on cAMP depending on not only AC isoform but also the duration of exposure.

Commentary: How ethanol short-circuits the cerebellum-actions on Golgi cells in freely-moving animals

This commentary discusses the important contributions of the article published in this journal by Huang and colleagues, titled, "Acute ethanol exposure increases firing and induces oscillations in cerebellar Golgi cells of freely moving rats." In this manuscript, Huang and colleagues present a number of interesting and important findings. While it has been shown previously that ethanol (EtOH) causes an increase in the firing of cerebellar Golgi cells in brain slice preparations and anesthetized animals, here the authors provide the first evidence that this action of EtOH occurs in vivo in freely moving, unanesthetized animals. These results also enhance our understanding of cerebellar functioning by describing the mechanism by which EtOH essentially de-afferentates (blocks specific inputs to) the cerebellum from the normal processing of sensory signals due to EtOH-induced Golgi neuron excitation, resulting in inhibition of granule cells. Furthermore, the authors characterize the novel observation of EtOH-induced neuronal oscillations, which was not previously observed in other preparations.

Magnaporthe oryzae cell wall hydrolysate induces ROS and fungistatic VOCs in rice cell cultures

Plants react to microbial attack with a number of defense mechanisms, including the synthesis of volatile organic compounds (VOCs) and the production of reactive oxygen species (ROS). These responses are triggered by elicitors derived from either the cell surface of pathogens or the incomplete hydrolysis of the plant cell wall. Here we show the response of rice (Oryza sativa L., cv Gigante Vercelli) cell cultures following treatment with cell wall hydrolysates prepared from the rice blast Magnaporthe oryzae. Elicitation prompted the production of several plant VOCs, which were analyzed by stir bar sorptive extraction from both the liquid and head-space phase (SBSE and HSSE, respectively) and gas chromatography coupled to mass spectrometry (GC-MS) analysis. VOCs included alkanes, alkenes and long-chain alcohols as well as cinnamyl alcohol, myristicin, a sesquiterpene alcohol (caryolan-1-ol), 1-butanamide and 2-pentylfuran. The major released compounds, 1-octanol and 1-decanol, were found to induce ROS production in both elicited and non-elicited rice cells and showed fungistatic activity against the pathogen M. oryzae. The possible role of induced VOCs and ROS production in the plant-pathogen interaction is discussed.

Effects of alcohols on recombinant adenylyl cyclase type 7 expressed in bacteria

BACKGROUND

Our previous studies showed that ethanol enhanced the activity of adenylyl cyclase (AC) in an isoform-specific manner and that alcohol cutoff point of AC was isoform specific. Recently, we showed that 2,3-butanediol inhibited AC type 7 (AC7) activity in a stereoisomer-specific manner and that this inhibition was also AC isoform specific. These observations strongly suggest that a major target of alcohol action on cAMP signaling is AC. We hypothesized that alcohols exhibit their effect on AC activity by direct interaction with AC proteins. However, experimental systems employed in past studies such as intact cells and membrane preparations are too complex and do not allow us to unequivocally test this hypothesis. In attempt to bypass, these complications of the membrane-bound AC, we decided to study the effect of alcohols on AC recombinant proteins expressed in bacteria.

METHODS

A recombinant AC, designated as AC7sol, consisting of the C(1a) and C(2) domains of the human AC7 was designed and expressed in bacteria. The activity of AC7sol was examined using lysate prepared from bacteria expressing AC7sol.

RESULTS

The activity of AC7sol was stimulated by manganese or by the α subunit of G protein that stimulates AC (G(sα) ). Forskolin by itself did not stimulate the activity of AC7sol. However, in the presence of activated G(sα) , forskolin stimulated the activity of AC7sol. A series of n-alkanols including ethanol enhanced the manganese-stimulated activity of AC7sol. The alcohol cutoff point of AC7sol was pentanol. Ethanol and butanol increased V(max) and K(M) values of AC7sol.

CONCLUSIONS

These results are consistent with our hypothesis and suggest that the enhancing effect of alcohols on AC activity is because of the increase in turnover number of AC. The current study demonstrates for the first time that the effect of alcohols requires only the C(1a) and C(2) domains of AC and no other domains of AC as well as no other mammalian proteins.

Effects of straight chain alcohols on specific isoforms of adenylyl cyclase

BACKGROUND

Our previous studies showed that the activity of adenylyl cyclase (AC) was enhanced by pharmacologically relevant concentrations of ethanol, that this enhancing effect of ethanol on AC activity was AC isoform specific, and that the alcohol cutoff effect for n-alkanol potentiation of AC activity was also AC isoform specific. Therefore, we hypothesized that within the cyclic AMP-generating system, AC is the target of ethanol's action and that alcohols interact directly with the AC molecules. To characterize the interaction between alcohols and AC proteins, the effects of a series of straight chain alcohols would be very valuable in understanding alcohol action at the molecular level. To our knowledge, straight chain alcohols other than n-alkanols and 1,Omega-diols have not been used extensively to study alcohol effects on the activity of AC or other proteins important in the alcohol research field.

METHODS

The effects of a series of straight chain alcohols on D1A dopamine receptor-stimulated activity of AC isoforms type 6, 7, and 9 (AC6, AC7, and AC9) were examined in transfected Hela cells by a cAMP accumulation assay.

RESULTS

In general, all 3 AC isoforms responded to a series of straight chain alcohols in a similar manner. The order of responsiveness is as follows: monoalcohol > diol > triol and tetraol. Within monoalcohols, 1-alcohols had larger effects than 2-alcohols. Two of 3 stereoisomers of 2,3-butanediol, [D-(-)-2,3-butanediol and meso-2,3-butanediol] showed similar enhancing effects on all 3 AC isoforms. However, the third stereoisomer, L-(+)-2,3-butanediol, inhibited AC7 activity, while it stimulated AC6 and AC9.

CONCLUSION

The number and the position of hydroxyl groups in straight chain alcohols play an important role in the magnitude of the enhancement on AC activity. Regardless of AC isoforms, the most effective of the straight chain alcohols seems to be the 1-alcohol (n-alkanol) for a given chain length. We found that one of the stereoisomers of 2,3-butanediol had opposite effects on AC activity depending on the AC isoform. Overall, the results are consistent with the hypotheses and demonstrate that a series of straight chain alcohols can be a valuable tool to study AC-alcohol interactions.

Prevention of pancreatic cancer by the beta-blocker propranolol

Pancreatic ductal adenocarcinoma (PDAC) is among the leading causes of cancer deaths and is unresponsive to existing therapy. Smoking and alcohol-induced pancreatitis are among the risk factors for PDAC. We have previously reported that beta-adrenergic receptors (beta-ARs) stimulate the proliferation and migration of human PDAC cells in vitro by cAMP-dependent signaling and that the nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) activates this pathway directly in vitro while additionally stimulating the release of noradrenaline/adrenaline by binding to alpha7 nicotinic acetylcholine receptors (alpha7 nAChR) in hamsters. In this study, we have tested the hypothesis that the beta-AR antagonist propranolol prevents the development of PDAC induced in hamsters with ethanol-induced pancreatitis by NNK. We found that propranolol had strong cancer preventive effects in this animal model. Western blots of pancreatic duct cells and PDAC cells harvested by laser capture microscopy showed significant upregulation of the alpha7 nAChR associated with significant inductions of p-CREB, p-ERK1/2, and increases in epidermal growth factor and vascular endothelial growth factor in PDAC cells of hamsters not treated with propranolol. These effects were reversed by treatment with propranolol. Our data suggest that propranolol may prevent the development of PDAC by blocking cAMP-dependent intracellular signaling, cAMP-dependent release of epidermal growth factor, and PKA-dependent release of vascular endothelial growth factor while additionally downregulating the alpha7 nAChR by inhibiting cAMP-mediated subunit assembly. We conclude that increased cAMP signaling is an important factor that drives the development and progression of PDAC and that the inhibition of cAMP formation is a promising new target for the prevention and adjuvant therapy of PDAC.

The role of multiple hydrogen-bonding groups in specific alcohol binding sites in proteins: insights from structural studies of LUSH

It is now generally accepted that many of the physiological effects of alcohol consumption are a direct result of binding to specific sites in neuronal proteins such as ion channels or other components of neuronal signaling cascades. Binding to these targets generally occurs in water-filled pockets and leads to alterations in protein structure and dynamics. However, the precise interactions required to confer alcohol sensitivity to a particular protein remain undefined. Using information from the previously solved crystal structures of the Drosophila melanogaster protein LUSH in complexes with short-chain alcohols, we have designed and tested the effects of specific amino acid substitutions on alcohol binding. The effects of these substitutions, specifically S52A, T57S, and T57A, were examined using a combination of molecular dynamics, X-ray crystallography, fluorescence spectroscopy, and thermal unfolding. These studies reveal that the binding of ethanol is highly sensitive to small changes in the composition of the alcohol binding site. We find that T57 is the most critical residue for binding alcohols; the T57A substitution completely abolishes binding, while the T57S substitution differentially affects ethanol binding compared to longer-chain alcohols. The additional requirement for a potential hydrogen-bond acceptor at position 52 suggests that both the presence of multiple hydrogen-bonding groups and the identity of the hydrogen-bonding residues are critical for defining an ethanol binding site. These results provide new insights into the detailed chemistry of alcohol's interactions with proteins.