Perception of Mattering and Suicide Ideation in the Australian Working Population: Evidence from a Cross-Sectional Survey

Thoughts about suicide are a risk factor for suicide deaths and attempts and are associated with a range of mental health outcomes. While there is considerable knowledge about risk factors for suicide ideation, there is little known about protective factors. The current study sought to understand the role of perceived mattering to others as a protective factor for suicide in a working sample of Australians using a cross-sectional research design. Logistic regression analysis indicated that people with a higher perception that they mattered had lower odds of suicide ideation than those with lower reported mattering, after controlling for psychological distress, demographic and relationship variables. These results indicate the importance of further research and intervention studies on mattering as a lever for reducing suicidality. Understanding more about protective factors for suicide ideation is important as this may prevent future adverse mental health and behavioural outcomes.

Most low-level microsatellite instability in colorectal cancers can be explained without an elevated slippage rate

Many cancers show a low level of microsatellite slippage and are labelled MSI-L (microsatellite instability--low). However, it is unclear whether this slippage can be attributed to some underlying genetic change that results in a mutator phenotype, analogous to mismatch repair deficiency in MSI-H cancers, or whether the apparent instability is the result of relatively frequent normal somatic slippage. Here, we have used a mathematical model of microsatellite slippage during cancer growth to estimate the degree of microsatellite slippage expected in a cancer due to normal somatic slippage. We compared the model to the slippage observed in 42 non-MSI-H cancers that were macro-dissected into four distinct regions and genotyped at N = 9 microsatellite loci. When the slippage rate was set at mu = 10(-5) per locus per division, ten cancers showed a level of slippage in at least one region that was too severe to be expected from normal somatic slippage alone, suggesting that these cancers had acquired MSI-L. Only one of these ten cancers had putative MSI-L in all four regions. When we considered a slightly higher slippage rate of mu = 5 x 10(-5), none of the cancers showed a degree of slippage that could not be reasonably explained by normal somatic slippage. Counting the number of 'unstable' loci was a poor indicator of putative MSI-L status. We conclude that most low-level microsatellite instability in colorectal cancers can be explained without requiring an elevated slippage rate during neoplastic development, and hence there is little evidence for a discrete MSI-L group of cancers. Putative MSI-L status is indicated by the presence of at least one locus that has multiple alleles that differ by at least five motif repeats from the germline. If an underlying genetic change does cause MSI-L, it appears to be a relatively uncommon event that occurs late in oncogenesis.

Analysis of copy number changes suggests chromosomal instability in a minority of large colorectal adenomas

We have examined chromosomal-scale mutations in 34 large colorectal adenomas (CRAs). A small number of changes (median = 2, IQR = 0-4) were found by array-comparative genomic hybridization (aCGH) in most tumours. The most common changes were deletions of chromosomes 1p, 9q, 17, 19, and 22, and gains of chromosomes 13 and 21. SNP-LOH analysis and pseudo-digital SNP-PCR analysis detected occasional copy-neutral LOH. Some aCGH changes found frequently in colorectal carcinomas, such as deletions of chromosomes 4q and 18q, were very infrequent in the adenomas. Almost all copy number changes were of small magnitude, far below the predicted levels even for single copy gain/loss; investigation suggested that these changes were either artefactual or occurred in sub-clones within the tumours. In some cases, these sub-clones may have represented progression towards carcinoma, but comparison with aCGH data from carcinomas showed this to be unlikely in most cases. In two adenomas, there was evidence of a large, outlying number of copy number changes, mostly resulting from part-chromosome deletions. Overall, moreover, there was evidence of a tendency towards part-chromosome deletions-consistent with chromosomal instability (CIN)--in about one-sixth of all tumours. However, there was no evidence of CIN in the form of whole-chromosome copy number changes. Our data did not support previous contentions that CRAs tend to show chromosome breakage at fragile sites owing to CIN associated with an elevated DNA damage response. Chromosomal-scale mutations occur in some CRAs; although CIN is not the norm in these lesions, it probably affects a minority of cases.

The metal-ion-dependent adhesion site in the Von Willebrand factor-A domain of alpha2delta subunits is key to trafficking voltage-gated Ca2+ channels

All auxiliary alpha2delta subunits of voltage-gated Ca2+ (Ca(V)) channels contain an extracellular Von Willebrand factor-A (VWA) domain that, in alpha2delta-1 and -2, has a perfect metal-ion-dependent adhesion site (MIDAS). Modeling of the alpha2delta-2 VWA domain shows it to be highly likely to bind a divalent cation. Mutating the three key MIDAS residues responsible for divalent cation binding resulted in a MIDAS mutant alpha2delta-2 subunit that was still processed and trafficked normally when it was expressed alone. However, unlike WT alpha2delta-2, the MIDAS mutant alpha2delta-2 subunit did not enhance and, in some cases, further diminished Ca(V)1.2, -2.1, and -2.2 currents coexpressed with beta1b by using either Ba2+ or Na+ as a permeant ion. Furthermore, expression of the MIDAS mutant alpha2delta-2 reduced surface expression and strongly increased the perinuclear retention of Ca(V)alpha1 subunits at the earliest time at which expression was observed in both Cos-7 and NG108-15 cells. Despite the presence of endogenous alpha2delta subunits, heterologous expression of alpha2delta-2 in differentiated NG108-15 cells further enhanced the endogenous high-threshold Ca2+ currents, whereas this enhancement was prevented by the MIDAS mutations. Our results indicate that alpha2delta subunits normally interact with the Ca(V)alpha1 subunit early in their maturation, before the appearance of functional plasma membrane channels, and an intact MIDAS motif in the alpha2delta subunit is required to promote trafficking of the alpha1 subunit to the plasma membrane by an integrin-like switch. This finding provides evidence for a primary role of a VWA domain in intracellular trafficking of a multimeric complex, in contrast to the more usual roles in binding extracellular ligands in other exofacial VWA domains.

Dominant-negative synthesis suppression of voltage-gated calcium channel Cav2.2 induced by truncated constructs

Voltage-gated calcium channel alpha1 subunits consist of four domains (I-IV), each with six transmembrane segments. A number of truncated isoforms have been identified to occur as a result of alternative splicing or mutation. We have examined the functional consequences for expression of full-length Ca(v)2.2 (alpha1B) of its coexpression with truncated constructs of Ca(v)2.2. Domains I-II or domains III-IV, when expressed individually, together with the accessory subunits beta1b and alpha2delta-1, did not form functional channels. When they were coexpressed, low-density whole-cell currents and functional channels with properties similar to wild-type channels were observed. However, when domain I-II, domain III-IV, or domain I alone were coexpressed with full-length Ca(v)2.2, they markedly suppressed its functional expression, although at the single channel level, when channels were recorded, there were no differences in their biophysical properties. Furthermore, when it was coexpressed with either domain I-II or domain I, the fluorescence of green fluorescent protein (GFP)-Ca(v)2.2 and expression of Ca(v)2.2 protein was almost abolished. Suppression does not involve sequestration of the Ca(v)beta subunit, because loss of GFP-Ca(v)2.2 expression also occurred in the absence of beta subunit, and the effect of domain I-II or domain I could not be mimicked by the cytoplasmic I-II loop of Ca(v)2.2. It requires transmembrane segments, because the isolated Ca(v)2.2 N terminus did not have any effect. Our results indicate that the mechanism of suppression of Ca(v)2.2 by truncated constructs containing domain I involves inhibition of channel synthesis, which may represent a role of endogenously expressed truncated Ca(v) isoforms.

Evidence for two concentration-dependent processes for beta-subunit effects on alpha1B calcium channels

beta-Subunits of voltage-dependent Ca(2+) channels regulate both their expression and biophysical properties. We have injected a range of concentrations of beta3-cDNA into Xenopus oocytes, with a fixed concentration of alpha1B (Ca(V)2.2) cDNA, and have quantified the corresponding linear increase of beta3 protein. The concentration dependence of a number of beta3-dependent processes has been studied. First, the dependence of the a1B maximum conductance on beta3-protein occurs with a midpoint around the endogenous concentration of beta3 (approximately 17 nM). This may represent the interaction of the beta-subunit, responsible for trafficking, with the I-II linker of the nascent channel. Second, the effect of beta3-subunits on the voltage dependence of steady-state inactivation provides evidence for two channel populations, interpreted as representing alpha1B without or with a beta3-subunit, bound with a lower affinity of 120 nM. Third, the effect of beta3 on the facilitation rate of G-protein-modulated alpha1B currents during a depolarizing prepulse to +100 mV provides evidence for the same two populations, with the rapid facilitation rate being attributed to Gbetagamma dissociation from the beta-subunit-bound alpha1B channels. The data are discussed in terms of two hypotheses, either binding of two beta-subunits to the alpha1B channel or a state-dependent alteration in affinity of the channel for the beta-subunit.

Ducky mouse phenotype of epilepsy and ataxia is associated with mutations in the Cacna2d2 gene and decreased calcium channel current in cerebellar Purkinje cells

The mouse mutant ducky, a model for absence epilepsy, is characterized by spike-wave seizures and ataxia. The ducky gene was mapped previously to distal mouse chromosome 9. High-resolution genetic and physical mapping has resulted in the identification of the Cacna2d2 gene encoding the alpha2delta2 voltage-dependent calcium channel subunit. Mutations in Cacna2d2 were found to underlie the ducky phenotype in the original ducky (du) strain and in a newly identified strain (du(2J)). Both mutations are predicted to result in loss of the full-length alpha2delta2 protein. Functional analysis shows that the alpha2delta2 subunit increases the maximum conductance of the alpha1A/beta4 channel combination when coexpressed in vitro in Xenopus oocytes. The Ca(2+) channel current in acutely dissociated du/du cerebellar Purkinje cells was reduced, with no change in single-channel conductance. In contrast, no effect on Ca(2+) channel current was seen in cerebellar granule cells, results consistent with the high level of expression of the Cacna2d2 gene in Purkinje, but not granule, neurons. Our observations document the first mammalian alpha2delta mutation and complete the association of each of the major classes of voltage-dependent Ca(2+) channel subunits with a phenotype of ataxia and epilepsy in the mouse.

A generalized adaptive dynamics framework can describe the evolutionary Ultimatum Game

Adaptive dynamics describes the evolution of games where the strategies are continuous functions of some parameters. The standard adaptive dynamics framework assumes that the population is homogeneous at any one time. Differential equations point to the direction of the mutant that has maximum payoff against the resident population. The population then moves towards this mutant. The standard adaptive dynamics formulation cannot deal with games in which the payoff is not differentiable. Here we present a generalized framework which can. We assume that the population is not homogeneous but distributed around an average strategy. This approach can describe the long-term dynamics of the Ultimatum Game and also explain the evolution of fairness in a one-parameter Ultimatum Game.

RPR203494 a pyrimidine analogue of the p38 inhibitor RPR200765A with an improved in vitro potency

Following the discovery of RPR200765, a series of pyrimidine analogues have been prepared as backups. Amongst them, RPR203494 was identified with a better in vitro profile than RPR200765A.

A model of primitive streak initiation in the chick embryo

Initiation of the primitive streak in avian embryos provides a well-studied example of a pattern-forming event that displays a striking capacity for regulation. The mechanisms underlying the regulative properties are, however, poorly understood and are not easily accounted for by traditional models of pattern formation, such as reaction-diffusion models. In this paper, we propose a new activator-inhibitor model for streak initiation. We show that the model is consistent with experimental observations, both in its pattern-forming properties and in its ability to form these patterns on the correct time-scales for biologically realistic parameter values. A key component of the model is a travelling wave of inhibition. We present a mathematical analysis of the speed of such waves in both diffusive and juxtacrine relay systems. We use the streak initiation model to make testable predictions. By varying parameters of the model, two very different types of patterning can be obtained, suggesting that our model may be applicable to other processes in addition to streak initiation.

Biophysical properties, pharmacology, and modulation of human, neuronal L-type (alpha(1D), Ca(V)1.3) voltage-dependent calcium currents

Voltage-dependent calcium channels (VDCCs) are multimeric complexes composed of a pore-forming alpha(1) subunit together with several accessory subunits, including alpha(2)delta, beta, and, in some cases, gamma subunits. A family of VDCCs known as the L-type channels are formed specifically from alpha(1S) (skeletal muscle), alpha(1C) (in heart and brain), alpha(1D) (mainly in brain, heart, and endocrine tissue), and alpha(1F) (retina). Neuroendocrine L-type currents have a significant role in the control of neurosecretion and can be inhibited by GTP-binding (G-) proteins. However, the subunit composition of the VDCCs underlying these G-protein-regulated neuroendocrine L-type currents is unknown. To investigate the biophysical and pharmacological properties and role of G-protein modulation of alpha(1D) calcium channels, we have examined calcium channel currents formed by the human neuronal L-type alpha(1D) subunit, co-expressed with alpha(2)delta-1 and beta(3a), stably expressed in a human embryonic kidney (HEK) 293 cell line, using whole cell and perforated patch-clamp techniques. The alpha(1D)-expressing cell line exhibited L-type currents with typical characteristics. The currents were high-voltage activated (peak at +20 mV in 20 mM Ba2+) and showed little inactivation in external Ba2+, while displaying rapid inactivation kinetics in external Ca2+. The L-type currents were inhibited by the 1,4 dihydropyridine (DHP) antagonists nifedipine and nicardipine and were enhanced by the DHP agonist BayK S-(-)8644. However, alpha(1D) L-type currents were not modulated by activation of a number of G-protein pathways. Activation of endogenous somatostatin receptor subtype 2 (sst2) by somatostatin-14 or activation of transiently transfected rat D2 dopamine receptors (rD2(long)) by quinpirole had no effect. Direct activation of G-proteins by the nonhydrolyzable GTP analogue, guanosine 5'-0-(3-thiotriphospate) also had no effect on the alpha(1D) currents. In contrast, in the same system, N-type currents, formed from transiently transfected alpha(1B)/alpha(2)delta-1/beta(3), showed strong G-protein-mediated inhibition. Furthermore, the I-II loop from the alpha(1D) clone, expressed as a glutathione-S-transferase (GST) fusion protein, did not bind Gbetagamma, unlike the alpha(1B) I-II loop fusion protein. These data show that the biophysical and pharmacological properties of recombinant human alpha(1D) L-type currents are similar to alpha(1C) currents, and these currents are also resistant to modulation by G(i/o)-linked G-protein-coupled receptors.

The spatial ultimatum game

In the ultimatum game, two players are asked to split a certain sum of money. The proposer has to make an offer. If the responder accepts the offer, the money will be shared accordingly. If the responder rejects the offer, both players receive nothing. The rational solution is for the proposer to offer the smallest possible share, and for the responder to accept it. Human players, in contrast, usually prefer fair splits. In this paper, we use evolutionary game theory to analyse the ultimatum game. We first show that in a non-spatial setting, natural selection chooses the unfair, rational solution. In a spatial setting, however, much fairer outcomes evolve.

Fairness versus reason in the ultimatum game

In the Ultimatum Game, two players are offered a chance to win a certain sum of money. All they must do is divide it. The proposer suggests how to split the sum. The responder can accept or reject the deal. If the deal is rejected, neither player gets anything. The rational solution, suggested by game theory, is for the proposer to offer the smallest possible share and for the responder to accept it. If humans play the game, however, the most frequent outcome is a fair share. In this paper, we develop an evolutionary approach to the Ultimatum Game. We show that fairness will evolve if the proposer can obtain some information on what deals the responder has accepted in the past. Hence, the evolution of fairness, similarly to the evolution of cooperation, is linked to reputation.

Calcium channel beta subunit promotes voltage-dependent modulation of alpha 1 B by G beta gamma

Voltage-dependent calcium channels (VDCCs) are heteromultimers composed of a pore-forming alpha1 subunit and auxiliary subunits, including the intracellular beta subunit, which has a strong influence on the channel properties. Voltage-dependent inhibitory modulation of neuronal VDCCs occurs primarily by activation of G-proteins and elevation of the free G beta gamma dimer concentration. Here we have examined the interaction between the regulation of N-type (alpha 1 B) channels by their beta subunits and by G beta gamma dimers, heterologously expressed in COS-7 cells. In contrast to previous studies suggesting antagonism of G protein inhibition by the VDCC beta subunit, we found a significantly larger G beta gamma-dependent inhibition of alpha 1 B channel activation when the VDCC alpha 1 B and beta subunits were coexpressed. In the absence of coexpressed VDCC beta subunit, the G beta gamma dimers, either expressed tonically or elevated via receptor activation, did not produce the expected features of voltage-dependent G protein modulation of N-type channels, including slowed activation and prepulse facilitation, while VDCC beta subunit coexpression restored all of the hallmarks of G beta gamma modulation. These results suggest that the VDCC beta subunit must be present for G beta gamma to induce voltage-dependent modulation of N-type calcium channels.

Scanning mutagenesis identifies amino acid side chains in transmembrane domain 5 of the M(1) muscarinic receptor that participate in binding the acetyl methyl group of acetylcholine

The exofacial part of transmembrane domain 5 (TMD 5) of the cationic amine-binding subclass of 7-transmembrane receptors is thought to be important in binding the side chain of the agonist. Residues Ile-188 through Ala-196 in TMD 5 of the M(1) muscarinic acetylcholine receptor (mAChR) have been studied by Cys- and Ala-scanning mutagenesis. The results are consistent with a helical conformation for this sequence. The positively charged sulfhydryl reagent N-trimethyl-2-aminoethyl methanethiosulfonate reacted selectively with Phe-190 --> Cys, Thr-192 --> Cys, and Ala-193 --> Cys, indicating that the face of TMD 5 accessible from the binding site crevice is consistent with a recent model by Baldwin and colleagues of the transmembrane domain of the 7-transmembrane receptors. In contrast, the acetylcholine derivative bromoacetylcholine reacted selectively with Thr-192 --> Cys, which forms the focus of a group of amino acids (Ile-188, Thr-189, Thr-192, Ala-196) whose mutation decreased the binding affinity of the transmitter ACh itself. The center of this patch of residues is offset to one side of the binding pocket, suggesting that a rotation of TMD 5, relative to that implied by the Baldwin model, may be necessary to optimize the anchoring of acetylcholine within the binding site of the M(1) mAChR. An induced rotation of TMD 5 could contribute to the formation of the activated state of the receptor.

The alpha1B Ca2+ channel amino terminus contributes determinants for beta subunit-mediated voltage-dependent inactivation properties

Co-expression of auxiliary beta subunits with the alpha1B Ca2+ channel subunit in COS-7 cells resulted in an increase in current density and a hyperpolarising shift in the mid-point of activation. Amongst the beta subunits, beta2a in particular, but also beta4 and beta1b caused a significant retardation of the voltage-dependent inactivation compared to currents with alpha1B alone, whilst no significant changes in inactivation properties were seen for the beta3 subunit in this system. Prevention of beta2a palmitoylation, by introducing cysteine to serine mutations (beta2a(C3,4S)), greatly reduced the ability of beta2a to retard voltage-dependent inactivation. Deletion of the proximal half of the alpha1B cytoplasmic amino terminus (alpha1BDelta1-55) differentially affected beta subunit-mediated voltage-dependent inactivation properties. These effects were prominent with the beta2a subunit and, to a lesser extent, with beta1b. For beta2a, the major effects of this deletion were a partial reversal of beta2a-mediated retardation of inactivation and the introduction of a fast component of inactivation, not seen with full-length alpha1B. Deletion of the amino terminus had no other major effects on the measured biophysical properties of alpha1B when co-expressed with beta subunits. Transfer of the whole alpha1B amino terminus into alpha1C (alpha1bCCCC) conferred a similar retardation of inactivation on alpha1C when co-expressed with beta2a to that seen in parental alpha1B. Individual (alpha1B(Q47A) and alpha1B(R52A)) and double (alpha1B(R52,54A)) point mutations within the amino terminus of alpha1B also opposed the beta2a-mediated retardation of alpha1B inactivation kinetics. These results indicate that the alpha1B amino terminus contains determinants for beta subunit-mediated voltage-dependent inactivation properties. Furthermore, effects were beta subunit selective. As deletion of the alpha1B amino terminus only partially opposed beta subunit-mediated changes in inactivation properties, the amino terminus is likely to contribute to a complex site necessary for complete beta subunit function.

Reassignment of fundamental vibrational modes of cyclic S4N3 cation

MP2/6 31G* calculations were carried out to investigate the vibrational spectrum of cyclic S4N3+. The results indicate that previous assignments of several fundamental vibrational modes are in error. On the basis of the calculated results, reassignments of these modes are proposed.

A new theory of cytotoxic T-lymphocyte memory: implications for HIV treatment

We use simple mathematical models to examine the dynamics of primary and secondary cytotoxic T-lymphocyte (CTL) responses to viral infections. In particular, we are interested in conditions required to resolve the infection and to protect the host upon secondary challenge. While protection against reinfection is only effective in a restricted set of circumstances, we find that resolution of the primary infection requires persistence of CTL precursors (GTLp), as well as a fast rate of activation of the CTLp. Since these are commonly the defining characteristics of CTL memory, we propose that CTL memory may have evolved in order to clear the virus during primary challenge. We show experimental data from lymphocytic choriomeningitis virus infection in mice, supporting our theory on CTL memory. We adapt our models to HIV and find that immune impairment during the primary phase of the infection may result in the failure to establish CTL memory which in turn leads to viral persistence. Based on our models we suggest conceptual treatment regimes which ensure establishment of CTL memory. This would allow the immune response to control HIV in the long term in the absence of continued therapy.

A functional role for the two-pore domain potassium channel TASK-1 in cerebellar granule neurons

Cerebellar granule neurons (CGNs) are one of the most populous cells in the mammalian brain. They express an outwardly rectifying potassium current, termed a "standing-outward" K(+) current, or IK(SO), which does not inactivate. It is active at the resting potential of CGNs, and blocking IK(SO) leads to cell depolarization. IK(SO) is blocked by Ba(2+) ions and is regulated by activation of muscarinic M(3) receptors, but it is insensitive to the classical broad-spectrum potassium channel blocking drugs 4-aminopyridine and tetraethylammonium ions. The molecular nature of this important current has yet to be established, but in this study, we provide strong evidence to suggest that IK(SO) is the functional correlate of the recently identified two-pore domain potassium channel TASK-1. We show that IK(SO) has no threshold for activation by voltage and that it is blocked by small extracellular acidifications. Both of these are properties that are diagnostic of TASK-1 channels. In addition, we show that TASK-1 currents expressed in Xenopus oocytes are inhibited after activation of endogenous M(3) muscarinic receptors. Finally, we demonstrate that mRNA for TASK-1 is found in CGNs and that TASK-1 protein is expressed in CGN membranes. This description of a functional two-pore domain potassium channel in the mammalian central nervous system indicates its physiological importance in controlling cell excitability and how agents that modify its activity, such as agonists at G protein-coupled receptors and hydrogen ions, can profoundly alter both the neuron's resting potential and its excitability.

Acidic motif responsible for plasma membrane association of the voltage-dependent calcium channel beta1b subunit

Voltage-dependent calcium channels consist of a pore-forming transmembrane alpha1-subunit, which is known to associate with a number of accessory subunits, including alpha2-delta- and beta-subunits. The beta-subunits, of which four have been identified (beta1-4), are intracellular proteins that have marked effects on calcium channel trafficking and function. In a previous study, we observed that the beta1b-subunit showed selective plasma membrane association when expressed alone in COS7 cells, whereas beta3 and beta4 did not. In this study, we have examined the basis for this, and have identified, by making chimeric beta-subunits, that the C-terminal region, which shows most diversity between beta-subunits, of beta1b is responsible for its plasma membrane association. Furthermore we have identified, by deletion mutations, an 11-amino acid motif present in the C terminus of beta1b but not in beta3 (amino acids 547-556 of beta1b, WEEEEDYEEE), which when deleted, reduces membrane association of beta1b. Future research aims to identify what is binding to this sequence in beta1b to promote membrane association of this calcium channel subunit. It is possible that such membrane association is important for the selective localization or clustering of particular calcium channels with which beta1b is associated.

Identification of residues in the N terminus of alpha1B critical for inhibition of the voltage-dependent calcium channel by Gbeta gamma

To examine the role of the intracellular N terminus in the G-protein modulation of the neuronal voltage-dependent calcium channel (VDCC) alpha1B, we have pursued two routes of investigation. First, we made chimeric channels between alpha1B and alpha1C, the latter not being modulated by Gbeta gamma subunits. VDCC alpha1 subunit constructs were coexpressed with accessory alpha2delta and beta2a subunits in Xenopus oocytes and mammalian (COS-7) cells. G-protein modulation of expressed alpha1 subunits was induced by activation of coexpressed dopamine (D2) receptors with quinpirole in oocytes, or by cotransfection of Gbeta1gamma2 subunits in COS-7 cells. For the chimeric channels, only those with the N terminus of alpha1B showed any G-protein modulation; further addition of the first transmembrane domain and I-II intracellular linker of alpha1B increased the degree of modulation. To determine the amino acids within the alpha1B N terminus, essential for G-protein modulation, we made mutations of this sequence and identified three amino acids (S48, R52, and R54) within an 11 amino acid sequence as being critical for G-protein modulation, with I49 being involved to a lesser extent. This sequence may comprise an essential part of a complex Gbeta gamma-binding site or be involved in its subsequent action.

Dissection of the calcium channel domains responsible for modulation of neuronal voltage-dependent calcium channels by G proteins

The molecular determinants for G-protein regulation of neuronal calcium channels remain controversial. We have generated a series of alpha 1B/alpha 1E chimeric channels, since rat brain alpha 1E (rbEII), unlike human alpha 1E, showed no G-protein modulation. The study, carried out in parallel using D2 receptor modulation of calcium currents in Xenopus oocytes of G beta gamma modulation of calcium currents in COS-7 cells, consistently showed an essential role for domain I (from the N terminus to the end of the I-II loop) of the alpha 1B Ca2+ channel in G-protein regulation, with no additional effect of the C terminal of alpha 1B. The I-II loop alone of alpha 1B, or the I-II loop together with the C-terminal tail, was insufficient to confer G-protein modulation of alpha 1E (rbEII). We have further observed that the alpha 1E clone rbEII is truncated at the N-terminus compared to other alpha 1 subunits, and we isolated a PCR product from rat brain equivalent to a longer N-terminal isoform. The long N-terminal alpha 1E, unlike the short form, showed G-protein modulation. Furthermore, the equivalent truncation of alpha 1B (delta N1-55) abolished G-protein modulation of alpha 1B. Thus, we propose that the N terminus of alpha 1B and alpha 1E calcium channels contains essential molecular determinants for membrane-delimited G-protein inhibition, and that other regions, including the I-II loop and the C terminus, do not play a conclusive role alone.

The role of charge interactions in muscarinic agonist binding, and receptor-response coupling

Site-directed mutagenesis has been used to evaluate the roles of the key aspartate and arginine residues in transmembrane domain three of the muscarinic receptors. The results suggest that the formation of an ionic bond between the Asp carboxylate group and the onium headgroup is essential to anchor acetylcholine in its active, bound conformation in both binary agonist-receptor and ternary agonist-receptor-G-protein complexes, but that secondary, non-productive binding modes, promoted by non-polar forces, may contribute to binary complex formation by other ligands. The positive charge of the arginyl side-chain is central to the recognition, and subsequent activation of G-proteins by the agonist-M1 mAChR complex.

Orally active indole N-oxide PDE4 inhibitors

This communication describes the synthesis and in vitro and in vivo evaluation of a novel potent series of phosphodiesterase type (IV) (PDE4) inhibitors. Several of the compounds presented possess low nanomolar IC50's for PDE4 inhibition and excellent in vivo activity for inhibition of TNF-alpha levels in LPS challenged mice (mouse endotoxemia model). Emesis studies (dog) and efficacy in a SCW arthritis model for the most potent PDE4 inhibitors are presented.

The synthesis and biological evaluation of a novel series of indole PDE4 inhibitors I

This communication describes the synthesis and in vitro evaluation of a novel potent series of phosphodiesterase type (IV) (PDE4) inhibitors. The compounds described contain an indole moiety which replaces the 'rolipram-like' 3-methoxy-4-cyclopentoxy motif. Several of the compounds presented possess low nanomolar IC50's for PDEIV inhibition. In vivo activities determined from measurement of serum TNF-alpha levels in LPS challenged mice (mouse endotoxemia model) are also reported.

The effect of overexpression of auxiliary Ca2+ channel subunits on native Ca2+ channel currents in undifferentiated mammalian NG108-15 cells

1. High voltage activated (HVA) Ca2+ channels are composed of a pore-forming alpha 1 subunit and the accessory beta and alpha2-delta subunits. However, the subunit composition of low voltage activated (LVA), or T-type, Ca2+ channels has yet to be elucidated. We have examined whether native calcium channels in NG108-15 mouse neuroblastoma x rat glioma hybrid cells, which express predominantly LVA currents when undifferentiated, are modulated by overexpression of accessory calcium channel subunits. 2. Endogenous alpha 1A, B, C, C, and E, and low levels of beta and alpha 2-delta subunit protein were demonstrated in undifferentiated NG108-15 cells. 3. The alpha 2-delta, beta 2a or beta 1b accessory subunits were overexpressed by transfection of the cDNAs into these cells, and the effect examined on the endogenous Ca2+ channel currents. Heterologous expression, particularly of alpha 2-delta but also of beta 2a subunits clearly affected the profile of these currents. Both subunits induced a sustained component in the currents evoked by depolarizing voltages above -30 mV, and alpha 2-delta additionally caused a depolarization in the voltage dependence of current activation, suggesting that it also affected the native T-type currents. In contrast, beta 1b overexpression had no effect on the endogenous Ca2+ currents, despite immunocytochemical evidence for its expression in the transfected cells. 4 These results suggest that in NG108-15 cells, overexpression of the Ca2+ channel accessory subunits alpha 2-delta and beta 2a induce a sustained component of HVA current, and alpha 2-delta also influences the voltage dependence of activation of the LVA current. It is possible that native T-type alpha 1 subunits are not associated with beta subunits.

Identification of the amino terminus of neuronal Ca2+ channel alpha1 subunits alpha1B and alpha1E as an essential determinant of G-protein modulation

We have examined the basis for G-protein modulation of the neuronal voltage-dependent calcium channels (VDCCs) alpha1E and alpha1B. A novel PCR product of alpha1E was isolated from rat brain. This contained an extended 5' DNA sequence and was subcloned onto the previously cloned isoform rbEII, giving rise to alpha1Elong whose N terminus was extended by 50 amino acids. VDCC alpha1 subunit constructs were co-expressed with the accessory alpha2-delta and beta2a subunits in Xenopus oocytes and mammalian (COS-7) cells. The alpha1Elong showed biophysical properties similar to those of rbEII; however, when G-protein modulation of expressed alpha1 subunits was induced by activation of co-expressed dopamine (D2) receptors with quinpirole (100 nM) in oocytes, or by co-transfection of Gbeta1gamma2 subunits in COS-7 cells, alpha1Elong, unlike alpha1E(rbEII), was found to be G-protein-modulated, in terms of both a slowing of activation kinetics and a reduction in current amplitude. However, alpha1Elong showed less modulation than alpha1B, and substitution of the alpha1E1-50 with the corresponding region of alpha1B1-55 produced a chimera alpha1bEEEE, with G-protein modulation intermediate between alpha1Elong and alpha1B. Furthermore, deletion of the N-terminal 1-55 sequence from alpha1B produced alpha1BDeltaN1-55, which could not be modulated, thus identifying the N-terminal domain as essential for G-protein modulation. Taken together with previous studies, these results indicate that the intracellular N terminus of alpha1E1-50 and alpha1B1-55 is likely to contribute to a multicomponent site, together with the intracellular I-II loop and/or the C-terminal tail, which are involved in Gbetagamma binding and/or in subsequent modulation of channel gating.

Role of domain I of neuronal Ca2+ channel alpha1 subunits in G protein modulation

1. We studied the G protein inhibition of heteromultimeric neuronal Ca2+ channels by constructing a series of chimeric channels between the strongly modulated alpha1B subunit and the alpha1E(rbEII) subunit, which showed no modulation. 2. In parallel studies, alpha1 subunit constructs were co-expressed together with the accessory Ca2+ channel alpha2-delta and beta2a subunits in mammalian (COS-7) cells and Xenopus oocytes. G protein inhibition of expressed Ca2+ channel currents was induced by co-transfection of Gbeta1 and Ggamma2 subunits in COS-7 cells or activation of co-expressed dopamine (D2) receptors by quinpirole (100 nM) in oocytes. 3. The data indicate that transfer of the alpha1B region containing the N-terminal, domain I and the I-II loop (i.e. the alpha1B1-483 sequence), conferred G protein modulation on alpha1E(rbEII), both in terms of a slowing of activation kinetics and a reduction in current amplitude. 4. In contrast, the data are not consistent with the I-II loop and/or the C-terminal forming a unique site for G protein modulation.

Voltage-dependent binding and calcium channel current inhibition by an anti-alpha 1D subunit antibody in rat dorsal root ganglion neurones and guinea-pig myocytes

1. The presence of calcium channel alpha 1D subunit mRNA in cultured rat dorsal root ganglion (DRG) neurones and guinea-pig cardiac myocytes was demonstrated using the reverse transcriptase-polymerase chain reaction. 2. An antipeptide antibody targeted at a region of the voltage-dependent calcium channel alpha 1D subunit C-terminal to the pore-forming SS1-SS2 loop in domain IV (amino acids 1417-1434) only bound to this exofacial epitope if the DRG neurones and cardiac myocytes were depolarized with 30 mM K+. 3. Incubation of cells under depolarizing conditions for 2-4 h with the antibody resulted in a maximal inhibition of inward current density of 49% (P < 0.005) for DRGs and 30% (P < 0.05) for cardiac myocytes when compared with controls. 4. S-(-)-Bay K 8644 (1 microM) enhanced calcium channel currents in DRGs by 75 +/- 19% (n = 5) in neurones incubated under depolarizing conditions with antibody that had been preabsorbed with its immunizing peptide (100 micrograms ml-1). This was significantly (P < 0.05) larger than the enhancement by S-(-)-Bay K 8644 that was seen with cells incubated under identical conditions but with antibody alone, which was 15 +/- 4% (n = 5). 5. These results demonstrate the presence of calcium channel alpha 1D subunits in rat DRG neurones and guinea-pig cardiac myocytes. They also show that amino acids 1417-1434 of the alpha 1D subunit are only exposed to the extracellular face of the membrane following depolarization and that the binding of an antibody to these amino acids attenuates calcium channel current and reduces the ability of S-(-)-Bay K 8644 to enhance this current, indicating that it is an L-type current that is attenuated.

Properties of cloned rat alpha1A calcium channels transiently expressed in the COS-7 cell line

The rat brain alpha1A calcium channel clone has been expressed in COS-7 cells together with the neuronal accessory subunits beta1b and alpha2-delta. From reverse transcriptase polymerase chain reaction (RT-PCR), immunocytochemistry and electrophysiology experiments, we have obtained no evidence that these cells contain any endogenous calcium channels. Transfected cells were identified by co-expression of a cDNA for the reporter Green Fluorescent Protein. From immunocytochemical evidence, a high degree of co-expression was obtained between Green Fluorescent Protein and individual calcium channel subunits. When all three calcium channel subunits (alpha1, alpha2-delta and beta1b) were co-expressed, evidence was obtained that all subunits were present at the cell membrane. Voltage-dependent calcium currents were observed between 24 and 72 h after transfection with the three calcium channel subunits. The current density for the combination alpha1A/alpha2-delta/beta1b was 4.19 +/- 0.69 pA.pF(-1) and the current produced was slowly inactivating. The time constant of inactivation of the maximum I(Ba) was 332 +/- 46 ms (n = 5). The voltage-dependence of activation and steady-state inactivation had voltages of half activation and inactivation of 9.5 +/- 2.5 mV and -30.4 +/- 1.5 mV respectively, and there was little overlap between the two curves. The alpha1A current was completely blocked by 100 microM Cd2+ and was also blocked by omega-conotoxin MVIIC (500 nM). Dose-inhibition curves and analysis of k(on) and k(off) for omega-agatoxin IVA both revealed apparent K(D) values of approximately 11 nM for alpha1A currents, with a k(on) of 7.8 x 10(4) M(-1).s(-1). The results suggest that alpha1A expressed in these cells has some resemblance to the P type component of calcium current observed in native neurons, although it shows a somewhat greater degree of inactivation than native P current, more similar to the Q type current component. It also has an affinity for omega-agatoxin IVA 2-5 fold lower than reported for P current, but approximately 9-fold higher than reported for Q current.

Importance of the different beta subunits in the membrane expression of the alpha1A and alpha2 calcium channel subunits: studies using a depolarization-sensitive alpha1A antibody

The plasma membrane expression of the rat brain calcium channel subunits alpha1A, alpha2-delta and the beta subunits beta1b, beta2a, beta3b and beta4 was examined by transient expression in COS-7 cells. Neither alpha1A nor alpha2-delta localized to the plasma membrane, either alone or when coexpressed. However, coexpression of alpha1A or alpha2-delta/alpha1A with any of the beta subunits caused alpha1A and alpha2 to be targetted to the plasma membrane. The alpha1A antibody is directed against an exofacial epitope at the mouth of the pore, which is not exposed unless cells are depolarized, both for native alpha1A channels in dorsal root ganglion neurons and for alpha1A expressed with a beta subunit. This subsidiary result provides evidence that either channel opening or inactivation causes a conformational change at the mouth of the pore of alpha1A. Immunostaining for alpha1A was obtained in depolarized non-permeabilized cells, indicating correct orientation in the membrane only when it was coexpressed with a beta subunit. In contrast, beta1b and beta2a were associated with the plasma membrane when expressed alone. However, this is not a prerequisite to target alpha1A to the membrane since beta3 and beta4 alone showed no differential localization, but did direct the translocation of alpha1A to the plasma membrane, suggesting a chaperone role for the beta subunits.

The intracellular loop between domains I and II of the B-type calcium channel confers aspects of G-protein sensitivity to the E-type calcium channel

Neuronal voltage-dependent calcium channels undergo inhibitory modulation by G-protein activation, generally involving both kinetic slowing and steady-state inhibition. We have shown previously that the beta-subunit of neuronal calcium channels plays an important role in this process, because when it is absent, greater receptor-mediated inhibition is observed (). We therefore hypothesized that the calcium channel beta-subunits normally may occlude G-protein-mediated inhibition. Calcium channel beta-subunits bind to the cytoplasmic loop between transmembrane domains I and II of the alpha1-subunits (). We have examined the hypothesis that this loop is involved in G-protein-mediated inhibition by making chimeras containing the I-II loop of alpha1B or alpha1A inserted into alpha1E (alpha1EBE and alpha1EAE, respectively). This strategy was adopted because alpha1B (the molecular counterpart of N-type channels) and, to a lesser extent, alpha1A (P/Q-type) are G-protein-modulated, whereas this has not been observed to any great extent for alpha1E. Although alpha1B, coexpressed with alpha2-delta and beta1b transiently expressed in COS-7 cells, showed both kinetic slowing and steady-state inhibition when recorded with GTPgammaS in the patch pipette, both of which were reversed with a depolarizing prepulse, the chimera alpha1EBE (and, to a smaller extent, alpha1EAE) showed only kinetic slowing in the presence of GTPgammaS, and this also was reversed by a depolarizing prepulse. These results indicate that the I-II loop may be the molecular substrate of kinetic slowing but that the steady-state inhibition shown by alpha1B may involve a separate site on this calcium channel.

Functional expression of rat brain cloned alpha1E calcium channels in COS-7 cells

The properties of the rat brain alpha1E Ca2+ channel subunit and its modulation by accessory rat brain alpha2-delta and beta1b subunits were studied by transient transfection in a mammalian cell line in order to attempt to reconcile the debate as to whether alpha1E forms a low-voltage-activated (LVA) or high-voltage-activated (HVA) Ca2+ channel and to examine its pharmacology in detail. alpha1E alone was capable of forming an ion-conducting pore in COS-7 cells. The properties of heteromultimeric alpha1E/alpha2-delta/beta1b channels were largely dictated by the presence of the beta1b subunit, which increased current density and tended to produce a hyperpolarizing shift in the voltage dependence of activation and inactivation. alpha1E/alpha2-delta/beta1b channels did not appear to be regulated by Ca2+-induced inactivation. alpha1E was shown to exhibit a unique pharmacological profile. omega-Agatoxin IVA blocked the current in a dose-dependent manner with an IC50 of approximately 50 nM and a maximum inhibition of about 80%, whilst omega-conotoxin MVIIC was without effect. The 1,4-dihydropyridine (DHP) antagonist nicardipine (1 micro;M) produced an inhibition of 51 +/- 7%, whereas the DHP agonist S-(-)BAY K 8644 was without effect. Our findings suggest a re-evaluation of the classification of the alpha1E Ca2+ channel subunit; we propose that rat brain alpha1E forms a novel Ca2+ channel with properties more similar to a subtype of LVA than HVA Ca2+ current.

Oxygen control of the Bradyrhizobium japonicum hemA gene

The hemA gene of Bradyrhizobium japonicum, which encodes the first enzyme in the heme biosynthetic pathway, is regulated by oxygen. Up to ninefold induction of beta-galactosidase activity is seen when cultures of B. japonicum containing either a plasmid-encoded or a chromosomally integrated hemA-lacZ fusion are shifted to restricted aeration. The oxygen effect is mediated via the FixLJ two-component regulatory system, which regulates the expression of a number of genes involved in the nitrogen fixation process in response to low-oxygen conductions; oxygen induction is lost when the hemA-lacZ fusion is expressed in strains of B. japonicum carrying mutations in fixL or fixJ. The B. japonicum hemA promoter region contains a sequence identical to the Escherichia coli Fnr binding site (positions -46 to -33 relative to the hemA transcription start site). Fnr is a regulatory protein necessary for the oxygen-regulated expression of anaerobic respiratory genes. Activity of a hemA-lacZ fusion construct in which the Fnr box-like sequence was replaced with a BglII site is not induced in B. japonicum cultures grown under restricted aeration. The fnr homolog fixK is FixLJ dependent. Collectively, these data suggest a role for the rhizobial Fnr-like protein, FixK, in the regulation of hemA. Furthermore, the coregulation of hemA with symbiotically important genes via FixLJ is consistent with the idea that hemA is required in the nodule as well as under free-living conditions.

The functional role of the binding site aspartate in muscarinic acetylcholine receptors, probed by site-directed mutagenesis

Mutation of the Asp in transmembrane domain three of the muscarinic receptors to Asn (M1) or Glu (M1 and M2) strongly reduced the high-affinity component of agonist binding, and the M1 phosphoinositide response. Formation of the acetylcholine-receptor binary complex was also strongly inhibited. In contrast, binary complex formation by other agonists, as well as the antagonist (-)-N-methylscopolamine, was less affected. Ionic bonding between the carboxylate oxyanion and the positively-charged headgroup probably anchors acetylcholine when it is bound in its active conformation, but alternative, non-productive, binding modes, promoted by non-polar forces, may contribute to binary complex formation by other ligands.

Effect of iron availability on expression of the Bradyrhizobium japonicum hemA gene

Bradyrhizobium japonicum produces delta-aminolevulinic acid, the universal precursor of tetrapyrroles, in a reaction catalyzed by the product of the hemA gene. Expression of the B. japonicum hemA gene is affected by iron availability. Activity of a hemA-lacZ fusion is increased approximately threefold by iron, and RNA analysis indicates that iron regulation is at the level of mRNA accumulation. To our knowledge, this is the first example of an iron-regulated heme biosynthetic gene in prokaryotes.

Characterization of the formate (for) locus, which encodes the cytosolic serine hydroxymethyltransferase of Neurospora crassa

Serine hydroxymethyltransferase (SHMT) occupies a central position in one-carbon (C1) metabolism, catalyzing the reaction of serine and tetrahydrofolate to yield glycine and 5,10-methylenetetrahydrofolate. Methylenetetrahydrofolate serves as a donor of C1 units for the synthesis of numerous compounds, including purines, thymidylate, lipids, and methionine. We provide evidence that the formate (for) locus of Neurospora crassa encodes cytosolic SHMT. The for+ gene was localized to a 2.8-kb BglII fragment by complementation (restoration to formate-independent growth) of a strain carrying a recessive for allele, which confers a growth requirement for formate. The for+ gene encodes a polypeptide of 479 amino acids which shows significant similarity to amino acid sequences of SHMT from bacterial and mammalian sources (47 and 60% amino acid identity, respectively). The for+ mRNA has several different start and stop sites. The abundance of for+ mRNA increased in response to amino acid imbalance induced by glycine supplementation, suggesting regulation by the N. crassa cross-pathway control system, which is analogous to general amino acid control in Saccharomyces cerevisiae. This was confirmed by documenting that for+ expression increased in response to histidine limitation (induced by 3-amino-1,2,4-triazole) and that this response was dependent on the presence of a functional cross-pathway control-1 (cpc-1) gene, which encodes CPC1, a positively acting transcription factor. There are at least five potential CPC1 binding sites upstream of the for+ transcriptional start, as well as one that exactly matches the consensus CPC1 binding site in the first intron of the for+ gene.

Determination of the novel hydroxymethyl glutaryl coenzyme A reductase inhibitor (RP 61969) and its dihydroxy acid hydrolysis product in human plasma by reversed-phase high-performance liquid chromatography

A method is described for the determination of the novel hydroxymethyl glutaryl coenzyme A reductase inhibitor RP 61969 (I) and its hydrolysis product, the dihydroxy acid RP 62420 (II), in human plasma. A structural isomer of I is used as internal standard. Both I and II were extracted from acidified plasma with diethyl ether. The dried residues were reconstituted in the high-performance liquid chromatography mobile phase and chromatographed on a 5 microns ODS2 column. The mobile phase used was aqueous dipotassium phosphate +tetra-n-butyl ammonium bromide (both 10 mM)-acetonitrile-methanol (60:40:5, v/v). At a flow-rate of 1.5 ml min-1 and ambient temperature, the retention time of II is 3.5 min, that of the internal standard is 5 min, and that of I is 8 min. The method has been validated and applied to the assay of plasma samples resulting from a cell-plasma distribution experiment in human whole blood.