The role of structural biology in the design of sirtuin activators

Sirtuins are NAD+-dependent protein lysine deacylases and mono-ADP-ribosylases whose activity regulates different pathways, including DNA damage repair, cell survival and metabolism, reactive oxygen species (ROS) detoxification, inflammation, cardiac function, and neuronal signaling. Considering the beneficial effects of specific sirtuin isoforms on health and lifespan, the past two decades have seen a mounting interest in the development of sirtuin activators. The availability of enzyme-activator co-crystal structures has proven significant throughout the years for elucidating the mechanisms of action of activators and designing more potent and selective molecules. In this review, we highlight the most interesting examples of sirtuin activators and provide comprehensive coverage of the role that structural biology played in their discovery and characterization.

Protocol for high-throughput screening of ACE2 enzymatic activators to treat COVID-19-induced metabolic complications

Drug repositioning represents a cost- and time-efficient strategy for drug development. Here, we present a workflow of in silico screening of ACE2 enzymatic activators to treat COVID-19-induced metabolic complications. By using structure-based virtual screening and signature-based off-target effect identification via the Connectivity Map database, we provide a ranked list of the repositioning candidates as potential ACE2 enzymatic activators to ameliorate COVID-19-induced metabolic complications. The workflow can also be applied to other diseases with ACE2 as a potential target.

For complete details on the use and execution of this protocol, please refer to Li et al. (2022).

•

Structure-based high-throughput virtual screening for ACE2 enzymatic activators

•

Signature-based drug repositioning for COVID-19-induced metabolic complications

•

Workflow applicable for other diseases with ACE2 as a potential target

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Thyroid Activating Enzyme, Deiodinase II Is Required for Photoreceptor Function in the Mouse Model of Retinopathy of Prematurity

Purpose

Retinopathy of prematurity (ROP) is a severe complication of premature infants, leading to vision loss when untreated. Presently, the molecular mechanisms underlying ROP are still far from being clearly understood. This study sought to investigate whether thyroid hormone (TH) signaling contributes to the neuropathology of ROP using the mouse model of ROP to evaluate longitudinal photoreceptor function.

Methods

Animals were exposed to hyperoxia from P7 to P12 to induce retinopathy, thereafter the animals were returned to room air (normoxia). The thyroid-activating enzyme type 2 deiodinases (Dio2) knockout (KO) mice and the littermate controls that were exposed to hyperoxia or maintained in room air and were then analyzed. The retinal function was evaluated using electroretinograms (ERGs) at three and seven weeks followed by histologic assessments with neuronal markers to detect cellular changes in the retina. Rhodopsin protein levels were measured to validate the results obtained from the immunofluorescence analyses.

Results

In the ROP group, the photoreceptor ERG responses are considerably lower both in the control and the Dio2 KO animals at P23 compared to the non-ROP group. In agreement with the ERG responses, loss of Dio2 results in mislocalized cone nuclei, and abnormal rod bipolar cell dendrites extending into the outer nuclear layer. The retinal function is compromised in the adult Dio2 KO animals, although the cellular changes are less severe. Despite the reduction in scotopic a-wave amplitudes, rhodopsin levels are similar in the adult mice, across all genotypes irrespective of exposure to hyperoxia.

Conclusions

Using the mouse model of ROP, we show that loss of Dio2 exacerbates the effects of hyperoxia-induced retinal deficits that persist in the adults. Our data suggest that aberrant Dio2/TH signaling is an important factor in the pathophysiology of the visual dysfunction observed in the oxygen-induced retinopathy model of ROP.

Essential Roles of the sppRA Fructose-Phosphate Phosphohydrolase Operon in Carbohydrate Metabolism and Virulence Expression by Streptococcus mutans

The dental caries pathogen Streptococcus mutans can ferment a variety of sugars to produce organic acids. Exposure of S. mutans to certain nonmetabolizable carbohydrates, such as xylitol, impairs growth and can cause cell death. Recently, the presence of a sugar-phosphate stress in S. mutans was demonstrated using a mutant lacking 1-phosphofructokinase (FruK) that accumulates fructose-1-phosphate (F-1-P). Here, we studied an operon in S. mutans, sppRA, which was highly expressed in the fruK mutant. Biochemical characterization of a recombinant SppA protein indicated that it possessed hexose-phosphate phosphohydrolase activity, with preferences for F-1-P and, to a lesser degree, fructose-6-phosphate (F-6-P). SppA activity was stimulated by Mg2+ and Mn2+ but inhibited by NaF. SppR, a DeoR family regulator, repressed the expression of the sppRA operon to minimum levels in the absence of the fructose-derived metabolite F-1-P and likely also F-6-P. The accumulation of F-1-P, as a result of growth on fructose, not only induced sppA expression, but it significantly altered biofilm maturation through increased cell lysis and enhanced extracellular DNA release. Constitutive expression of sppA, via a plasmid or by deleting sppR, greatly alleviated fructose-induced stress in a fruK mutant, enhanced resistance to xylitol, and reversed the effects of fructose on biofilm formation. Finally, by identifying three additional putative phosphatases that are capable of promoting sugar-phosphate tolerance, we show that S. mutans is capable of mounting a sugar-phosphate stress response by modulating the levels of certain glycolytic intermediates, functions that are interconnected with the ability of the organism to manifest key virulence behaviors.IMPORTANCEStreptococcus mutans is a major etiologic agent for dental caries, primarily due to its ability to form biofilms on the tooth surface and to convert carbohydrates into organic acids. We have discovered a two-gene operon in S. mutans that regulates fructose metabolism by controlling the levels of fructose-1-phosphate, a potential signaling compound that affects bacterial behaviors. With fructose becoming increasingly common and abundant in the human diet, we reveal the ways that fructose may alter bacterial development, stress tolerance, and microbial ecology in the oral cavity to promote oral diseases.

Viscothionin isolated from Korean mistletoe improves nonalcoholic fatty liver disease via the activation of adenosine monophosphate-activated protein kinase

The present study investigated the effects of viscothionin, a compound isolated from Korean mistletoe (Viscum album coloratum), on nonalcoholic fatty liver disease (NAFLD) in both in vitro and in vivo models. A connection was discovered between viscothionin and the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway, which is involved in lipid metabolism. Viscothionin was shown to significantly attenuate lipid accumulation in HepG2 cells treated with oleic acid, which induces lipid accumulation. Moreover, the phosphorylation of AMPK and acetyl-coenzyme A carboxylase in HepG2 cells was increased by viscothionin treatment. Viscothionin was orally administered to high fat diet-induced obese mice and subsequently histopathological analysis associated with AMPK signaling pathways was evaluated. A significant reduction in the extent of hepatic steatosis was revealed in viscothionin-treated obese mice. Thus, viscothionin mediates its beneficial effects on NAFLD via AMPK signaling pathways, suggesting that it may be a potential target for novel NAFLD treatments.

An oxidant and organic solvent tolerant alkaline lipase by P. aeruginosa mutant: downstream processing and biochemical characterization

An extracellular alkaline lipase from Pseudomonas aeruginosa mutant has been purified to homogeneity using acetone precipitation followed by anion exchange and gel filtration chromatography and resulted in 27-fold purification with 19.6% final recovery. SDS-PAGE study suggested that the purified lipase has an apparent molecular mass of 67 kDa. The optimum temperature and pH for the purified lipase were 45 °C and 8.0, respectively. The enzyme showed considerable stability in pH range of 7.0-11.0 and temperature range 35-55 °C. The metal ions Ca(2+), Mg(2+) and Na(+) tend to increase the enzyme activity, whereas, Fe(2+) and Mn(2+) ions resulted in discreet decrease in the activity. Divalent cations Ca(+2) and Mg(+2) seemed to protect the enzyme against thermal denaturation at high temperatures and in presence of Ca(+2) (5 mM) the optimum temperature shifted from 45 °C to 55 °C. The purified lipase displayed significant stability in the presence of several hydrophilic and hydrophobic organic solvents (25%, v/v) up to 168 h. The pure enzyme preparation exhibited significant stability and compatibility with oxidizing agents and commercial detergents as it retained 40-70% of its original activities. The values of K(m) and Vmax for p-nitrophenyl palmitate (p-NPP) under optimal conditions were determined to be 2.0 mg.mL(-1) and 5000 μg.mL(-1).min(-1), respectively.

[Current status and issues of clinical development of novel anti-diabetic drugs]

Clinical development of new antidiabetic drugs such as SGLT2 inhibitor, GPR40 agonist, GPR119 agonist, and GKA has been progressing world wide. Action mechanism of each drug is unique and clearly distinguished from the existing drugs. The effect of SGLT2 inhibitors is independent of insulin action and characterized by inhibition of glucose reabsorption in the kidney accompanying with significant body weight reduction. It is known that GPR40 agonist stimulates insulin secretion in glucose independent manner. GKA potentiates glucose-stimulated insulin secretion from pancreatic beta cells and stimulates glucose uptake into the liver. Selective SGLT2 inhibitors and GPR40 agonist are expected to enter into the market in near future.

Differential salt tolerance in seedlings derived from dimorphic seeds of Atriplex centralasiatica: from physiology to molecular analysis

Seed dimorphism provides plants with alternative strategies for survival in unfavorable environments. Here, we investigated the physiological responses and differential gene expression caused by salinity exposure in Atriplex centralasiatica plants grown from the two different seed morphs. Seedlings derived from yellow seeds (YS) showed a greater salt tolerance than those derived from brown seeds (BS). Salt treatment induced nitric oxide (NO) synthesis in roots, and seedlings derived from YS produced greater amounts of NO than did those from BS. Analyses of NO scavenging during salt stress revealed that NO contributed to the differential salt tolerance in seedlings derived from the two seed morphs by modulating antioxidative enzyme activity, hydrogen peroxide accumulation and the ion equilibrium. We also applied transcriptomics and subsequent microarray analysis to evaluate the differential gene expression during salt treatment. These genes encoded proteins related to osmotic and ionic homeostasis, redox equilibrium and signal transduction. A select group of genes including GH3.3, CAT1/2, TIP1, SIHP1 and EXP1 were further confirmed with RT-PCR analysis. These results revealed that the enhanced salt tolerance of seedlings from YS appeared to be governed by a superior ability to achieve ionic homeostasis and redox equilibrium, a rapid response to salt stress, and ultimately better growth potential. NO serves as a vital regulator in these processes.

Two seemingly homologous noncoding RNAs act hierarchically to activate glmS mRNA translation

Small noncoding RNAs (sRNA) can function as posttranscriptional activators of gene expression to regulate stress responses and metabolism. We here describe the mechanisms by which two sRNAs, GlmY and GlmZ, activate the Escherichia coli glmS mRNA, coding for an essential enzyme in amino-sugar metabolism. The two sRNAs, although being highly similar in sequence and structure, act in a hierarchical manner. GlmZ, together with the RNA chaperone, Hfq, directly activates glmS mRNA translation by an anti-antisense mechanism. In contrast, GlmY acts upstream of GlmZ and positively regulates glmS by antagonizing GlmZ RNA inactivation. We also report the first example, to our knowledge, of mRNA expression being controlled by the poly(A) status of a chromosomally encoded sRNA. We show that in wild-type cells, GlmY RNA is unstable due to 3′ end polyadenylation; whereas in an E. coli pcnB mutant defective in RNA polyadenylation, GlmY is stabilized and accumulates, which in turn stabilizes GlmZ and causes GlmS overproduction. Our study reveals hierarchical action of two well-conserved sRNAs in a complex regulatory cascade that controls the glmS mRNA. Similar cascades of noncoding RNA regulators may operate in other organisms.

Hierarchical action of regulators is a fundamental principle in gene expression control, and is well understood in protein-based signaling pathways. We have discovered that small noncoding RNAs (sRNAs), a new class of gene expression regulators, can also act hierarchically and form a regulatory cascade. Two highly similar sRNAs function after transcription to activate the Escherichia coli glmS mRNA, which codes for an essential function in amino-sugar metabolism. It is somewhat unusual for two sRNAs to act upon the same target mRNA, and despite their seeming homology, these two sRNAs (GlmY and GlmZ) employ different molecular mechanisms and function hierarchically to activate glmS expression: GlmZ directly activates glmS translation via disruption of an mRNA structure that inhibits translation, whereas GlmY controls the processing of GlmZ to prevent the inactivation of this direct activator. We also found that GlmY is itself controlled by an RNA processing event (3′ end polyadenylation), which typically destabilizes bacterial RNA. Our data unequivocally demonstrate that E. coli glmS is exceptionally dependent on RNA-based mechanisms for its genetic control. Given the large number of noncoding RNAs of unknown function, we believe that similar regulatory RNA cascades may operate in other organisms.

A regulatory RNA cascade that posttranscriptionally activates the glmS mRNA is identified, with two highly similar small noncoding RNAs acting hierarchically in a manner thus far known only in protein-based regulatory circuits.

Regulation of Saccharomyces cerevisiae DNA polymerase eta transcript and protein

RAD30-encoded DNA polymerase eta functions as a translesion polymerase that can bypass the most frequent types of UV-induced pyrimidine photoproducts in an error-free manner. Although its transcript is UV-inducible in Saccharomyces cerevisiae, Rad30 (studied as a Rad30-Myc fusion) is a stable protein whose levels do not fluctuate following UV treatment or during cell cycle progression. Rad30 protein is subject to monoubiquitination whose level is upregulated in G1 and downregulated during S-phase reentry. This downregulation is accelerated in UV-treated cells. A missense mutation (L577Q) of the ubiquitin binding domain (UBZ) confers a reduced degree of ubiquitination outside of G1 and a complete failure to stably interact with ubiquitinated substrates. This mutation confers a phenotype resembling a complete RAD30 deletion, thus attesting to the significance of the UBZ motif for polymerase eta function in vivo.

New prion inactivation treatment presented

Information on breakthroughs in prion decontamination and detection were presented by Dr Graham Jackson, head of molecular diagnostics at the Medical Research Council, to a Central Sterilising Club meeting held in Manchester earlier this year.

Three-dimensional structure and ligand interactions of the low molecular weight protein tyrosine phosphatase from Campylobacter jejuni

A putative low molecular weight protein tyrosine phosphatase (LMW-PTP) was identified in the genome sequence of the bacterial pathogen, Campylobacter jejuni. This novel gene, cj1258, has sequence homology with a distinctive class of phosphatases widely distributed among prokaryotes and eukaryotes. We report here the solution structure of Cj1258 established by high-resolution NMR spectroscopy using NOE-derived distance restraints, hydrogen bond data, and torsion angle restraints. The three-dimensional structure consists of a central four-stranded parallel beta-sheet flanked by five alpha-helices, revealing an overall structural topology similar to those of the eukaryotic LMW-PTPs, such as human HCPTP-A, bovine BPTP, and Saccharomyces cerevisiae LTP1, and to those of the bacterial LMW-PTPs MPtpA from Mycobacterium tuberculosis and YwlE from Bacillus subtilis. The active site of the enzyme is flexible in solution and readily adapts to the binding of ligands, such as the phosphate ion. An NMR-based screen was carried out against a number of potential inhibitors and activators, including phosphonomethylphenylalanine, derivatives of the cinnamic acid, 2-hydroxy-5-nitrobenzaldehyde, cinnamaldehyde, adenine, and hypoxanthine. Despite its bacterial origin, both the three-dimensional structure and ligand-binding properties of Cj1258 suggest that this novel phosphatase may have functional roles close to those of eukaryotic and mammalian tyrosine phosphatases. The three-dimensional structure along with mapping of small-molecule binding will be discussed in the context of developing high-affinity inhibitors of this novel LMW-PTP.

Mitochondria primed by death signals determine cellular addiction to antiapoptotic BCL-2 family members

We show that the antiapoptotic proteins BCL-2, BCL-XL, MCL-1, BFL-1, and BCL-w each bear a unique pattern of interaction with a panel of peptides derived from BH3 domains of BH3-only proteins. Cellular dependence on an antiapoptotic protein for survival can be decoded based on the pattern of mitochondrial sensitivity to this peptide panel, a strategy that we call BH3 profiling. Dependence on antiapoptotic proteins correlates with sequestration of activator BH3-only proteins like BID or BIM by antiapoptotic proteins. Sensitivity to the cell-permeable BCL-2 antagonist ABT-737 is also related to priming of BCL-2 by activator BH3-only molecules. Our data allow us to distinguish a cellular state we call "primed for death," which can be determined by BH3 profiling and which correlates with dependence on antiapoptotic family members for survival.

Reduction of hexavalent chromium by cell-free extract of Bacillus sphaericus AND 303 isolated from serpentine soil

Cell-free extracts (CFEs) of chromium-resistant bacterium Bacillus sphaericus AND 303 isolated from serpentine soil of Andaman, India reduced Cr(VI) in in vitro condition, and the reductase activity was solely localized in the soluble cell-fractions (S12, S32, and S150). The enzyme was constitutive as the CFEs from cells grown in Cr(VI)-free and Cr(VI)-containing media reduced a more or less equal amount of Cr(VI). Optimum Cr(VI) reductase activity was obtained at an enzyme (S150) concentration equivalent to 4.56 mg protein/mL, 300 microM: Cr(VI) and pH 6.0 after 30 min incubation at 30 degrees C. The enzyme was heat labile; 80% of its activity was lost when exposed at 70 degrees C for 15 min. Kinetics of Cr(VI) reductase activity fit well with the linearized Lineweaver-Burk plot and showed a V(max) of 1.432 micromol Cr(VI)/mg protein/min and K(m) of 158.12 microM: Cr(VI). The presence of additional electron donors accelerated Cr(VI) reductase activity of CFE, and an increase of 28% activity over control was recorded with 1.0 microM: NADH. Heavy metal ions such as Ni(II), Cu(II), and Cd(II) were strong inhibitors of Cr(VI) reductase unlike that of 100 microM: Co(II), which retained 93% activity over control.

Protein kinase A affectsGalleria mellonella(Insecta: Lepidoptera) larval haemocyte non‐self responses

We used the protein kinase A (PKA) specific activator Sp-8-Br-cAMPS and type I inhibitor Rp-8-Br-cAMPS alone and in combination to define the role of PKA in the non-self responses of larval Galleria mellonella haemocytes in vitro and in vivo. Active PKA depressed haemocyte responses whereas PKA inhibition enhanced activities, including bacterial phagocytosis, the number of haemocytes with adherent bacteria, bacterial-induced haemocytic protein release and haemocyte adhesion to slides in vitro, as well as in vivo bacterial removal from the haemolymph. Non-attached haemocytes had more PKA activity than attached haemocytes; therefore, active PKA limited haemocyte response to foreign materials. We found that (i) PKA inhibitor alone induced non-self responses, including haemocyte protein discharge and lowered haemocyte counts in vivo, and induced nodulation; (ii) the enzyme activator produced effects opposite to those of the inhibitor; and (iii) together, the modulators offset each others' effects and influenced haemocyte lysate PKA activity. These findings establish PKA as a mediator of haemocytic non-self responses.

Naked DNA prevents soman intoxication

Paraoxonase (Q isoenzyme, PON1) can effectively hydrolyze chlorpyrifos-oxon (CPO), soman, sarin, and other organophosphates. Previous studies had indicated that the levels of serum PON1 in gene therapy with adenoviral vector could decrease the toxicity of CPO. In our study, plasmid pcDNA/PON1 injected into the tail vein of mice gave excellent expression at 24h after delivery, and PON1 activity decreased gradually along with days. The PON1 activities of mice treated with different doses of the plasmid (150, 300, and 600 microg/mouse) indicated a very good dose-effect relationship. Toxicity study has been performed using one lethal dose of soman (200 microg/kg). The mean death latency of mice pre-treated with 150, 300, 600, and 1200 microg pcDNA/PON1 extended and the mortality decreased vs control mice received the null pcDNA. These results demonstrate that increasing serum PON1 by naked DNA can offer protection toward the acute toxicity of soman.

Adenosine activating A(2A)-receptors coupled to adenylate cyclase/cyclic AMP pathway downregulates nicotinic autoreceptor function at the rat myenteric nerve terminals

In addition to the somatodendritic region, myenteric motoneuron terminals are endowed with nicotinic autoreceptors. We aimed at investigating the effect of nicotinic receptor (nAChR) activation on [3H]-acetylcholine ([3H]-ACh) release from longitudinal muscle-myenteric plexus of the rat ileum and to evaluate whether this could be modulated by adenosine, an endogenous neuromodulator typically operating changes in intracellular cyclic AMP. The nAChR agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP, 1-30 microM, 3 min) increased [3H]-ACh release in a concentration-dependent manner. DMPP (30 microM)-induced [3H]-ACh outflow was attenuated by hexamethonium (0.1-1 mM), tubocurarine (1-5 microM), or by removing external Ca2+ (plus EGTA, 1 mM). In contrast to veratridine (0.2-10 microM)-induced [3H]-ACh release, the DMPP (30 microM)-induced outflow was resistant to tetrodotoxin (1 microM) and cadmium (0.5 mM). Pretreatment with adenosine deaminase (0.5 U/mL) or with the adenosine A(2A)-receptor antagonist, ZM 241385 (50 nM), enhanced nAChR-induced transmitter release. Activation of A(2A) receptors with CGS 21680C (3 nM) reduced the DMPP-induced release of [3H]-ACh. CGS 21680C (3 nM) inhibition was prevented by MDL 12,330A (10 microM, an adenylate cyclase inhibitor) and by H-89 (10 microM, an inhibitor of protein kinase A), but was potentiated by rolipram (300 microM, a phosphodiesterase inhibitor). DMPP-induced transmitter release was decreased by 8-bromo-cyclic AMP (1 mM, a protein kinase A activator), rolipram (300 microM), and forskolin (3 microM, an activator of adenylate cyclase). Both MDL 12,330A (10 microM) and H-89 (10 microM) facilitated DMPP-induced release of [3H]-ACh. The results indicate that nAChR-induced [3H]-ACh release is triggered by the influx of Ca2+, independent of voltage-sensitive calcium channels, presumably directly through nAChRs located on myenteric axon terminals. It was also shown that endogenous adenosine, activating A(2A) receptors coupled to the adenylate cyclase/cyclic AMP transducing system, is tonically downregulating this nAChR-mediated control of [3H]-ACh release.

Induction of c-fos expression in the mouse brain associated with hyperalgesia induced by intrathecal injection of protein kinase C activator

Here, we found that a single intrathecal (i.t.) administration of a protein kinase C (PKC) activator, phorbol 12,13-dibutyrate (PDBu), induced pain-like behaviors in mice. Furthermore, i.t.-administered PDBu caused the increased c-fos-like immunoreactivity in the parafascicular nuclei (PF), amygdala and cingulate cortex (CG), but not hippocampus. These findings suggest that the stimulation of spinal PKC results in an enhancement of neuronal activity in the PF, amygdala and CG associated with hyperalgesia.

Development of a quantification system of ionic dissociative metabolites using an FT-IR/ATR method

A simultaneous quantification system of ionic dissociative metabolites was developed using a Fourier transform mid-infrared spectroscopic method by focusing our attention on the enzyme reaction from glucose 6-phosphate to fructose 6-phosphate with phosphoglucose isomerase (PGI). We studied the pH dependency of the infrared spectra of the mixture solution for which the PGI reaction was assumed. The infrared spectra of ionic dissociative components in the mixture solution were extracted by multiple linear regression analysis under the assumption of ionic dissociation equilibrium. Additionally, we constructed a simultaneous quantification system using the extracted spectra of the ionic dissociative components on the basis of the ionic dissociation equilibrium. We could accurately estimate the pH value and the concentrations of the ionic dissociative materials in their mixture solution by using this quantification system. In addition, the stability of quantification results for a pK shift was also verified.

Sensitization of adenylate cyclase: a general mechanism of neuroadaptation to persistent activation of Galpha(i/o)-coupled receptors?

Acute activation of Galphas-coupled receptors stimulates cyclic AMP accumulation leading to the activation of downstream signaling cascades. These Galphas-mediated events can be countered by acute activation of inhibitory G proteins (Galpha(i/o)), which inhibit the activity of adenylate cyclase, thereby attenuating cyclic AMP accumulation. Furthermore, an additional, less direct mechanism for Galpha(i/o) proteins modulation of cyclic AMP signaling also has been described. Persistent activation of several Galpha(i/o)-coupled receptors has been shown to result in a subsequent paradoxical enhancement of adenylate cyclase activity in response to drug-stimulated cyclic AMP accumulation. This sensitization of adenylate cyclase likely represents a cellular adaptive response following prolonged activation of inhibitory receptors. Recent advances in our knowledge of G protein signaling, adenylate cyclase regulation, and other cellular signaling mechanisms have extensively increased our insight into this phenomenon. It is now thought that sensitization occurs as part of a compensatory mechanism by which the cell adapts to chronic inhibitory input. Such a mechanism may be involved in modulating Galphas-coupled receptor signaling following neurotransmitter elevations that occur in psychiatric disease states or following the administration of many drugs of abuse. This review will focus on recent advances in the understanding of molecular signaling pathways that are involved in sensitization and describe the potential role of sensitization in neuronal cell function.

The activator-binding site of Onchocerca volvulus S-adenosylmethionine decarboxylase, a potential drug target

S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in polyamine biosynthesis. In many eukaryotes its activity is stimulated specifically by putrescine. The AdoMetDC of the filarial parasite Onchocerca volvulus, however, is not only stimulated by putrescine but also by the naturally occuring polyamines spermidine and spermine. Several diamines, acetylated polyamines and polyamine analogues were used to analyse what molecular prerequisites are needed to stimulate nematode AdoMetDC activity. In the absence of an activator, the O. volvulus enzyme exhibits an extremely low specific activity. This fact, together with the unspecificity of activator binding, was thought to be useful for a new strategy to inhibit nematode AdoMetDC activity. Therefore, different polyamine analogues were tested as competitive inhibitors towards the stimulatory effect putrescine has on the O. volvulus and, in comparison, on the Caenorhabditis elegans and human AdoMetDC. Bis(aralkyl)- and bis(alkyl)-substituted polyamine analogues with a 3-7-3 backbone were found to inhibit AdoMetDC activities, however, probably without interfering with the putrescine stimulation. The best inhibitor, BW-1, was about 10-fold more effective against O. volvulus AdoMetDC than against the human enzyme. Unexpectedly, BW-1 was determined to be a competitive inhibitor with respect to AdoMet, having a Ki value of 310 microM for the putrescine-stimulated human AdoMetDC. Furthermore, we show for the O. volvulus and the human enzyme that the degree of inhibition by BW-1 depends on the actual putrescine concentration.

Characterization of aspartate transcarbamylase activity from gonads of the soft shell clam, Mya arenaria

Aspartate transcarbamylase (ATCase, EC 2.1.3.2) has been shown to be a good index of the reproductive cycle in marine molluscs. However, this enzyme has never been studied in the soft shell clam Mya arenaria. The characteristics of gonadal ATCase of the soft shell clam, Mya arenaria were therefore determined since we need powerful tools to assess the degree of effects of endocrine disruptors in this species at risk. Enzyme kinetic values observed at pH 8.3 were significantly lower than those measured at pH 9.4. The optimal conditions for the enzyme assays were reached in the presence of a 10 mM of substrate concentration and at pH 9.2 for 60 min at 37 degrees C. We have found that the enzyme was heat sensitive, markedly activated by DMSO and DMF, but no effect was observed with ethanol, ATP or CTP. However, clam ATCase activity was partly inhibited by the addition of CuSO(4) and PHMB to the medium, an inhibition that could be attributed to the presence of SH sites in cysteine residues localized in the catalytic site of this enzyme. All these results will be very useful in the near future to study the gametogenetic process of Mya arenaria, since little is known about the factors that control the physiological process of reproduction in this bivalve of ecological and economic importance. Studies of variations of the activity of aspartate transcarbamylase will also be useful as a potential biomarker to evaluate the disruption of gametogenesis in clams exposed to endocrine disruptors in situ.

Cloning and expression of a new Tibetan hulless barley (Hordeum vulgare) beta-1,3-glucanase gene

A new full-length beta-1,3-glucanase cDNA was obtained by RT-PCR and RACE techniques from Tibet hulless barley and its complete gene sequence obtained by DNA Walking. Sequence alignment with the BLAST program showed that cDNA has high similarity with barley beta-1,3-glucanase II. The gene was functionally expressed in E. coli and the recombinant protein catalysed the hydrolysis of beta-1,3-glucan with an action pattern characteristic of a beta-1,3-glucan endohydrolase (EC 3.2.1.39). Southern blot analysis indicated that the gene is a member of a small gene family. RT-PCR and northern blot analysis indicated it is constitutively expressed in barley shoots.

Isozymes delta of phosphoinositide-specific phospholipase C and their role in signal transduction in the cell

Phospholipase C (PLC, EC 3.1.4.11) is an enzyme crucial for the phosphoinositol pathway and whose activity is involved in eukaryotic signal transduction as it generates two second messengers: diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). There are four major types of phospholipase C named: beta, gamma, delta and the recently discovered epsilon, but this review will focus only on the recent advances for the delta isozymes of PLC. So far, four delta isozymes (named delta1-4) have been discovered and examined. They differ with regard to cellular distribution, activities, biochemical features and involvement in human ailments.

Observational series on women using the contraceptive Mirena concurrently with anti-epileptic and other enzyme-inducing drugs

CONTEXT

Contraception for women on enzyme-inducing drugs.

OBJECTIVE

To gather preliminary information on the contraceptive efficacy of the hormone-releasing intrauterine system (IUS) Mirena, when used concurrently with enzyme-inducers.

DESIGN

Observational series.

SETTING/PARTICIPANTS

Mirena users on enzyme-inducers were recruited from within the Margaret Pyke Centre and via doctors from throughout the UK. Data were collected systematically on structured questionnaires with particular reference to duration of Mirena use, exposure to pregnancy risk, type of concurrent medication, and reasons for drop-out.

MAIN OUTCOME MEASURE

Accidental pregnancies.

RESULTS

To date, 56 women have provided follow-up information. Most took enzyme-inducers for epilepsy. They have accumulated 1454 months of use, of which 1075 months represent exposure to pregnancy risk. Only one apparently true Mirena failure has been documented, representing a failure rate of 1.1 per 100 woman-years (95% CI 0.03-6.25). Including a second pregnancy, probably conceived after the Mirena had been removed,would raise the failure rate to 2.2 per 100 woman-years (95% CI 0.27-8.07). Although 9/30 Mirena removals were followed by re-insertion, only the first segment of use is analysed.

CONCLUSION

As this is a pilot study, no firm conclusions can be drawn, but our preliminary results suggest that any increased pregnancy risk, if it exists, falls within acceptable bounds.

Ceramide inhibition of mammalian phospholipase D1 and D2 activities is antagonized by phosphatidylinositol 4,5-bisphosphate

Ceramides inhibit phospholipase D (PLD) activity in several mammalian cell types. These effects have been related to preventing activation by ARF1, RhoA, and protein kinase C-alpha and -beta and therefore indicate that PLD1 is inhibited. In the present work, we investigated the effects of ceramides in inhibiting both PLD1 and PLD2 and the interaction with another activator, phosphatidylinositol 4,5-bisphosphate (PIP2). PLD1 and PLD2 were overexpressed separately in Sf9 insect cells using baculovirus vectors. In our cell-free system, PLD1 activity was inhibited completely by C2-ceramide at sub-optimum concentrations of PIP2 (3 and 6 microM), whereas at supra-optimum PIP2 concentrations (18 and 24 microM) C2-ceramide did not inhibit PLD1 activity. Partially purified PLD2 exhibited an absolute requirement for PIP2 when the activity was measured using Triton X-100 micelles. Ceramides inhibited PLD2 activity, and this inhibition was decreased as PIP2 concentrations increased. However, C2-ceramide also reversibly inhibited the activity of PLD1 and PLD2 mutants in which binding of PIP2 was decreased, indicating that ceramides are interacting with the catalytic core of the mammalian PLDs. By contrast, C2-ceramide failed to produce a significant inhibition of PLDs from bacteria and plants. Our results provide a novel demonstration that ceramides reversibly inhibit mammalian PLD2 as well as PLD1 activities and that both of these actions are more pronounced when PIP2 concentrations are rate-limiting.

Lessons from life. The biology of business transformation

Biology and business face similar challenges when it comes to change. Living organisms experience constant change. And successful health care organizations must be ready and willing to embrace transition if they are to survive. Take an in-depth look at the biology-to-business metaphor and see how to better manage information technology changes in your organization.

Roles of JNK, p38 and ERK mitogen-activated protein kinases in the growth inhibition and apoptosis induced by cadmium

Cadmium (Cd), a human carcinogen, can induce apoptosis in various cell types. Three major mitogen-activated protein kinases (MAPKs), c-JUN N-terminal kinase (JNK), p38 and extracellular signal-regulated kinase (ERK), have been shown to regulate apoptosis. In this study we explore the ability of Cd to activate JNK, p38 and ERK, including their effects on Cd-mediated growth inhibition and apoptosis in a human non-small cell lung carcinoma cell line, CL3. The kinase activity of JNK was induced dose-dependently by 30-160 microM CdCl(2). High cytotoxic doses of Cd (130-160 microM) markedly activated p38, but low Cd doses did not. Conversely, the activities of ERK1 and ERK2 were decreased by low cytotoxic doses of Cd (</=80 microM) and moderately activated by high Cd doses. Low cytotoxic doses of Cd transiently activated JNK and simultaneously reduced ERK activity, whereas high cytotoxic doses of Cd persistently activated JNK and p38. PD98059, an inhibitor of ERK upstream activators MAPK kinase (MKK) 1 and MKK2, greatly enhanced cytotoxicity and apoptosis in cells treated with low Cd doses. In contrast, SB202190, an inhibitor of p38, decreased the cytotoxicity and apoptosis induced by high Cd doses. Transient expression of a dominant negative form of JNK1, but not that of JNK2, significantly increased the viability and prevented apoptosis of Cd-treated cells. However, expression of wild-type JNK1 did not affect viability and apoptosis of Cd-treated cells. Transfection of wild-type JNK2 or p38 enhanced apoptosis of cells exposed to low Cd doses but did not affect those exposed to high Cd doses. The JNK activity stimulated by low Cd doses was partially suppressed by expression of a dominant negative form of MKK7, but not a dominant negative form of MKK4, indicating that MKK7 is involved in JNK activation by Cd. Together, the results of this study suggest that JNK and p38 cooperatively participate in apoptosis induced by Cd and that the decreased ERK signal induced by low Cd doses contributes to growth inhibition or apoptosis.

Transmembrane phosphoprotein Cbp regulates the activities of Src-family tyrosine kinases

The Src family of protein tyrosine kinases (Src-PTKs) is important in the regulation of growth and differentiation of eukaryotic cells. The activity of Src-PTKs in cells of different types is negatively controlled by Csk, which specifically phosphorylates a conserved regulatory tyrosine residue at the carboxy-terminal tail of the Src-PTKs. Csk is mainly cytoplasmic and Src-PTKs are predominantly membrane-associated. This raises a question about the mechanism of interaction between these enzymes. Here we present Cbp--a transmembrane phosphoprotein that is ubiquitously expressed and binds specifically to the SH2 domain of Csk. Cbp is involved in the membrane localization of Csk and in the Csk-mediated inhibition of c-Src. In the plasma membrane Cbp is exclusively localized in the GM1 ganglioside-enriched detergent-insoluble membrane domain, which is important in receptor-mediated signalling. These findings reveal Cbp as a new component of the regulatory mechanism controlling the activity of membrane-associated Src-PTKs.

Protease-activated receptors: sentries for inflammation?

Cell-surface protease-activated receptors (PARs) appear to have evolved to detect extracellular enzymatically active serine proteases such as trypsin and thrombin. The predominant location of PARs on endothelia and epithelia and the discovery of enzymes such as trypsin within these tissues, together with the linkage of PARs to cytoprotective pathways, provide new information on autocrine and paracrine signalling within these critical barriers. In this article, the ways in which the distribution and function of PARs could be harnessed by pharmacologists as novel anti-inflammatory therapeutic strategies are discussed.

Differential regulation of mammalian brain-specific proline transporter by calcium and calcium-dependent protein kinases

1. This study examined the role of [Ca2+]I and Ca(2+)-dependent kinases in the modulation of high-affinity, mammalian brain-specific L-proline transporter (PROT). 2. beta-PMA (phorbol 12-myristate 13-acetate), an activator of protein kinase C (PKC), inhibits PRO uptake, and bisindolymalemide I (BIM), a potent PKC inhibitor, prevents beta-PMA inhibition. Down-regulation of PKC by chronic treatment with beta-PMA enhances PROT function indicating PROT regulation by tonic activity of PKC. 3. Thapsigargin, which increases [Ca2+]I levels by inhibiting Ca(2+)-ATPase, inhibits PROT and exhibits additive inhibition when co-treated with beta-PMA. KN-62, a Ca2+/calmodulin-dependent kinase II (CaMK II) inhibitor, but not BIM (a PKC inhibitor) prevents the inhibition by thapsigargin. These data suggest that PKC and CaMK II modulate PROT and that thapsigargin mediates its effect via CaMK II. 4. Thapsigargin raises [Ca2+]I and increases PRO-induced current on a second time scale, whereas the inhibitory effect of thapsigargin occurs only after 10 min of treatment. These data suggest that Ca2+ differentially regulate PROT: Ca2+ initially enhances PRO transport but eventually inhibits transport function through CaMK II pathway. 5. Ca(2+)-induced stimulation exemplifies the acute regulation of a neurotransmitter transporter, which may play a critical role in the profile of neurotransmitters during synaptic transmission.

Growth retardation in mice lacking the proteasome activator PA28gamma

The proteasome activator PA28 binds to both ends of the central catalytic machine, known as the 20 S proteasome, in opposite orientations to form the enzymatically active proteasome. The PA28 family is composed of three members designated alpha, beta, and gamma; PA28alpha and PA28beta form the heteropolymer mainly located in the cytoplasm, whereas PA28gamma forms a homopolymer that predominantly occurs in the nucleus. Available evidence indicates that the heteropolymer of PA28alpha and PA28beta is involved in the processing of intracellular antigens, but the function of PA28gamma remains elusive. To investigate the role of PA28gamma in vivo, we generated mice deficient in the PA28gamma gene. The PA28gamma-deficient mice were born without appreciable abnormalities in all tissues examined, but their growth after birth was retarded compared with that of PA28gamma(+/-) or PA28gamma(+/+) mice. We also investigated the effects of the PA28gamma deficiency using cultured embryonic fibroblasts; cells lacking PA28gamma were larger and displayed a lower saturation density than their wild-type counterparts. Neither the expression of PA28alpha/beta nor the subcellular localization of PA28alpha was affected in PA28gamma(-/-) cells. These results indicate that PA28gamma functions as a regulator of cell proliferation and body growth in mice and suggest that neither PA28alpha nor PA28beta compensates for the PA28gamma deficiency.