Chemical genetics reveals an RGS/G-protein role in the action of a compound

RGS2 and female common diseases: a guard of women's health

Currently, women around the world are still suffering from various female common diseases with the high incidence, such as ovarian cancer, uterine fibroids and preeclampsia (PE), and some diseases are even with the high mortality rate. As a negative feedback regulator in G Protein-Coupled Receptor signaling (GPCR), the Regulator of G-protein Signaling (RGS) protein family participates in regulating kinds of cell biological functions by destabilizing the enzyme-substrate complex through the transformation of hydrolysis of G Guanosine Triphosphate (GTP). Recent work has indicated that, the Regulator of G-protein Signaling 2 (RGS2), a member belonging to the RGS protein family, is closely associated with the occurrence and development of certain female diseases, providing with the evidence that RGS2 functions in sustaining women's health. In this review paper, we summarize the current knowledge of RGS2 in female common diseases, and also tap and discuss its therapeutic potential by targeting multiple mechanisms.

Antiaging agents: safe interventions to slow aging and healthy life span extension

Human longevity has increased dramatically during the past century. More than 20% of the 9 billion population of the world will exceed the age of 60 in 2050. Since the last three decades, some interventions and many preclinical studies have been found to show slowing aging and increasing the healthy lifespan of organisms from yeast, flies, rodents to nonhuman primates. The interventions are classified into two groups: lifestyle modifications and pharmacological/genetic manipulations. Some genetic pathways have been characterized to have a specific role in controlling aging and lifespan. Thus, all genes in the pathways are potential antiaging targets. Currently, many antiaging compounds target the calorie-restriction mimetic, autophagy induction, and putative enhancement of cell regeneration, epigenetic modulation of gene activity such as inhibition of histone deacetylases and DNA methyltransferases, are under development. It appears evident that the exploration of new targets for these antiaging agents based on biogerontological research provides an incredible opportunity for the healthcare and pharmaceutical industries. The present review focus on the properties of slow aging and healthy life span extension of natural products from various biological resources, endogenous substances, drugs, and synthetic compounds, as well as the mechanisms of targets for antiaging evaluation. These bioactive compounds that could benefit healthy aging and the potential role of life span extension are discussed.

Acute and 28-days subacute toxicity studies of Gαq-RGS2 signaling inhibitor

Background

The aim of study was to evaluate the single oral dose and 28 day repeated oral administration toxicity profile of the synthetic compound Gαq-RGS2 signaling inhibitor, (1-(5-chloro-2-hydroxyphenyl)-3-(4-(trifluoromethyl)phenyl)-1 H-1,2,4-triazol-5(4 H)-one) as per OECD guideline 425 (2008a) and 407 (2008b), respectively.

Results

In acute toxicity study, a single oral dose administration of Gαq-RGS2 signaling inhibitor did not show any mortality at doses of 5, 50, 300 and 2000 mg/kg within 24 h and 14 days. The treatment of Gαq-RGS2 signaling inhibitor at dose 10 and 100 mg/kg for 28 days did not show any mortality, significant changes in the increase of body weight, various organ damage markers, hematological parameters, relative organ/body weight ratio and microscopic anatomical texture of essential organs as compared to vehicle and normal control.

Conclusions

A single oral administration of Gαq-RGS2 signaling inhibitor up to dose of 2000 mg/kg in mice and repeated administration of Gαq-RGS2 signaling inhibitor at higher dose 100 mg/kg for 28 days in the rats is safe.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42826-021-00093-1.

Studies of an insecticidal inhibitor of acetyl-CoA carboxylase in the nematode C. elegans

We have studied the mode of action of the insecticide spirotetramat in the nematode Caenorhabditis elegans. A combination of symptomology, forward genetics and genome editing show that spirotetramat acts on acetyl-CoA carboxylase (ACC) in C. elegans, as it does in insects. We found C. elegans embryos exposed to spirotetramat show a cell division defect which closely resembles the phenotype of loss-of-function mutations in the gene pod-2, which encodes ACC. We then identified two mutations in the carboxyl transferase domain of pod-2 (ACC) which confer resistance and were confirmed using CRISPR/Cas9. One of these mutations substitutes an invertebrate-specific amino acid with one ubiquitous in other taxa; this residue may, therefore, be a determinant of the selectivity of spirotetramat for invertebrates. Such a mutation may also be the target of selection for resistance in the field. Our study is a further demonstration of the utility of C. elegans in studying bioactive chemicals.

Regulator of G-Protein Signaling (RGS) Protein Modulation of Opioid Receptor Signaling as a Potential Target for Pain Management

Opioid drugs are the gold standard for the management of pain, but their use is severely limited by dangerous and unpleasant side effects. All clinically available opioid analgesics bind to and activate the mu-opioid receptor (MOR), a heterotrimeric G-protein-coupled receptor, to produce analgesia. The activity of these receptors is modulated by a family of intracellular RGS proteins or regulators of G-protein signaling proteins, characterized by the presence of a conserved RGS Homology (RH) domain. These proteins act as negative regulators of G-protein signaling by serving as GTPase accelerating proteins or GAPS to switch off signaling by both the Gα and βγ subunits of heterotrimeric G-proteins. Consequently, knockdown or knockout of RGS protein activity enhances signaling downstream of MOR. In this review we discuss current knowledge of how this activity, across the different families of RGS proteins, modulates MOR activity, as well as activity of other members of the opioid receptor family, and so pain and analgesia in animal models, with particular emphasis on RGS4 and RGS9 families. We discuss inhibition of RGS proteins with small molecule inhibitors that bind to sensitive cysteine moieties in the RH domain and the potential for targeting this family of intracellular proteins as adjuncts to provide an opioid sparing effect or as standalone analgesics by promoting the activity of endogenous opioid peptides. Overall, we conclude that RGS proteins may be a novel drug target to provide analgesia with reduced opioid-like side effects, but that much basic work is needed to define the roles for specific RGS proteins, particularly in chronic pain, as well as a need to develop newer inhibitors.

Regulator of G-protein signaling (RGS) proteins as drug targets: Progress and future potentials

G protein-coupled receptors (GPCRs) play critical roles in regulating processes such as cellular homeostasis, responses to stimuli, and cell signaling. Accordingly, GPCRs have long served as extraordinarily successful drug targets. It is therefore not surprising that the discovery in the mid-1990s of a family of proteins that regulate processes downstream of GPCRs generated great excitement in the field. This finding enhanced the understanding of these critical signaling pathways and provided potentially new targets for pharmacological intervention. These regulators of G-protein signaling (RGS) proteins were viewed by many as nodes downstream of GPCRs that could be targeted with small molecules to tune signaling processes. In this review, we provide a brief overview of the discovery of RGS proteins and of the gradual and continuing discovery of their roles in disease states, focusing particularly on cancer and neurological disorders. We also discuss high-throughput screening efforts that have led to the discovery first of peptide-based and then of small-molecule inhibitors targeting a subset of the RGS proteins. We explore the unique mechanisms of RGS inhibition these chemical tools have revealed and highlight the most up-to-date studies using these tools in animal experiments. Finally, we discuss the future opportunities in the field, as there are clearly more avenues left to be explored and potentials to be realized.

Protective effects of Gαq-RGS2 signalling inhibitor in aminophylline induced cardiac arrhythmia

An over activation of GPCR mediated Gαq dependent signalling pathway is widely associated with the development of cardiovascular abnormalities. The objective of study was to evaluate the effects of (1-(5-chloro-2-hydroxyphenyl)-3-(4-(trifluoromethyl)phenyl)-1H-1,2,4-triazol-5(4H)-one) Gαq-RGS2 signalling inhibitor on aminophylline induced cardiac arrhythmia in rats. Rats were divided into four groups; normal rats, disease control (DC, aminophylline treated 100 mg/kg/d, i.p., 7 days), Gαq-RGS2 signalling inhibitor (1 and 10 mg/kg/d, p.o., 7 days) treated arrhythmic rats. Gαq-RGS2 signalling inhibitor was administered 1 hour prior to the administration of aminophylline from 1st day. At the end of study, heart rate (HR), QRS complex, QT and RR interval were measured by electrocardiogram (ECG) of anesthetized rats. Systolic and diastolic blood pressure (SBP, DBP) by invasive method, cardiac damage markers (CK-MB, LDH) in the serum, antioxidant enzymes (SOD, catalase, glutathione) and cAMP level were measured. The treatment of Gαq-RGS2 signalling inhibitor (10 mg/kg) significantly abolished the aminophylline induced increase of heart rate, prolongation of RR and QT interval as compared to DC rats. Gαq-RGS2 signalling inhibitor (1 and 10 mg/kg) significantly attenuated the prolongation in QRS complex, increase of SBP, DBP and cardiac damage markers as compared to DC. Gαq-RGS2 signalling inhibitor treatment (10 mg/kg) significantly reduced the cAMP level and increased the antioxidant enzyme level as compared to DC. Gαq-RGS2 signalling inhibitor (10 mg/kg) showed the protective effect against the aminophylline induced cardiac arrhythmia and it might be due to improvement in cAMP level and antioxidant enzymes.

Inactivity periods and postural change speed can explain atypical postural change patterns of Caenorhabditis elegans mutants

BACKGROUND

With rapid advances in genome sequencing and editing technologies, systematic and quantitative analysis of animal behavior is expected to be another key to facilitating data-driven behavioral genetics. The nematode Caenorhabditis elegans is a model organism in this field. Several video-tracking systems are available for automatically recording behavioral data for the nematode, but computational methods for analyzing these data are still under development.

RESULTS

In this study, we applied the Gaussian mixture model-based binning method to time-series postural data for 322 C. elegans strains. We revealed that the occurrence patterns of the postural states and the transition patterns among these states have a relationship as expected, and such a relationship must be taken into account to identify strains with atypical behaviors that are different from those of wild type. Based on this observation, we identified several strains that exhibit atypical transition patterns that cannot be fully explained by their occurrence patterns of postural states. Surprisingly, we found that two simple factors-overall acceleration of postural movement and elimination of inactivity periods-explained the behavioral characteristics of strains with very atypical transition patterns; therefore, computational analysis of animal behavior must be accompanied by evaluation of the effects of these simple factors. Finally, we found that the npr-1 and npr-3 mutants have similar behavioral patterns that were not predictable by sequence homology, proving that our data-driven approach can reveal the functions of genes that have not yet been characterized.

CONCLUSION

We propose that elimination of inactivity periods and overall acceleration of postural change speed can explain behavioral phenotypes of strains with very atypical postural transition patterns. Our methods and results constitute guidelines for effectively finding strains that show "truly" interesting behaviors and systematically uncovering novel gene functions by bioimage-informatic approaches.

RGS proteins as targets in the treatment of intestinal inflammation and visceral pain: New insights and future perspectives

Regulators of G protein signaling (RGS) proteins provide timely termination of G protein-coupled receptor (GPCR) responses. Serving as a central control point in GPCR signaling cascades, RGS proteins are promising targets for drug development. In this review, we discuss the involvement of RGS proteins in the pathophysiology of the gastrointestinal inflammation and their potential to become a target for anti-inflammatory drugs. Specifically, we evaluate the emerging evidence for modulation of selected receptor families: opioid, cannabinoid and serotonin by RGS proteins. We discuss how the regulation of RGS protein level and activity may modulate immunological pathways involved in the development of intestinal inflammation. Finally, we propose that RGS proteins may serve as a prognostic factor for survival rate in colorectal cancer. The ideas introduced in this review set a novel conceptual framework for the utilization of RGS proteins in the treatment of gastrointestinal inflammation, a growing major concern worldwide.

Pharmacological lifespan extension of invertebrates

There is considerable interest in identifying small, drug-like compounds that slow aging in multiple species, particularly in mammals. Such compounds may prove to be useful in treating and retarding age-related disease in humans. Just as invertebrate models have been essential in helping us understand the genetic pathways that control aging, these model organisms are also proving valuable in discovering chemical compounds that influence longevity. The nematode Caenorhabditis elegans has numerous advantages for such studies including its short lifespan and has been exploited by a number of investigators to find compounds that impact aging. Here, we summarize the progress being made in identifying compounds that extend the lifespan of invertebrates, and introduce the challenges we face in translating this research into human therapies.

Regulators of G-protein signaling and their Gα substrates: promises and challenges in their use as drug discovery targets

Because G-protein coupled receptors (GPCRs) continue to represent excellent targets for the discovery and development of small-molecule therapeutics, it is posited that additional protein components of the signal transduction pathways emanating from activated GPCRs themselves are attractive as drug discovery targets. This review considers the drug discovery potential of two such components: members of the "regulators of G-protein signaling" (RGS protein) superfamily, as well as their substrates, the heterotrimeric G-protein α subunits. Highlighted are recent advances, stemming from mouse knockout studies and the use of "RGS-insensitivity" and fast-hydrolysis mutations to Gα, in our understanding of how RGS proteins selectively act in (patho)physiologic conditions controlled by GPCR signaling and how they act on the nucleotide cycling of heterotrimeric G-proteins in shaping the kinetics and sensitivity of GPCR signaling. Progress is documented regarding recent activities along the path to devising screening assays and chemical probes for the RGS protein target, not only in pursuits of inhibitors of RGS domain-mediated acceleration of Gα GTP hydrolysis but also to embrace the potential of finding allosteric activators of this RGS protein action. The review concludes in considering the Gα subunit itself as a drug target, as brought to focus by recent reports of activating mutations to GNAQ and GNA11 in ocular (uveal) melanoma. We consider the likelihood of several strategies for antagonizing the function of these oncogene alleles and their gene products, including the use of RGS proteins with Gα(q) selectivity.

A RasGRP, C. elegans RGEF-1b, couples external stimuli to behavior by activating LET-60 (Ras) in sensory neurons

RasGRPs, which load GTP onto Ras and Rap1, are expressed in vertebrate and invertebrate neurons. The functions, regulation, and mechanisms of action of neuronal RasGRPs are unknown. Here, we show how C. elegans RGEF-1b, a prototypical neuronal RasGRP, regulates a critical behavior. Chemotaxis to volatile odorants was disrupted in RGEF-1b-deficient (rgef-1⁻/⁻) animals and wild-type animals expressing dominant-negative RGEF-1b in AWC sensory neurons. AWC-specific expression of RGEF-1b-GFP restored chemotaxis in rgef-1⁻/⁻ mutants. Signals disseminated by RGEF-1b in AWC neurons activated a LET-60 (Ras)-MPK-1 (ERK) signaling cascade. Other RGEF-1b and LET-60 effectors were dispensable for chemotaxis. A bifunctional C1 domain controlled intracellular targeting and catalytic activity of RGEF-1b and was essential for sensory signaling in vivo. Chemotaxis was unaffected when Ca²+-binding EF hands and a conserved phosphorylation site of RGEF-1b were inactivated. Diacylglycerol-activated RGEF-1b links external stimuli (odorants) to behavior (chemotaxis) by activating the LET-60-MPK-1 pathway in specific neurons.

Insights into RGS protein function from studies in Caenorhabditis elegans

The nematode worm, Caenorhabditis elegans, contains orthologs of most regulator of G protein signaling (RGS) protein subfamilies and all four G protein α-subunit subfamilies found in mammals. Every C. elegans RGS and Gα gene has been knocked out, and the in vivo functions and Gα targets of a number of RGS proteins have been characterized in detail. This has revealed a complex relationship between the RGS and Gα proteins, in which multiple RGS proteins can regulate the same Gα protein, either by acting redundantly or by exerting control over signaling under different circumstances or in different cells. RGS proteins that are coexpressed can also show specificity for distinct Gα targets in vivo, and the determinants of such specificity can reside outside of the RGS domain. This review will discuss how analysis in C. elegans may aid us in achieving a full understanding of the physiological functions of RGS proteins.

Polyplexed flow cytometry protein interaction assay: a novel high-throughput screening paradigm for RGS protein inhibitors

Intracellular signaling cascades are a series of regulated protein-protein interactions that may provide a number of targets for potential drug discovery. Here, the authors examine the interaction of regulators of G-protein signaling (RGS) proteins with the G-protein Galphao, using a flow cytometry protein interaction assay (FCPIA). FCPIA accurately measures nanomolar binding constants of this protein-protein interaction and has been used in high-throughput screening. This report focuses on 5 RGS proteins (4, 6, 7, 8, and 16). To increase the content of screens, the authors assessed high-throughput screening of these RGS proteins in multiplex, by establishing binding constants of each RGS with Galphao in isolation, and then in a multiplex format with 5 RGS proteins present. To use this methodology as a higher-content multiplex protein-protein interaction screen, they established Z-factor values for RGS proteins in multiplex of 0.73 to 0.92, indicating this method is suitable for screening using FCPIA. To increase throughput, they also compressed a set of 8000 compounds by combining 4 compounds in a single assay well. Subsequent deconvolution of the compounds mixtures verified the identification of active compounds at specific RGS targets in their mixtures using the polyplexed FCPIA method.

Invertebrate and fungal model organisms: emerging platforms for drug discovery

Early-stage translational research programs have increasingly exploited yeast, worms and flies to model human disease. These genetically tractable organisms represent flexible platforms for small molecule and drug target discovery. This review highlights recent examples of how model organisms are integrated into chemical genomic approaches to drug discovery with an emphasis on fungal yeast, nematode Caenorhabditis elegans and fruit fly Drosophila melanogaster. The roles of these organisms are expanding as novel models of human disease are developed and novel high-throughput screening technologies are created and adapted for drug discovery.

The anticonvulsant ethosuximide disrupts sensory function to extend C. elegans lifespan

Ethosuximide is a medication used to treat seizure disorders in humans, and we previously demonstrated that ethosuximide can delay age-related changes and extend the lifespan of the nematode Caenorhabditis elegans. The mechanism of action of ethosuximide in lifespan extension is unknown, and elucidating how ethosuximide functions is important for defining endogenous processes that influence lifespan and for exploring the potential of ethosuximide as a therapeutic for age-related diseases. To identify genes that mediate the activity of ethosuximide, we conducted a genetic screen and identified mutations in two genes, che-3 and osm-3, that cause resistance to ethosuximide-mediated toxicity. Mutations in che-3 and osm-3 cause defects in overlapping sets of chemosensory neurons, resulting in defective chemosensation and an extended lifespan. These findings suggest that ethosuximide extends lifespan by inhibiting the function of specific chemosensory neurons. This model is supported by the observation that ethosuximide-treated animals displayed numerous phenotypic similarities with mutants that have chemosensory defects, indicating that ethosuximide inhibits chemosensory function. Furthermore, ethosuximide extends lifespan by inhibiting chemosensation, since the long-lived osm-3 mutants were resistant to the lifespan extension caused by ethosuximide. These studies demonstrate a novel mechanism of action for a lifespan-extending drug and indicate that sensory perception has a critical role in controlling lifespan. Sensory perception also influences the lifespan of Drosophila, suggesting that sensory perception has an evolutionarily conserved role in lifespan control. These studies highlight the potential of ethosuximide and related drugs that modulate sensory perception to extend lifespan in diverse animals.

Aging is a major factor that contributes to disease and disability in humans, but no medicines have been demonstrated to delay human aging. We previously conducted a screen for FDA-approved drugs that can extend the lifespan of the nematode worm C. elegans, resulting in the identification of ethosuximide, a medicine used to treat epilepsy. To elucidate the mechanism of action of ethosuximide in lifespan extension, we conducted a genetic screen for C. elegans mutations that cause resistance to ethosuximide. Here, we describe the identification of genes that are critical for ethosuximide sensitivity. These genes are necessary for the function of neurons that mediate sensory perception. Furthermore, ethosuximide treatment caused defects in sensory perception. These results indicate that ethosuximide affects lifespan by inhibiting neurons that function in the perception of sensory cues. These studies highlight the importance of sensory neurons in lifespan determination and demonstrate that a drug can act on specific cells within the nervous system to extend lifespan. Sensory perception also modulates Drosophila lifespan, suggesting this is an evolutionarily conserved relationship. Our results indicate that sensory perception may be a promising target for pharmacological extension of lifespan in a variety of animals.

C. elegans: A Model for Understanding Lipid Accumulation

Regulation and coordination of lipid metabolism involve complex interactions between the feeding regulatory centres in the nervous system and the regulated uptake, intracellular transport, storage, and utilization of stored lipids. As energy is essential to all cellular processes, it is thought that complex networks have evolved to ensure survival by maintaining adequate energy reservoirs. However, in times of nutrient abundance and imbalance, improper regulation and coordination of these networks can lead to obesity and other metabolic diseases and syndromes. Obesity genes must be considered as molecular components of such networks which function at an organismal level to orchestrate energy intake and expenditure. Thus, the functions of obesity genes must be understood within the context of these networks in intact animals. Since the majority of genes required for lipid homeostasis are evolutionarily conserved, much information can be obtained relevant to complex organisms by studying simple eukaryotes like C. elegans. Its genetic tractability makes C. elegans a highly attractive platform for identifying lipid regulatory pathways, drugs, and their molecular targets which ultimately will help us to understand the origin of metabolic diseases such as obesity and diabetes. Here we briefly present some central aspects of lipid accumulation in C. elegans and discuss its merits as a platform for identification and development of novel bioactive compounds regulating lipid storage.

Whole organism approaches to chemical genomics: the promising role of zebrafish (Danio rerio)

Chemical genomics is a new and rapidly developing field. It refers to the use of cell-permeable small molecules, which are highly specific for their protein targets, in order to dissect biological pathways and to discover new drug leads. Small-molecule screening is usually limited to high-throughput approaches that use defined cell lines; however, whole organism screening is gaining increasing attention. This review addresses the latter concept and highlights the advances in whole organism-based screening, with an emphasis on the use of the zebrafish (Danio rerio).

Evolutionary conservation of drug action on lipoprotein metabolism-related targets

Genetic analysis has shown that the slower than normal rhythmic defecation behavior of the clk-1 mutants of Caenorhabditis elegans is the result of altered lipoprotein metabolism. We show here that this phenotype can be suppressed by drugs that affect lipoprotein metabolism, including drugs that affect HMG-CoA reductase activity, reverse cholesterol transport, or HDL levels. These pharmacological effects are highly specific, as these drugs affect defecation only in clk-1 mutants and not in the wild-type and do not affect other behaviors of the mutants. Furthermore, drugs that affect processes not directly related to lipid metabolism show no or minimal activity. Based on these findings, we carried out a compound screen that identified 190 novel molecules that are active on clk-1 mutants, 15 of which also specifically decrease the secretion of apolipoprotein B (apoB) from HepG2 hepatoma cells. The other 175 compounds are potentially active on lipid-related processes that cannot be targeted in cell culture. One compound, CHGN005, was tested and found to be active at reducing apoB secretion in intestinal Caco-2 cells as well as in HepG2 cells. This compound was also tested in a mouse model of dyslipidemia and found to decrease plasma cholesterol and triglyceride levels. Thus, target processes for pharmacological intervention on lipoprotein synthesis, transport, and metabolism are conserved between nematodes and vertebrates, which allows the use of C. elegans for drug discovery.

CCG-1423: a small-molecule inhibitor of RhoA transcriptional signaling

Lysophosphatidic acid receptors stimulate a Galpha(12/13)/RhoA-dependent gene transcription program involving the serum response factor (SRF) and its coactivator and oncogene, megakaryoblastic leukemia 1 (MKL1). Inhibitors of this pathway could serve as useful biological probes and potential cancer therapeutic agents. Through a transcription-based high-throughput serum response element-luciferase screening assay, we identified two small-molecule inhibitors of this pathway. Mechanistic studies on the more potent CCG-1423 show that it acts downstream of Rho because it blocks SRE.L-driven transcription stimulated by Galpha(12)Q231L, Galpha(13)Q226L, RhoA-G14V, and RhoC-G14V. The ability of CCG-1423 to block transcription activated by MKL1, but not that induced by SRF-VP16 or GAL4-VP16, suggests a mechanism targeting MKL/SRF-dependent transcriptional activation that does not involve alterations in DNA binding. Consistent with its role as a Rho/SRF pathway inhibitor, CCG-1423 displays activity in several in vitro cancer cell functional assays. CCG-1423 potently (<1 mumol/L) inhibits lysophosphatidic acid-induced DNA synthesis in PC-3 prostate cancer cells, and whereas it inhibits the growth of RhoC-overexpressing melanoma lines (A375M2 and SK-Mel-147) at nanomolar concentrations, it is less active on related lines (A375 and SK-Mel-28) that express lower levels of Rho. Similarly, CCG-1423 selectively stimulates apoptosis of the metastasis-prone, RhoC-overexpressing melanoma cell line (A375M2) compared with the parental cell line (A375). CCG-1423 inhibited Rho-dependent invasion by PC-3 prostate cancer cells, whereas it did not affect the Galpha(i)-dependent invasion by the SKOV-3 ovarian cancer cell line. Thus, based on its profile, CCG-1423 is a promising lead compound for the development of novel pharmacologic tools to disrupt transcriptional responses of the Rho pathway in cancer.

Chemical genetics: reshaping biology through chemistry

To understand biological processes, biologists typically study how perturbations of protein functions affect the phenotype. Protein activity in living cells can be influenced in many different ways: by manipulation of the genomic information, by injecting inhibitory antibodies, or, more recently, by the use of ribonucleic acid-medicated interference (RNAi). All these methods have proven to be extremely helpful, as they possess a high degree of specificity. However, they are less suitable for experiments requiring precise timing and fast reversibility of the perturbation. The advantage of small molecules is that they specifically interact with their target on a fast time scale and often in a reversible manner. In the last 15 years, this approach, termed "chemical genetics," has received a lot of attention. The term genetics pays tribute to the analogy between chemical genetics and the classic genetic approach, where manipulations at the gene level are used to draw conclusions about the function of the corresponding protein. Chemical genetics has only recently been used as a systematic approach in biology. The term was coined in the 1990's, when combinatorial chemistry was developed as a fast method to synthesize large compound libraries [Mitchison (1994) "Towards a pharmacological genetics," Chem. Biol. 1, 3-6; Schreiber (1998) "Chemical genetics resulting from a passion for synthetic organic chemistry," Bioorg. Med. Chem. 6, 1127-1152].

The RGS protein inhibitor CCG-4986 is a covalent modifier of the RGS4 Galpha-interaction face

Regulator of G-protein signaling (RGS) proteins accelerate GTP hydrolysis by Galpha subunits and are thus crucial to the timing of G protein-coupled receptor (GPCR) signaling. Small molecule inhibition of RGS proteins is an attractive therapeutic approach to diseases involving dysregulated GPCR signaling. Methyl-N-[(4-chlorophenyl)sulfonyl]-4-nitrobenzenesulfinimidoate (CCG-4986) was reported as a selective RGS4 inhibitor, but with an unknown mechanism of action [D.L. Roman, J.N. Talbot, R.A. Roof, R.K. Sunahara, J.R. Traynor, R.R. Neubig, Identification of small-molecule inhibitors of RGS4 using a high-throughput flow cytometry protein interaction assay, Mol. Pharmacol. 71 (2007) 169-75]. Here, we describe its mechanism of action as covalent modification of RGS4. Mutant RGS4 proteins devoid of surface-exposed cysteine residues were characterized using surface plasmon resonance and FRET assays of Galpha binding, as well as single-turnover GTP hydrolysis assays of RGS4 GAP activity, demonstrating that cysteine-132 within RGS4 is required for sensitivity to CCG-4986 inhibition. Sensitivity to CCG-4986 can be engendered within RGS8 by replacing the wildtype residue found in this position to cysteine. Mass spectrometry analysis identified a 153-Dalton fragment of CCG-4986 as being covalently attached to the surface-exposed cysteines of the RGS4 RGS domain. We conclude that the mechanism of action of the RGS protein inhibitor CCG-4986 is via covalent modification of Cys-132 of RGS4, likely causing steric hindrance with the all-helical domain of the Galpha substrate.

Caenorhabditis elegans: a versatile platform for drug discovery

Drug discovery and drug target identification are two intimately linked facets of intervention strategies aimed at effectively combating pathological conditions in humans. Simple model organisms provide attractive platforms for devising and streamlining efficient drug discovery and drug target identification methodologies. The nematode worm Caenorhabditis elegans has emerged as a particularly convenient and versatile tool that can be exploited to achieve these goals. Although C. elegans is a relatively modern addition to the arsenal of model organisms, its biology has already been investigated to an exceptional level. This, coupled with effortless handling and a notable low cost of cultivation and maintenance, allows seamless implementation of high-throughput drug screening approaches as well as in-depth genetic and biochemical studies of the molecular pathways targeted by specific drugs. In this review, we introduce C. elegans as a model organism with significant advantages toward the identification of molecular drug targets. In addition, we discuss the value of the worm in the development of drug screening and drug evaluation protocols. The unique features of C. elegans, which greatly facilitate drug studies, hold promise for both deciphering disease pathogenesis and formulating educated and effective therapeutic interventions.

Experimental approaches to identify genetic networks

Systems biology offers the promise of a fully integrated view of cellular physiology. To realize this potential requires the analysis of diverse genome-wide datasets and the incorporation of these analyses into integrated networks. In the past decade, the budding yeast Saccharomyces cerevisiae has provided the benchmark for the design of such large-scale experiments. Many of these experimental approaches have been adopted and adapted to study other systems, including worm, fly, fish and mammalian cultured cells, using an ingenious set of molecular tools.