PKA regulatory subunits mediate synergy among conserved G-protein-coupled receptor cascades

Calcium sensing receptor regulate claudin-14 via PKA-STAT3 pathway in rat model of nephrolithiasis

Background

The calcium-sensitive receptor (CaSR) has been identified as a key factor in the formation of kidney stones. A substantial body of research has illuminated the function of CaSR in stone formation with respect to oxidative stress, epithelial injury, crystal adhesion, and stone-associated proteins. Nevertheless, as a pivotal molecule in renal calcium excretion, its pathway that contributes to stone formation by regulating calcium supersaturation remains underexplored.

Methods

An in vitro rat calcium oxalate kidney stone model was established through the co-cultivation of calcium oxalate monohydrate (COM) with NRK-52E cells, while an in vivo model was constructed using the ethylene glycol method. Subsequently, the level of the CaSR-claudin-14 pathway was determined. To further elucidate the molecular pathway of CaSR-mediated regulation of claudin-14, drugs were selectively added to the in vitro and ex vivo kidney stone models, and the expression of claudin-14 and the levels of stone formation were detected. Moreover, the direct regulation of claudin-14 by CaSR with STAT3 serving as a transcription factor was examined via the dual luciferase assay. Eventually, a Cldn-14 knockout rat model and a model of kidney stone induction by ethylene glycol were generated using CRISPR-Cas9 technology to further clarify the role of claudin-14 in the CaSR-regulated formation of kidney stones.

Results

In vitro and in vivo observations revealed that calcium oxalate induces high expression of CaSR-claudin-14. Specifically, CaSR regulates claudin-14 expression through phosphorylation modification of STAT3 via protein kinase A (PKA). In vitro, the intervention of PKA and STAT3 reversed the elevated claudin-14 levels and stone formation induced by CaSR. Finally, we generated cldn-14 knockout rats using CRISPR-Cas9 technology and observed that ethylene glycol still induced stone formation in these animals. Nevertheless, the specific activation or inhibition of CaSR demonstrated no notable impact on stone formation.

Conclusion

The results of our study indicate that calcium oxalate crystals induce the activation of the pro-stone pathway of CaSR. That is, activated CaSR regulates claudin-14 levels via the PKA-STAT3 pathway, which further promotes calcium salt stone formation. The role of CaSR in the regulation of stone homeostasis is further enriched.

Synaptic retrograde regulation of the PKA-induced SNAP-25 and Synapsin-1 phosphorylation

BACKGROUND

Bidirectional communication between presynaptic and postsynaptic components contribute to the homeostasis of the synapse. In the neuromuscular synapse, the arrival of the nerve impulse at the presynaptic terminal triggers the molecular mechanisms associated with ACh release, which can be retrogradely regulated by the resulting muscle contraction. This retrograde regulation, however, has been poorly studied. At the neuromuscular junction (NMJ), protein kinase A (PKA) enhances neurotransmitter release, and the phosphorylation of the molecules of the release machinery including synaptosomal associated protein of 25 kDa (SNAP-25) and Synapsin-1 could be involved.

METHODS

Accordingly, to study the effect of synaptic retrograde regulation of the PKA subunits and its activity, we stimulated the rat phrenic nerve (1 Hz, 30 min) resulting or not in contraction (abolished by µ-conotoxin GIIIB). Changes in protein levels and phosphorylation were detected by western blotting and cytosol/membrane translocation by subcellular fractionation. Synapsin-1 was localized in the levator auris longus (LAL) muscle by immunohistochemistry.

RESULTS

Here we show that synaptic PKA Cβ subunit regulated by RIIβ or RIIα subunits controls activity-dependent phosphorylation of SNAP-25 and Synapsin-1, respectively. Muscle contraction retrogradely downregulates presynaptic activity-induced pSynapsin-1 S9 while that enhances pSNAP-25 T138. Both actions could coordinately contribute to decreasing the neurotransmitter release at the NMJ.

CONCLUSION

This provides a molecular mechanism of the bidirectional communication between nerve terminals and muscle cells to balance the accurate process of ACh release, which could be important to characterize molecules as a therapy for neuromuscular diseases in which neuromuscular crosstalk is impaired.

Michaelis-Menten Quantification of Ligand Signaling Bias Applied to the Promiscuous Vasopressin V2 Receptor

Activation of G protein-coupled receptors by agonists may result in the activation of one or more G proteins and recruitment of arrestins. The extent of the activation of each of these pathways depends on the intrinsic efficacy of the ligand. Quantification of intrinsic efficacy relative to a reference compound is essential for the development of novel compounds. In the operational model, changes in efficacy can be compensated by changes in the "functional" affinity, resulting in poorly defined values. To separate the effects of ligand affinity from the intrinsic activity of the receptor, we developed a Michaelis-Menten based quantification of G protein activation bias that uses experimentally measured ligand affinities and provides a single measure of ligand efficacy. We used it to evaluate the signaling of a promiscuous model receptor, the Vasopressin V2 receptor (V2R). Using BRET-based biosensors, we show that the V2R engages many different G proteins across all G protein subfamilies in response to its primary endogenous agonist, arginine vasopressin, including Gs and members of the Gi/o and G12/13 families. These signaling pathways are also activated by the synthetic peptide desmopressin, oxytocin, and the nonmammalian hormone vasotocin. We compared bias quantification using the operational model with Michaelis-Menten based quantification; the latter accurately quantified ligand efficacies despite large difference in ligand affinities. Together, these results showed that the V2R is promiscuous in its ability to engage several G proteins and that its' signaling profile is biased by small structural changes in the ligand. SIGNIFICANCE STATEMENT: By modelling the G protein activation as Michaelis-Menten reaction, we developed a novel way of quantifying signalling bias. V2R activates, or at least engages, G proteins from all G protein subfamilies, including Gi2, Gz, Gq, G12, and G13. Their relative activation may explain its Gs-independent signalling.

Tracking mutation and drug-driven alterations of oncokinase conformations

Numerous kinases act as central nodes of cellular signaling networks. As such, many of these enzymes function as molecular switches for coordinating spatiotemporal signal transmission. Typically, it is the compartmentalized phosphorylation of protein substrates which relays the transient input signal to determine decisive physiological cell responses. Genomic alterations affect kinase abundance and/or their activities which contribute to the malignant transformation, progression, and metastasis of human cancers. Thus, major drug discovery efforts have been made to identify lead molecules targeting clinically relevant oncokinases. The concept of personalized medicine aims to apply the therapeutic agent with the highest efficacy towards a patient-specific mutation. Here, we discuss the implementation of a cell-based reporter system which may foster the decision-making process to identify the most promising lead-molecules. We present a modular kinase conformation (KinCon) biosensor platform for live-cell analyses of kinase activity states. This biosensor facilitates the recording of kinase activity conformations of the wild-type and the respective mutated kinase upon lead molecule exposure. We reflect proof-of-principle studies demonstrating how this technology has been extended to profile drug properties of the full-length kinases BRAF and MEK1 in intact cells. Further, we pinpoint how this technology may open new avenues for systematic and patient-tailored drug discovery efforts. Overall, this precision-medicineoriented biosensor concept aims to determine kinase inhibitor specificity and anticipate their drug efficacies.

Regulator of G Protein Signaling Contributes to the Development and Aflatoxin Biosynthesis in Aspergillus flavus through the Regulation of Gα Activity

Heterotrimeric G-proteins play crucial roles in growth, asexual development, and pathogenicity of fungi. The regulator of G-protein signaling (RGS) proteins function as negative regulators of the G proteins to control the activities of GTPase in Gα subunits. In this study, we functionally characterized the six RGS proteins (i.e., RgsA, RgsB, RgsC, RgsD, RgsE, and FlbA) in the pathogenic fungus Aspergillus flavus. All the aforementioned RGS proteins were also found to be functionally different in conidiation, aflatoxin (AF) biosynthesis, and pathogenicity in A. flavus. Apart from FlbA, all other RGS proteins play a negative role in regulating both the synthesis of cyclic AMP (cAMP) and the activation of protein kinase A (PKA). Additionally, we also found that although RgsA and RgsE play a negative role in regulating the FadA-cAMP/PKA pathway, they function distinctly in aflatoxin biosynthesis. Similarly, RgsC is important for aflatoxin biosynthesis by negatively regulating the GanA-cAMP/PKA pathway. PkaA, which is the cAMP-dependent protein kinase catalytic subunit, also showed crucial influences on A. flavus phenotypes. Overall, our results demonstrated that RGS proteins play multiple roles in the development, pathogenicity, and AF biosynthesis in A. flavus through the regulation of Gα subunits and cAMP-PKA signals. IMPORTANCE RGS proteins, as crucial regulators of the G protein signaling pathway, are widely distributed in fungi, while little is known about their roles in Aspergillus flavus development and aflatoxin. In this study, we identified six RGS proteins in A. flavus and revealed that these proteins have important functions in the regulation of conidia, sclerotia, and aflatoxin formation. Our findings provide evidence that the RGS proteins function upstream of cAMP-PKA signaling by interacting with the Gα subunits (GanA and FadA). This study provides valuable information for controlling the contamination of A. flavus and mycotoxins produced by this fungus in pre- and postharvest of agricultural crops.

The implications of the purinergic signaling throughout pregnancy

Purinergic signaling is a necessary mechanism to trigger or even amplify cell communication. Its ligands, notably adenosine triphosphate (ATP) and adenosine, modulate specific membrane-bound receptors in virtually all human cells. Regardless of the stage of the pregnancy, cellular communication between maternal, placental, and fetal cells is the paramount mechanism to sustain its optimal status. In this review, we describe the crucial role of purinergic signaling on the regulation of the maternal-fetal trophic exchanges, immune control, and endocrine exchanges throughout pregnancy. The nature of the modulation of both ATP and adenosine on the embryo-maternal interface, going through placental invasion until birth delivery depends on the general maternal-fetal health state and consequently on the selective activation of their specific receptors. In addition, an increasing number of studies have been demonstrating the pivotal role of ATP and adenosine in modulating deleterious effects of suboptimal conditions of pregnancy. Here, we discuss the role of purinergic signaling on the balance that coordinates the embryo-maternal exchanges and a promising therapeutic venue in the context of pregnancy disorders.

Feedback control of the Gpr161-Gαs-PKA axis contributes to basal Hedgehog repression in zebrafish

Hedgehog (Hh) ligands act as morphogens to direct patterning and proliferation during embryonic development. Protein kinase A (PKA) is a central negative regulator of Hh signalling, and in the absence of Hh ligands, PKA activity prevents inappropriate expression of Hh target genes. The orphan G-protein-coupled receptor Gpr161 contributes to the basal Hh repression machinery by activating PKA. Gpr161 acts as an A-kinase-anchoring protein, and is itself phosphorylated by PKA, but the functional significance of PKA phosphorylation of Gpr161 in the context of Hh signalling remains unknown. Here, we show that loss of Gpr161 in zebrafish leads to constitutive activation of medium and low, but not maximal, levels of Hh target gene expression. Furthermore, we find that PKA phosphorylation-deficient forms of Gpr161, which we show directly couple to G_αs, display an increased sensitivity to Shh, resulting in excess high-level Hh signalling. Our results suggest that PKA feedback-mediated phosphorylation of Gpr161 may provide a mechanism for fine-tuning Gpr161 ciliary localisation and PKA activity.

PRKAR2A deficiency protects mice from experimental colitis by increasing IFN-stimulated gene expression and modulating the intestinal microbiota

Protein kinase A (PKA) plays an important role in regulating inflammation via its catalytic subunits. Recently, PKA regulatory subunits have been reported to directly modulate some signaling pathways and alleviate inflammation. However, the role of PKA regulatory subunits in colonic inflammation remains unclear. Therefore, we conducted this study to investigate the role of the PKA regulatory subunit PRKAR2A in colitis. We observed that PRKAR2A deficiency protected mice from dextran sulfate sodium (DSS)-induced experimental colitis. Our experiments revealed that the intestinal epithelial cell-specific deletion of Prkar2a contributed to this protection. Mechanistically, the loss of PRKAR2A in Prkar2a^-/- mice resulted in an increased IFN-stimulated gene (ISG) expression and altered gut microbiota. Inhibition of ISGs partially reversed the protective effects against DSS-induced colitis in Prkar2a^-/- mice. Antibiotic treatment and cross-fostering experiments demonstrated that the protection against DSS-induced colitis in Prkar2a^-/- mice was largely dependent on the gut microflora. Altogether, our work demonstrates a previously unidentified function of PRKAR2A in promoting DSS-induced colitis.

KinCon: Cell-based recording of full-length kinase conformations

The spectrum of kinase alterations displays distinct functional characteristics and requires kinase mutation-oriented strategies for therapeutic interference. Besides phosphotransferase activity, protein abundance, and intermolecular interactions, particular patient-mutations promote pathological kinase conformations. Despite major advances in identifying lead molecules targeting clinically relevant oncokinase functions, still many kinases are neglected and not part of drug discovery efforts. One explanation is attributed to challenges in tracking kinase activities. Chemical probes are needed to functionally annotate kinase functions, whose activities may not always depend on catalyzing phospho-transfer. Such non-catalytic kinase functions are related to transitions of full-length kinase conformations. Recent findings underline that cell-based reporter systems can be adapted to record conformation changes of kinases. Here, we discuss the possible applications of an extendable kinase conformation (KinCon) reporter toolbox for live-cell recording of kinase states. KinCon is a genetically encoded bioluminescence-based biosensor platform, which can be subjected for measurements of conformation dynamics of mutated kinases upon small molecule inhibitor exposure. We hypothesize that such biosensors can be utilized to delineate the molecular modus operandi for kinase and pseudokinase regulation. This should pave the path for full-length kinase-targeted drug discovery efforts aiming to identify single and combinatory kinase inhibitor therapies with increased specificity and efficacy.

The M2 muscarinic receptor, in association to M1 , regulates the neuromuscular PKA molecular dynamics

Muscarinic acetylcholine receptor 1 subtype (M₁ ) and muscarinic acetylcholine receptor 2 subtype (M₂ ) presynaptic muscarinic receptor subtypes increase and decrease, respectively, neurotransmitter release at neuromuscular junctions. M₂ involves protein kinase A (PKA), although the muscarinic regulation to form and inactivate the PKA holoenzyme is unknown. Here, we show that M₂ signaling inhibits PKA by downregulating Cβ subunit, upregulating RIIα/β and liberating RIβ and RIIα to the cytosol. This promotes PKA holoenzyme formation and reduces the phosphorylation of the transmitter release target synaptosome-associated protein 25 and the gene regulator cAMP response element binding. Instead, M₁ signaling, which is downregulated by M₂ , opposes to M₂ by recruiting R subunits to the membrane. The M₁ and M₂ reciprocal actions are performed through the anchoring protein A kinase anchor protein 150 as a common node. Interestingly, M₂ modulation on protein expression needs M₁ signaling. Altogether, these results describe the dynamics of PKA subunits upon M₂ muscarinic signaling in basal and under presynaptic nerve activity, uncover a specific involvement of the M₁ receptor and reveal the M₁ /M₂ balance to activate PKA to regulate neurotransmission. This provides a molecular mechanism to the PKA holoenzyme formation and inactivation which could be general to other synapses and cellular models.

Hedgehog and Gpr161: Regulating cAMP Signaling in the Primary Cilium

Compartmentalization of diverse types of signaling molecules contributes to the precise coordination of signal propagation. The primary cilium fulfills this function by acting as a spatiotemporally confined sensory signaling platform. For the integrity of ciliary signaling, it is mandatory that the ciliary signaling pathways are constantly attuned by alterations in both oscillating small molecules and the presence or absence of their sensor/effector proteins. In this context, ciliary G protein-coupled receptor (GPCR) pathways participate in coordinating the mobilization of the diffusible second messenger molecule 3',5'-cyclic adenosine monophosphate (cAMP). cAMP fluxes in the cilium are primarily sensed by protein kinase A (PKA) complexes, which are essential for the basal repression of Hedgehog (Hh) signaling. Here, we describe the dynamic properties of underlying signaling circuits, as well as strategies for second messenger compartmentalization. As an example, we summarize how receptor-guided cAMP-effector pathways control the off state of Hh signaling. We discuss the evidence that a macromolecular, ciliary-localized signaling complex, composed of the orphan GPCR Gpr161 and type I PKA holoenzymes, is involved in antagonizing Hh functions. Finally, we outline how ciliary cAMP-linked receptor pathways and cAMP-sensing signalosomes may become targets for more efficient combinatory therapy approaches to counteract dysregulation of Hh signaling.

cAMP-dependent activation of the Rac guanine exchange factor P-REX1 by type I protein kinase A (PKA) regulatory subunits

Regulatory subunits of protein kinase A (PKA) inhibit its kinase subunits. Intriguingly, their potential as cAMP-dependent signal transducers remains uncharacterized. We recently reported that type I PKA regulatory subunits (RIα) interact with phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchange factor 1 (P-REX1), a chemotactic Rac guanine exchange factor (RacGEF). Because P-REX1 is known to be phosphorylated and inhibited by PKA, its interaction with RIα suggests that PKA regulatory and catalytic subunits may fine-tune P-REX1 activity or those of its target pools. Here, we tested whether RIα acts as a cAMP-dependent factor promoting P-REX1-mediated Rac activation and cell migration. We observed that Gs-coupled EP2 receptors indeed promote endothelial cell migration via RIα-activated P-REX1. Expression of the P-REX1-PDZ1 domain prevented RIα/P-REX1 interaction, P-REX1 activation, and EP2-dependent cell migration, and P-REX1 silencing abrogated RIα-dependent Rac activation. RIα-specific cAMP analogs activated P-REX1, but lost this activity in RIα-knockdown cells, and cAMP pulldown assays revealed that P-REX1 preferentially interacts with free RIα. Moreover, purified RIα directly activated P-REX1 in vitro We also found that the RIα CNB-B domain is critical for the interaction with P-REX1, which was increased in RIα mutants, such as the acrodysostosis-associated mutant, that activate P-REX1 at basal cAMP levels. RIα and Cα PKA subunits targeted distinct P-REX1 molecules, indicated by an absence of phosphorylation in the active fraction of P-REX1. This was in contrast to the inactive fraction in which phosphorylated P-REX1 was present, suggesting co-existence of dual stimulatory and inhibitory effects. We conclude that PKA's regulatory subunits are cAMP-dependent signal transducers.

Drug addiction: a curable mental disorder?

Drug addiction is a chronic, relapsing brain disorder. Multiple neural networks in the brain including the reward system (e.g., the mesocorticolimbic system), the anti-reward/stress system (e.g., the extended amygdala), and the central immune system, are involved in the development of drug addiction and relapse after withdrawal from drugs of abuse. Preclinical and clinical studies have demonstrated that it is promising to control drug addiction by pharmacologically targeting the addiction-related systems in the brain. Here we review the pharmacological targets within the dopamine system, glutamate system, trace amine system, anti-reward system, and central immune system, which are of clinical interests. Furthermore, we discuss other potential therapies, e.g., brain stimulation, behavioral treatments, and therapeutic gene modulation, which could be effective to treat drug addiction. We conclude that, although drug addiction is a complex disorder that involves complicated neural mechanisms and psychological processes, this mental disorder is treatable and may be curable by therapies such as gene modulation in the future.

Counterregulation of cAMP-directed kinase activities controls ciliogenesis

The primary cilium emanates from the cell surface of growth-arrested cells and plays a central role in vertebrate development and tissue homeostasis. The mechanisms that control ciliogenesis have been extensively explored. However, the intersection between GPCR signaling and the ubiquitin pathway in the control of cilium stability are unknown. Here we observe that cAMP elevation promotes cilia resorption. At centriolar satellites, we identify a multimeric complex nucleated by PCM1 that includes two kinases, NEK10 and PKA, and the E3 ubiquitin ligase CHIP. We show that NEK10 is essential for ciliogenesis in mammals and for the development of medaka fish. PKA phosphorylation primes NEK10 for CHIP-mediated ubiquitination and proteolysis resulting in cilia resorption. Disarrangement of this control mechanism occurs in proliferative and genetic disorders. These findings unveil a pericentriolar kinase signalosome that efficiently links the cAMP cascade with the ubiquitin-proteasome system, thereby controlling essential aspects of ciliogenesis.

Temporal Bias: Time-Encoded Dynamic GPCR Signaling

Evidence suggests that cells can time-encode signals for secure transport and perception of information, and it appears that this dynamic signaling is a common principle of nature to code information in time. G-protein-coupled receptor (GPCR) signaling networks are no exception as their composition and signal transduction appear temporally flexible. In this review, we discuss the potential mechanisms by which GPCRs code biological information in time to create 'temporal bias.' We highlight dynamic signaling patterns from the second messenger to the receptor-ligand level and shed light on the dynamics of G-protein cycles, the kinetics of ligand-receptor interaction, and the occurrence of distinct signaling waves within the cell. A dynamic feature such as temporal bias adds to the complexity of GPCR signaling bias and gives rise to the question whether this trait could be exploited to gain control over time-encoded cell physiology.

The many faces of compartmentalized PKA signalosomes

Cellular signal transmission requires the dynamic formation of spatiotemporally controlled molecular interactions. At the cell surface information is received by receptor complexes and relayed through intracellular signaling platforms which organize the actions of functionally interacting signaling enzymes and substrates. The list of hormone or neurotransmitter pathways that utilize the ubiquitous cAMP-sensing protein kinase A (PKA) system is expansive. This requires that the specificity, duration, and intensity of PKA responses are spatially and temporally restricted. Hereby, scaffolding proteins take the center stage for ensuring proper signal transmission. They unite second messenger sensors, activators, effectors, and kinase substrates within cellular micro-domains to precisely control and route signal propagation. A-kinase anchoring proteins (AKAPs) organize such subcellular signalosomes by tethering the PKA holoenzyme to distinct cell compartments. AKAPs differ in their modular organization showing pathway specific arrangements of interaction motifs or domains. This enables the cell- and compartment- guided assembly of signalosomes with unique enzyme composition and function. The AKAP-mediated clustering of cAMP and other second messenger sensing and interacting signaling components along with functional successive enzymes facilitates the rapid and precise dissemination of incoming signals. This review article delineates examples for different means of PKA regulation and for snapshots of compartmentalized PKA signalosomes.

Systematic Quantification of GPCR/cAMP-Controlled Protein Kinase A Interactions

The diffusible second messenger cyclic AMP (cAMP) originates from multiple G protein-coupled receptor (GPCR) cascades activating the intracellular key effector protein kinase A (PKA). Spatially and temporally restricted cAMP-fluxes are directly sensed by macromolecular PKA complexes. The consequences are alterations of molecular interactions, which lead to activation of compartmentalized PKA phosphotransferase activities, regulating a vast array of cellular functions. To decode cell-type and cell-compartment specific PKA functions, the spatio-temporal dynamics of small molecule:protein interactions, protein:protein interactions (PPIs), cAMP-mobilization, and phosphotransferase activities need to be determined directly in the appropriate cellular context. A collection of cell-based reporters has been developed to either visualize or quantitatively measure kinase activities or PKA complex formation/dissociation. In this review, we list a collection of unimolecular and bimolecular PKA biosensors, followed by the specification of the modular design of a Renilla luciferase based protein-fragment complementation assay (PCA) platform for measuring PKA network interactions. We discuss the application spectrum of the PCA reporter to identify, quantify, and dissect dynamic and transient PKA complexes downstream of specific GPCR activities. We specify the implementation of a PCA PKA platform to systematically quantify the concurrent involvement of receptor-cAMP signaling, post-translational modifications, and kinase subunit mutations/perturbations in PKA activation. The systematic quantification of transient PKA network interactions will contribute to a better understanding how GPCR-recognized input signals are streamlined through the compartmentalized and cAMP-interacting PKA signalosome.

Synergistic regulation of serotonin and opioid signaling contributes to pain insensitivity in Nav1.7 knockout mice

Genetic loss of the voltage-gated sodium channel Na_v1.7 (Na_v1.7^-/-) results in lifelong insensitivity to pain in mice and humans. One underlying cause is an increase in the production of endogenous opioids in sensory neurons. We analyzed whether Na_v1.7 deficiency altered nociceptive heterotrimeric guanine nucleotide-binding protein-coupled receptor (GPCR) signaling, such as initiated by GPCRs that respond to serotonin (pronociceptive) or opioids (antinociceptive), in sensory neurons. We found that the nociceptive neurons of Na_v1.7 knockout (Na_v1.7^-/-) mice, but not those of Na_v1.8 knockout (Na_v1.8^-/-) mice, exhibited decreased pronociceptive serotonergic signaling through the 5-HT₄ receptors, which are Gα_s-coupled GPCRs that stimulate the production of cyclic adenosine monophosphate resulting in protein kinase A (PKA) activity, as well as reduced abundance of the RIIβ regulatory subunit of PKA. Simultaneously, the efficacy of antinociceptive opioid signaling mediated by the Gα_i-coupled mu opioid receptors was increased. Consequently, opioids inhibited more efficiently tetrodotoxin-resistant sodium currents, which are important for pain-initiating neuronal activity in nociceptive neurons. Thus, Na_v1.7 controls the efficacy and balance of GPCR-mediated pro- and antinociceptive intracellular signaling, such that without Na_v1.7, the balance is shifted toward antinociception, resulting in lifelong endogenous analgesia.

Protein-Fragment Complementation Assays for Large-Scale Analysis, Functional Dissection, and Spatiotemporal Dynamic Studies of Protein-Protein Interactions in Living Cells

Protein-fragment complementation assays (PCAs) comprise a family of assays that can be used to study protein-protein interactions (PPIs), conformation changes, and protein complex dimensions. We developed PCAs to provide simple and direct methods for the study of PPIs in any living cell, subcellular compartments or membranes, multicellular organisms, or in vitro. Because they are complete assays, requiring no cell-specific components other than reporter fragments, they can be applied in any context. PCAs provide a general strategy for the detection of proteins expressed at endogenous levels within appropriate subcellular compartments and with normal posttranslational modifications, in virtually any cell type or organism under any conditions. Here we introduce a number of applications of PCAs in budding yeast, Saccharomyces cerevisiae These applications represent the full range of PPI characteristics that might be studied, from simple detection on a large scale to visualization of spatiotemporal dynamics.

Real-Time Protein-Fragment Complementation Assays for Studying Temporal, Spatial, and Spatiotemporal Dynamics of Protein-Protein Interactions in Living Cells

Here, we present detailed protocols for direct, real-time protein-fragment complementation assays (PCAs) for studying the spatiotemporal dynamics of protein-protein interactions (PPIs). The assays require the use of two fluorescent reporter proteins-the "Venus" version of yellow fluorescent protein (vYFP), and the monomeric infrared fluorescent protein 1.4 (IFP 1.4)-or two luciferase reporter proteins-Renilla (Rluc) and Gaussia (Gluc). The luciferase PCAs can be used to study the temporal dynamics of PPIs in any cellular compartment and on membranes. The full reversibility of these PCAs assures accurate measurements of the kinetics of PPI assembly/disassembly for processes that occur anywhere in a living cell and over time frames of seconds to hours. vYFP PCA, and all PCAs based on green fluorescent protein and its variants, are irreversible and can be used to trap and visualize rare and transient complexes and follow dynamic relocalization of constitutive complexes. vYFP PCA is limited in that accurate measurements of temporal changes in PPIs are not possible owing to the slow maturation time of vYFP (minutes to hours) and the irreversibility of its PCA that traps the complexes, thereby preventing the dissociation of PPIs that, in some instances, might cause spurious mislocalization of protein complexes. The limitations of vYFP PCA are overcome with IFP PCA, which is fully reversible and thus can be used to study spatiotemporal dynamics of PPIs on the timescale of seconds. All of these PCAs are sensitive enough to detect interactions among proteins expressed at endogenous levels in vivo.

Systematic Protein-Protein Interaction Analysis Reveals Intersubcomplex Contacts in the Nuclear Pore Complex

The nuclear pore complex (NPC) enables transport across the nuclear envelope. It is one of the largest multiprotein assemblies in the cell, built from about 30 proteins called nucleoporins (Nups), organized into distinct subcomplexes. Structure determination of the NPC is a major research goal. The assembled ∼40-112 MDa NPC can be visualized by cryoelectron tomography (cryo-ET), while Nup subcomplexes are studied crystallographically. Docking the crystal structures into the cryo-ET maps is difficult because of limited resolution. Further, intersubcomplex contacts are not well characterized. Here, we systematically investigated direct interactions between Nups. In a comprehensive, structure-based, yeast two-hybrid interaction matrix screen, we mapped protein-protein interactions in yeast and human. Benchmarking against crystallographic and coaffinity purification data from the literature demonstrated the high coverage and accuracy of the data set. Novel intersubcomplex interactions were validated biophysically in microscale thermophoresis experiments and in intact cells through protein fragment complementation. These intersubcomplex interaction data provide direct experimental evidence toward possible structural arrangements of architectural elements within the assembled NPC, or they may point to assembly intermediates. Our data favors an assembly model in which major architectural elements of the NPC, notably the Y-complex, exist in different structural contexts within the scaffold.

Gpr161 anchoring of PKA consolidates GPCR and cAMP signaling

Scaffolding proteins organize the information flow from activated G protein-coupled receptors (GPCRs) to intracellular effector cascades both spatially and temporally. By this means, signaling scaffolds, such as A-kinase anchoring proteins (AKAPs), compartmentalize kinase activity and ensure substrate selectivity. Using a phosphoproteomics approach we identified a physical and functional connection between protein kinase A (PKA) and Gpr161 (an orphan GPCR) signaling. We show that Gpr161 functions as a selective high-affinity AKAP for type I PKA regulatory subunits (RI). Using cell-based reporters to map protein-protein interactions, we discovered that RI binds directly and selectively to a hydrophobic protein-protein interaction interface in the cytoplasmic carboxyl-terminal tail of Gpr161. Furthermore, our data demonstrate that a binary complex between Gpr161 and RI promotes the compartmentalization of Gpr161 to the plasma membrane. Moreover, we show that Gpr161, functioning as an AKAP, recruits PKA RI to primary cilia in zebrafish embryos. We also show that Gpr161 is a target of PKA phosphorylation, and that mutation of the PKA phosphorylation site affects ciliary receptor localization. Thus, we propose that Gpr161 is itself an AKAP and that the cAMP-sensing Gpr161:PKA complex acts as cilium-compartmentalized signalosome, a concept that now needs to be considered in the analyzing, interpreting, and pharmaceutical targeting of PKA-associated functions.

Staphylococcus aureus Protein A Mediates Interspecies Interactions at the Cell Surface of Pseudomonas aeruginosa

While considerable research has focused on the properties of individual bacteria, relatively little is known about how microbial interspecies interactions alter bacterial behaviors and pathogenesis. Staphylococcus aureus frequently coinfects with other pathogens in a range of different infectious diseases. For example, coinfection by S. aureus with Pseudomonas aeruginosa occurs commonly in people with cystic fibrosis and is associated with higher lung disease morbidity and mortality. S. aureus secretes numerous exoproducts that are known to interact with host tissues, influencing inflammatory responses. The abundantly secreted S. aureus staphylococcal protein A (SpA) binds a range of human glycoproteins, immunoglobulins, and other molecules, with diverse effects on the host, including inhibition of phagocytosis of S. aureus cells. However, the potential effects of SpA and other S. aureus exoproducts on coinfecting bacteria have not been explored. Here, we show that S. aureus-secreted products, including SpA, significantly alter two behaviors associated with persistent infection. We found that SpA inhibited biofilm formation by specific P. aeruginosa clinical isolates, and it also inhibited phagocytosis by neutrophils of all isolates tested. Our results indicate that these effects were mediated by binding to at least two P. aeruginosa cell surface structures—type IV pili and the exopolysaccharide Psl—that confer attachment to surfaces and to other bacterial cells. Thus, we found that the role of a well-studied S. aureus exoproduct, SpA, extends well beyond interactions with the host immune system. Secreted SpA alters multiple persistence-associated behaviors of another common microbial community member, likely influencing cocolonization and coinfection with other microbes.

Bacteria rarely exist in isolation, whether on human tissues or in the environment, and they frequently coinfect with other microbes. However, relatively little is known about how microbial interspecies interactions alter bacterial behaviors and pathogenesis. We identified a novel interaction between two bacterial species that frequently infect together—Staphylococcus aureus and Pseudomonas aeruginosa. We show that the S. aureus-secreted protein staphylococcal protein A (SpA), which is well-known for interacting with host targets, also binds to specific P. aeruginosa cell surface molecules and alters two persistence-associated P. aeruginosa behaviors: biofilm formation and uptake by host immune cells. Because S. aureus frequently precedes P. aeruginosa in chronic infections, these findings reveal how microbial community interactions can impact persistence and host interactions during coinfections.

praja2 regulates KSR1 stability and mitogenic signaling

The kinase suppressor of Ras 1 (KSR1) has a fundamental role in mitogenic signaling by scaffolding components of the Ras/MAP kinase pathway. In response to Ras activation, KSR1 assembles a tripartite kinase complex that optimally transfers signals generated at the cell membrane to activate ERK. We describe a novel mechanism of ERK attenuation based on ubiquitin-dependent proteolysis of KSR1. Stimulation of membrane receptors by hormones or growth factors induced KSR1 polyubiquitination, which paralleled a decline of ERK1/2 signaling. We identified praja2 as the E3 ligase that ubiquitylates KSR1. We showed that praja2-dependent regulation of KSR1 is involved in the growth of cancer cells and in the maintenance of undifferentiated pluripotent state in mouse embryonic stem cells. The dynamic interplay between the ubiquitin system and the kinase scaffold of the Ras pathway shapes the activation profile of the mitogenic cascade. By controlling KSR1 levels, praja2 directly affects compartmentalized ERK activities, impacting on physiological events required for cell proliferation and maintenance of embryonic stem cell pluripotency.

IL23R (Interleukin 23 Receptor) Variants Protective against Inflammatory Bowel Diseases (IBD) Display Loss of Function due to Impaired Protein Stability and Intracellular Trafficking

Genome-wide association studies as well as murine models have shown that the interleukin 23 receptor (IL23R) pathway plays a pivotal role in chronic inflammatory diseases such as Crohn disease (CD), ulcerative colitis, psoriasis, and type 1 diabetes. Genome-wide association studies and targeted re-sequencing studies have revealed the presence of multiple potentially causal variants of the IL23R. Specifically the G149R, V362I, and R381Q IL23Rα chain variants are linked to protection against the development of Crohn disease and ulcerative colitis in humans. Moreover, the exact mechanism of action of these receptor variants has not been elucidated. We show that all three of these IL23Rα variants cause a reduction in IL23 receptor activation-mediated phosphorylation of the signal-transducing activator of transcription 3 (STAT3) and phosphorylation of signal transducing activator of transcription 4 (STAT4). The reduction in signaling is due to lower levels of cell surface receptor expression. For G149R, the receptor retention in the endoplasmic reticulum is due to an impairment of receptor maturation, whereas the R381Q and V362I variants have reduced protein stability. Finally, we demonstrate that the endogenous expression of IL23Rα protein from V362I and R381Q variants in human lymphoblastoid cell lines exhibited lower expression levels relative to susceptibility alleles. Our results suggest a convergent cause of IL23Rα variant protection against chronic inflammatory disease.

Protein Kinase A (PKA) Type I Interacts with P-Rex1, a Rac Guanine Nucleotide Exchange Factor: EFFECT ON PKA LOCALIZATION AND P-Rex1 SIGNALING

Morphology of migrating cells is regulated by Rho GTPases and fine-tuned by protein interactions and phosphorylation. PKA affects cell migration potentially through spatiotemporal interactions with regulators of Rho GTPases. Here we show that the endogenous regulatory (R) subunit of type I PKA interacts with P-Rex1, a Rac guanine nucleotide exchange factor that integrates chemotactic signals. Type I PKA holoenzyme interacts with P-Rex1 PDZ domains via the CNB B domain of RIα, which when expressed by itself facilitates endothelial cell migration. P-Rex1 activation localizes PKA to the cell periphery, whereas stimulation of PKA phosphorylates P-Rex1 and prevents its activation in cells responding to SDF-1 (stromal cell-derived factor 1). The P-Rex1 DEP1 domain is phosphorylated at Ser-436, which inhibits the DH-PH catalytic cassette by direct interaction. In addition, the P-Rex1 C terminus is indirectly targeted by PKA, promoting inhibitory interactions independently of the DEP1-PDZ2 region. A P-Rex1 S436A mutant construct shows increased RacGEF activity and prevents the inhibitory effect of forskolin on sphingosine 1-phosphate-dependent endothelial cell migration. Altogether, these results support the idea that P-Rex1 contributes to the spatiotemporal localization of type I PKA, which tightly regulates this guanine exchange factor by a multistep mechanism, initiated by interaction with the PDZ domains of P-Rex1 followed by direct phosphorylation at the first DEP domain and putatively indirect regulation of the C terminus, thus promoting inhibitory intramolecular interactions. This reciprocal regulation between PKA and P-Rex1 might represent a key node of integration by which chemotactic signaling is fine-tuned by PKA.

Impact of kinase activating and inactivating patient mutations on binary PKA interactions

The second messenger molecule cAMP links extracellular signals to intracellular responses. The main cellular cAMP effector is the compartmentalized protein kinase A (PKA). Upon receptor initiated cAMP-mobilization, PKA regulatory subunits (R) bind cAMP thereby triggering dissociation and activation of bound PKA catalytic subunits (PKAc). Mutations in PKAc or RIa subunits manipulate PKA dynamics and activities which contribute to specific disease patterns. Mutations activating cAMP/PKA signaling contribute to carcinogenesis or hormone excess, while inactivating mutations cause hormone deficiency or resistance. Here we extended the application spectrum of a Protein-fragment Complementation Assay based on the Renilla Luciferase to determine binary protein:protein interactions (PPIs) of the PKA network. We compared time- and dose-dependent influences of cAMP-elevation on mutually exclusive PPIs of PKAc with the phosphotransferase inhibiting RIIb and RIa subunits and the protein kinase inhibitor peptide (PKI). We analyzed PKA dynamics following integration of patient mutations into PKAc and RIa. We observed that oncogenic modifications of PKAc(L206R) and RIa(Δ184-236) as well as rare disease mutations in RIa(R368X) affect complex formation of PKA and its responsiveness to cAMP elevation. With the cell-based PKA PPI reporter platform we precisely quantified the mechanistic details how inhibitory PKA interactions and defined patient mutations contribute to PKA functions.

In vivo quantification and perturbation of Myc-Max interactions and the impact on oncogenic potential

The oncogenic bHLH-LZ transcription factor Myc forms binary complexes with its binding partner Max. These and other bHLH-LZ-based protein-protein interactions (PPI) in the Myc-Max network are essential for the physiological and oncogenic activities of Myc. We have generated a genetically determined and highly specific protein-fragment complementation assay based on Renilla luciferase to analyze the dynamic interplay of bHLH-LZ transcription factors Myc, Max, and Mxd1 in vivo. We also applied this PPI reporter to quantify alterations of nuclear Myc-Max complexes in response to mutational events, competitive binding by the transcriptional repressor Mxd1, or perturbations by small-molecule Myc inhibitors, including recently identified potent PPI inhibitors from a Kröhnke pyridine library. We show that the specificity of Myc-Max PPI reduction by the pyridine inhibitors directly correlates with their efficient and highly specific potential to interfere with the proliferation of human and avian tumor cells displaying deregulated Myc expression. In a direct comparison with known Myc inhibitors using human and avian cell systems, the pyridine compounds reveal a unique inhibitory potential even at sub-micromolar concentrations combined with remarkable specificity for the inhibition of Myc-driven tumor cell proliferation. Furthermore, we show in direct comparisons using defined avian cell systems that different Max PPI profiles for the variant members of the Myc protein family (c-Myc, v-Myc, N-Myc, L-Myc) correlate with their diverse oncogenic potential and their variable sensitivity to the novel pyridine inhibitors.

In-vivo detection of binary PKA network interactions upon activation of endogenous GPCRs

Membrane receptor-sensed input signals affect and modulate intracellular protein-protein interactions (PPIs). Consequent changes occur to the compositions of protein complexes, protein localization and intermolecular binding affinities. Alterations of compartmentalized PPIs emanating from certain deregulated kinases are implicated in the manifestation of diseases such as cancer. Here we describe the application of a genetically encoded Protein-fragment Complementation Assay (PCA) based on the Renilla Luciferase (Rluc) enzyme to compare binary PPIs of the spatially and temporally controlled protein kinase A (PKA) network in diverse eukaryotic model systems. The simplicity and sensitivity of this cell-based reporter allows for real-time recordings of mutually exclusive PPIs of PKA upon activation of selected endogenous G protein-coupled receptors (GPCRs) in cancer cells, xenografts of mice, budding yeast, and zebrafish embryos. This extends the application spectrum of Rluc PCA for the quantification of PPI-based receptor-effector relationships in physiological and pathological model systems.

Phospho-tyrosine dependent protein-protein interaction network

Post-translational protein modifications, such as tyrosine phosphorylation, regulate protein–protein interactions (PPIs) critical for signal processing and cellular phenotypes. We extended an established yeast two-hybrid system employing human protein kinases for the analyses of phospho-tyrosine (pY)-dependent PPIs in a direct experimental, large-scale approach. We identified 292 mostly novel pY-dependent PPIs which showed high specificity with respect to kinases and interacting proteins and validated a large fraction in co-immunoprecipitation experiments from mammalian cells. About one-sixth of the interactions are mediated by known linear sequence binding motifs while the majority of pY-PPIs are mediated by other linear epitopes or governed by alternative recognition modes. Network analysis revealed that pY-mediated recognition events are tied to a highly connected protein module dedicated to signaling and cell growth pathways related to cancer. Using binding assays, protein complementation and phenotypic readouts to characterize the pY-dependent interactions of TSPAN2 (tetraspanin 2) and GRB2 or PIK3R3 (p55γ), we exemplarily provide evidence that the two pY-dependent PPIs dictate cellular cancer phenotypes.

Systematic identification of signal integration by protein kinase A

Cellular processes and homeostasis control in eukaryotic cells is achieved by the action of regulatory proteins such as protein kinase A (PKA). Although the outbound signals from PKA directed to processes such as metabolism, growth, and aging have been well charted, what regulates this conserved regulator remains to be systematically identified to understand how it coordinates biological processes. Using a yeast PKA reporter assay, we identified genes that influence PKA activity by measuring protein-protein interactions between the regulatory and the two catalytic subunits of the PKA complex in 3,726 yeast genetic-deletion backgrounds grown on two carbon sources. Overall, nearly 500 genes were found to be connected directly or indirectly to PKA regulation, including 80 core regulators, denoting a wide diversity of signals regulating PKA, within and beyond the described upstream linear pathways. PKA regulators span multiple processes, including the antagonistic autophagy and methionine biosynthesis pathways. Our results converge toward mechanisms of PKA posttranslational regulation by lysine acetylation, which is conserved between yeast and humans and that, we show, regulates protein complex formation in mammals and carbohydrate storage and aging in yeast. Taken together, these results show that the extent of PKA input matches with its output, because this kinase receives information from upstream and downstream processes, and highlight how biological processes are interconnected and coordinated by PKA.

AIP inactivation leads to pituitary tumorigenesis through defective Gαi-cAMP signaling

The aryl hydrocarbon receptor interacting protein (AIP) is a tumor-suppressor gene underlying the pituitary adenoma predisposition. Thus far, the exact molecular mechanisms by which inactivated AIP exerts its tumor-promoting action have been unclear. To better understand the role of AIP in pituitary tumorigenesis, we performed gene expression microarray analysis to examine changes between Aip wild-type and knockout mouse embryonic fibroblast (MEF) cell lines. Transcriptional analyses implied that Aip deficiency causes a dysfunction in cyclic adenosine monophosphate (cAMP) signaling, as well as impairments in signaling cascades associated with developmental and immune-inflammatory responses. In vitro experiments showed that AIP deficiency increases intracellular cAMP concentrations in both MEF and murine pituitary adenoma cell lines. Based on knockdown of various G protein α subunits, we concluded that AIP deficiency leads to elevated cAMP concentrations through defective Gαi-2 and Gαi-3 proteins that normally inhibit cAMP synthesis. Furthermore, immunostaining of Gαi-2 revealed that AIP deficiency is associated with a clear reduction in Gαi-2 protein expression levels in human and mouse growth hormone (GH)-secreting pituitary adenomas, thus indicating defective Gαi signaling in these tumors. By contrast, all prolactin-secreting tumors showed prominent Gαi-2 protein levels, irrespective of Aip mutation status. We additionally observed reduced expression of phosphorylated extracellular signal-regulated kinases 1/2 and cAMP response element-binding protein levels in mouse and human AIP-deficient somatotropinomas. This study implies for the first time that a failure to inhibit cAMP synthesis through dysfunctional Gαi signaling underlies the development of GH-secreting pituitary adenomas in AIP mutation carriers.

Proteolysis of MOB1 by the ubiquitin ligase praja2 attenuates Hippo signalling and supports glioblastoma growth

Human glioblastoma is the most frequent and aggressive form of brain tumour in the adult population. Proteolytic turnover of tumour suppressors by the ubiquitin–proteasome system is a mechanism that tumour cells can adopt to sustain their growth and invasiveness. However, the identity of ubiquitin–proteasome targets and regulators in glioblastoma are still unknown. Here we report that the RING ligase praja2 ubiquitylates and degrades Mob, a core component of NDR/LATS kinase and a positive regulator of the tumour-suppressor Hippo cascade. Degradation of Mob through the ubiquitin–proteasome system attenuates the Hippo cascade and sustains glioblastoma growth in vivo. Accordingly, accumulation of praja2 during the transition from low- to high-grade glioma is associated with significant downregulation of the Hippo pathway. These findings identify praja2 as a novel upstream regulator of the Hippo cascade, linking the ubiquitin proteasome system to deregulated glioblastoma growth.

Tumour suppressors can be inactivated in cancer not only as a result of mutation, but also by proteolytic degradation. Here the authors show that, during glioma development, the accumulation of the ubiquitin ligase praja2 sustains tumour growth by degrading MOB1—a core component of the Hippo pathway.

Interplay of PKA and Rac: fine-tuning of Rac localization and signaling

Cellular membrane receptors sense environmental changes and relay the reshaped signal through spatially and temporally organized protein-protein interactions (PPI). Many of such PPI are transient and occur in a certain cell-dependent context. Molecular switches such as kinases and GTPases are engaged in versatile PPI. Recently, we have identified dynamic interaction and reciprocal regulation of cAMP-dependent protein kinase A (PKA) and Rho-GTPase Rac signaling. We demonstrated that GTP-activated Rac acts as a dual kinase-tuning scaffold for p21-activated kinase (PAK) and PKA activities. We showed that receptor-triggered PKA trans-phosphorylation of GTP-Rac-organized PAK contributes to elevations of nuclear Erk1/2 signaling and proliferation. We discuss these recent observations and we provide additional insights how the cAMP-PKA axis might also participate in the regulation of Rac localization.

Reciprocal regulation of PKA and Rac signaling

Activated G protein-coupled receptors (GPCRs) and receptor tyrosine kinases relay extracellular signals through spatial and temporal controlled kinase and GTPase entities. These enzymes are coordinated by multifunctional scaffolding proteins for precise intracellular signal processing. The cAMP-dependent protein kinase A (PKA) is the prime example for compartmentalized signal transmission downstream of distinct GPCRs. A-kinase anchoring proteins tether PKA to specific intracellular sites to ensure precision and directionality of PKA phosphorylation events. Here, we show that the Rho-GTPase Rac contains A-kinase anchoring protein properties and forms a dynamic cellular protein complex with PKA. The formation of this transient core complex depends on binary interactions with PKA subunits, cAMP levels and cellular GTP-loading accounting for bidirectional consequences on PKA and Rac downstream signaling. We show that GTP-Rac stabilizes the inactive PKA holoenzyme. However, β-adrenergic receptor-mediated activation of GTP-Rac-bound PKA routes signals to the Raf-Mek-Erk cascade, which is critically implicated in cell proliferation. We describe a further mechanism of how cAMP enhances nuclear Erk1/2 signaling: It emanates from transphosphorylation of p21-activated kinases in their evolutionary conserved kinase-activation loop through GTP-Rac compartmentalized PKA activities. Sole transphosphorylation of p21-activated kinases is not sufficient to activate Erk1/2. It requires complex formation of both kinases with GTP-Rac1 to unleash cAMP-PKA-boosted activation of Raf-Mek-Erk. Consequently GTP-Rac functions as a dual kinase-tuning scaffold that favors the PKA holoenzyme and contributes to potentiate Erk1/2 signaling. Our findings offer additional mechanistic insights how β-adrenergic receptor-controlled PKA activities enhance GTP-Rac-mediated activation of nuclear Erk1/2 signaling.

Anti hyperglycaemic study of natural inhibitors for Insulin receptor

Diabetes is a metabolic disorder associated with either improper functioning of the beta-cells or wherein cells fail to use insulin properly. Insulin, the principal hormone regulates uptake of glucose from the blood into most of the cells except central nervous system. Therefore, deficiency of insulin or the insensitivity of its receptors plays a key role in all forms of diabetes. In the present work, attempt has been made to find out plant sources which show anti hyperglycaemic activity (AhG) (i.e. compounds that bring down the blood glucose level in the body). Ayurvedic plants showing AhG activity formed the basis of our study by using the platform of Computer Aided Drug Designing (CADD). Among 600 plants showing AhG activity, 500 compounds were selected and screened, out of which 243 compounds showed drug likeness property that can be used as therapeutic ligand/drug. Initial screening of such compounds was done based on their drug likeness or biochemical properties. Dynamic interaction of these molecules was captured through Protein-Ligand study. It also gave an insight of the binding pockets involved. Bench marking of all the parameters were done using the diabetic inhibitor drug, Glipizide. Pharmacokinetic studies of the compounds such as Aloins, Capparisine, Funiculosin and Rhein exhibited less toxicity on various levels of the body. As a conclusion these ligands can lay a foundation for a better anti-diabetic therapy.

ABBREVIATIONS

AhG - Anti hyperglycaemic, CADD - Computer Aided Drug Designing.

Zebrafish Cxcr4a determines the proliferative response to Hedgehog signalling

The Hedgehog (Hh) pathway plays dual roles in proliferation and patterning during embryonic development, but the mechanism(s) that distinguish the mitogenic and patterning activities of Hh signalling are not fully understood. An additional level of complexity is provided by the observation that Hh signalling can both promote and inhibit cell proliferation. One model to account for this apparent paradox is that Hh signalling primarily regulates cell cycle kinetics, such that activation of Hh signalling promotes fast cycling and an earlier cell cycle exit. Here we report that activation of Hh signalling promotes endodermal cell proliferation but inhibits proliferation in neighbouring non-endodermal cells, suggesting that the cell cycle kinetics model is insufficient to account for the opposing proliferative responses to Hh signalling. We show that expression of the chemokine receptor Cxcr4a is a critical parameter that determines the proliferative response to Hh signalling, and that loss of Cxcr4a function attenuates the transcription of cell cycle regulator targets of Hh signalling without affecting general transcriptional targets. We show that Cxcr4a inhibits PKA activity independently of Hh signalling, and propose that Cxcr4a enhances Hh-dependent proliferation by promoting the activity of Gli1. Our results indicate that Cxcr4a is required for Hh-dependent cell proliferation but not for Hh-dependent patterning, and suggest that the parallel activation of Cxcr4a is required to modulate the Hh pathway to distinguish between patterning and proliferation.

Assembly of allosteric macromolecular switches: lessons from PKA

Protein kinases are dynamic molecular switches that have evolved to be only transiently activated. Kinase activity is embedded within a conserved kinase core, which is typically regulated by associated domains, linkers and interacting proteins. Moreover, protein kinases are often tethered to large macromolecular complexes to provide tighter spatiotemporal control. Thus, structural characterization of kinase domains alone is insufficient to explain protein kinase function and regulation in vivo. Recent progress in structural characterization of cyclic AMP-dependent protein kinase (PKA) exemplifies how our knowledge of kinase signalling has evolved by shifting the focus of structural studies from single kinase subunits to macromolecular complexes.