Use of a Schizosaccharomyces pombe PKA-repressible reporter to study cGMP metabolising phosphodiesterases

The injection of one recombinant C-type lectin (LvLec) induced the immune response of hemocytes in Litopenaeus vannamei

To explore the immune function of C-type lectin in shrimp, one recombinant C-type lectin (LvLec) was injected into Litopenaeus vannamei. There were four treatments in the experiment: saline group (as control group), recombinant C-type lectin group (LvLec, 1 mg mL^-1), Vibrio harveyi group (V. harveyi, 10⁶ cfu mL^-1) and recombinant C-type lectin combined with Vibrio harveyi group (LvLec + V. harveyi, 1 mg mL^-1 + 10⁶ cfu mL^-1). The sampling time was set at 0, 3, 6, 9, 12, 24 h after the injection. The results showed that the total hemocyte count decreased significantly and the phagocytic activity improved notably after the injection of LvLec, V. harveyi or LvLec + V. harveyi. Prophenoloxidase (proPO) activity decreased, while phenoloxidase (PO) activity increased and the changing degree of each group exhibited a significant difference. The hemagglutinating activity and bacteriolytic activity improved significantly, while the antimicrobial activity did not show a remarkable change in all of the groups. There were also changes that occurred in the levels of second messengers (cAMP, cGMP) and protein kinase (PKA, PKG). After the injection of LvLec, V. harveyi or LvLec + V. harveyi, the concentration of cGMP and PKA increased significantly, while the concentration of cAMP and PKG did not change remarkably. The results above suggested that rLvLec could induce nonspecific immune response, including phagocytosis, release of PO, hemagglutination and bacteriolysis through cGMP-PKA pathway in vivo.

Use of a Fission Yeast Platform to Identify and Characterize Small Molecule PDE Inhibitors

Cyclic nucleotide phosphodiesterases (PDEs) have been proven to be targets for which highly selective and potent drugs can be developed. Mammalian genomes possess 21 genes whose products are pharmacologically grouped into 11 families; however related genes from pathogenic organisms display sufficient divergence from the mammalian homologs such that PDE inhibitors to these enzymes could be used to treat parasitic infections without acting on the related human PDEs. We have developed a platform for expressing cloned PDEs in the fission yeast Schizosaccharomyces pombe, allowing for inexpensive, but robust screening for small molecule inhibitors that are cell permeable. Such compounds typically display the expected biological activity when tested in cell culture, including anti-inflammatory properties for PDE4 and PDE7 inhibitors. The genetic pliability of S. pombe also allows for molecular genetic screens to identify mutations in target PDE genes that confer some resistance to these inhibitors as a way of investigating the PDE-inhibitor interaction. This screening method is readily accessible to academic laboratories as it does not require the purification of large quantities of a target protein. This allows for the discovery and profiling of PDE inhibitors to treat inflammation or of inhibitors of targets such as pathogen PDEs for which there may not be a sufficient financial motivation for pharmaceutical companies to identify selective PDE inhibitors using more traditional in vitro enzyme-based screening methods.

Methods to Assess Phosphodiesterase and/or Adenylyl Cyclase Activity Via Heterologous Expression in Fission Yeast

Heterologous expression of cyclic nucleotide phosphodiesterases (PDEs) and adenylyl cyclases (ACs) in the fission yeast Schizosaccharomyces pombe can be used in combination with PKA-repressed reporters to either carry out high throughput screens for small molecule inhibitors of these target enzymes or to assess hit compounds and their analogs from such screens. Here, we describe two methods for testing panels of such compounds. The first uses a growth assay for which growth in medium containing the pyrimidine analog 5-fluoro orotic acid (5FOA) occurs in response to inhibiting PDE activity to activate PKA. The second uses mass spectrometry to directly measure the impact of compound treatment to study compounds that modulate either PDE or AC activity.

Role of mitochondrial complex III/IV in the activation of transcription factor Rst2 in Schizosaccharomyces pombe

Mitochondria play essential roles in eukaryotic cells for glucose metabolism to produce ATP. In Schizosaccharomyces pombe, transcription factor Rst2 can be activated upon glucose deprivation. However, the link between Rst2 and mitochondrial function remains elusive. Here, we monitored Rst2 transcriptional activity in living cells using a Renilla luciferase reporter system, and found that inhibition of mitochondrial complex III/IV caused cells to produce reactive oxygen species (ROS) and nitric oxide (NO), which in turn activated Rst2. Furthermore, Rst2-GFP was observed to translocate from cytoplasm to nucleus upon mitochondrial complex III/IV inhibitors treatment, and deletion of genes associated with complex III/IV resulted in delayed process of Rst2-GFP nuclear exportation under glucose-rich condition. In particular, we found that Rst2 was phosphorylated following the treatment of complex III/IV inhibitors or SNAP. Altogether, our findings suggest that mitochondrial complex III/IV participates in the activation of Rst2 through ROS and NO generation in Schizosaccharomyces pombe.

Cloning and functional complementation of ten Schistosoma mansoni phosphodiesterases expressed in the mammalian host stages

Only a single drug against schistosomiasis is currently available and new drug development is urgently required but very few drug targets have been validated and characterised. However, regulatory systems including cyclic nucleotide metabolism are emerging as primary candidates for drug discovery. Here, we report the cloning of ten cyclic nucleotide phosphodiesterase (PDE) genes of S. mansoni, out of a total of 11 identified in its genome. We classify these PDEs by homology to human PDEs. Male worms displayed higher expression levels for all PDEs, in mature and juvenile worms, and schistosomula. Several functional complementation approaches were used to characterise these genes. We constructed a Trypanosoma brucei cell line in which expression of a cAMP-degrading PDE complements the deletion of TbrPDEB1/B2. Inhibitor screens of these cells expressing only either SmPDE4A, TbrPDEB1 or TbrPDEB2, identified highly potent inhibitors of the S. mansoni enzyme that elevated the cellular cAMP concentration. We further expressed most of the cloned SmPDEs in two pde1Δ/pde2Δ strains of Saccharomyces cerevisiae and some also in a specialised strain of Schizosacharomyces pombe. Five PDEs, SmPDE1, SmPDE4A, SmPDE8, SmPDE9A and SmPDE11 successfully complemented the S. cerevisiae strains, and SmPDE7var also complemented to a lesser degree, in liquid culture. SmPDE4A, SmPDE8 and SmPDE11 were further assessed in S. pombe for hydrolysis of cAMP and cGMP; SmPDE11 displayed considerable preferrence for cGMP over cAMP. These results and tools enable the pursuit of a rigorous drug discovery program based on inhibitors of S. mansoni PDEs.

Metabolic role of cGMP in S. cerevisiae: the murine phosphodiesterase-5 activity affects yeast cell proliferation by altering the cAMP/cGMP equilibrium

In higher eukaryotes, cAMP and cGMP are signal molecules of major transduction pathways while phosphodiesterases (PDE) are a superfamily of cAMP/cGMP hydrolysing enzymes, modulatory components of these routes. Saccharomyces cerevisiae harbours two genes for PDE: Pde2 is a high affinity cAMP-hydrolysing enzyme, while Pde1 can hydrolyse both cAMP and cGMP. To gain insight into the metabolic role of cGMP in the physiology of yeast, the murine Pde5a1 gene encoding a specific cGMP-hydrolysing enzyme, was expressed in S. cerevisiae pdeΔ strains. pde1Δ and pde2Δ PDE5A1-transformed strain displayed opposite growth-curve profiles; while PDE5A1 recovered the growth delay of pde1Δ, PDE5A1 reversed the growth profile of pde2Δ to that of the untransformed pde1Δ. Growth test analysis and the use of Adh2 and Adh1 as respiro-fermentative glycolytic flux markers confirmed that PDE5A1 altered the metabolism by acting on Pde1-Pde2/cyclic nucleotides content and also on the TORC1 nutrient-sensing cascade. cGMP is required during the log-phase of cell proliferation to adjust/modulate cAMP levels inside well-defined ranges. A model is presented proposing the role of cGMP in the cAMP/PKA pathway. The expression of the PDE5A1 cassette in other mutant strains might constitute the starting tool to define cGMP metabolic role in yeast nutrient signaling.

One recombinant C-type lectin (LvLec) from white shrimp Litopenaeus vannamei affected the haemocyte immune response in vitro

C-type lectin has received widespread attention in animal immunomodulation functions since it was discovered, but it is still limited in crustaceans. The present study is to explore effects of one recombinant C-type lectin (LvLec protein) on haemocyte immune response in Litopenaeus vannamei (L. vannamei). The methods of keeping haemocyte immune activity were optimised by the Key Laboratory of Mariculture. The experiment was divided into four groups: control group, recombinant protein group (LvLec protein, 1.0 mg mL^-1), Lipopolysaccharide group (LPS, 1.0 mg mL^-1), and LPS combine with LvLec protein group (LPS + LvLec protein, 1.0 mg mL^-1 + 1.0 mg mL^-1), while each group processes 0, 3, 6, 9, 12, and 24 h respectively. The results showed that the haemocyte count reduced, while the exocytosis PO activity, hemagglutinating activity and phagocytic activity promoted, and the concentration of cGMP and PKA increased after LvLec protein treatment. However, the levels of antibacterial activity and bacteriolytic activity as well as the concentrations of cAMP and PKG did not change significantly after treating with LvLec protein, LPS or LPS + LvLec protein. Therefore, these results suggest that LvLec protein can stimulate the exocytosis PO activity through cGMP-PKA pathway to affect the phagocytic activity and hemagglutinating activity of L. vannamei haemocytes in vitro.

A fission yeast platform for heterologous expression of mammalian adenylyl cyclases and high throughput screening

The fission yeast Schizosaccharomyces pombe uses a cAMP signaling pathway to link glucose-sensing to Protein Kinase A activity in order to regulate cell growth, sexual development, gluconeogenesis, and exit from stationary phase. We previously used a PKA-repressed fbp1-ura4 reporter to conduct high throughput screens (HTSs) for inhibitors of heterologously-expressed mammalian cyclic nucleotide phosphodiesterases (PDEs). Here, we describe the successful expression of all ten mammalian adenylyl cyclase (AC) genes, along with the human GNAS Gα_s gene. By measuring expression of an fbp1-GFP reporter together with direct measurements of intracellular cAMP levels, we can detect both basal AC activity from all ten AC genes as well as GNAS-stimulated activity from eight of the nine transmembrane ACs (tmACs; AC2-AC9). The ability to use this platform to conduct HTS for novel chemical probes that reduce PKA activity was demonstrated by a pilot screen of the LOPAC®¹²⁸⁰ library, leading to the identification of diphenyleneiodonium chloride (DPI) as an inhibitor of basal AC activity. This screening technology could open the door to the development of therapeutic compounds that target GNAS or the ACs, an area in which there is significant unmet need.

Identification and characterization of a potent and biologically-active PDE4/7 inhibitor via fission yeast-based assays

We previously constructed a collection of fission yeast strains that express various mammalian cyclic nucleotide phosphodiesterases (PDEs) and developed a cell-based high throughput screen (HTS) for small molecule PDE inhibitors. Here we describe a compound, BC54, that is a selective inhibitor of enzymes from the cAMP-specific PDE4 and PDE7 families. Consistent with the biological effect of other PDE4 and PDE7 inhibitors, BC54 displays potent anti-inflammatory properties and is superior to a combination of rolipram (a PDE4 inhibitor) and BRL50481 (a PDE7A inhibitor) for inducing apoptosis in chronic lymphocytic leukemia (CLL) cells. We further exploited PKA-regulated growth phenotypes in fission yeast to isolate two mutant alleles of the human PDE4B2 gene that encode enzymes possessing single amino acid changes that confer partial resistance to BC54. We confirm this resistance to both BC54 and rolipram via yeast-based assays and, for PDE4B2T407A, in vitro enzyme assays. Thus, we are able to use this system for both chemical screens to identify biologically-active PDE inhibitors and molecular genetic studies to characterize the interaction of these molecules with their target enzymes. Based on its potency, selectivity, and effectiveness in cell culture, BC54 should be a useful tool to study biological processes regulated by PDE4 and PDE7 enzymes.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Copper catalyzed aerobic oxidative cyclization and ketonization: one pot synthesis of benzoimidazo[1,2-a]imidazolones

A highly efficient synthesis of benzoimidazo[1,2-a]imidazolone through a novel oxidative 5-exo-dig cyclization-ketonization cascade of 2-aminobenzimidazole, aldehyde and terminal alkyne has been explored under aerobic conditions.

A yeast-based high-throughput screen for modulators of phosphodiesterase activity

Cell-based high-throughput screens (HTSs) targeting heterologously expressed proteins in yeast identify compounds that often display relevant biological activity when tested in cell culture. We developed a fission yeast-based HTS to detect small-molecule inhibitors of mammalian cyclic nucleotide phosphodiesterases (PDEs). These screens are carried out in Schizosaccharomyces pombe using a PKA-repressed fbp1-ura4 reporter whose expression due to low PKA activity prevents cells from growing in medium containing the pyrimidine analog 5-fluoro orotic acid (5FOA). We describe here the steps required to construct strains for screening and to optimize conditions for successful screens.

A central role for TOR signalling in a yeast model for juvenile CLN3 disease

Yeasts provide an excellent genetically tractable eukaryotic system for investigating the function of genes in their biological context, and are especially relevant for those conserved genes that cause disease. We study the role of btn1, the orthologue of a human gene that underlies an early onset neurodegenerative disease (juvenile CLN3 disease, neuronal ceroid lipofuscinosis (NCLs) or Batten disease) in the fission yeast Schizosaccharomyces pombe. A global screen for genetic interactions with btn1 highlighted a conserved key signalling hub in which multiple components functionally relate to this conserved disease gene. This signalling hub includes two major mitogen-activated protein kinase (MAPK) cascades, and centers on the Tor kinase complexes TORC1 and TORC2. We confirmed that yeast cells modelling CLN3 disease exhibit features consistent with dysfunction in the TORC pathways, and showed that modulating TORC function leads to a comprehensive rescue of defects in this yeast disease model. The same pathways may be novel targets in the development of therapies for the NCLs and related diseases.

Use of PKA-mediated phenotypes for genetic and small-molecule screens in Schizosaccharomyces pombe

PKA (protein kinase A) in the fission yeast Schizosaccharomyces pombe controls transcription of genes involved in metabolism, cell growth and sexual development. In the present review, we discuss phenotypes associated with either high or low PKA activity in the context of how they can be used to carry out genetic or small-molecule screens that affect components of the PKA pathway. Although our recent research has focused on the study of heterologously expressed cyclic nucleotide PDEs (phosphodiesterases), these same methods can be used to target other S. pombe proteins or their functionally equivalent orthologues that act in the PKA pathway.

A yeast-based chemical screen identifies a PDE inhibitor that elevates steroidogenesis in mouse Leydig cells via PDE8 and PDE4 inhibition

A cell-based high-throughput screen (HTS) was developed to detect phosphodiesterase 8 (PDE8) and PDE4/8 combination inhibitors. By replacing the Schizosaccharomyces pombe PDE gene with the murine PDE8A1 gene in strains lacking adenylyl cyclase, we generated strains whose protein kinase A (PKA)-stimulated growth in 5-fluoro orotic acid (5FOA) medium reflects PDE8 activity. From our previously-identified PDE4 and PDE7 inhibitors, we identified a PDE4/8 inhibitor that allowed us to optimize screening conditions. Of 222,711 compounds screened, ∼0.2% displayed composite Z scores of >20. Additional yeast-based assays using the most effective 367 compounds identified 30 candidates for further characterization. Among these, compound BC8-15 displayed the lowest IC₅₀ value for both PDE4 and PDE8 inhibition in in vitro enzyme assays. This compound also displays significant activity against PDE10A and PDE11A. BC8-15 elevates steroidogenesis in mouse Leydig cells as a single pharmacological agent. Assays using BC8-15 and two structural derivatives support a model in which PDE8 is a primary regulator of testosterone production by Leydig cells, with an additional role for PDE4 in this process. BC8-15, BC8-15A, and BC8-15C, which are commercially available compounds, display distinct patterns of activity against PDE4, PDE8, PDE10A, and PDE11A, representing a chemical toolkit that could be used to examine the biological roles of these enzymes in cell culture systems.

Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments

Cyclic nucleotide phosphodiesterases (PDEs) that specifically inactivate the intracellular messengers cAMP and cGMP in a compartmentalized manner represent an important enzyme class constituted by 11 gene-related families of isozymes (PDE1 to PDE11). Downstream receptors, PDEs play a major role in controlling the signalosome at various levels of phosphorylations and protein/protein interactions. Due to the multiplicity of isozymes, their various intracellular regulations and their different cellular and subcellular distributions, PDEs represent interesting targets in intracellular pathways. Therefore, the investigation of PDE isozyme alterations related to various pathologies and the design of specific PDE inhibitors might lead to the development of new specific therapeutic strategies in numerous pathologies. This manuscript (i) overviews the different PDEs including their endogenous regulations and their specific inhibitors; (ii) analyses the intracellular implications of PDEs in regulating signalling cascades in pathogenesis, exemplified by two diseases affecting cell cycle and proliferation; and (iii) discusses perspectives for future therapeutic developments.

Identification of biologically active PDE11-selective inhibitors using a yeast-based high-throughput screen

The biological roles of cyclic nucleotide phosphodiesterase 11 (PDE11) enzymes are poorly understood, in part due to the lack of selective inhibitors. To address the need for such compounds, we completed an ~200,000 compound high-throughput screen (HTS) for PDE11 inhibitors using a yeast-based growth assay, and identified 4 potent and selective PDE11 inhibitors. One compound, along with two structural analogs, elevates cAMP and cortisol levels in human adrenocortical cells, consistent with gene association studies that link PDE11 activity to adrenal function. As such, these compounds can immediately serve as chemical tools to study PDE11 function in cell culture, and as leads to develop therapeutics for the treatment of adrenal insufficiencies. Our results further validate this yeast-based HTS platform for the discovery of potent, selective, and biologically active PDE inhibitors.