The cAMP signaling pathway as a therapeutic target in lymphoid malignancies

Host cell cAMP-Epac-Rap1b pathway inhibition by hawthorn extract as a potential target against Trypanosoma cruzi infection

Although the two drugs currently available for the treatment of Chagas disease, Benznidazole and Nifurtimox, have proven to be effective in the acute phase of the disease, the 60-90-day treatment leads to high toxicity and unwanted side effects, presenting, in addition, a low efficacy in the chronic phase of the disease. For this reason, new therapies that are more effective are needed. In this regard, we have recently shown that the inhibition of the Epac-Rap1b pathway suppressed the cAMP-mediated host cell invasion by Trypanosoma cruzi. Interestingly, it has been described that vitexin, a natural flavone that protects against ischemia-reperfusion damage, acts by inhibiting the expression of Epac and Rap1 proteins. Vitexin can be found in plants of the genus Crataegus spp., traditionally known as hawthorn, which are of great interest considering their highly documented use as cardio-protectors. Pre-treating cells with an extract of Crataegus oxyacantha produced levels of T. cruzi invasion comparable to the ones observed for the commercially available Epac1-specific inhibitor, ESI-09. In addition, extract-treated cells exhibited a decrease in the activation of Rap1b, suggesting that the effects of the extract would be mediated by the inhibition of the cAMP-Epac-Rap1 signaling pathway. Using HPLC-HRMS2, we could confirm the presence of vitexin, and other flavones that could act as inhibitors of Epac/Rap1b, in the extracts of C. oxyacantha. Most significantly, when cells were treated with the extract of C. oxyacantha in conjunction with Nifurtimox, an increased modulation of invasion was observed.

Pharmacological Evidence That Dictyostelium Differentiation-Inducing Factor 1 Promotes Glucose Uptake Partly via an Increase in Intracellular cAMP Content in Mouse 3T3-L1 Cells

Differentiation-inducing factor 1 (DIF-1) isolated from the cellular slime mold Dictyostelium discoideum can inhibit mammalian calmodulin-dependent cAMP/cGMP phosphodiesterase (PDE1) in vitro. DIF-1 also promotes glucose uptake, at least in part, via a mitochondria- and AMPK-dependent pathway in mouse 3T3-L1 fibroblast cells, but the mechanism underlying this effect has not been fully elucidated. In this study, we investigated the effects of DIF-1 on intracellular cAMP and cGMP levels, as well as the effects that DIF-1 and several compounds that increase cAMP and cGMP levels have on glucose uptake in confluent 3T3-L1 cells. DIF-1 at 20 μM (a concentration that promotes glucose uptake) increased the level of intracellular cAMP by about 20% but did not affect the level of intracellular cGMP. Neither the PDE1 inhibitor 8-methoxymethyl-3-isobutyl-1-methylxanthine at 10-200 μM nor the broad-range PDE inhibitor 3-isobutyl-1-methylxanthine at 40-400 μM had any marked effects on glucose uptake. The membrane-permeable cAMP analog 8-bromo-cAMP at 200-1000 μM significantly promoted glucose uptake (by 20-25%), whereas the membrane-permeable cGMP analog 8-bromo-cGMP at 3-100 μM did not affect glucose uptake. The adenylate cyclase activator forskolin at 1-10 μM promoted glucose uptake by 20-30%. Thus, DIF-1 may promote glucose uptake by 3T3-L1 cells, at least in part, via an increase in intracellular cAMP level.

Discovery of 2-(Methylcarbonylamino) thiazole as PDE4 inhibitors via virtual screening and biological evaluation

Phosphodiesterase-4, the primary enzyme responsible for cAMP degradation in the majority of immune and inflammatory cells, plays a critical role in the regulation of intracellular cAMP levels. Consequently, small molecular entities capable of inhibiting PDE4 have been employed in the treatment of inflammation-associated disorders, such as chronic obstructive pulmonary disease (COPD), psoriasis, atopic dermatitis (AD), inflammatory bowel diseases (IBD), rheumatic arthritis (RA). In the present investigation, a multi-faceted approach was employed to identify novel PDE4 inhibitors, utilizing the co-crystallization structure of PDE4B available in the Protein Data Bank (PDB) database, drug-like screening, false positive filtration, similarity and ADMET screen, as well as molecular docking via multiple software platforms, in conjunction with bioactivity assays. A thiazol-3-propanamides derivative, designated MR9, was discovered to inhibit PDE4B activity with IC50 values of 2.12 μM and suppress cellular inflammatory factor TNF-α release with an EC50 value of 3.587 μM. These findings suggest that the innovative active scaffold of MR9 offers a promising foundation for further structural refinement aimed at developing more potent PDE4 inhibitors.

The TSPO Ligands MGV-1 and 2-Cl-MGV-1 Differentially Inhibit the Cigarette Smoke-Induced Cytotoxicity to H1299 Lung Cancer Cells

Simple Summary

In this study, we investigated the impact of CS on various TSPO-related mitochondrial processes, and the protective ability of our novel TSPO ligands against such CS-induced cellular damages. Our results support the previously reported role of TSPO in apoptotic cell death. Moreover, the present data demonstrate the protective effect of our TSPO ligands against CS-induced cellular damage.

Abstract

TSPO is involved in cigarette smoke (CS)-induced cellular toxicity, which may result in oral and pulmonary diseases and lung cancer. H1299 lung cancer cells were exposed directly to CS. The H1299 cells were pretreated with our TSPO ligands MGV-1 and 2-Cl-MGV-1 (Ki = 825 nM for both) at a concentration of 25 µM 24 h prior to CS exposure. Cell death and apoptotic markers were measured, in addition to TSPO expression levels, ATP synthase activity, generation of reactive oxygen species (ROS), depolarization of mitochondrial membrane potential (ΔΨm), cAMP and LDH levels. Pretreatment with MGV-1 and 2-Cl-MGV-1 (25 µM), 24 h prior to CS exposure, differentially attenuated the CS-induced cellular insult as well as cell death in H1299 lung cancer cells. These protective effects included prevention of ATP synthase reversal, ROS generation, depolarization of the mitochondrial membrane and elevation in LDH. The preventive efficacy of 2-Cl-MGV-1 was superior to that achieved by MGV-1. Both ligands did not prevent the elevation in cAMP. These findings may indicate a mild protective effect of these TSPO ligands in CS-related pulmonary and keratinocyte cellular pathology.

Effect of cAMP Signaling Regulation in Osteogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells

The successful implementation of adipose-derived mesenchymal stem cells (ADSCs) in bone regeneration depends on efficient osteogenic differentiation. However, a literature survey and our own experience demonstrated that current differentiation methods are not effective enough. Since the differentiation of mesenchymal stem cells (MSCs) into osteoblasts and adipocytes can be regulated by cyclic adenosine monophosphate (cAMP) signaling, we investigated the effects of cAMP activator, forskolin, and inhibitor, SQ 22,536, on the early and late osteogenic differentiation of ADSCs cultured in spheroids or in a monolayer. Intracellular cAMP concentration, protein kinase A (PKA) activity, and inhibitor of DNA binding 2 (ID2) expression examination confirmed cAMP up- and downregulation. cAMP upregulation inhibited the cell cycle and protected ADSCs from osteogenic medium (OM)-induced apoptosis. Surprisingly, the upregulation of cAMP level at the early stages of osteogenic differentiation downregulated the expression of osteogenic markers RUNX2, Osterix, and IBSP, which was more significant in spheroids, and it is used for the more efficient commitment of ADSCs into preosteoblasts, according to the previously reported protocol. However, cAMP upregulation in a culture of ADSCs in spheroids resulted in significantly increased osteocalcin production and mineralization. Thus, undifferentiated and predifferentiated ADSCs respond differently to cAMP pathway stimulation in terms of osteogenesis, which might explain the ambiguous results from the literature.

Drug repurposing for targeting cyclic nucleotide transporters in acute leukemias - A missed opportunity

While current treatment regimens for acute leukemia can dramatically improve patient survival, there remains room for improvement. Due to its roles in cell differentiation, cell survival, and apoptotic signaling, modulation of the cyclic AMP (cAMP) pathway has provided a meaningful target in hematological malignancies. Several studies have demonstrated that gene expression profiles associated with increased pro-survival cAMP activity or downregulation of various pro-apoptotic factors associated with the cAMP pathway are apparent in acute leukemia patients. Previous work to increase leukemia cell intracellular cAMP focused on the use of cAMP analogs, stimulating cAMP production via transmembrane-associated adenylyl cyclases, or decreasing cAMP degradation by inhibiting phosphodiesterase activity. However, targeting cyclic nucleotide efflux by ATP-binding cassette (ABC) transporters represents an unexplored approach for modulation of intracellular cyclic nucleotide levels. Preliminary studies have shown that inhibition of cAMP efflux can stimulate leukemia cell differentiation, cell growth arrest, and apoptosis, indicating that targeting cAMP efflux may show promise for future therapeutic development. Furthermore, inhibition of cyclic nucleotide transporter activity may also contribute multiple anticancer benefits by reducing extracellular pro-survival signaling in malignant cells. Hence, several opportunities for drug repurposing may exist for targeting cyclic nucleotide transporters.

Effects of Cigarette Smoke on TSPO-related Mitochondrial Processes

The 18 kDa translocator protein (TSPO) is an initiator of the mitochondrial apoptosis cascade. Cigarette smoke (CS) exposure provokes alterations in TSPO expression as well as upregulation of its related functions such as mitochondrial membrane potential (ΔψM) and reactive oxygen species generation, which are associated with cell death. In the current study, H1299 lung cancer cell line exposed to CS for various time periods (30 mins, 60 mins and 120 mins) and TSPO expression and cell death processes were studied. CS exposure for 30 mins resulted in a non-significant increase in TSPO expression by 24% (p > 0.05 vs. control). CS exposure for 60 mins and 120 mins resulted in a significant increase by 43% (p < 0.05 vs. control) and by 47% (p < 0.01 vs. control), respectively. Furthermore, TSPO-related mitochondrial functions were upregulated at the 120 mins time point following CS exposure. TSPO expression is upregulated by CS, suggesting that TSPO plays a role in cell death processes induced by CS exposure. Alterations in TSPO-related cell death processes suggest that TSPO may be involved in the tissue damage caused by CS.

A small molecule screen to identify regulators of let-7 targets

The let-7 family of miRNAs has been shown to be crucial in many aspects of biology, from the regulation of developmental timing to cancer. The available methods to regulate this family of miRNAs have so far been mostly genetic and therefore not easily performed experimentally. Here, we describe a small molecule screen designed to identify regulators of let-7 targets in human cells. In particular, we focused our efforts on the identification of small molecules that could suppress let-7 targets, as these could serve to potentially intercede in tumors driven by loss of let-7 activity. After screening through roughly 36,000 compounds, we identified a class of phosphodiesterase inhibitors that suppress let-7 targets. These compounds stimulate cAMP levels and raise mature let-7 levels to suppress let-7 target genes in multiple cancer cell lines such as HMGA2 and MYC. As a result, these compounds also show growth inhibitory activity on cancer cells.

Therapeutic potentials of natural compounds acting on cyclic nucleotide phosphodiesterase families

Intracellular cyclic AMP and/or cyclic GMP are characterized in the 1960th. These second messengers, hydrolysed specifically by cyclic nucleotide phosphodiesterase (PDE), play a major role in intracellular signalling. Natural products have been a rich source of drug discovery, Theophylline and Methylxanthine originated from tea leaves used for asthma treatment, whereas, Papaverine, a natural isoquinolein originated from Papaver somniferum traditionally used in impotency, altogether as caffeine where firstly described as PDE-inhibiting compounds. Since that time, the knowledge in PDE field has been drastically increased, allowing the design and development of new therapeutic drugs acting against different pathologies in the nanomolar range. During this period some natural compounds have been identified as PDE inhibitors and used in that context to investigate their therapeutic potential effects. The aim of this literature review is to point out the reported data and demonstrating the contribution of natural characterized molecules as PDE inhibitors in various pathologies that can open new fields of research for drug discovery, notably in epigenetic regulation.

Epstein-Barr Virus (EBV)-BamHI-A Rightward Transcript (BART)-6 and Cellular MicroRNA-142 Synergistically Compromise Immune Defense of Host Cells in EBV-Positive Burkitt Lymphoma

Background

This study was designed to explore the molecular mechanism underlying the effect of cellular miRNAs and EBV miRNA upon the expression of targets such as PTEN, and their involvement in the pathogenesis of Burkitt lymphoma.

Material/Methods

In this study, we examined several differentially expressed cellular miRNAs in EBV-positive versus EBV-negative Burkett lymphoma tissue samples, and confirmed PTEN as targets of cellular miR-142 by using a bioinformatics tool, luciferase reporter system, oligo transfection, real-time PCR, and Western blot analysis.

Results

We further confirmed the binding site of miR-142 in the 3′UTR of the target genes, and established the negative regulatory relationship between miRNA and mRNAs with luciferase activity assay. To verify the regulatory relationship between the miRNAs and PTEN, we evaluated the expression of PTEN in the tissue samples, and found that PTEN was downregulated in EBV- positive Burkett lymphoma. Additionally, lymphoma cells were transfected with EBV-BART-6-3p and miR-142 and we found that EBV-BART-6-3p and miR-142 synergistically reduced expression of IL-6R and PTEN. Furthermore, we also examined viability of the cells in each treatment group, and showed that EBV-BART-6-3p and miR-142 synergistically promoted proliferation of the cells.

Conclusions

These findings improve our knowledge about the role of miR-142/EBV-BART-6-3p and their target, PTEN, in the development of Burkett lymphoma; they could be novel therapeutic targets for the treatment of EBV-positive Burkett lymphoma.

PI3K/AKT and Mdm2 activation are associated with inhibitory effect of cAMP increasing agents on DNA damage-induced cell death in human pre-B NALM-6 cells

DNA damage response (DDR) consists of both proapoptotic and prosurvival signaling branches. Superiority of each signaling branch determines the outcome of DNA damage: death or allowing the repair. The present authors have previously shown that an increased intracellular level of cAMP disrupts p53-mediated apoptosis in human pre-B NALM-6 cells and inhibition of NF-κB prevents prosurvival effect of cAMP during DNA damage. AKT/PKB (protein kinase B) is a general mediator of survival signaling. AKT signaling inhibits p53-mediated transcription and apoptosis. The results of present study showed that cAMP disrupted DNA damage/p53-mediated apoptosis through AKT and subsequent NF-κB activation. These results suggested that AKT may be found as part of a complex with scaffolding proteins, beta-arrestins and PDE4D. cAMP disarticulated the complex through binding to PDE4D compartment. It seems that release of AKT protein potentiated DDR activated pro-survival AKT in NALM-6 cells. Taken together, the present data indicated that regulation of AKT signaling may determine the fate of cells exposed to genotoxic stress.

A polysaccharide from Ganoderma atrum inhibits tumor growth by induction of apoptosis and activation of immune response in CT26-bearing mice

Ganoderma atrum is one species of edible and pharmaceutical mushroom with various biological activities. Recently, a novel polysaccharide, PSG-1, was purified from G. atrum. The antitumor activity and its mechanism of action were studied. In vitro, PSG-1 has little effect on inhibiting proliferation of CT26 tumor cells. However, the tumor size was significantly decreased in PSG-1-treated mice. The results showed that PSG-1 induced apoptosis in CT26 cells. Moreover, the intracellular cyclic AMP (cAMP) level and protein kinase A (PKA) activity were markedly increased in PSG-1-treated mice. In contrast, the contents of cyclic GMP and DAG and the PKC activity were decreased. Similarly, the expression of PKA protein was upregulated, while PKC protein expression in PSG-1-treated group was lowered. Additionally, PSG-1 increased the immune organ index and serum biochemistry parameter. In general, PSG-1 enhances the antitumor immune response, induces apoptosis in CT26-bearing mice, and could be a safe and effective adjuvant for tumor therapy or functional food.

Role of soluble adenylyl cyclase in cell death and growth

cAMP signaling is an evolutionarily conserved intracellular communication system controlling numerous cellular functions. Until recently, transmembrane adenylyl cyclase (tmAC) was considered the major source for cAMP in the cell, and the role of cAMP signaling was therefore attributed exclusively to the activity of this family of enzymes. However, increasing evidence demonstrates the role of an alternative, intracellular source of cAMP produced by type 10 soluble adenylyl cyclase (sAC). In contrast to tmAC, sAC produces cAMP in various intracellular microdomains close to specific cAMP targets, e.g., in nucleus and mitochondria. Ongoing research demonstrates involvement of sAC in diverse physiological and pathological processes. The present review is focused on the role of cAMP signaling, particularly that of sAC, in cell death and growth. Although the contributions of sAC to the regulation of these cellular functions have only recently been discovered, current data suggest that sAC plays key roles in mitochondrial bioenergetics and the mitochondrial apoptosis pathway, as well as cell proliferation and development. Furthermore, recent reports suggest the importance of sAC in several pathologies associated with apoptosis as well as in oncogenesis. This article is part of a Special Issue entitled: The role of soluble adenylyl cyclase in health and disease.

Head and neck cancers, the neglected malignancies: present and future treatment strategies

Head and neck cancers are the most prevalent cancers in Asia and result in 50% of deaths due to all cancers in that region. However, treatment regimen has not changed in the past two decades and there are no specific drugs for this cancer. As a result of this, treatment outcomes remain poor. Furthermore, there are no new breakthrough therapies on the horizon, in part, due to low commercial interest in these cancers. What is needed is new thinking, which combines targeted and risk mitigation approaches to develop novel drugs. This editorial will focus on summarising the present approaches to treatment and propose new targets for these cancers.

miR-181b promotes cell proliferation and reduces apoptosis by repressing the expression of adenylyl cyclase 9 (AC9) in cervical cancer cells

MicroRNAs are a class of small, endogenous, non-coding RNAs that function as post-transcriptional regulators. In this study, we found that miR-181b promoted cell proliferation and inhibited cell apoptosis in cervical cancer cells. And we validated a new miR-181b target gene, adenylyl cyclase 9 (AC9). miR-181b restricted cAMP production by post-transcriptionally downregulating AC9 expression. Phenotypic experiments indicated that miR-181b and AC9 exerted opposite effects on cell proliferation and apoptosis.

New approaches for the identification of drug targets in protozoan parasites

Antiparasitic chemotherapy is an important issue for drug development. Traditionally, novel compounds with antiprotozoan activities have been identified by screening of compound libraries in high-throughput systems. More recently developed approaches employ target-based drug design supported by genomics and proteomics of protozoan parasites. In this chapter, the drug targets in protozoan parasites are reviewed. The gene-expression machinery has been among the first targets for antiparasitic drugs and is still under investigation as a target for novel compounds. Other targets include cytoskeletal proteins, proteins involved in intracellular signaling, membranes, and enzymes participating in intermediary metabolism. In apicomplexan parasites, the apicoplast is a suitable target for established and novel drugs. Some drugs act on multiple subcellular targets. Drugs with nitro groups generate free radicals under anaerobic growth conditions, and drugs with peroxide groups generate radicals under aerobic growth conditions, both affecting multiple cellular pathways. Mefloquine and thiazolides are presented as examples for antiprotozoan compounds with multiple (side) effects. The classic approach of drug discovery employing high-throughput physiological screenings followed by identification of drug targets has yielded the mainstream of current antiprotozoal drugs. Target-based drug design supported by genomics and proteomics of protozoan parasites has not produced any antiparasitic drug so far. The reason for this is discussed and a synthesis of both methods is proposed.

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.

Cyclic AMP is both a pro-apoptotic and anti-apoptotic second messenger

The second messenger cyclic AMP (cAMP) can either stimulate or inhibit programmed cell death (apoptosis). Here, we review examples of cell types that show pro-apoptotic or anti-apoptotic responses to increases in cAMP. We also show that cells can have both such responses, although predominantly having one or the other. Protein kinase A (PKA)-promoted changes in phosphorylation and gene expression can mediate pro-apoptotic responses, such as in murine S49 lymphoma cells, based on evidence that mutants lacking PKA fail to undergo cAMP-promoted, mitochondria-dependent apoptosis. Mechanisms for the anti-apoptotic response to cAMP likely involve Epac (Exchange protein activated by cAMP), a cAMP-regulated effector that is a guanine nucleotide exchange factor (GEF) for the low molecular weight G-protein, Rap1. Therapeutic approaches that activate PKA-mediated pro-apoptosis or block Epac-mediated anti-apoptotisis may provide a means to enhance cell killing, such as in certain cancers. In contrast, efforts to block PKA or stimulate Epac have the potential to be useful in diseases settings (such as heart failure) associated with cAMP-promoted apoptosis.

Phosphodiesterase function and endocrine cells: links to human disease and roles in tumor development and treatment

Phosphodiesterases (PDEs) are enzymes that regulate the intracellular levels of cyclic adenosine monophosphate and cyclic guanosine monophosphate, and, consequently, exhibit a central role in multiple cellular functions. The pharmacological exploitation of the ability of PDEs to regulate specific pathways has led to the discovery of drugs with selective action against specific PDE isoforms. Considerable attention has been given to the development of selective PDE inhibitors, especially after the therapeutic success of PDE5 inhibitors in the treatment of erectile dysfunction. Several associations between PDE genes and genetic diseases have been described, and more recently PDE11A and PDE8B have been implicated in predisposition to tumor formation. This review focuses on the possible function of PDEs in a variety of tumors, primarily in endocrine glands, both in tumor predisposition and as potential therapeutic targets.

An oncogenic role of miR-142-3p in human T-cell acute lymphoblastic leukemia (T-ALL) by targeting glucocorticoid receptor-α and cAMP/PKA pathways

MicroRNAs (miRNAs) are a family of 19-24 nucleotide non-coding RNAs with posttranscriptional regulatory functions. The involvement of miRNAs in normal hematopoiesis implies that deregulated miRNAs might contribute to leukemogenesis. To date, although certain miRNAs have been established a clear oncogenic role in hematological malignancies, other individual miRNAs potentially involved in human leukemogenesis still remain elusive. In this report, we showed that miR-142-3p was upregulated in human T-leukemic cell lines and primary T-leukemic cells isolated from T-cell acute lymphoblastic leukemia (T-ALL) patients and its expressive levels were correlated with patients' prognosis. Such an oncogenic role of miR-142-3p could be explained by its targeting cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and glucocorticoid receptor alpha (GRα). High levels of miR-142-3p resulted in low levels of cAMP and weak activity of PKA, thus relieving the inhibitory effect of PKA on T-leukemic cell proliferation. Meanwhile, miR-142-3p decreased GRα protein expression by directly targeting the 3'-untranslational region of GRα mRNA, leading to glucocorticoid resistance. Transfection of the miR-142-3p inhibitor effectively converted glucocorticoid resistance, because of the resultant increase of GRα expression and PKA activity. These findings suggest that miR-142-3p is critical in T-cell leukemogenesis and may serve as a potential therapeutic target in T-ALL patients.

Cytotoxic T lymphocyte antigen-2 alpha induces apoptosis of murine T-lymphoma cells and cardiac fibroblasts and is regulated by cAMP/PKA

The mechanism of cAMP-promoted apoptosis is not well defined. In wild-type (WT) murine S49 lymphoma cells, cAMP promotes apoptosis in a protein kinase A (PKA)-dependent manner. We find that treatment of WT S49 cells with 8-CPT-cAMP prominently increases the expression (as determined by DNA microarray analysis, real-time PCR and immunblotting) of cytotoxic T lymphocyte antigen-2α (CTLA-2α), a cathepsin L-like cysteine protease inhibitor. By contrast, CTLA-2α expression is only slightly increased by 8-CPT-cAMP treatment of D-S49 cells, which lack cAMP/PKA-promoted apoptosis. Raising endogenous cAMP (by use of forskolin or inhibition of phosphodiesterase [PDE] 4) or a PKA-selective, but not an Epac-selective, cAMP analogue, increases CTLA-2α mRNA expression; PKA, and not Epac, thus mediates the increase in CTLA-2α expression. An adenoviral CLTA-2α (Ad-CTLA-2α) construct induces apoptosis and enhances cAMP-promoted apoptosis in WT S49 cells but such cells do not have an increase in cathepsin L activity nor does a cathepsin L inhibitor alter cAMP-promoted apoptosis. 8-CPT-cAMP also increases CTLA-2α expression and induces apoptosis in murine cardiac fibroblasts; knockdown of CTLA-2α expression by siRNA blocks 8-CPT-cAMP-promoted apoptosis. Thus, cAMP increases CTLA-2α expression in murine lymphoma and cardiac fibroblasts and this increase in CTLA-2α contributes to cAMP/PKA-promoted apoptosis by mechanisms that are independent of the ability of CTLA-2α to inhibit cathepsin L.

Cyclic-AMP-dependent protein kinase A regulates apoptosis by stabilizing the BH3-only protein Bim

The proapoptotic Bcl2 homology domain 3(BH3)-only protein Bim is controlled by stringent post-translational regulation, predominantly through alterations in phosphorylation status. To identify new kinases involved in its regulation, we carried out a yeast two-hybrid screen using a non-spliceable variant of the predominant isoform--Bim(EL)--as the bait and identified the regulatory subunit of cyclic-AMP-dependent protein kinase A--PRKAR1A--as an interacting partner. We also show that protein kinase A (PKA) is a Bim(EL) isoform-specific kinase that promotes its stabilization. Inhibition of PKA or mutation of the PKA phosphorylation site within Bim(EL) resulted in its accelerated proteasome-dependent degradation. These results might have implications for human diseases that are characterized by abnormally increased PKA activity, such as the Carney complex and dilated cardiomyopathy.

Pharmacologic interception in T-cell leukemia 1A associated pathways as a treatment rationale for chronic lymphocytic leukemia

Recent therapeutic advances in chronic lymphocytic leukemia (CLL) are reflected by high response rates in most subsets of patients. However, refractory disease remains a problem, and virtually all of even the most sensitive tumors eventually recur. Therefore, ongoing efforts aim at the development of optimized interventional designs that more specifically target the strong pro-survival signature of the transformed B cell. Stimuli from the CLL microenvironment are considered the predominant force that sets this high anti-apoptotic threshold. We introduce here our concept that the oncogene T-cell leukemia 1A (TCL1A), which induces CLL-like disease in transgenic mice, significantly enhances such milieu-derived signaling, propagates associated resistance, and therefore represents a targetable pathway in CLL. We discuss inhibitory strategies that are based on TCL1A's activation of the growth modulating kinase AKT and on influences that regulate TCL1A expression. Respective preliminary data indicate that differential response categories of CLL exist. Future studies will test TCL1A's inherent predictive information.

Direct detection of diverse metabolic changes in virally transformed and tax-expressing cells by mass spectrometry

Background

Viral transformation of a cell starts at the genetic level, followed by changes in the proteome and the metabolome of the host. There is limited information on the broad metabolic changes in HTLV transformed cells.

Methods and Principal Findings

Here, we report the detection of key changes in metabolites and lipids directly from human T-lymphotropic virus type 1 and type 3 (HTLV1 and HTLV3) transformed, as well as Tax1 and Tax3 expressing cell lines by laser ablation electrospray ionization (LAESI) mass spectrometry (MS). Comparing LAESI-MS spectra of non-HTLV1 transformed and HTLV1 transformed cells revealed that glycerophosphocholine (PC) lipid components were dominant in the non-HTLV1 transformed cells, and PC(O-32∶1) and PC(O-34∶1) plasmalogens were displaced by PC(30∶0) and PC(32∶0) species in the HTLV1 transformed cells. In HTLV1 transformed cells, choline, phosphocholine, spermine and glutathione, among others, were downregulated, whereas creatine, dopamine, arginine and AMP were present at higher levels. When comparing metabolite levels between HTLV3 and Tax3 transfected 293T cells, there were a number of common changes observed, including decreased choline, phosphocholine, spermine, homovanillic acid, and glycerophosphocholine and increased spermidine and N-acetyl aspartic acid. These results indicate that the lipid metabolism pathway as well as the creatine and polyamine biosynthesis pathways are commonly deregulated after expression of HTLV3 and Tax3, indicating that the noted changes are likely due to Tax3 expression. N-acetyl aspartic acid is a novel metabolite that is upregulated in all cell types and all conditions tested.

Conclusions and Significance

We demonstrate the high throughput in situ metabolite profiling of HTLV transformed and Tax expressing cells, which facilitates the identification of virus-induced perturbations in the biochemical processes of the host cells. We found virus type-specific (HTLV1 vs. HTLV3), expression-specific (Tax1 vs. Tax3) and cell-type–specific (T lymphocytes vs. kidney epithelial cells) changes in the metabolite profiles. The new insight on the affected metabolic pathways can be used to better understand the molecular mechanisms of HTLV induced transformation, which in turn can result in new treatment strategies.

Involvement of cAMP in nerve growth factor-triggered p35/Cdk5 activation and differentiation in PC12 cells

The signaling mechanisms underlying cell differentiation have been extensively studied with the use of rat PC12 cells as a model system. Nerve growth factor (NGF) is a trophic factor inducing PC12 cell differentiation through the activation of the p35/cyclin-dependent kinase 5 (Cdk5) complex. It has been reported that adenylyl cyclase activation and cAMP production may be involved in NGF-dependent actions. Our previous results indicate that cAMP activates the p35/Cdk5 complex in reproductive cells. Therefore, the role of cAMP in NGF-triggered p35/Cdk5 activation and PC12 differentiation was interesting to explore. Our results indicate that roscovitine, a molecular inhibitor of Cdk5, blocks cAMP-triggered PC12 differentiation, which was evaluated by neurite initiation, a decrease in proliferation, and cell cycle G(1) arrest. The following data show that cAMP treatment increased Cdk5 activity through p35 upregulation. cAMP downstream components, protein kinase A (PKA) and phosphorylated cAMP response element binding protein (CREB), are involved in this regulation. The immunocytochemical results indicate that PKA inhibition disrupted cAMP-triggered p35/Cdk5 localization in PC12 cells. In addition, adenylyl cyclase inhibition was found to diminish NGF-induced intracellular cAMP production, CREB phosphorylation, and p35 expression. The cAMP antagonist and the PKA inhibitors reduced NGF-induced p35 expression. Finally, NGF-triggered PC12 differentiation was partially decreased by adenylyl cyclase or PKA inhibitors. In conclusion, these results demonstrate that cAMP may play a role in NGF-p35/Cdk5-dependent PC12 differentiation.

Data recovery and integration from public databases uncovers transformation-specific transcriptional downregulation of cAMP-PKA pathway-encoding genes

BACKGROUND

The integration of data from multiple genome-wide assays is essential for understanding dynamic spatio-temporal interactions within cells. Such integration, which leads to a more complete view of cellular processes, offers the opportunity to rationalize better the high amount of "omics" data freely available in several public databases.In particular, integration of microarray-derived transcriptome data with other high-throughput analyses (genomic and mutational analysis, promoter analysis) may allow us to unravel transcriptional regulatory networks under a variety of physio-pathological situations, such as the alteration in the cross-talk between signal transduction pathways in transformed cells.

RESULTS

Here we sequentially apply web-based and statistical tools to a case study: the role of oncogenic activation of different signal transduction pathways in the transcriptional regulation of genes encoding proteins involved in the cAMP-PKA pathway. To this end, we first re-analyzed available genome-wide expression data for genes encoding proteins of the downstream branch of the PKA pathway in normal tissues and human tumor cell lines. Then, in order to identify mutation-dependent transcriptional signatures, we classified cancer cells as a function of their mutational state. The results of such procedure were used as a starting point to analyze the structure of PKA pathway-encoding genes promoters, leading to identification of specific combinations of transcription factor binding sites, which are neatly consistent with available experimental data and help to clarify the relation between gene expression, transcriptional factors and oncogenes in our case study.

CONCLUSIONS

Genome-wide, large-scale "omics" experimental technologies give different, complementary perspectives on the structure and regulatory properties of complex systems. Even the relatively simple, integrated workflow presented here offers opportunities not only for filtering data noise intrinsic in high throughput data, but also to progressively extract novel information that would have remained hidden otherwise. In fact we have been able to detect a strong transcriptional repression of genes encoding proteins of cAMP/PKA pathway in cancer cells of different genetic origins. The basic workflow presented herein may be easily extended by incorporating other tools and can be applied even by researchers with poor bioinformatics skills.

Influence of cyclic AMP on facial nerve regeneration in rats

Promoting facial nerve regeneration is a significant challenge.

Aim

To evaluate the possible neurotrophic influence of cyclic AMP on facial nerve regeneration of Wistar rats.

Method

The right facial nerve of thirty-two animals were completely transected and immediately sutured, followed by exposure or not to topical cyclic AMP. Behavioral and histometric analyses were done at 14 and 28 days.

Results

Statistical differences (p<0.05) were found in the behavioral and histometric analyses on the 14th day, suggesting an early regenerative response of the facial nerve to cAMP exposure.

Conclusion

This study demonstrates a possible neurotrophic effect of cAMP on facial nerve regeneration in rats.

Drug development targeting the glycogen synthase kinase-3beta (GSK-3beta)-mediated signal transduction pathway: inhibitors of the Wnt/beta-catenin signaling pathway as novel anticancer drugs

Accumulating evidence suggests that the Wnt/beta-catenin signaling pathway is often involved in oncogenesis and cancer development. Accordingly, a novel anticancer drug can be developed using inhibitors of this pathway. However, at present, there is no selective inhibitor of this pathway available as a therapeutic agent. Although all the components of the Wnt/beta-catenin signaling pathway can be a target for drug development, glycogen synthase kinase-3beta (GSK-3beta), in particular, may be a good target because GSK-3beta is an essential component of the pathway, and activation of this kinase results in the inhibition of the Wnt signaling pathway. We found that the differentiation-inducing factors (DIFs), putative morphogens for Dictyostelium discoideum, inhibit the Wnt/beta-catenin signaling pathway via the activation of GSK-3beta, resulting in the cell-cycle arrest of human cancer cell lines. In this review, we summarize our recent findings on the antiproliferative effect of DIFs and show the possibility for development of a novel anticancer drug from DIFs and their derivatives.

G protein-coupled receptor connectivity to NF-kappaB in inflammation and cancer

Complex intracellular network interactions regulate gene expression and cellular behavior. Whether at the site of inflammation or within a tumor, individual cells are exposed to a plethora of signals. The transcription factor nuclear factor-kappaB (NF-kappaB) regulates genes that control key cellular activities involved in inflammatory diseases and cancer. NF-kappaB is regulated by several distinct signaling pathways that may be activated individually or simultaneously. Multiple ligands and heterologous cell-cell interactions have an impact on NF-kappaB activity. The G protein-coupled receptor (GPCR) superfamily makes up the largest class of transmembrane receptors in the human genome and has multiple molecularly distinct natural ligands. GPCRs regulate proliferation, differentiation, and chemotaxis and play a major role in inflammatory diseases and cancer. Both GPCRs and NF-kappaB have been, and continue to be, major targets for drug discovery. A clear understanding of network interactions between GPCR signaling pathways and those that control NF-kB may be valuable for the development of better drugs and drug combinations.

Perinatal exposure to oestradiol and bisphenol A alters the prostate epigenome and increases susceptibility to carcinogenesis

An important and controversial health concern is whether low-dose exposures to hormonally active environmental oestrogens such as bisphenol A can promote human diseases including prostate cancer. Our studies in rats have shown that pharmacological doses of oestradiol administered during the critical window of prostate development result in marked prostate pathology in adulthood that progress to neoplastic lesions with ageing. Our recent studies have also demonstrated that transient developmental exposure of rats to low, environmentally relevant doses of bisphenol A or oestradiol increases prostate gland susceptibility to adult-onset precancerous lesions and hormonal carcinogenesis. These findings indicate that a wide range of oestrogenic exposures during development can predispose to prostatic neoplasia that suggests a potential developmental basis for this adult disease. To identify a molecular basis for oestrogen imprinting, we screened for DNA methylation changes over time in the exposed prostate glands. We found permanent alterations in DNA methylation patterns of multiple cell signalling genes suggesting an epigenetic mechanism of action. For phosphodiesterase type 4 variant 4 (PDE4D4), an enzyme responsible for intracellular cyclic adenosine monophosphate breakdown, a specific methylation cluster was identified in the 5'-flanking CpG island that was gradually hypermethylated with ageing in normal prostates resulting in loss of gene expression. However, in prostates exposed to neonatal oestradiol or bisphenol A, this region became hypomethylated with ageing resulting in persistent and elevated PDE4D4 expression. In total, these findings indicate that low-dose exposures to ubiquitous environmental oestrogens impact the prostate epigenome during development and in so doing, promote prostate disease with ageing.

Developmental estrogen exposures predispose to prostate carcinogenesis with aging

Prostate morphogenesis occurs in utero in humans and during the perinatal period in rodents. While largely driven by androgens, there is compelling evidence for a permanent influence of estrogens on prostatic development. If estrogenic exposures are abnormally high during the critical developmental period, permanent alterations in prostate morphology and function are observed, a process referred to as developmental estrogenization. Using the neonatal rodent as an animal model, it has been shown that early exposure to high doses of estradiol results in an increased incidence of prostatic lesions with aging which include hyperplasia, inflammatory cell infiltration and prostatic intraepithelial neoplasia or PIN, believed to be the precursor lesion for prostatic adenocarcinoma. The present review summarizes research performed in our laboratory to characterize developmental estrogenization and identify the molecular pathways involved in mediating this response. Furthermore, recent studies performed with low-dose estradiol exposures during development as well as exposures to environmentally relevant doses of the endocrine disruptor bisphenol A show increased susceptibility to PIN lesions with aging following additional adult exposure to estradiol. Gene methylation analysis revealed a potential epigenetic basis for the estrogen imprinting of the prostate gland. Taken together, our results suggest that a full range of estrogenic exposures during the postnatal critical period - from environmentally relevant bisphenol A exposure to low-dose and pharmacologic estradiol exposures - results in an increased incidence and susceptibility to neoplastic transformation of the prostate gland in the aging male which may provide a fetal basis for this adult disease.

Apoptosis induced by cAMP requires Smac/DIABLO transcriptional upregulation

Smac/DIABLO is a mitochondrial protein that participates in apoptotic cell death by means of sequestering several members of the inhibitor of apoptosis protein family. This action allows caspase activation, cleavage of key cellular substrates and death. Release from mitochondria is considered the main regulatory step of Smac/DIABLO activity. Nevertheless, the fact that at least one isoform, Smac-beta, does not reside in this organelle implies that transcriptional regulation could also be important. cAMP is a well known second messenger with important apoptotic effects. To analyze if cAMP could be involved in Smac/DIABLO gene regulation, we analyzed 2903 base pairs upstream of the coding sequence and characterized the minimal promoter, which contains a consensus CRE site. We found that cAMP/PKA/CREB pathway is indeed an important regulator of Smac/DIABLO transcription, since exposure to the cAMP analog 8-CPT-cAMP, the adenylyl cyclase activator forskolin, the inhibitor of phosphodiesterase isobutylmethylxanthine or by hindering PKA activation with H89, regulated the promoter activity, as shown by gene reporter and RT-PCR assays. Additionally, the results of site-directed mutagenesis revealed that the consensus CRE site was biologically functional and required for cAMP-induced promoter activity in human HeLa cells. Supporting these results, a negative dominant version of the protein kinase A responsive factor, KCREB, reduced basal Smac/DIABLO expression and rendered the promoter unresponsive to cAMP. Reducing Smac expression using an antisense approach blocked the apoptosis effects of cAMP in cervical cancer cells. These results show that cAMP is an important modulator of the apoptotic threshold in cancer cell by means of regulating Smac/DIABLO expression.

Involvement of GSK-3beta and DYRK1B in differentiation-inducing factor-3-induced phosphorylation of cyclin D1 in HeLa cells

Differentiation-inducing factors (DIFs) are putative morphogens that induce cell differentiation in Dictyostelium discoideum. We previously reported that DIF-3 activates glycogen synthase kinase-3beta (GSK-3beta), resulting in the degradation of cyclin D1 in HeLa cells. In this study, we investigated the effect of DIF-3 on cyclin D1 mutants (R29Q, L32A, T286A, T288A, and T286A/T288A) to clarify the precise mechanisms by which DIF-3 degrades cyclin D1 in HeLa cells. We revealed that T286A, T288A, and T286A/T288A mutants were resistant to DIF-3-induced degradation compared with wild-type cyclin D1, indicating that the phosphorylation of Thr(286) and Thr(288) were critical for cyclin D1 degradation induced by DIF-3. Indeed, DIF-3 markedly elevated the phosphorylation level of cyclin D1, and mutations introduced to Thr(286) and/or Thr(288) prevented the phosphorylation induced by DIF-3. Depletion of endogenous GSK-3beta and dual-specificity tyrosine phosphorylation regulated kinase 1B (DYRK1B) by RNA interference attenuated the DIF-3-induced cyclin D1 phosphorylation and degradation. The effect of DIF-3 on DYRK1B activity was examined and we found that DIF-3 also activated this kinase. Further, we found that not only GSK-3beta but also DYRK1B modulates cyclin D1 subcellular localization by the phosphorylation of Thr(288). These results suggest that DIF-3 induces degradation of cyclin D1 through the GSK-3beta- and DYRK1B-mediated threonine phosphorylation in HeLa cells.

The Trypanosoma brucei cAMP phosphodiesterases TbrPDEB1 and TbrPDEB2: flagellar enzymes that are essential for parasite virulence

Cyclic nucleotide specific phosphodiesterases (PDEs) are pivotal regulators of cellular signaling. They are also important drug targets. Besides catalytic activity and substrate specificity, their subcellular localization and interaction with other cell components are also functionally important. In contrast to the mammalian PDEs, the significance of PDEs in protozoal pathogens remains mostly unknown. The genome of Trypanosoma brucei, the causative agent of human sleeping sickness, codes for five different PDEs. Two of these, TbrPDEB1 and TbrPDEB2, are closely similar, cAMP-specific PDEs containing two GAF-domains in their N-terminal regions. Despite their similarity, these two PDEs exhibit different subcellular localizations. TbrPDEB1 is located in the flagellum, whereas TbrPDEB2 is distributed between flagellum and cytoplasm. RNAi against the two mRNAs revealed that the two enzymes can complement each other but that a simultaneous ablation of both leads to cell death in bloodstream form trypanosomes. RNAi against TbrPDEB1 and TbrPDEB2 also functions in vivo where it completely prevents infection and eliminates ongoing infections. Our data demonstrate that TbrPDEB1 and TbrPDEB2 are essential for virulence, making them valuable potential targets for new PDE-inhibitor based trypanocidal drugs. Furthermore, they are compatible with the notion that the flagellum of T. brucei is an important site of cAMP signaling.

Phenotype-based screening of mechanistically annotated compounds in combination with gene expression and pathway analysis identifies candidate drug targets in a human squamous carcinoma cell model

The squamous cell carcinoma HeLa cell line and an epithelial cell line hTERT-RPE with a nonmalignant phenotype were interrogated for HeLa cell selectivity in response to 1267 annotated compounds representing 56 pharmacological classes. Selective cytotoxic activity was observed for 14 of these compounds dominated by cyclic adenosine monophosphate (cAMP) selective phosphodiesterase (PDE) inhibitors, which tended to span a representation of the chemical descriptor space of the library. The PDE inhibitors induced delayed cell death with features compatible with classical apoptosis. The PDE inhibitors were largely inactive when tested against a cell line panel consisting of hematological and nonsquamous epithelial phenotypes. In a genome-wide DNA microarray analysis, PDE3A and PDE2A were found to be significantly increased in HeLa cells compared to the other cell lines. The pathway analysis software PathwayAssist was subsequently used to extract a list of proteins and small molecules retrieved from Medline abstracts associated with the hit compounds. The resulting list consisted of major parts of the cAMP-protein kinase A pathway linking to ERK, P38, and AKT. This molecular network may provide a basis for further exploitation of novel candidate targets for the treatment of squamous cell carcinoma.

Differentiation-inducing factor-1 alters canonical Wnt signaling and suppresses alkaline phosphatase expression in osteoblast-like cell lines

Because DIF-1 has been shown to affect Wnt/beta-catenin signaling pathway, the effects of DIF-1 on osteoblast-like cell lines, SaOS-2 and MC3T3-E1, were examined. We found that DIF-1 inhibited this pathway, resulting in the suppression of ALP promoter activity through the TCF/LEF binding site.

INTRODUCTION

Differentiation-inducing factor-1 (DIF-1), a morphogen of Dictyostelium, inhibits cell proliferation and induces cell differentiation in several mammalian cells. Previous studies showed that DIF-1 activated glycogen synthase kinase-3beta, suggesting that this chemical could affect the Wnt/beta-catenin signaling pathway. This pathway has been shown to be involved in bone biology.

MATERIALS AND METHODS

We studied the effects of DIF-1 on SaOS-2 and MC3T3-E1, osteosarcoma cell lines widely used as a model system for ostoblastic cells and murine osteoblast-like cell line, respectively. Reporter gene assays were also carried out to examine the effect of DIF-1 on the Wnt/beta-catenin signaling pathway.

RESULTS

DIF-1 inhibited SaOS-2 proliferation and reduced alkaline phosphatase (ALP) activity in a concentration- and a time-dependent manner. The expression of ALP was markedly suppressed by DIF-1-treatment in protein and mRNA levels. DIF-1 also suppressed the expression of other osteoblast differentiation markers, including core binding factor alpha1, type I collagen, and osteocalcin, in protein and mRNA levels and inhibited osteoblast-mediated mineralization. Subsequently, we examined the effect of DIF-1 on the Wnt/beta-catenin signaling pathway. We found that DIF-1 suppressed the expression of beta-catenin protein and the activity of the reporter gene containing T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) consensus binding sites. We examined the effect of DIF-1 on a reporter gene driven by the human ALP promoter and found that DIF-1 significantly reduced the ALP reporter gene activity through the TCF/LEF binding site (-1023/-1017 bp). Furthermore, the effect of DIF-1 on MC3T3-E1, a murine osteoblast-like cell line, was examined, and it was found that DIF-1 suppressed ALP mRNA expression by the reduction of the ALP reporter gene activity through the TCF/LEF binding site.

CONCLUSIONS

Our data suggest that DIF-1 inhibits Wnt/beta-catenin signaling, resulting in the suppression of ALP promoter activity. To our knowledge, this is the first report to analyze the role of the TCF/LEF binding site (-1023/-1017 bp) of the ALP gene promoter in osteoblast-like cell lines.

Developmental exposure to estradiol and bisphenol A increases susceptibility to prostate carcinogenesis and epigenetically regulates phosphodiesterase type 4 variant 4

Early developmental perturbations have been linked to adult-onset prostate pathology, including excessive exposure to estrogenic compounds; however, the molecular basis for this imprinting event is not known. An important and controversial health concern is whether low-dose exposures to hormonally active environmental estrogens, such as bisphenol A, can promote human diseases, including prostate cancer. Here, we show that transient developmental exposure of rats to low, environmentally relevant doses of bisphenol A or estradiol increases prostate gland susceptibility to adult-onset precancerous lesions and hormonal carcinogenesis. We found permanent alterations in the DNA methylation patterns of multiple cell signaling genes, suggesting an epigenetic basis for estrogen imprinting. For phosphodiesterase type 4 variant 4 (PDE4D4), an enzyme responsible for cyclic AMP breakdown, a specific methylation cluster was identified in the 5'-flanking CpG island that was gradually hypermethylated with aging in normal prostates, resulting in loss of gene expression. Early and prolonged hypomethylation at this site following neonatal estradiol or bisphenol A exposure resulted in continued, elevated PDE4D4 expression. Cell line studies confirmed that site-specific methylation is involved in transcriptional silencing of the PDE4D4 gene and showed hypomethylation of this gene in prostate cancer cells. Importantly, the PDE4D4 alterations in the estrogen-exposed prostates were distinguishable before histopathologic changes of the gland, making PDE4D4 a candidate molecular marker for prostate cancer risk assessment as a result of endocrine disruptors. In total, these findings indicate that low-dose exposures to ubiquitous environmental estrogens affect the prostate epigenome during development and, in so doing, promote prostate disease with aging.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.

Insights into gene expression changes impacting B-cell transformation: cross-species microarray analysis of bovine leukemia virus tax-responsive genes in ovine B cells

Large-animal models for leukemia have the potential to aid in the understanding of networks that contribute to oncogenesis. Infection of cattle and sheep with bovine leukemia virus (BLV), a complex retrovirus related to human T-cell leukemia virus type 1 (HTLV-1), is associated with the development of B-cell leukemia. Whereas the natural disease in cattle is characterized by a low tumor incidence, experimental infection of sheep leads to overt leukemia in the majority of infected animals, providing a model for studying the pathogenesis associated with BLV and HTLV-1. Tax(BLV), the major oncoprotein, initiates a cascade of events leading toward malignancy, although the basis of transformation is not fully understood. We have taken a cross-species ovine-to-human microarray approach to identify Tax(BLV)-responsive transcriptional changes in two sets of cultured ovine B cells following retroviral vector-mediated delivery of Tax(BLV). Using cDNA-spotted microarrays comprising 10,336 human genes/expressed sequence tags, we identified a cohort of differentially expressed genes, including genes related to apoptosis, DNA transcription, and repair; proto-oncogenes; cell cycle regulators; transcription factors; small Rho GTPases/GTPase-binding proteins; and previously reported Tax(HTLV-1)-responsive genes. Interestingly, genes known to be associated with human neoplasia, especially B-cell malignancies, were extensively represented. Others were novel or unexpected. The results suggest that Tax(BLV) deregulates a broad network of interrelated pathways rather than a single B-lineage-specific regulatory process. Although cross-species approaches do not permit a comprehensive analysis of gene expression patterns, they can provide initial clues for the functional roles of genes that participate in B-cell transformation and pinpoint molecular targets not identified using other methods in animal models.

The synthetic compound CC-5079 is a potent inhibitor of tubulin polymerization and tumor necrosis factor-alpha production with antitumor activity

We have found that the synthetic compound CC-5079 potently inhibits cancer cell growth in vitro and in vivo by a novel combination of molecular mechanisms. CC-5079 inhibits proliferation of cancer cell lines from various organs and tissues at nanomolar concentrations. Its IC(50) value ranges from 4.1 to 50 nmol/L. The effect of CC-5079 on cell growth is associated with cell cycle arrest in G(2)-M phase, increased phosphorylation of G(2)-M checkpoint proteins, and apoptosis. CC-5079 prevents polymerization of purified tubulin in a concentration-dependent manner in vitro and depolymerizes microtubules in cultured cancer cells. In competitive binding assays, CC-5079 competes with [(3)H]colchicine for binding to tubulin; however, it does not compete with [(3)H]paclitaxel (Taxol) or [(3)H]vinblastine. Our data indicate that CC-5079 inhibits cancer cell growth with a mechanism of action similar to that of other tubulin inhibitors. However, CC-5079 remains active against multidrug-resistant cancer cells unlike other tubulin-interacting drugs, such as Taxol and colchicine. Interestingly, CC-5079 also inhibits tumor necrosis factor-alpha (TNF-alpha) secretion from lipopolysaccharide-stimulated human peripheral blood mononuclear cells (IC(50), 270 nmol/L). This inhibitory effect on TNF-alpha production is related to its inhibition of phosphodiesterase type 4 enzymatic activity. Moreover, in a mouse xenograft model using HCT-116 human colorectal tumor cells, CC-5079 significantly inhibits tumor growth in vivo. In conclusion, our data indicate that CC-5079 represents a new chemotype with novel mechanisms of action and that it has the potential to be developed for neoplastic and inflammatory disease therapy.

Overexpression of RhoA-GTP induces activation of the Epidermal Growth Factor Receptor, dephosphorylation of focal adhesion kinase and increased motility in breast cancer cells

Rho GTPases are overexpressed in human tumors and are involved in a variety of cellular processes such as organization of the actin cytoskeleton, cell-cell contact and malignant transformation. EGFR activation plays a key role in the acquisition of motile properties in carcinoma cells, and it has been proposed that downregulation of FAK activity is one of its most relevant consequences. In the present study, using mammary MCF-7 cells, we demonstrated that overexpression of the active form of the small GTPase RhoA induced the activation of EGFR by a phenomenon that depends on the activity of a metalloproteinase (MMP), which presumably cleaves a membrane-bound EGFR ligand. The EGFR tyrosine phosphorylation correlates with ERK1,2 activation and the stimulation of urokinase production. An aggressive mammary cell line (MDA-MB-231) that overexpresses both RhoA and EGFR in their active forms also displayed an MMP-dependent activation mechanism of EGFR. RhoA-GTP-transfected cells showed a cortical array of F-actin, rounded morphology, reduced spreading potential and a dephosphorylation of FAK that was released by integrin-dependent fibronectin adhesion and a specific EGFR tyrosine kinase inhibitor. Our results suggest that the MMP-dependent EGFR activation observed in V14 RhoA cells represents the starting point of a signaling route that promotes cell motility by activation of ERK1,2 and further enhancement of proteases production.

Gap junctions and the propagation of cell survival and cell death signals

Gap junctions are a unique type of intercellular channels that connect the cytoplasm of adjoining cells. Each gap junction channel is comprised of two hemichannels or connexons and each connexon is formed by the aggregation of six protein subunits known as connexins. Gap junction channels allow the intercellular passage of small (< 1.5 kDa) molecules and regulate essential processes during development and differentiation. However, their role in cell survival and cell death is poorly understood. We review experimental data that support the hypothesis that gap junction channels may propagate cell death and survival modulating signals. In addition, we explore the hypothesis that hemichannels (or unapposed connexons) might be used as a paracrine conduit to spread factors that modulate the fate of the surrounding cells. Finally, direct signal transduction activity of connexins in cell death and survival pathways is addressed.

Differential phosphodiesterase expression and cytosolic Ca2+in human CNS tumour cells and in non-malignant and malignant cells of rat origin

A promising attempt in the field of tumour therapy is the modulation of intracellular, proliferation-associated signalling pathways. The role of cyclic nucleotide phosphodiesterases (PDEs), key enzymes in cAMP/cGMP signal transduction, was investigated in two human CNS tumour cell lines as well as in the rat glioblastoma cell line C6 in comparison with rat cerebellar astrocytes with the emphasis on target evaluation. We found differential PDE expression patterns in human CNS tumour cell lines as well as in CNS cells of rat origin. In human glioblastoma cells, intracellular cAMP and Ca(2+) levels correlated well with the PDE expression pattern. There were, however, marked differences in PDE expression and Ca(2+) kinetics between the human glioblastoma cell lines. In contrast to human epithelial tumour cells, shown earlier by us to express significantly enhanced cAMP-specific PDE activity, this was not the case in rat glioblastoma cells compared with non-malignant rat astrocytes. Despite different levels of PDE1 and PDE4 expression and activity, cyclic nucleotide and Ca(2+) levels in non-malignant and malignant rat CNS cells were similar. These in vitro data do not support the concept of PDE1C representing a target exploitable for drug treatment of malignant CNS tumours.

Changes of Plasma Membrane Properties in a Human Pre-T Cell Line Undergoing Apoptosis

A variety of cellular functions are modulated by the physical properties of the cell membrane, and the modification of intracellular transfer, resulting from loss of membrane integrity, may contribute toward setting the cell onto the pathway of apoptosis. Apoptosis in lymphoid cells can be induced in different ways and biochemical modifications occur at an early phase of cell death, while the morphological features of apoptosis are evident later. We previously reported that DMSO is an efficient apoptosis-inducing factor in the human RPMI-8402 pre-T cell line. The aim of the present study was to verify the effect of DMSO on the plasma membrane fluidity, the intracellular calcium concentration and the phosphodiesterase activity in DMSO-induced apoptosis. Our results show a modification of membrane fluidity associated with an increase of intracellular Ca(2+) concentration. Moreover, we demonstrate that these modifications are related to a decrease in the phosphodiesterase (PDE) activity. The correlation between the proceedings of added DMSO and the induction of apoptosis will provide significant information regarding the first part of the apoptotic process.

Type 4 cAMP phosphodiesterase (PDE4) inhibitors augment glucocorticoid-mediated apoptosis in B cell chronic lymphocytic leukemia (B-CLL) in the absence of exogenous adenylyl cyclase stimulation

cAMP-mediated signaling potentiates glucocorticoid-mediated apoptosis in lymphoid cells, but an effective means by which to take advantage of this observation in the treatment of lymphoid malignancies has not been identified. The primary objective of the current study was to determine whether PDE4 inhibitors, a class of compounds in late clinical development that raise intracellular cAMP levels by inhibiting type 4 cyclic nucleotide phosphodiesterases (PDE4), increase the efficacy of glucocorticoid-mediated apoptosis in leukemic cells from patients with B cell chronic lymphocytic leukemia (B-CLL). Rolipram, a prototypic PDE4 inhibitor, synergized with glucocorticoids in inducing B-CLL but not T cell apoptosis. Rolipram also augmented glucocorticoid receptor element (GRE) transactivation in B-CLL cells. In contrast, inhibition of protein kinase A (PKA) with the cAMP antagonist Rp-8Br-cAMPS reversed both glucocorticoid-induced apoptosis and GRE transactivation. CCRF-CEM cells, a well-studied model of glucocorticoid and cAMP-induced apoptosis, differed from B-CLL cells in that stimulation of adenylyl cyclase with the diterpene forskolin was required to increase both glucocorticoid-mediated apoptosis and GRE activation, while PDE4 inhibition had no effect. Consistent with these results, inhibition of PDE4 induced cAMP elevation in B-CLL but not CCRF-CEM cells, while forskolin augmented cAMP levels in CCRF-CEM but not B-CLL cells. While rolipram treatment up-regulated PDE4B in B-CLL, forskolin treatment up-regulated PDE4D in CCRF-CEM cells. These studies suggest that PKA is required for and enhances glucocorticoid-induced apoptosis in B-CLL by modulating glucocorticoid receptor signal transduction. Clinical trials that examine whether PDE4 inhibitors enhance the efficacy of glucocorticoid-containing chemotherapy regimens in B-CLL are indicated.

Gene expression microarray technologies in the development of new therapeutic agents

We review in detail how gene expression microarray technology is benefiting all phases of the discovery, development and subsequent use of new cancer therapeutics. Global gene expression profiling is valuable in cancer classification, elucidation of biochemical pathways and the identification of potential targets for novel molecular therapeutics. We exemplify the value in tissue culture and animal models of cancer, as well as in clinical studies. The power of expression profiling alongside gene knockout or knockdown methods such as RNA interference is illustrated. The use of basal or constitutive gene expression profiling to understand and predict drug sensitivity or resistance is described. The ability of expression profiling to define detailed molecular signatures of drug action is emphasised. The approach can identify on-target and off-target effects. It can be used to identify molecular biomarkers for proof of concept studies, pharmacodynamic endpoints and prognostic markers for predicting outcome and patient selection.

Calmodulin-dependent cyclic nucleotide phosphodiesterase (PDE1) is a pharmacological target of differentiation-inducing factor-1, an antitumor agent isolated from Dictyostelium

The differentiation-inducing factor-1 (DIF-1) isolated from Dictyostelium discoideum is a potent antiproliferative agent that induces growth arrest and differentiation in mammalian cells in vitro. However, the specific target molecule(s) of DIF-1 has not been identified. In this study, we have tried to identify the target molecule(s) of DIF-1 in mammalian cells, examining the effects of DIF-1 and its analogs on the activity of some candidate enzymes. DIF-1 at 10-40 micro M dose-dependently suppressed cell growth and increased the intracellular cyclic AMP concentration in K562 leukemia cells. It was then found that DIF-1 at 0.5-20 micro M inhibited the calmodulin (CaM)-dependent cyclic nucleotide phosphodiesterase (PDE1) in vitro in a dose-dependent manner. Kinetic analysis revealed that DIF-1 acted as a competitive inhibitor of PDE1 versus the substrate cyclic AMP. Because DIF-1 did not significantly affect the activity of other PDEs or CaM-dependent enzymes and, in addition, an isomer of DIF-1 was a less potent inhibitor, we have concluded that PDE1 is a pharmacological and specific target of DIF-1.