Regulatory subunits of PKA define an axis of cellular proliferation/differentiation in ovarian cancer cells

Ovarian Cancer: A Landscape of Mitochondria with Emphasis on Mitochondrial Dynamics

Ovarian cancer (OC) represents the main cause of death from gynecological malignancies in western countries. Altered cellular and mitochondrial metabolism are considered hallmarks in cancer disease. Several mitochondrial aspects have been found altered in OC, such as the oxidative phosphorylation system, oxidative stress and mitochondrial dynamics. Mitochondrial dynamics includes cristae remodeling, fusion, and fission processes forming a dynamic mitochondrial network. Alteration of mitochondrial dynamics is associated with metabolic change in tumour development and, in particular, the mitochondrial shaping proteins appear also to be responsible for the chemosensitivity and/or chemoresistance in OC. In this review a focus on the mitochondrial dynamics in OC cells is presented.

cAMP-Dependent Signaling and Ovarian Cancer

cAMP-dependent pathway is one of the most significant signaling cascades in healthy and neoplastic ovarian cells. Working through its major effector proteins-PKA and EPAC-it regulates gene expression and many cellular functions. PKA promotes the phosphorylation of cAMP response element-binding protein (CREB) which mediates gene transcription, cell migration, mitochondrial homeostasis, cell proliferation, and death. EPAC, on the other hand, is involved in cell adhesion, binding, differentiation, and interaction between cell junctions. Ovarian cancer growth and metabolism largely depend on changes in the signal processing of the cAMP-PKA-CREB axis, often associated with neoplastic transformation, metastasis, proliferation, and inhibition of apoptosis. In addition, the intracellular level of cAMP also determines the course of other pathways including AKT, ERK, MAPK, and mTOR, that are hypo- or hyperactivated among patients with ovarian neoplasm. With this review, we summarize the current findings on cAMP signaling in the ovary and its association with carcinogenesis, multiplication, metastasis, and survival of cancer cells. Additionally, we indicate that targeting particular stages of cAMP-dependent processes might provide promising therapeutic opportunities for the effective management of patients with ovarian cancer.

Phosphodiesterase 10A (PDE10A) as a novel target to suppress β-catenin and RAS signaling in epithelial ovarian cancer

A leading theory for ovarian carcinogenesis proposes that inflammation associated with incessant ovulation is a driver of oncogenesis. Consistent with this theory, nonsteroidal anti-inflammatory drugs (NSAIDs) exert promising chemopreventive activity for ovarian cancer. Unfortunately, toxicity is associated with long-term use of NSAIDs due to their cyclooxygenase (COX) inhibitory activity. Previous studies suggest the antineoplastic activity of NSAIDs is COX independent, and rather may be exerted through phosphodiesterase (PDE) inhibition. PDEs represent a unique chemopreventive target for ovarian cancer given that ovulation is regulated by cyclic nucleotide signaling. Here we evaluate PDE10A as a novel therapeutic target for ovarian cancer. Analysis of The Cancer Genome Atlas (TCGA) ovarian tumors revealed PDE10A overexpression was associated with significantly worse overall survival for patients. PDE10A expression also positively correlated with the upregulation of oncogenic and inflammatory signaling pathways. Using small molecule inhibitors, Pf-2545920 and a novel NSAID-derived PDE10A inhibitor, MCI-030, we show that PDE10A inhibition leads to decreased ovarian cancer cell growth and induces cell cycle arrest and apoptosis. We demonstrate these pro-apoptotic properties occur through PKA and PKG signaling by using specific inhibitors to block their activity. PDE10A genetic knockout in ovarian cancer cells through CRISP/Cas9 editing lead to decreased cell proliferation, colony formation, migration and invasion, and in vivo tumor growth. We also demonstrate that PDE10A inhibition leads to decreased Wnt-induced β-catenin nuclear translocation, as well as decreased EGF-mediated activation of RAS/MAPK and AKT pathways in ovarian cancer cells. These findings implicate PDE10A as novel target for ovarian cancer chemoprevention and treatment.

Measuring Spatiotemporal cAMP Dynamics Within an Endogenous Signaling Compartment Using FluoSTEP-ICUE

cAMP is a ubiquitous second messenger involved in the regulation of diverse cellular processes. Spatiotemporal regulation of cAMP through compartmentalization within various subcellular microdomains is essential to ensure specific signaling. In the following protocol, we describe a method for directly visualizing signaling dynamics within cAMP microdomains using fluorescent sensors targeted to endogenous proteins (FluoSTEPs). Instead of overexpressing a biosensor-tagged protein of interest to target a microdomain, FluoSTEP Indicator of cAMP using Epac (FluoSTEP-ICUE) utilizes spontaneously complementing split GFP and CRISPR-Cas9 genome editing to localize a FRET-based cAMP biosensor to an endogenously expressed protein of interest. Utilizing this approach, FluoSTEP-ICUE can be used to measure cAMP levels within endogenous signaling compartments, thus providing a powerful tool for studying the spatiotemporal regulation of cAMP signaling.

AKAP2 is upregulated in ovarian cancer, and promotes growth and migration of cancer cells

Mutations of A‑kinase anchoring protein 2 (AKAP2) have been reported to be associated with adolescent idiopathic scoliosis. However, its role in cancer is poorly understood. In the present study, the mRNA levels of AKAP2 in ovarian cancer tissues were examined using qPCR. The effects of AKAP2 on the growth and migration of cancer cells were examined using crystal violet and Boyden chamber assays. An in vivo image system was used to evaluate the effect of AKAP2 on the metastasis of ovarian cancer cells. The present study demonstrated that the expression of AKAP2 was elevated in ovarian cancer. Furthermore, overexpression of AKAP2 promoted the growth and migration of ovarian cancer cells, whereas knockdown of AKAP2 expression reduced the growth and migration of ovarian cancer cells. Analysis of the molecular mechanism indicated that AKAP2 activated β‑catenin/T cell factor signaling and regulated the expression of several target genes. Furthermore, analysis of the in vivo metastatic capacity demonstrated that downregulation of AKAP2 inhibited the invasion of ovarian cancer cells. Taken together, the present study demonstrated an oncogenic role for AKAP2 in ovarian cancer, indicating that AKAP2 may be a therapeutic target for ovarian cancer.

8-Cl-cAMP and PKA I-selective cAMP analogs effectively inhibit undifferentiated thyroid cancer cell growth

The main purpose of our work was to evaluate the effects of different cyclic adenosine monophosphate analogs on thyroid cancer-derived cell lines. In particular we studied 8-chloroadenosine-3',5'-cyclic monophosphate, the most powerful cyclic adenosine monophosphate analog, and the protein kinase A I-selective combination of 8-hexylaminoadenosine-3',5'cyclic monophosphate and 8-piperidinoadenosine-3',5'-cyclic monophosphate. The cyclic adenosine monophosphate/protein kinase A pathway plays a fundamental role in the regulation of thyroid cells growth. Site-selective cyclic adenosine monophosphate analogs are a class of cyclic adenosine monophosphate-derivate molecules that has been synthesized to modulate protein kinase A activity. Although the cyclic adenosine monophosphate/protein kinase A pathway plays a fundamental role in the regulation of thyroid cells proliferation, there are currently no studies exploring the role of cyclic adenosine monophosphate analogs in thyroid cancer. We evaluated the effects on cell proliferation, apoptosis activation and alterations of different intracellular pathways using 3-(4,5-dimetylthiazole-2-yl)-2,5-diphenyltetrazolium bromide assay, flow cytofluorimetry, western blotting, and kinase inhibitors. Our results show that both compounds have antiproliferative potential. Both treatments were able to modify protein kinase A RI/RII ratio, thus negatively influencing cancer cells growth. Moreover, the two treatments differentially modulated various signaling pathways that regulate cell proliferation and apoptosis. Both treatments demonstrated interesting characteristics that prompt further studies aiming to understand the intimate interaction between different intracellular pathways and possibly develop novel anticancer therapies for undifferentiated thyroid cancer.

miR-200c dampens cancer cell migration via regulation of protein kinase A subunits

Expression of miR-200c is a molecular switch to determine cellular fate towards a mesenchymal or epithelial phenotype. miR-200c suppresses the early steps of tumor progression by preventing epithelial-mesenchymal transition (EMT) and intravasation of tumor cells. Unraveling the underlying molecular mechanisms might pinpoint to novel therapeutic options. To better understand these mechanisms it is crucial to identify targets of miR-200c. Here, we employ a combination of quantitative proteomic and bioinformatic strategies to identify novel miR-200c targets. We identify and confirm two subunits of the central cellular kinase protein kinase A (PKA), namely PRKAR1A and PRKACB, to be directly regulated by miR-200c. Notably, siRNA-mediated downregulation of both proteins phenocopies the migratory behavior of breast cancer cells after miR-200c overexpression. Patient data from publicly accessible databases supports a miR-200c-PKA axis. Thus, our study identifies the PKA heteroprotein as an important mediator of miR-200c induced repression of migration in breast cancer cells. By bioinformatics, we define a miRNA target cluster consisting of PRKAR1A, PRKAR2B, PRKACB, and COF2, which is targeted by a group of 14 miRNAs.

Expression of protein kinase A regulatory subunits in benign and malignant human thyroid tissues: A systematic review

In this review, we discuss the molecular mechanisms and prognostic implications of the protein kinase A (PKA) signaling pathway in human tumors, with special emphasis on the malignant thyroid. The PKA signaling pathway is differentially activated by the expression of regulatory subunits 1 (R1) and 2 (R2), whose levels change during development, differentiation, and neoplastic transformation. Following the identification of gene mutations within the PKA regulatory subunit R1A (PRKAR1A) that cause Carney complex-associated neoplasms, several investigators have studied PRKAR1A expression in sporadic thyroid tumors. The PKA regulatory subunit R2B (PRKAR2B) is highly expressed in benign, as well as in malignant differentiated and undifferentiated lesions. PRKAR1A is highly expressed in follicular adenomas and malignant lesions with a statistically significant gradient between benign and malignant tumors; however, it is not expressed in hyperplastic nodules. Although the importance of PKA in human malignancy outcomes is not completely understood, PRKAR1A expression correlates with tumor dimension in malignant lesions. Additional studies are needed to determine whether a relationship exists between PKA subunit expression and clinical outcomes, particularly in undifferentiated tumors. In conclusion, the R1A subunit might be a good molecular candidate for the targeted treatment of malignant thyroid tumors.

Dichotomous role of protein kinase A type I (PKAI) in the tumor microenvironment: a potential target for 'two-in-one' cancer chemoimmunotherapeutics

An emerging trend in cancer chemoimmunotherapeutics is to develop 'two-in-one' therapies, which directly inhibit tumor growth and progression, as well as enhance anti-tumor immune surveillance. Protein kinase A (PKA) is a cAMP-dependent protein kinase that mediates signal transduction of G-protein coupled receptors (GPCRs). The regulatory subunit of PKA exists in two isoforms, RI and RII, which distinguish the PKA isozymes, PKA type I (PKAI) and PKA type II (PKAII). The differential expression of both PKA isozymes has long been linked to growth regulation and differentiation. RI/PKAI is particularly implicated in cellular proliferation and neoplastic transformation. Emerging experimental and pre-clinical data also indicate that RI/PKAI plays a key role in tumor-induced immune suppression. More briefly, RI/PKAI possesses a dichotomous role in the tumor microenvironment: not only contributes to tumor growth and progression, but also takes part in tumor-induced suppression of the innate and adaptive arms of anti-tumor immunosurveillance. This review specifically discusses this dichotomous role of RI/PKAI with respect to 'two-in-one' chemoimmunotherapeutic manipulation. The reviewed experimental and pre-clinical data provide the proof of concept validation that RI/PKAI may be regarded as an attractive target for a new, single-targeted, 'two hit' chemoimmunotherapeutic approach against cancer.

Broad-scale phosphoprotein profiling of beta adrenergic receptor (β-AR) signaling reveals novel phosphorylation and dephosphorylation events

β-adrenergic receptors (β-ARs) are model G-protein coupled receptors that mediate signal transduction in the sympathetic nervous system. Despite the widespread clinical use of agents that target β-ARs, the signaling pathways that operate downstream of β-AR stimulation have not yet been completely elucidated. Here, we utilized a lysate microarray approach to obtain a broad-scale perspective of phosphoprotein signaling downstream of β-AR. We monitored the time course of phosphorylation states of 54 proteins after β-AR activation mouse embryonic fibroblast (MEF) cells. In response to stimulation with the non-selective β-AR agonist isoproterenol, we observed previously described phosphorylation events such as ERK1/2(T202/Y204) and CREB(S133), but also novel phosphorylation events such as Cdc2(Y15) and Pyk2(Y402). All of these events were mediated through cAMP and PKA as they were reproduced by stimulation with the adenylyl cyclase activator forskolin and were blocked by treatment with H89, a PKA inhibitor. In addition, we also observed a number of novel isoproterenol-induced protein dephosphorylation events in target substrates of the PI3K/AKT pathway: GSK3β(S9), 4E-BP1(S65), and p70s6k(T389). These dephosphorylations were dependent on cAMP, but were independent of PKA and correlated with reduced PI3K/AKT activity. Isoproterenol stimulation also led to a cAMP-dependent dephosphorylation of PP1α(T320), a modification known to correlate with enhanced activity of this phosphatase. Dephosphorylation of PP1α coincided with the secondary decline in phosphorylation of some PKA-phosphorylated substrates, suggesting that PP1α may act in a feedback loop to return these phosphorylations to baseline. In summary, lysate microarrays are a powerful tool to profile phosphoprotein signaling and have provided a broad-scale perspective of how β-AR signaling can regulate key pathways involved in cell growth and metabolism.

Implementing fluorescence anisotropy screening and crystallographic analysis to define PKA isoform-selective activation by cAMP analogs

Cyclic AMP (cAMP) is a ubiquitous second messenger that regulates many proteins, most notably cAMP-dependent protein kinase (PKA). PKA holoenzymes (comprised of two catalytic (C) and two regulatory (R) subunits) regulate a wide variety of cellular processes, and its functional diversity is amplified by the presence of four R-subunit isoforms, RIα, RIβ, RIIα, and RIIβ. Although these isoforms all respond to cAMP, they are functionally nonredundant and exhibit different biochemical properties. In order to understand the functional differences between these isoforms, we screened cAMP derivatives for their ability to selectively activate RI and RII PKA holoenzymes using a fluorescence anisotropy assay. Our results indicate that RIα holoenzymes are selectively activated by C8-substituted analogs and RIIβ holoenzymes by N6-substituted analogs, where HE33 is the most prominent RII activator. We also solved the crystal structures of both RIα and RIIβ bound to HE33. The RIIβ structure shows the bulky aliphatic substituent of HE33 is fully encompassed by a pocket comprising of hydrophobic residues. RIα lacks this hydrophobic lining in Domain A, and the side chains are displaced to accommodate the HE33 dipropyl groups. Comparison between cAMP-bound structures reveals that RIIβ, but not RIα, contains a cavity near the N6 site. This study suggests that the selective activation of RII over RI isoforms by N6 analogs is driven by the spatial and chemical constraints of Domain A and paves the way for the development of potent noncyclic nucleotide activators to specifically target PKA iso-holoenyzmes.

PEA-15 unphosphorylated at both serine 104 and serine 116 inhibits ovarian cancer cell tumorigenicity and progression through blocking β-catenin

Ovarian cancer is a major cause of death among women; there remains an urgent need to develop new effective therapies to target this cancer. Phosphoprotein enriched in astrocytes (PEA-15) is a 15-kDa phosphoprotein that is known to bind ERK1/2, thus blocking cell proliferation. The physiological activity of PEA-15 is dependent on the phosphorylation status of serine 104 (Ser104) and Ser116. However, little is known about the impact of PEA-15 phosphorylation on tumor progression. We have previously shown that overexpression of PEA-15 has an antitumor effect against both breast and ovarian cancer cells. Here, we report that using a human ovarian cancer tissue microarray, we found that tissues from patients with ovarian cancer were significantly more likely than adjacent normal tissues to express PEA-15 phosphorylated at both sites. Using phosphomimetic and nonphosphorylatable mutants of PEA-15, we found that mutant double-unphosphorylated PEA-15 in which Ser104 and Ser116 were substituted with alanine (PEA-15-AA) had a more potent antitumorigenic effect in ovarian cancer than did phosphomimetic PEA-15 in which Ser104 and Ser116 were substituted with aspartic acid (PEA-15-DD). Further, we observed that the antitumorigenic effect of PEA-15-AA was a result of inhibition of the migration capacity of cells and inhibition of in vivo angiogenesis. This inhibition was partially dependent on inhibition of β-catenin expression and nuclear translocalization. Taken together, our results suggest that phosphorylated PEA-15 is an important contributor to the aggressiveness of ovarian cancer and justify the development of PEA-15-AA as an effective therapeutic molecule in the treatment of ovarian cancer.

Signaling through the neuropeptide GPCR PAC₁ induces neuritogenesis via a single linear cAMP- and ERK-dependent pathway using a novel cAMP sensor

Both cAMP and ERK are necessary for neuroendocrine cell neuritogenesis, and pituitary adenylate cyclase-activating polypeptide (PACAP) activates each. It is important to know whether cAMP and ERK are arranged in a novel, linear pathway or in two parallel pathways using known signaling mechanisms. Native cellular responses [cAMP elevation, ERK phosphorylation, cAMP responsive element binding (CREB) phosphorylation, and neuritogenesis] and promoter-reporter gene activation after treatment with forskolin, cAMP analogs, and PACAP were measured in Neuroscreen-1 (NS-1) cells, a PC12 variant enabling simultaneous morphological, molecular biological, and biochemical analysis. Forskolin (25 μM) and cAMP analogs (8-bromo-cAMP, dibutyryl-cAMP, and 8-chlorophenylthio-cAMP) stimulated ERK phosphorylation and neuritogenesis in NS-1 cells. Both ERK phosphorylation and neuritogenesis were MEK dependent (blocked by 10 μM U0126) and PKA independent (insensitive to 30 μM H-89 or 100 nM myristoylated protein kinase A inhibitor). CREB phosphorylation induced by PACAP was blocked by H-89. The exchange protein activated by cAMP (Epac)-selective 8-(4-chlorophenylthio)-2'-O-Me-cAMP (100-500 μM) activated Rap1 without affecting the other cAMP-dependent processes. Thus, PACAP-38 potently stimulated two distinct and independent cAMP pathways leading to CREB or ERK activation in NS-1 cells. Drug concentrations for appropriate effect were derived from control data for all compounds. In summary, a novel PKA- and Epac-independent signaling pathway: PACAP → adenylate cyclase → cAMP → ERK → neuritogenesis has been identified.

Protein kinase A activity and anchoring are required for ovarian cancer cell migration and invasion

Epithelial ovarian cancer (EOC) is the deadliest of the gynecological malignancies, due in part to its clinically occult metastasis. Therefore, understanding the mechanisms governing EOC dissemination and invasion may provide new targets for antimetastatic therapies or new methods for detection of metastatic disease. The cAMP-dependent protein kinase (PKA) is often dysregulated in EOC. Furthermore, PKA activity and subcellular localization by A-kinase anchoring proteins (AKAPs) are important regulators of cytoskeletal dynamics and cell migration. Thus, we sought to study the role of PKA and AKAP function in both EOC cell migration and invasion. Using the plasma membrane-directed PKA biosensor, pmAKAR3, and an improved migration/invasion assay, we show that PKA is activated at the leading edge of migrating SKOV-3 EOC cells, and that inhibition of PKA activity blocks SKOV-3 cell migration. Furthermore, we show that while the PKA activity within the leading edge of these cells is mediated by anchoring of type-II regulatory PKA subunits (RII), inhibition of anchoring of either RI or RII PKA subunits blocks cell migration. Importantly, we also show--for the first time--that PKA activity is up-regulated at the leading edge of SKOV-3 cells during invasion of a three-dimensional extracellular matrix and, as seen for migration, inhibition of either PKA activity or AKAP-mediated PKA anchoring blocks matrix invasion. These data are the first to demonstrate that the invasion of extracellular matrix by cancer cells elicits activation of PKA within the invasive leading edge and that both PKA activity and anchoring are required for matrix invasion. These observations suggest a role for PKA and AKAP activity in EOC metastasis.

Construction of a eukaryotic expression plasmid encoding the human PKAR IIβ gene and its expression in human gastric cancer BGC-823 cells

AIM: To construct a eukaryotic expression plasmid encoding the human protein kinase A regulatory subunit II beta (PKAR IIβ) gene and to examine its expression and localization in BGC-823 gastric cells using green fluorescent protein as a reporter.

METHODS: The coding sequence of the PKAR IIβ gene was amplified from the plasmid pRSETB-PKARIIβ by PCR and subcloned into pEGFP-C1 vector after digestion with Xho I and EcoR I. After the identity of recombinant plasmid was verified by direct sequencing, the plasmid was transfected into BGC-823 cells. The expression of the recombinant plasmid in BGC-823 cells was detected by Western blot. The localization of GFP-PKARIIβ in BGC-823 cells was observed by laser scanning confocal microscopy.

RESULTS: The coding sequence of the PKARIIβ gene was inserted into the pEGFP-C1 vector successfully. Restriction enzymes digestion showed that the length of the insert was 1.2 kb, matching the expected size. The expression of GFP-PKARIIβ fusion protein, which had a molecular weight of 72 000 Da, was detected in BGC-823 cells by Western blot. The GFP-PKARIIβ protein was localized predominantly to the cytoplasm but sparsely to the nucleus of HEK293 and BGC-823 cells.

CONCLUSION: A recombinant plasmid expressing the PKARIIβ gene has been successfully constructed and provides a tool for future investigation of PKARIIβ functions. The GFP-PKARIIβ fusion protein was expressed mainly in the cytoplasm of HEK293 and BGC7901 cells.

Protein kinase A regulates caspase-1 via Ets-1 in bone stromal cell-derived lesions: a link between cyclic AMP and pro-inflammatory pathways in osteoblast progenitors

Patients with genetic defects of the cyclic (c) adenosine-monophosphate (AMP)-signaling pathway and those with neonatal-onset multisystem inflammatory disease (NOMID) develop tumor-like lesions of the long bones. The molecular basis of this similarity is unknown. NOMID is caused by inappropriate caspase-1 activity, which in turn activates the inflammasome. The present study demonstrates that NOMID bone lesions are derived from the same osteoblast progenitor cells that form fibroblastoid tumors in mice and humans with defects that lead to increased cAMP-dependent protein kinase A (PKA) signaling. NOMID tumor cells showed high PKA activity, and an increase in their cAMP signaling led to PKA-specific activation of caspase-1. Increased PKA led to inflammation-independent activation of caspase-1 via over-expression of the proto-oncogene (and early osteoblast factor) Ets-1. In NOMID tumor cells, as in cells with defective PKA regulation, increased prostaglandin E2 (PGE2) led to increased cAMP levels and activation of Wnt signaling, like in other states of inappropriate PKA activity. Caspase-1 and PGE2 inhibition led to a decrease in cell proliferation of both NOMID and cells with abnormal PKA. These data reveal a previously unsuspected link between abnormal cAMP signaling and defective regulation of the inflammasome and suggest that caspase-1 and PGE2 inhibition may be therapeutic targets in bone lesions associated with defects of these two pathways.

Phosphodiesterase Inhibitor 3-Isobutyl-1-Methyl-Xanthine Affects Ovarian Morphology and Stimulates Reproduction in Rabbits

The aim of our study is to examine the influence of administration of 3-isobutyl-l-methyl-xanthine (IBMX), inhibitor of cAMP and cGMP phosphodiesterases on ovarian functions (folliculogenesis, atresia and luteogenesis), as well as on some reproductive parameters in rabbits whose ovarian cycle and ovulation was induced by gonadotropins. Ovarian cycle and ovulation of control rabbits were induced by PMSG followed by hCG administration. Experimental animals received 20IU/kg PMSG and 35IU/kg hCG together with IBMX (at 5, 25 or 50 μg/animal). After ovulation and mating, the animals were sacrificed. Histological slides of ovaries were prepared, and the presence of follicles and different stages of luteinisation and atresia were evaluated by light microscopy. The pronuclear stage eggs were flushed out from the oviducts and cultured up to blastocyst cell stage. Numbers of ovarian Corpora lutea, ovulated oocytes and oocyte-derived embryos reaching blastocyst stage were determined. Administration of IBMX was able to increase the proportion of luteinised follicles. Furthermore, IBMX treatment promoted occurrence of atresia in the remaining follicles after the gonadotropin treatment. Finally, IBMX increased the number of Corpora lutea, number of harvested zygotes and embryos at blastocyst stage derived from these zygotes after culture. These data demonstrate that IBMX can enhance the stimulatory effect of gonadotropins on the rabbit ovarian follicle luteinisation, atresia, ovulation, zygote and embryo yield and development. Furthermore, they confirm the involvement of cyclic nucleotide-dependent intracellular mechanisms in the control of rabbit reproductive functions and potential practical usefulness of IBMX in improvement of farm animal reproduction and fertility.

The cAMP analogue, dbcAMP affects release of steroid hormones by cultured rabbit ovarian cells and their response to FSH, IGF-I and ghrelin

The aim of the present study was to examine possible involvement of cAMP-dependent intracellular mechanisms in control of ovarian cell steroidogenesis and its response to hormonal regulators. For this purpose, we examined the influence of administration of dbcAMP, a cAMP analogue (50 microg/animal) in vivo, on release of progesterone, testosterone and estradiol by isolated ovarian fragments, as well their response to hormonal regulators of ovarian steroidogenesis-FSH, IGF-I and ghrelin (all added at doses of 100 ng/ml). It was observed, that administration of dbcAMP resulted reduction in progesterone and testosterone, but not of estradiol release by isolated ovarian fragments. In ovarian tissue isolated from control animals, additions of hormones were able to reduce release of progesterone (FSH, IGF-I and ghrelin) and increase release of testosterone (ghrelin) but did not change estradiol output. Previous administration of dbcAMP modified action of exogenous hormones: it inverted inhibitory action of FSH, IGF-I and ghrelin on progesterone release to stimulatory action and induced stimulatory action of IGF-I on testosterone release and stimulatory effect of FSH on estradiol output. The present observations confirm involvement of peptide hormones FSH, IGF-I and ghrelin in the control of rabbit ovarian steroid hormones release and demonstrate the involvement of cAMP-dependent intracellular mechanisms in down-regulation of rabbit ovarian steroidogenesis and in modification, but not in mediating effect of FSH, IGF-I and ghrelin on ovarian steroid hormones release.

Targeting cancer with phosphodiesterase inhibitors

IMPORTANCE OF THE FIELD

For many cancers, there has been a shift from management with traditional, nonspecific cytotoxic chemotherapies to treatment with molecule-specific targeted therapies that are used either alone or in combination with traditional chemotherapy and radiation therapy. Accumulating data suggest that multi-targeted agents may produce greater benefits than those observed with single-targeted therapies, may have acceptable tolerability profiles, and may be active against a broader range of tumour types. Thus, regulation of cyclic nucleotide signalling is properly regarded as a composite of multiple component pathways involved in diverse aspects of tumour cell function. The impairment of cAMP and/or cGMP generation by overexpression of PDE isoforms that has been described in various cancer pathologies, and the effects of PDE inhibitors in tumour models in vitro and in vivo, may offer promising insight into future cancer treatments because of the numerous advantages of PDE inhibitors.

AREAS COVERED IN THIS REVIEW

In this review, we focus on the expression and regulation of cyclic nucleotide phosphodiesterases (PDEs) in tumour progression and provide evidence that PDE inhibitors may be effective agents for treating cancer; the review covers literature from the past several years.

WHAT THE READER WILL GAIN

PDEs have been studied in a variety of tumours; data have suggested that the levels of PDE activity are elevated and, therefore, the ratio of cGMP to cAMP is affected. In addition, PDE inhibitors may be potential targets for tumour cell growth inhibition and induction of apoptosis. This review explores the prospects of targeting PDEs with therapeutic agents for cancer, as well as the shortcomings of this approach such as dose-limiting side effects, toxicity/efficacy ratio and selectivity towards tumour tissue. In addition, it includes opinions and suggestion for developing PDE inhibition for cancer treatment from initial concept to potential therapeutic application and final relevance in clinical use.

TAKE HOME MESSAGE

Impaired cAMP and/or cGMP generation upon overexpression of PDE isoforms has been described in various cancer pathologies. Inhibition of selective PDE isoforms, which raises the levels of intracellular cAMP and/or cGMP, induces apoptosis and cell cycle arrest in a broad spectrum of tumour cells and regulates the tumour microenvironment. Therefore, the development and clinical application of inhibitors specific for individual PDE isoenzymes may selectively restore normal intracellular signalling, providing antitumour therapy with reduced adverse effects.

Mouse Prkar1a haploinsufficiency leads to an increase in tumors in the Trp53+/- or Rb1+/- backgrounds and chemically induced skin papillomas by dysregulation of the cell cycle and Wnt signaling

PRKAR1A inactivation leads to dysregulated cAMP signaling and Carney complex (CNC) in humans, a syndrome associated with skin, endocrine and other tumors. The CNC phenotype is not easily explained by the ubiquitous cAMP signaling defect; furthermore, Prkar1a(+/-) mice did not develop skin and other CNC tumors. To identify whether a Prkar1a defect is truly a generic but weak tumorigenic signal that depends on tissue-specific or other factors, we investigated Prkar1a(+/-) mice when bred within the Rb1(+/-) or Trp53(+/-) backgrounds, or treated with a two-step skin carcinogenesis protocol. Prkar1a(+/-) Trp53(+/-) mice developed more sarcomas than Trp53(+/-) mice (P < 0.05) and Prkar1a(+/-) Rb1(+/-) mice grew more (and larger) pituitary and thyroid tumors than Rb1(+/-) mice. All mice with double heterozygosity had significantly reduced life-spans compared with their single-heterozygous counterparts. Prkar1a(+/-) mice also developed more papillomas than wild-type animals. A whole-genome transcriptome profiling of tumors produced by all three models identified Wnt signaling as the main pathway activated by abnormal cAMP signaling, along with cell cycle abnormalities; all changes were confirmed by qRT-PCR array and immunohistochemistry. siRNA down-regulation of Ctnnb1, E2f1 or Cdk4 inhibited proliferation of human adrenal cells bearing a PRKAR1A-inactivating mutation and Prkar1a(+/-) mouse embryonic fibroblasts and arrested both cell lines at the G0/G1 phase of the cell cycle. In conclusion, Prkar1a haploinsufficiency is a relatively weak tumorigenic signal that can act synergistically with other tumor suppressor gene defects or chemicals to induce tumors, mostly through Wnt-signaling activation and cell cycle dysregulation, consistent with studies in human neoplasms carrying PRKAR1A defects.