Protein kinase A as a biological target in cancer therapy

Renal cancer: signaling pathways and advances in targeted therapies

Renal cancer is a highlyheterogeneous malignancy characterized by rising global incidence and mortalityrates. The complex interplay and dysregulation of multiple signaling pathways,including von Hippel-Lindau (VHL)/hypoxia-inducible factor (HIF), phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR), Hippo-yes-associated protein (YAP), Wnt/ß-catenin, cyclic adenosine monophosphate (cAMP), and hepatocyte growth factor (HGF)/c-Met, contribute to theinitiation and progression of renal cancer. Although surgical resection is thestandard treatment for localized renal cancer, recurrence and metastasiscontinue to pose significant challenges. Advanced renal cancer is associatedwith a poor prognosis, and current therapies, such as targeted agents andimmunotherapies, have limitations. This review presents a comprehensiveoverview of the molecular mechanisms underlying aberrant signaling pathways inrenal cancer, emphasizing their intricate crosstalk and synergisticinteractions. We discuss recent advancements in targeted therapies, includingtyrosine kinase inhibitors, and immunotherapies, such as checkpoint inhibitors.Moreover, we underscore the importance of multiomics approaches and networkanalysis in elucidating the complex regulatory networks governing renal cancerpathogenesis. By integrating cutting-edge research and clinical insights, this review contributesto the development of innovative diagnostic and therapeutic strategies, whichhave the potential to improve risk stratification, precision medicine, andultimately, patient outcomes in renal cancer.

The Effect of the cAMP Signaling Pathway on HTR8/SV-Neo Cell Line Proliferation, Invasion, and Migration After Treatment with Forskolin

Pre-eclampsia (PE) is thought to be related to placental dysfunction, particularly poor extravillous trophoblast (EVT) invasion and migration abilities. However, the pathogenic mechanism is not fully understood. This article describes the impact of the cyclic adenosine monophosphate(cAMP) signaling pathway on EVT behavior, focusing on EVT proliferation, invasion, and migration. Here, we used the HTR8/SV-neo cell line to study human EVT function in vitro. HTR8/SV-neo cells were treated with different concentrations of forskolin (cAMP pathway-specific agonist) to alter intracellular cAMP levels, and dimethyl sulfoxide (DMSO) was used as the control. First, a cAMP assay was performed to measure the cAMP concentration in HTR8/SV-neo cells treated with different forskolin concentrations, and cell proliferation was assessed by constructing cell growth curves and assessing colony formation. Cell invasion and migration were observed by Transwell experiments, and intracellular epithelial-mesenchymal transition (EMT) marker expression was evaluated by quantitative real-time polymerase chain reaction (qPCR) and Western blotting (WB). According to our research, the intracellular cAMP levels in HTR8/SV-neo cells were increased in a dose-dependent manner, and HTR8/SV-neo cell proliferation, invasion and migration were significantly enhanced. The expression of EMT and angiogenesis markers was upregulated. Additionally, with the increase in intracellular cAMP levels, the phosphorylation of intracellular mitogen-activated protein kinase (MAPK) signaling pathway components was significantly increased. These results suggested that the cAMP signaling pathway promoted the phosphorylation of MAPK signaling components, thus enhancing EVT functions, including proliferation, invasion, and migration, and to a certain extent, providing a novel direction for the treatment of PE patients.

Biochemical pharmacology of adenylyl cyclases in cancer

Globally, despite extensive research and pharmacological advancement, cancer remains one of the most common causes of mortality. Understanding the signaling pathways involved in cancer progression is essential for the discovery of new drug targets. The adenylyl cyclase (AC) superfamily comprises glycoproteins that regulate intracellular signaling and convert ATP into cyclic AMP, an important second messenger. The present review highlights the involvement of ACs in cancer progression and suppression, broken down for each specific mammalian AC isoform. The precise mechanisms by which ACs contribute to cancer cell proliferation and invasion are not well understood and are variable among cancer types; however, AC overactivation, along with that of downstream regulators, presents a potential target for novel anticancer therapies. The expression patterns of ACs in numerous cancers are discussed. In addition, we highlight inhibitors of AC-related signaling that are currently under investigation, with a focus on possible anti-cancer strategies. Recent discoveries with small molecules regarding more direct modulation AC activity are also discussed in detail. A more comprehensive understanding of different components in AC-related signaling could potentially lead to the development of novel therapeutic strategies for personalized oncology and might enhance the efficacy of chemoimmunotherapy in the treatment of various cancers.

Molecular insight into renal cancer and latest therapeutic approaches to tackle it: an updated review

Renal cell carcinoma (RCC) is one of the most lethal genitourinary cancers, with the highest mortality rate, and may remain undetected throughout its development. RCC can be sporadic or hereditary. Exploring the underlying genetic abnormalities in RCC will have important implications for understanding the origins of nonhereditary renal cancers. The treatment of RCC has evolved over centuries from the era of cytokines to targeted therapy to immunotherapy. A surgical cure is the primary treatment modality, especially for organ-confined diseases. Furthermore, the urologic oncology community focuses on nephron-sparing surgical approaches and ablative procedures when small renal masses are detected incidentally in conjunction with interventional radiologists. In addition to new combination therapies approved for RCC treatment, several trials have been conducted to investigate the potential benefits of certain drugs. This may lead to durable responses and more extended survival benefits for patients with metastatic RCC (mRCC). Several approved drugs have reduced the mortality rate of patients with RCC by targeting VEGF signaling and mTOR. This review better explains the signaling pathways involved in the RCC progression, oncometabolites, and essential biomarkers in RCC that can be used for its diagnosis. Further, it provides an overview of the characteristics of RCC carcinogenesis to assist in combating treatment resistance, as well as details about the current management and future therapeutic options. In the future, multimodal and integrated care will be available, with new treatment options emerging as we learn more about the disease.

Discovery and Synthesis of a Naturally Derived Protein Kinase Inhibitor that Selectively Inhibits Distinct Classes of Serine/Threonine Kinases

The DNAJB1-PRKACA oncogenic gene fusion results in an active kinase enzyme, J-PKAcα, that has been identified as an attractive antitumor target for fibrolamellar hepatocellular carcinoma (FLHCC). A high-throughput assay was used to identify inhibitors of J-PKAcα catalytic activity by screening the NCI Program for Natural Product Discovery (NPNPD) prefractionated natural product library. Purification of the active agent from a single fraction of an Aplidium sp. marine tunicate led to the discovery of two unprecedented alkaloids, aplithianines A (1) and B (2). Aplithianine A (1) showed potent inhibition against J-PKAcα with an IC50 of ∼1 μM in the primary screening assay. In kinome screening, 1 inhibited wild-type PKA with an IC50 of 84 nM. Further mechanistic studies including cocrystallization and X-ray diffraction experiments revealed that 1 inhibited PKAcα catalytic activity by competitively binding to the ATP pocket. Human kinome profiling of 1 against a panel of 370 kinases revealed potent inhibition of select serine/threonine kinases in the CLK and PKG families with IC50 values in the range ∼11-90 nM. An efficient, four-step total synthesis of 1 has been accomplished, enabling further evaluation of aplithianines as biologically relevant kinase inhibitors.

Development of Kinase-Centric Drugs: A Computational Perspective

Kinases are prominent drug targets in the pharmaceutical and research community due to their involvement in signal transduction, physiological responses, and upon dysregulation, in diseases such as cancer, neurological and autoimmune disorders. Several FDA-approved small-molecule drugs have been developed to combat human diseases since Gleevec was approved for the treatment of chronic myelogenous leukemia. Kinases were considered "undruggable" in the beginning. Several FDA-approved small-molecule drugs have become available in recent years. Most of these drugs target ATP-binding sites, but a few target allosteric sites. Among kinases that belong to the same family, the catalytic domain shows high structural and sequence conservation. Inhibitors of ATP-binding sites can cause off-target binding. Because members of the same family have similar sequences and structural patterns, often complex relationships between kinases and inhibitors are observed. To design and develop drugs with desired selectivity, it is essential to understand the target selectivity for kinase inhibitors. To create new inhibitors with the desired selectivity, several experimental methods have been designed to profile the kinase selectivity of small molecules. Experimental approaches are often expensive, laborious, time-consuming, and limited by the available kinases. Researchers have used computational methodologies to address these limitations in the design and development of effective therapeutics. Many computational methods have been developed over the last few decades, either to complement experimental findings or to forecast kinase inhibitor activity and selectivity. The purpose of this review is to provide insight into recent advances in theoretical/computational approaches for the design of new kinase inhibitors with the desired selectivity and optimization of existing inhibitors.

Increased TCP11 gene expression can inhibit the proliferation, migration and promote apoptosis of cervical cancer cells

BACKGROUND

Cervical cancer is a common gynecological malignancy. Gene microarray found that TCP11 gene was highly expressed in cervical cancer. However, the effect of TCP11 gene on the proliferation, apoptosis and migration of cervical cancer cells and its underlying molecular mechanisms are unclear.

METHODS

GEPIA database, tissue microarray, western blot and qRT-PCR were used to analyze the expression of TCP11 gene in cervical cancer tissues and cells and its relationship with patients' survival rate. The cell cycle and apoptosis were detected by flow cytometry, and the expressions of cell cycle and apoptosis related molecules and EMT-related molecules were detected by Western blot and qRT-PCR.

RESULTS

The results showed that TCP11 gene was highly expressed in cervical cancer tissues and cells compared with normal cervical tissues and cells, and its expression was positively correlated with patients' survival rate. The results of proliferation and migration assays showed that TCP11 overexpression inhibited the proliferation and migration of HeLa and SiHa cells. The results showed that TCP11 overexpression blocked the cell cycle of HeLa and SiHa cells, decreased the expression of CDK1 and Cyclin B1, and increased the apoptosis and the expression of caspase-3, cleaved-caspase-3 and cleaved-PARP. TCP11 overexpression increased the protein and mRNA expression of EMT-related molecules ZO-1 and E-cadherin. Conversely, TCP11 knockdown promoted the proliferation of HeLa and SiHa cells and the migration of HeLa cells.

CONCLUSIONS

TCP11 overexpression significantly inhibited the occurrence and development of cervical cancer cells, it may be a potentially beneficial biomarker for cervical cancer.

Parathyroid Hormone-Related Protein Promotes the Proliferation of Patient-Derived Glioblastoma Stem Cells via Activating cAMP/PKA Signaling Pathway

Background and Objectives

Glioblastoma (GBM) is an aggressive primary brain tumor characterized by its heterogeneity and high recurrence and lethality rates. Glioblastoma stem cells (GSCs) play a crucial role in therapy resistance and tumor recurrence. Therefore, targeting GSCs is a key objective in developing effective treatments for GBM. The role of Parathyroid hormone-related peptide (PTHrP) in GBM and its impact on GSCs remains unclear. This study aimed to investigate the effect of PTHrP on GSCs and its potential as a therapeutic target for GBM.

Methods and Results

Using the Cancer Genome Atlas (TCGA) database, we found higher expression of PTHrP in GBM, which correlated inversely with survival. GSCs were established from three human GBM samples obtained after surgical resection. Exposure to recombinant human PTHrP protein (rPTHrP) at different concentrations significantly enhanced GSCs viability. Knockdown of PTHrP using target-specific siRNA (siPTHrP) inhibited tumorsphere formation and reduced the number of BrdU-positive cells. In an orthotopic xenograft mouse model, suppression of PTHrP expression led to significant inhibition of tumor growth. The addition of rPTHrP in the growth medium counteracted the antiproliferative effect of siPTHrP. Further investigation revealed that PTHrP increased cAMP concentration and activated the PKA signaling pathway. Treatment with forskolin, an adenylyl cyclase activator, nullified the antiproliferative effect of siPTHrP.

Conclusions

Our findings demonstrate that PTHrP promotes the proliferation of patient-derived GSCs by activating the cAMP/PKA signaling pathway. These results uncover a novel role for PTHrP and suggest its potential as a therapeutic target for GBM treatment.

When Just One Phosphate Is One Too Many: The Multifaceted Interplay between Myc and Kinases

Myc transcription factors are key regulators of many cellular processes, with Myc target genes crucially implicated in the management of cell proliferation and stem pluripotency, energy metabolism, protein synthesis, angiogenesis, DNA damage response, and apoptosis. Given the wide involvement of Myc in cellular dynamics, it is not surprising that its overexpression is frequently associated with cancer. Noteworthy, in cancer cells where high Myc levels are maintained, the overexpression of Myc-associated kinases is often observed and required to foster tumour cells' proliferation. A mutual interplay exists between Myc and kinases: the latter, which are Myc transcriptional targets, phosphorylate Myc, allowing its transcriptional activity, highlighting a clear regulatory loop. At the protein level, Myc activity and turnover is also tightly regulated by kinases, with a finely tuned balance between translation and rapid protein degradation. In this perspective, we focus on the cross-regulation of Myc and its associated protein kinases underlying similar and redundant mechanisms of regulation at different levels, from transcriptional to post-translational events. Furthermore, a review of the indirect effects of known kinase inhibitors on Myc provides an opportunity to identify alternative and combined therapeutic approaches for cancer treatment.

SR Splicing Factors Promote Cancer via Multiple Regulatory Mechanisms

Substantial emerging evidence supports that dysregulated RNA metabolism is associated with tumor initiation and development. Serine/Arginine-Rich proteins (SR) are a number of ultraconserved and structurally related proteins that contain a characteristic RS domain rich in arginine and serine residues. SR proteins perform a critical role in spliceosome assembling and conformational transformation, contributing to precise alternative RNA splicing. Moreover, SR proteins have been reported to participate in multiple other RNA-processing-related mechanisms than RNA splicing, such as genome stability, RNA export, and translation. The dysregulation of SR proteins has been reported to contribute to tumorigenesis through multiple mechanisms. Here we reviewed the different biological roles of SR proteins and strategies for functional rectification of SR proteins that may serve as potential therapeutic approaches for cancer.

Endogenous and Exogenous Regulatory Signaling in the Secretory Pathway: Role of Golgi Signaling Molecules in Cancer

The biosynthetic transport route that constitutes the secretory pathway plays a fundamental role in the cell, providing to the synthesis and transport of around one third of human proteins and most lipids. Signaling molecules within autoregulatory circuits on the intracellular membranes of the secretory pathway regulate these processes, especially at the level of the Golgi complex. Indeed, cancer cells can hijack several of these signaling molecules, and therefore also the underlying regulated processes, to bolster their growth or gain more aggressive phenotypes. Here, we review the most important autoregulatory circuits acting on the Golgi, emphasizing the role of specific signaling molecules in cancer. In fact, we propose to draw awareness to highlight the Golgi-localized regulatory systems as potential targets in cancer therapy.

The Interactions among Hypertension, Cancer, and COVID-19: Perspectives from Ca2+/cAMP Signalling

BACKGROUND

The hypothesis that hypertension is clinically associated with an enhanced risk for developing cancer has been highlighted. However, the working principles involved in this link are still under intensive discussion. A correlation among inflammation, hypertension, and cancer could accurately describe the clinical link between these diseases. In addition, a dyshomeostasis of Ca²⁺ has been considered as a topic involved in both cancer and hypertension and inflammation. There is a strong link between Ca²⁺ signalling, e.g. enhanced Ca²⁺ signals, and inflammatory outcomes. cAMP also modulates pro- and anti-inflammatory outcomes: pharmaceuticals, which increase intracellular cAMP levels, can decrease the production of proinflammatory mediators and enhance the production of anti-inflammatory outcomes.

OBJECTIVE

This article has discussed the participation of Ca²⁺/cAMP signalling in the clinical association among inflammation, hypertension, and an enhanced risk for the development of cancer. In addition, considering coronavirus disease 2019 (COVID-19) is a rapidly evolving field, this article also reviews recent reports about the role of Ca²⁺ channel blockers for restoring Ca²⁺ signalling disruption due to COVID-19, including the relationship among COVID-19, cancer, and hypertension.

CONCLUSION

Understanding the association among these diseases could expand current pharmacotherapy, including that involving Ca²⁺ channel blockers and pharmaceuticals which rise cAMP levels.

A Potent N-(piperidin-4-yl)-1H-pyrrole-2-carboxamide Inhibitor of Adenylyl Cyclase of G. lamblia: Biological Evaluation and Molecular Modelling Studies

In this work, we report a derivative of N-(piperidin-4-yl)-1H-pyrrole-2-carboxamide as a new inhibitor for adenylyl cyclase of Giardia lamblia which was obtained from a study using structural data of the nucleotidyl cyclase 1 (gNC1) of this parasite. For such a study, we developed a model for this specific enzyme by using homology techniques, which is the first model reported for gNC1 of G. lamblia. Our studies show that the new inhibitor has a competitive mechanism of action against this enzyme. 2-Hydroxyestradiol was used as the reference compound for comparative studies. Results in this work are important from two points of view. on the one hand, an experimentally corroborated model for gNC1 of G. lamblia obtained by molecular modelling is presented; on the other hand, the new inhibitor obtained is an undoubtedly excellent starting structure for the development of new metabolic inhibitors for G. lamblia.

From purines to purinergic signalling: molecular functions and human diseases

Purines and their derivatives, most notably adenosine and ATP, are the key molecules controlling intracellular energy homoeostasis and nucleotide synthesis. Besides, these purines support, as chemical messengers, purinergic transmission throughout tissues and species. Purines act as endogenous ligands that bind to and activate plasmalemmal purinoceptors, which mediate extracellular communication referred to as "purinergic signalling". Purinergic signalling is cross-linked with other transmitter networks to coordinate numerous aspects of cell behaviour such as proliferation, differentiation, migration, apoptosis and other physiological processes critical for the proper function of organisms. Pathological deregulation of purinergic signalling contributes to various diseases including neurodegeneration, rheumatic immune diseases, inflammation, and cancer. Particularly, gout is one of the most prevalent purine-related disease caused by purine metabolism disorder and consequent hyperuricemia. Compelling evidence indicates that purinoceptors are potential therapeutic targets, with specific purinergic agonists and antagonists demonstrating prominent therapeutic potential. Furthermore, dietary and herbal interventions help to restore and balance purine metabolism, thus addressing the importance of a healthy lifestyle in the prevention and relief of human disorders. Profound understanding of molecular mechanisms of purinergic signalling provides new and exciting insights into the treatment of human diseases.

8-Alkylmercaptocaffeine derivatives: antioxidant, molecular docking, and in-vitro cytotoxicity studies

Due to their unique pharmacological characteristics, methylxanthines are known as therapeutic agents in a fascinating range of medicinal scopes. In this report, we aimed to examine some biological effects of previously synthesized 8-alkylmercaptocaffeine derivatives. Cytotoxic and antioxidative activity of 8-alkylmercaptocaffeine derivatives were measured in malignant A549, MCF7, and C152 cell lines. Assessment of cGMP levels and caspase-3 activity were carried out using a colorimetric competitive ELISA kit. Computational approaches were employed to discover the inhibitory mechanism of synthesized compounds. Among the twelve synthesized derivatives, three compounds (C1, C5, and C7) bearing propyl, heptyl, and 3-methyl-butyl moieties showed higher and more desirable cytotoxic activity against all the studied cell lines (IC₅₀ < 100 µM). Furthermore, C5 synergistically enhanced cisplatin-induced cytotoxicity in MCF-7 cells (CI < 1). Both C5 and C7 significantly increased caspase-3 activity and intracellular cGMP levels at specific time intervals in all studied cell lines (P < 0.05). However, these derivatives did not elevate LDH leakage (P > 0.05) and exhibited no marked ameliorating effects on oxidative damage (P > 0.05). Computational studies showed that H-bond formation between the nitrogen atom in pyrazolo[4,3-D] pyrimidine moiety with Gln817 and creating a hydrophobic cavity result in the stability of the alkyl group in the PDE5A active site. We found that synthesized 8-alkylmercaptocaffeine derivatives induced cell death in different cancer cells through the cGMP pathway. These findings will help us to get a deeper insight into the role of methylxanthines as useful alternatives to conventional cancer therapeutics.

Selective autophagy of AKAP11 activates cAMP/PKA to fuel mitochondrial metabolism and tumor cell growth

Autophagy is a catabolic pathway that provides self-nourishment and maintenance of cellular homeostasis. Autophagy is a fundamental cell protection pathway through metabolic recycling of various intracellular cargos and supplying the breakdown products. Here, we report an autophagy function in governing cell protection during cellular response to energy crisis through cell metabolic rewiring. We observe a role of selective type of autophagy in direct activation of cyclic AMP protein kinase A (PKA) and rejuvenation of mitochondrial function. Mechanistically, autophagy selectively degrades the inhibitory subunit RI of PKA holoenzyme through A-kinase-anchoring protein (AKAP) 11. AKAP11 acts as an autophagy receptor that recruits RI to autophagosomes via LC3. Glucose starvation induces AKAP11-dependent degradation of RI, resulting in PKA activation that potentiates PKA-cAMP response element-binding signaling, mitochondria respiration, and ATP production in accordance with mitochondrial elongation. AKAP11 deficiency inhibits PKA activation and impairs cell survival upon glucose starvation. Our results thus expand the view of autophagy cytoprotection mechanism by demonstrating selective autophagy in RI degradation and PKA activation that fuels the mitochondrial metabolism and confers cell resistance to glucose deprivation implicated in tumor growth.

Targeting the Aryl Hydrocarbon Receptor Signaling Pathway in Breast Cancer Development

Activation of the aryl hydrocarbon receptor (AhR) through environmental exposure to known human carcinogens including dioxins can lead to the promotion of breast cancer. While the repressor protein of the AhR (AhRR) blocks the canonical AhR pathway, the function of AhRR in the development of breast cancer is not well-known. In the current study we examined the impact of suppressing AhR activity using its dedicated repressor protein AhRR. AhRR is a putative tumor suppressor and is silenced in several cancer types, including breast, where its loss correlates with shorter patient survival. Using the AhRR transgenic mouse, we demonstrate that AhRR overexpression opposes AhR-driven and inflammation-induced growth of mammary tumors in two different murine models of breast cancer. These include a syngeneic model using E0771 mammary tumor cells as well as the Polyoma Middle T antigen (PyMT) transgenic model. Further AhRR overexpression or knockout of AhR in human breast cancer cells enhanced apoptosis induced by chemotherapeutics and inhibited the growth of mouse mammary tumor cells. This study provides the first in vivo evidence that AhRR suppresses mammary tumor development and suggests that strategies which lead to its functional restoration and expression may have therapeutic benefit.

Proteome and phosphoproteome reveal mechanisms of action of atorvastatin against esophageal squamous cell carcinoma

Statins comprise a class of prescription drugs used for reducing cholesterol. Evidence has also showed that statins could reduce cancer incidence. However, the anti-tumor mechanism of statins has not been fully defined. Here, we found that atorvastatin inhibited proliferation of esophageal squamous cell carcinoma (ESCC) cells. The underlying mechanisms were explored by mass spectrometry. The proteome data revealed that atorvastatin inhibited the cAMP and Rap1 signal pathways, except for Ras signal pathway. Interestingly, phosphoproteome profiles suggested that ERK^T185/Y187, CDK1^T14, and BRAC1^S1189 phosphorylation–mediated Th17 cell differentiation, Gap junction and the Platinum drug resistance pathway were down-regulated after atorvastatin treatment. The phosphorylation levels of ERK^T185/Y187, CDK1^T14 and BRAC1^S1189 were confirmed by western blotting in KYSE150 cells. More importantly, atorvastatin suppresses ESCC tumor growth in PDX models. The molecular changes in tumor tissues were confirmed by immunohistochemistry. In conclusion, deep-proteome and phosphoproteome analysis reveal a comprehensive mechanism that contributes to atorvastatin’s anti-tumor effect.

Identification of MRP4/ABCC4 as a Target for Reducing the Proliferation of Pancreatic Ductal Adenocarcinoma Cells by Modulating the cAMP Efflux

Pancreatic cancer is one of the most lethal types of tumors with no effective therapy available; is currently the third leading cause of cancer in developed countries; and is predicted to become the second deadliest cancer in the United States by 2030. Due to the marginal benefits of current standard chemotherapy, the identification of new therapeutic targets is greatly required. Considering that cAMP pathway is commonly activated in pancreatic ductal adenocarcinoma (PDAC) and its premalignant lesions, we aim to investigate the multidrug resistance-associated protein 4 (MRP4)-dependent cAMP extrusion process as a cause of increased cell proliferation in human PDAC cell lines. Our results from in silico analysis indicate that MRP4 expression may influence PDAC patient outcome; thus, high MRP4 levels could be indicators of poor survival. In addition, we performed in vitro experiments and identified an association between higher MRP4 expression levels and more undifferentiated and malignant models of PDAC and cAMP extrusion capacity. We studied the antiproliferative effect and the overall cAMP response of three MRP4 inhibitors, probenecid, MK571, and ceefourin-1 in PDAC in vitro models. Moreover, MRP4-specific silencing in PANC-1 cells reduced cell proliferation (P < 0.05), whereas MRP4 overexpression in BxPC-3 cells significantly incremented their growth rate in culture (P < 0.05). MRP4 pharmacological inhibition or silencing abrogated cell proliferation through the activation of the cAMP/Epac/Rap1 signaling pathway. Also, extracellular cAMP reverted the antiproliferative effect of MRP4 blockade. Our data highlight the MRP4-dependent cAMP extrusion process as a key participant in cell proliferation, indicating that MRP4 could be an exploitable therapeutic target for PDAC. SIGNIFICANCE STATEMENT: ABCC4/MRP4 is the main transporter responsible for cAMP efflux. In this work, we show that MRP4 expression may influence PDAC patient outcome and identify an association between higher MRP4 expression levels and more undifferentiated and malignant in vitro models of PDAC. Findings prove the involvement of MRP4 in PDAC cell proliferation through a novel extracellular cAMP mitogenic pathway and further support MRP4 inhibition as a promising therapeutic strategy for PDAC treatment.

Ultrasensitive amplification-free detection of protein kinase based on catalyzed assembly and enumeration of gold nanoparticles

A single-particle enumeration method based on phosphorylation-directed in situ assembly of gold nanoparticles is developed for the ultrasensitive sensing of cellular protein kinase A activity. In comparison to existing strategies, the proposed new method demonstrates five orders of linear range and improves the detection limit up to 10-to-1000 fold without the involvement of target amplification.

Creating a potential diagnostic for prostate cancer risk stratification (InformMDx™) by translating novel scientific discoveries concerning cAMP degrading phosphodiesterase-4D7 (PDE4D7)

Increased PSA-based screening for prostate cancer has resulted in a growing number of diagnosed cases. However, around half of these are ‘indolent’, neither metastasizing nor leading to disease specific death. Treating non-progressing tumours with invasive therapies is currently regarded as unnecessary over-treatment with patients being considered for conservative regimens, such as active surveillance (AS). However, this raises both compliance and protocol issues. Great clinical benefit could accrue from a biomarker able to predict long-term patient outcome accurately at the time of biopsy and initial diagnosis. Here we delineate the translation of a laboratory discovery through to the precision development of a clinically validated, novel prognostic biomarker assay (InformMDx™). This centres on determining transcript levels for phosphodiesterase-4D7 (PDE4D7), an enzyme that breaks down cyclic AMP, a signalling molecule intimately connected with proliferation and androgen receptor function. Quantifiable detection of PDE4D7 mRNA transcripts informs on the longitudinal outcome of post-surgical disease progression. The risk of post-surgical progression increases steeply for patients with very low ‘PDE4D7 scores’, while risk decreases markedly for those patients with very high ‘PDE4D7 scores’. Combining clinical risk variables, such as the Gleason or CAPRA (Cancer of the Prostate Risk Assessment) score, with the ‘PDE4D7 score’ further enhances the prognostic power of this personalized, precision assessment. Thus the ‘PDE4D7 score’ has the potential to define, more effectively, appropriate medical intervention/AS strategies for individual prostate cancer patients.

The A2B adenosine receptor in MDA-MB-231 breast cancer cells diminishes ERK1/2 phosphorylation by activation of MAPK-phosphatase-1

It was previously shown that the estrogen-receptor negative breast cancer cell line MBA-MD-231 expresses high levels of A_2B adenosine receptors as the sole adenosine receptor subtype. These receptors couple to both, stimulation of adenylyl cyclase and a Ca²⁺ signal. In order to establish a potential role of A_2B adenosine receptors in tumor growth and development MAPK signaling was investigated in these breast cancer cells. Although it is known that A_2B adenosine receptors may stimulate MAPK it was found that in MBA-MD-231 cells ERK1/2 phosphorylation is reduced upon agonist-stimulation of A_2B adenosine receptors. This reduction is also triggered by forskolin, but abolished by the PKA inhibitor H89, suggesting an important role for the cAMP-PKA pathway. Likewise, a role for intracellular Ca²⁺ was established as the Ca²⁺ chelator 1,2-bis-(o-aminophenoxy)-ethane-N,N,N’,N’-tetraacetic acid, tetraacetoxymethyl ester (BAPTA-AM) abolished the reduction of ERK1/2 phosphorylation triggered by A_2B stimulation. It was shown that various pathways downstream from A_2B adenosine receptors resulted in a stimulation of MAPK phosphatase-1 (MKP-1) which dephosphorylates phospho ERK1/2, and thus plays a critical role in the regulation of the phosphorylation state of ERK1/2. The reduction of ERK1/2 phosphorylation mediated by A_2B adenosine receptors might provide an interesting approach for adjuvant treatment leading to reduced growth of certain tumors expressing the A_2B subtype.

The heat-shock, or HSF1-mediated proteotoxic stress, response in cancer: from proteomic stability to oncogenesis

The heat-shock, or HSF1-mediated proteotoxic stress, response (HSR/HPSR) is characterized by induction of heat-shock proteins (HSPs). As molecular chaperones, HSPs facilitate the folding, assembly, transportation and degradation of other proteins. In mammals, heat shock factor 1 (HSF1) is the master regulator of this ancient transcriptional programme. Upon proteotoxic insults, the HSR/HPSR is essential to proteome homeostasis, or proteostasis, thereby resisting stress and antagonizing protein misfolding diseases and ageing. Contrasting with these benefits, an unexpected pro-oncogenic role of the HSR/HPSR is unfolding. Whereas HSF1 remains latent in primary cells without stress, it becomes constitutively activated within malignant cells, rendering them addicted to HSF1 for their growth and survival. Highlighting the HSR/HPSR as an integral component of the oncogenic network, several key pathways governing HSF1 activation by environmental stressors are causally implicated in malignancy. Importantly, HSF1 impacts the cancer proteome systemically. By suppressing tumour-suppressive amyloidogenesis, HSF1 preserves cancer proteostasis to support the malignant state, both providing insight into how HSF1 enables tumorigenesis and suggesting disruption of cancer proteostasis as a therapeutic strategy. This review provides an overview of the role of HSF1 in oncogenesis, mechanisms underlying its constitutive activation within cancer cells and its pro-oncogenic action, as well as potential HSF1-targeting strategies.This article is part of the theme issue 'Heat shock proteins as modulators and therapeutic targets of chronic disease: an integrated perspective'.

Chemoresistance: Intricate Interplay Between Breast Tumor Cells and Adipocytes in the Tumor Microenvironment

Excess adipose tissue is a hallmark of an overweight and/or obese state as well as a primary risk factor for breast cancer development and progression. In an overweight/obese state adipose tissue becomes dysfunctional due to rapid hypertrophy, hyperplasia, and immune cell infiltration which is associated with sustained low-grade inflammation originating from dysfunctional adipokine synthesis. Evidence also supports the role of excess adipose tissue (overweight/obesity) as a casual factor for the development of chemotherapeutic drug resistance. Obesity-mediated effects/modifications may contribute to chemotherapeutic drug resistance by altering drug pharmacokinetics, inducing chronic inflammation, as well as altering tumor-associated adipocyte adipokine secretion. Adipocytes in the breast tumor microenvironment enhance breast tumor cell survival and decrease the efficacy of chemotherapeutic agents, resulting in chemotherapeutic resistance. A well-know chemotherapeutic agent, doxorubicin, has shown to negatively impact adipose tissue homeostasis, affecting adipose tissue/adipocyte functionality and storage. Here, it is implied that doxorubicin disrupts adipose tissue homeostasis affecting the functionality of adipose tissue/adipocytes. Although evidence on the effects of doxorubicin on adipose tissue/adipocytes under obesogenic conditions are lacking, this narrative review explores the potential role of obesity in breast cancer progression and treatment resistance with inflammation as an underlying mechanism.

Overexpression of G-protein-coupled receptors 65 in glioblastoma predicts poor patient prognosis

OBJECTIVE

G-protein-coupled receptors 65 (GPR65), identified as an acid-sensing receptor, is overexpressed in several malignancies and promote tumor development. Our aim was to investigate the expression and prognostic value of GPR65 in glioblastoma.

MATERIALS AND METHODS

We determined the expression of GPR65 protein using immunohistochemistry in tissue microarrays containing 11 Grade I, 107 Grade II, 47 Grade III, and 102 Grade IV gliomas and 16 normal brains. Then we evaluated its association with pathological grades, prognosis, and recurrence. The Cancer Genome Atlas (TCGA) group (N=528) was further employed to examine transcriptional level of GPR65 in glioblastoma and the correlation between GPR65 expression and clinical outcome.

RESULTS

In our cohort, GPR65 expression was positively related to glioma pathological grade (p<0.01) and elevated in glioblastoma (p<0.01). High expression of GPR65 was associated with significantly short overall survival (OS) (p=0.013) and progression-free survival (PFS) (p=0.029), and could be identified as an independent risk factor for OS of glioblastoma patients (Hazard Ratio [HR]=1.596, p=0.037). As an aiding evidence, increased GPR65 mRNA expression was also found in TCGA glioblastoma group (p<0.001) and its high level predicted a poor clinical outcome (OS, p=0.003; PFS, p=0.001).

CONCLUSION

Our findings suggest that GPR65 is overexpressed in glioblastoma and its high expression predicts unfavorable clinical outcome for patients. Targeting GPR65 may serve as a potential therapy for treating glioblastoma.

Protein phosphatase 1 regulatory subunit 1A in ewing sarcoma tumorigenesis and metastasis

Protein phosphatase inhibitors are often considered as tumor promoters. Protein phosphatase 1 regulatory subunit 1A (PPP1R1A) is a potent protein phosphatase 1 (PP1) inhibitor; however, its role in tumor development is largely undefined. Here we characterize, for the first time, the functions of PPP1R1A in Ewing sarcoma (ES) pathogenesis. We found that PPP1R1A is one of the top ranked target genes of EWS/FLI, the master regulator of ES, and is upregulated by EWS/FLI via a GGAA microsatellite enhancer element. Depletion of PPP1R1A resulted in a significant decrease in oncogenic transformation and cell migration in vitro as well as xenograft tumor growth and metastasis in an orthotopic mouse model. RNA-sequencing and functional annotation analyses revealed that PPP1R1A regulates genes associated with various cellular functions including cell junction, adhesion and neurogenesis. Interestingly, we found a significant overlap of PPP1R1A-regulated gene set with that of ZEB2 and EWS, which regulates metastasis and neuronal differentiation in ES, respectively. Further studies for characterization of the molecular mechanisms revealed that activation of PPP1R1A by PKA phosphorylation at Thr35, and subsequent PP1 binding and inhibition, was required for PPP1R1A-mediated tumorigenesis and metastasis, likely by increasing the phosphorylation levels of various PP1 substrates. Furthermore, we found that a PKA inhibitor impaired ES cell proliferation, tumor growth and metastasis, which was rescued by the constitutively active PPP1R1A. Together, these results offered new insights into the role and mechanism of PPP1R1A in tumor development and identified an important kinase and phosphatase pathway, PKA/PPP1R1A/PP1, in ES pathogenesis. Our findings strongly suggest a potential therapeutic value of inhibition of the PKA/PPP1R1A/PP1 pathway in the treatment of primary and metastatic ES.

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.

cAMP-dependent regulation of RhoA/Rho-kinase attenuates detrusor overactivity in a novel mouse experimental model

OBJECTIVE

To investigate detrusor function and cAMP activation as a possible target for detrusor overactivity in an experimental model lacking a key denitrosylation enzyme, S-nitrosoglutathione reductase (GSNOR).

MATERIALS AND METHODS

GSNOR-deficient (GSNOR^-/- ) (n = 30) and wild-type (WT) mice (n = 26) were treated for 7 days with the cAMP activator, colforsin (1 mg/kg), or vehicle intraperitoneally. Cystometric studies or molecular analyses of bladder specimens were performed. Bladder function indices and expression levels of proteins that regulate detrusor relaxation (nitric oxide synthase pathway) or contraction (RhoA/Rho-kinase pathway) and oxidative stress were assessed. For statistical analysis the Student's t-test and one-way analysis of variance were used.

RESULTS

GSNOR^-/- mice had significantly higher (P < 0.05) voiding and non-voiding contraction frequencies compared to WT mice (Cohen's effect size values d = 1.82 and 2.52, respectively). Colforsin normalised these abnormalities (Cohen's effect size values d = 1.85 and 1.28, respectively). Western blot analyses showed an up-regulation of the RhoA/Rho-kinase pathway reflected by significantly higher (P < 0.05) phosphorylated myosin phosphatase target subunit 1 (P-MYPT-1) expression in GSNOR^-/- mouse bladders, which was reversed by colforsin treatment. There was a higher level (P < 0.05) of gp91^phox expression in the bladders of GSNOR^-/- mice without significant change after colforsin treatment. Neuronal and endothelial nitric oxide synthase phosphorylation on Ser-1412 and Ser-1177, respectively, did not differ between GSNOR^-/- and WT mouse bladders irrespective of colforsin treatment.

CONCLUSION

Impaired denitrosylation is associated with detrusor overactivity, which is linked with upregulated RhoA/Rho-kinase signalling. Colforsin reverses physiological and molecular abnormalities. This study describes a novel model of detrusor overactivity and suggests a possible basis for its treatment.

Triple negative breast cancer development can be selectively suppressed by sustaining an elevated level of cellular cyclic AMP through simultaneously blocking its efflux and decomposition

Triple negative breast cancer (TNBC) has the highest mortality among all breast cancer types and lack of targeted therapy is a key factor contributing to its high mortality rate. In this study, we show that 8-bromo-cAMP, a cyclic adenosine monophosphate (cAMP) analog at high concentration (> 1 mM) selectively suppresses TNBC cell growth. However, commonly-used cAMP-elevating agents such as adenylyl cyclase activator forskolin and pan phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) are ineffective. Inability of cAMP elevating agents to inhibit TNBC cell growth is due to rapid diminution of cellular cAMP through efflux and decomposition. By performing bioinformatics analyses with publically available gene expression datasets from breast cancer patients/established breast cancer cell lines and further validating using specific inhibitors/siRNAs, we reveal that multidrug resistance-associated protein 1/4 (MRP1/4) mediate rapid cAMP efflux while members PDE4 subfamily facilitate cAMP decomposition. When cAMP clearance is prevented by specific inhibitors, forskolin blocks TNBC's in vitro cell growth by arresting cell cycle at G1/S phase. Importantly, cocktail of forskolin, MRP inhibitor probenecid and PDE4 inhibitor rolipram suppresses TNBC in vivo tumor development. This study suggests that a TNBC-targeted therapeutic strategy can be developed by sustaining an elevated level of cAMP through simultaneously blocking its efflux and decomposition.

An expression based REST signature predicts patient survival and therapeutic response for glioblastoma multiforme

Proper regulation of neuronal gene expression is crucial for the development and differentiation of the central nervous system. The transcriptional repressor REST (repressor element-1 silencing transcription factor) is a key regulator in differentiation of pluripotent stem cells to neuronal progenitors and mature neurons. Dysregulated REST activity has been implicated in various diseases, among which the most deadly is glioblastoma multiforme (GBM). Here we have developed an expression-based REST signature (EXPREST), a device providing quantitative measurements of REST activity for GBM tumors. EXPREST robustly quantifies REST activity (REST score) using gene expression profiles in absence of clinic-pathologic assessments of REST. Molecular characterization of REST activity identified global alterations at the DNA, RNA, protein and microRNA levels, suggesting a widespread role of REST in GBM tumorigenesis. Although originally aimed to capture REST activity, REST score was found to be a prognostic factor for overall survival. Further, cell lines with enhanced REST activity was found to be more sensitive to IGF1R, VEGFR and ABL inhibitors. In contrast, cell lines with low REST score were more sensitive to cytotoxic drugs including Mitomycin, Camptothecin and Cisplatin. Together, our work suggests that therapeutic targeting of REST provides a promising opportunity for GBM treatment.

An in vivo screening system to identify tumorigenic genes

Screening for oncogenes has mostly been performed by in vitro transformation assays. However, some oncogenes might not exhibit their transforming activities in vitro unless putative essential factors from in vivo microenvironments are adequately supplied. Here, we have developed an in vivo screening system that evaluates the tumorigenicity of target genes. This system uses a retroviral high-efficiency gene transfer technique, a large collection of human cDNA clones corresponding to ~70% of human genes and a luciferase-expressing immortalized mouse mammary epithelial cell line (NMuMG-luc). From 845 genes that were highly expressed in human breast cancer cell lines, we focused on 205 genes encoding membrane proteins and/or kinases as that had the greater possibility of being oncogenes or drug targets. The 205 genes were divided into five subgroups, each containing 34-43 genes, and then introduced them into NMuMG-luc cells. These cells were subcutaneously injected into nude mice and monitored for tumor development by in vivo imaging. Tumors were observed in three subgroups. Using DNA microarray analyses and individual tumorigenic assays, we found that three genes, ADORA2B, PRKACB and LPAR3, were tumorigenic. ADORA2B and LPAR3 encode G-protein-coupled receptors and PRKACB encodes a protein kinase A catalytic subunit. Cells overexpressing ADORA2B, LPAR3 or PRKACB did not show transforming phenotypes in vitro, suggesting that transformation by these genes requires in vivo microenvironments. In addition, several clinical data sets, including one for breast cancer, showed that the expression of these genes correlated with lower overall survival rate.

Protein kinase A can block EphA2 receptor-mediated cell repulsion by increasing EphA2 S897 phosphorylation

The EphA2 receptor plays multiple roles in cancer through two distinct signaling mechanisms. In a novel cross-talk, the β2-adrenoceptor/cAMP/PKA axis can promote EphA2 pro-oncogenic, ligand-independent signaling, blocking cell repulsion induced by ligand-dependent signaling. PKA emerges as a third kinase, besides AKT and RSK, that can regulate EphA2.

The EphA2 receptor tyrosine kinase plays key roles in tissue homeostasis and disease processes such as cancer, pathological angiogenesis, and inflammation through two distinct signaling mechanisms. EphA2 “canonical” signaling involves ephrin-A ligand binding, tyrosine autophosphorylation, and kinase activity; EphA2 “noncanonical” signaling involves phosphorylation of serine 897 (S897) by AKT and RSK kinases. To identify small molecules counteracting EphA2 canonical signaling, we developed a high-content screening platform measuring inhibition of ephrin-A1–induced PC3 prostate cancer cell retraction. Surprisingly, most hits from a screened collection of pharmacologically active compounds are agents that elevate intracellular cAMP by activating G protein–coupled receptors such as the β2-adrenoceptor. We found that cAMP promotes phosphorylation of S897 by protein kinase A (PKA) as well as increases the phosphorylation of several nearby serine/threonine residues, which constitute a phosphorylation hotspot. Whereas EphA2 canonical and noncanonical signaling have been viewed as mutually exclusive, we show that S897 phosphorylation by PKA can coexist with EphA2 tyrosine phosphorylation and block cell retraction induced by EphA2 kinase activity. Our findings reveal a novel paradigm in EphA2 function involving the interplay of canonical and noncanonical signaling and highlight the ability of the β2-adrenoceptor/cAMP/PKA axis to rewire EphA2 signaling in a subset of cancer cells.

Cyclic AMP efflux inhibitors as potential therapeutic agents for leukemia

Apoptotic evasion is a hallmark of cancer. We propose that some cancers may evade cell death by regulating 3'-5'-cyclic adenosine monophosphate (cAMP), which is associated with pro-apoptotic signaling. We hypothesize that leukemic cells possess mechanisms that efflux cAMP from the cytoplasm, thus protecting them from apoptosis. Accordingly, cAMP efflux inhibition should result in: cAMP accumulation, activation of cAMP-dependent downstream signaling, viability loss, and apoptosis. We developed a novel assay to assess cAMP efflux and performed screens to identify inhibitors. In an acute myeloid leukemia (AML) model, several identified compounds reduced cAMP efflux, appropriately modulated pathways that are responsive to cAMP elevation (cAMP-responsive element-binding protein phosphorylation, and deactivation of Very Late Antigen-4 integrin), and induced mitochondrial depolarization and caspase activation. Blocking adenylyl cyclase activity was sufficient to reduce effects of the most potent compounds. These compounds also decreased cAMP efflux and viability of B-lineage acute lymphoblastic leukemia (B-ALL) cell lines and primary patient samples, but not of normal primary peripheral blood mononuclear cells. Our data suggest that cAMP efflux is a functional feature that could be therapeutically targeted in leukemia. Furthermore, because some of the identified drugs are currently used for treating other illnesses, this work creates an opportunity for repurposing.

Effect of Glucuronidation on the Potential of Kaempferol to Inhibit Serine/Threonine Protein Kinases

To study the effect of metabolic conjugation of flavonoids on the potential to inhibit protein kinase activity, the inhibitory effects of the dietary flavonol kaempferol and its major plasma conjugate kaempferol-3-O-glucuronide on protein kinases were studied. To this end, the inhibition of the phosphorylation activity of recombinant protein kinase A (PKA) and of cell lysate from the hepatocellular carcinoma cell line HepG2 on 141 putative serine/threonine phosphorylation sites derived from human proteins was assessed. Glucuronidation reduced the inhibitory potency of kaempferol on the phosphorylation activity of PKA and HepG2 lysate on average about 16 and 3.5 times, respectively, but did not appear to affect the target selectivity for kinases present in the lysate. The data demonstrate that, upon glucuronidation, kaempferol retains part of its intrinsic kinase inhibition potential, which implies that K3G does not necessarily need to be deconjugated to the aglycone for a potential inhibitory effect on protein kinases.

The cAMP analogs have potent anti-proliferative effects on medullary thyroid cancer cell lines

The oncogenic activation of the rearranged during transfection (RET) proto-oncogene has a main role in the pathogenesis of medullary thyroid cancer (MTC). Several lines of evidence suggest that RET function could be influenced by cyclic AMP (cAMP)-dependent protein kinase A (PKA) activity. We evaluated the in vitro anti-tumor activity of 8-chloroadenosine-3',5'-cyclic monophosphate (8-Cl-cAMP) and PKA type I-selective cAMP analogs [equimolar combination of the 8-piperidinoadenosine-3',5'-cyclic monophosphate (8-PIP-cAMP) and 8-hexylaminoadenosine-3',5'-cyclic monophosphate (8-HA-cAMP) in MTC cell lines (TT and MZ-CRC-1)]. 8-Cl-cAMP and the PKA I-selective cAMP analogs showed a potent anti-proliferative effect in both cell lines. In detail, 8-Cl-cAMP blocked significantly the transition of TT cell population from G2/M to G0/G1 phase and from G0/G1 to S phase and of MZ-CRC-1 cells from G0/G1 to S phase. Moreover, 8-Cl-cAMP induced apoptosis in both cell lines, as demonstrated by FACS analysis for annexin V-FITC/propidium iodide, the activation of caspase-3 and PARP cleavage. On the other hand, the only effect induced by PKA I-selective cAMP analogs was a delay in G0/G1-S and S-G2/M progression in TT and MZ-CRC-1 cells, respectively. In conclusion, these data demonstrate that cAMP analogs, particularly 8-Cl-cAMP, significantly suppress in vitro MTC proliferation and provide rationale for a potential clinical use of cAMP analogs in the treatment of advanced MTC.

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.

Distinct regulation of Maf1 for lifespan extension by Protein kinase A and Sch9

The Protein kinase A (PKA) and Sch9 regulates cell growth as well as lifespan in Saccharomyces cerevisiae. Maf1 is a RNA polymerase III (PolIII) inhibitor that tailors 5S rRNA and tRNA production in response to various environmental cues. Both PKA and Sch9 have been shown to phosphorylate Maf1 in vitro at similar amino acids, suggesting a redundancy in Maf1 regulation. However, here we find that activating PKA by bcy1 deletion cannot replace Sch9 for Maf1 phosphorylation and cytoplasmic retention; instead, such modulation lowers Maf1 protein levels. Consistently, loss of MAF1 or constitutive PKA activity reverses the stress resistance and the extended lifespan of sch9Δ cells. Overexpression of MAF1 partially rescues the extended lifespan of sch9Δ in bcy1Δsch9Δ mutant, suggesting that PKA suppresses sch9Δ longevity at least partly through Maf1 abundance. Constitutive PKA activity also reverses the reduced tRNA synthesis and slow growth of sch9Δ, which, however, is not attributed to Maf1 protein abundance. Therefore, regulation of lifespan and growth can be decoupled. Together, we reveal that lifespan regulation by PKA and Sch9 are mediated by Maf1 through distinct mechanisms.

From canonical to non-canonical cyclic nucleotides as second messengers: pharmacological implications

This review summarizes our knowledge on the non-canonical cyclic nucleotides cCMP, cUMP, cIMP, cXMP and cTMP. We place the field into a historic context and discuss unresolved questions and future directions of research. We discuss the implications of non-canonical cyclic nucleotides for experimental and clinical pharmacology, focusing on bacterial infections, cardiovascular and neuropsychiatric disorders and reproduction medicine. The canonical cyclic purine nucleotides cAMP and cGMP fulfill the criteria of second messengers. (i) cAMP and cGMP are synthesized by specific generators, i.e. adenylyl and guanylyl cyclases, respectively. (ii) cAMP and cGMP activate specific effector proteins, e.g. protein kinases. (iii) cAMP and cGMP exert specific biological effects. (iv) The biological effects of cAMP and cGMP are terminated by phosphodiesterases and export. The effects of cAMP and cGMP are mimicked by (v) membrane-permeable cyclic nucleotide analogs and (vi) bacterial toxins. For decades, the existence and relevance of cCMP and cUMP have been controversial. Modern mass-spectrometric methods have unequivocally demonstrated the existence of cCMP and cUMP in mammalian cells. For both, cCMP and cUMP, the criteria for second messenger molecules are now fulfilled as well. There are specific patterns by which nucleotidyl cyclases generate cNMPs and how they are degraded and exported, resulting in unique cNMP signatures in biological systems. cNMP signaling systems, specifically at the level of soluble guanylyl cyclase, soluble adenylyl cyclase and ExoY from Pseudomonas aeruginosa are more promiscuous than previously appreciated. cUMP and cCMP are evolutionary new molecules, probably reflecting an adaption to signaling requirements in higher organisms.

cAMP signalling in the normal and tumorigenic pituitary gland

cAMP signalling plays a key role in the normal physiology of the pituitary gland, regulating cellular growth and proliferation, hormone production and release. Deregulation of the cAMP signalling pathway has been reported to be a common occurrence in pituitary tumorigenesis. Several mechanisms have been implicated including somatic mutations, gene-gene interactions and gene-environmental interactions. Somatic mutations in G-proteins and protein kinases directly alter cAMP signalling, while malfunctioning of other signalling pathways such as the Raf/MAPK/ERK, PI3K/Akt/mTOR and Wnt pathways which normally interact with the cAMP pathway may mediate indirect effects on cAMP and varying downstream effectors. The aryl hydrocarbon receptor signalling pathway has been implicated in pituitary tumorigenesis and we review its role in general and specifically in relation to cAMP de-regulation.

Overexpression of cytoplasmic β-catenin inhibits the metastasis of the murine osteosarcoma cell line LM8

Background

Previously, we found that treatment of LM8 murine osteosarcoma cells with genistein, an isoflavone found in soy, increased the cellular level of β-catenin and decreased its invasive and motile potential. The purpose of this study is to investigate whether the expression of β-catenin in LM8 cells is associated with metastatic potential in nude mice. To this end, we used untreated and genistein-treated LM8 cells.

Methods

LM8 cells were treated for 3 days with or without 50 μM genistein and harvested by trypsinization. Untreated (the control group) and genistein-treated (the genistein group) cells were subcutaneously inoculated into the backs of male nude mice. After 25 days of inoculation, the tumors, lungs, and livers were excised, fixed in 10% formalin, and embedded in paraffin. The sections of formalin-fixed, paraffin-embedded lungs and livers were stained with hematoxylin-eosin (H&E) to confirm the absence or presence of metastatic tumors. The expression of β-catenin within the primary tumor was immunohistochemically examined.

Results

All mice in the control group (n = 8) exhibited large primary tumors, while in the genistein group (n = 8), one mouse showed no tumor formation and the remaining seven mice exhibited smaller primary tumors compared with the control group. The tumor mass of the genistein group was 23% of that of the control group. In the control group, multiple metastatic tumors were found in the lung and/or liver and the metastatic incidence was 100% in the lung and 87.5% in the liver. Six of seven tumor-bearing mice in the genistein group developed no metastatic tumors in the lung or liver, and this group was termed the genistein/metastasis(-) subgroup. Positive β-catenin immunostaining was observed in the cytoplasm of tumor cells, and the β-catenin-labeling index was higher in the genistein/metastasis(-) subgroup than in the control group. The intensity of cytoplasmic β-catenin immunostaining was stronger in the genistein/metastasis(-) subgroup compared with the control group, and the β-catenin-labeling score was 1.9-times higher in the former subgroup than in the latter group.

Conclusions

Overexpression of cytoplasmic β-catenin in LM8 cells causes inhibition of the growth of primary tumors and loss of the metastatic potential to the lung and liver.

Activation of the PKC pathway stimulates ovarian cancer cell proliferation, migration, and expression of MMP7 and MMP10

Postmenopausal women are at a higher risk of ovarian cancer due, in part, to increased levels of gonadotropins such as luteinizing hormone (LH). Gonadotropins and other stimuli are capable of activating two pathways, PKA and PKC, that are altered in ovarian cancer. To determine the role of LH on ovarian cancer, we explored the effects of human chorionic gonadotropin (hCG), an LH mimic, and an activator of the PKC pathway, phorbol-12-myristate 13-acetate (PMA), on ovarian cancer cell-cycle kinetics and apoptosis in Ovcar3 cells. PMA treatment increased cells in the S phase of the cell cycle and initially increased apoptosis after 4 h before diminishing apoptosis after 8 h. Treatment of ovarian cancer cells with hCG had no effect on these parameters. The PKC pathway is known to differentially regulate matrix metalloproteinase (MMP) expression. Results showed that ovarian cancer cells treated with PMA increased MMP7 and MMP10 mRNA levels after 8 h of treatment, and expression remained high after 12 h before decreasing at 24 h. The mRNA expression of extracellular matrix metalloproteinase inducer (BSG), an activator of MMPs, was unaffected by PMA. Due to the role that MMPs play in migration, we investigated the effect of PMA activation of MMPs on ovarian cancer cell migration. The use of the MMP inhibitor GM6001 blocked the increased migratory effects of PMA on ovarian cancer cells. Together, these studies show that activating the PKC pathway causes significant changes in cell cycle kinetics and selective expression of MMPs that are involved in enhancing ovarian cancer cell proliferation and migration.

Effects of matrine on the proliferation of HT29 human colon cancer cells and its antitumor mechanism

Matrine is one of the main active components that is extracted from the dry roots of Sophora flavescens. The compound has potent antitumor activity in various cancer cell lines. However, the anticancer activity of matrine in colon cancer cells remains unclear. The purpose of the present study was to investigate the effects of matrine on the growth of human colon cancer cells and the expression of the associated proteins. Cancer cell proliferation was measured by 3-(4,5-dimethylthiazolyl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. The cell cycle distribution and apoptosis were analyzed by flow cytometry (FCM). The activation of the caspases and the expression of pro-apoptotic and anti-apoptotic factors were examined using western blot analysis. Matrine was shown to significantly inhibit the proliferation of HT29 cells in a dose- and time-dependent manner, and also to reduce the percentage of cells in the G₂/M phase, which was most frequently associated with an increase of cells arrested in the G₀/G₁ phase of the cell cycle. Western blot analysis revealed that matrine induced the activation of caspase-3 and -9 and the release of cytochrome C (Cyto C) from the mitochondria to the cytosol. Furthermore, the pro-apoptotic factor, Bax, was upregulated and the anti-apoptotic factor, Bcl-2, was downregulated, eventually leading to a reduction in the ratio of Bcl-2/Bax proteins. The results demonstrated that matrine inhibits proliferation and induces apoptosis of HT29 human cells in vitro. The induction of apoptosis appears to occur through the upregulation of Bax, the downregulation of Bcl-2, the release of Cyto C from the mitochondria to the cytosol and the activation of caspase-3 and caspase-9, which subsequently trigger major apoptotic cascades. Matrine has potent antitumor activity in HT29 cells and may be used as a novel effective reagent in the treatment of colon cancer.

Cyclic AMP can promote APL progression and protect myeloid leukemia cells against anthracycline-induced apoptosis

We show that cyclic AMP (cAMP) elevating agents protect blasts from patients with acute promyelocytic leukemia (APL) against death induced by first-line anti-leukemic anthracyclines like daunorubicin (DNR). The cAMP effect was reproduced in NB4 APL cells, and shown to depend on activation of the generally cytoplasmic cAMP-kinase type I (PKA-I) rather than the perinuclear PKA-II. The protection of both NB4 cells and APL blasts was associated with (inactivating) phosphorylation of PKA site Ser118 of pro-apoptotic Bad and (activating) phosphorylation of PKA site Ser133 of the AML oncogene CREB. Either event would be expected to protect broadly against cell death, and we found cAMP elevation to protect also against 2-deoxyglucose, rotenone, proteasome inhibitor and a BH3-only mimetic. The in vitro findings were mirrored by the findings in NSG mice with orthotopic NB4 cell leukemia. The mice showed more rapid disease progression when given cAMP-increasing agents (prostaglandin E₂ analog and theophylline), both with and without DNR chemotherapy. The all-trans retinoic acid (ATRA)-induced terminal APL cell differentiation is a cornerstone in current APL treatment and is enhanced by cAMP. We show also that ATRA-resistant APL cells, believed to be responsible for treatment failure with current ATRA-based treatment protocols, were protected by cAMP against death. This suggests that the beneficial pro-differentiating and non-beneficial pro-survival APL cell effects of cAMP should be weighed against each other. The results suggest also general awareness toward drugs that can affect bone marrow cAMP levels in leukemia patients.

Syk inhibits the activity of protein kinase A by phosphorylating tyrosine 330 of the catalytic subunit

The Syk protein-tyrosine kinase can have multiple effects on cancer cells, acting in some as a tumor suppressor by inhibiting motility and in others as a tumor promoter by enhancing survival. Phosphoproteomic analyses identified PKA as a Syk-specific substrate. Syk catalyzes the phosphorylation of the catalytic subunit of PKA (PKAc) both in vitro and in cells on Tyr-330. Tyr-330 lies within the adenosine-binding motif in the C-terminal tail of PKAc within a cluster of acidic amino acids (DDYEEEE), which is a characteristic of Syk substrates. The phosphorylation of PKAc on Tyr-330 by Syk strongly inhibits its catalytic activity. Molecular dynamics simulations suggest that this additional negative charge prevents the C-terminal tail from interacting with the substrate and the nucleotide-binding site to stabilize the closed conformation of PKAc, thus preventing catalysis from occurring. Phosphoproteomic analyses and Western blotting studies indicate that Tyr-330 can be phosphorylated in a Syk-dependent manner in MCF7 breast cancer cells and DT40 B cells. The phosphorylation of a downstream substrate of PKAc, cAMP-responsive element-binding protein (CREB), is inhibited in cells expressing Syk but can be rescued by a selective inhibitor of Syk. Modulation of CREB activity alters the expression of the CREB-regulated gene BCL2 and modulates cellular responses to genotoxic agents. Thus, PKA is a novel substrate of Syk, and its phosphorylation on Tyr-330 inhibits its participation in downstream signaling pathways.

Death of multiple myeloma cells induced by cAMP-signaling involves downregulation of Mcl-1 via the JAK/STAT pathway

There is a continuous search for new therapeutic targets for treatment of multiple myeloma (MM). Here we investigated the mechanisms involved in cAMP-induced apoptosis of human MM cells. cAMP-increasing agents rapidly inhibited activation of JAK1 and its substrate STAT3. In line with STAT3 being a regulator of Mcl-1 transcription, the expression of this pro-survival factor was rapidly and selectively reduced. Notably, exogenous interleukin-6 neither prevented the inhibition of JAK1/STAT3 nor the death of MM cells induced by cAMP. Our results suggest that cAMP-mediated killing of MM cells involves inhibition of the JAK/STAT pathway, making the cAMP-pathway a promising target for treatment of MM.