Cyclic GMP/protein kinase G type-Iα (PKG-Iα) signaling pathway promotes CREB phosphorylation and maintains higher c-IAP1, livin, survivin, and Mcl-1 expression and the inhibition of PKG-Iα kinase activity synergizes with cisplatin in non-small cell lung cancer cells

Pre-IVM with C-type natriuretic peptide promotes mitochondrial biogenesis of bovine oocytes via activation of CREB

The aim of this study was to evaluate the effects of C-type natriuretic peptide (CNP) treatment prior to in vitro maturation (IVM) on mitochondria biogenesis in bovine oocyte matured in vitro and explore the related causes. The results showed that treatment with CNP before IVM significantly improved mitochondrial content, elevated the expression of genes related to mitochondria biogenesis, and increased the protein levels of phosphorylation of cAMP-response element binding protein (p-CREB) in bovine oocytes following IVM. However, further studies revealed that treatment with CNP before IVM could not increased the protein levels of p-CREB in bovine oocytes when natriuretic peptide receptor 2 activities was inhibited using the relative specific inhibitor Gö6976. In addition, treatment with CNP before IVM could not improved mitochondrial content or elevated the expression of genes related to mitochondria biogenesis in bovine oocytes when CREB activities was abolished using the specific inhibitor 666-15. In summary, these results provide evidence that treatment of bovine oocytes with CNP before IVM promotes mitochondrial biogenesis in vitro, possibly by activating CREB.

Dual-Specificity Phosphatase 4 Promotes Malignant Features in Colorectal Cancer Through Cyclic-AMP Response Element Binding Protein/Protein Kinase CAMP-Activated Catalytic Subunit Beta Activation

INTRODUCTION

Previous studies have demonstrated that Dual-specificity phosphatase 4 (DUSP4) plays an important role in the progression of different tumor types. However, the role and mechanism of DUSP4 in colorectal cancer (CRC) remain unclear.

AIMS

We investigate the role and mechanisms of DUSP4 in CRC.

METHODS

Immunohistochemistry was used to investigate DUSP4 expression in CRC tissues. Cell proliferation, apoptosis and migration assays were used to validate DUSP4 function in vitro and in vivo. RNA-sequence assay was used to identify the target genes of DUSP4. Human phosphokinase array and inhibitor assays were used to explore the downstream signaling of DUSP4.

RESULTS

DUSP4 expression was upregulated in CRC tissues relative to normal colorectal tissues, and DUSP4 expression showed a significant positive correlation with CRC stage. Consistently, we found that DUSP4 was highly expressed in colorectal cancer cells compared to normal cells. DUSP4 knockdown inhibits CRC cell proliferation, migration and promotes apoptosis. Furthermore, the ectopic expression of DUSP4 enhanced CRC cell proliferation, migration and diminished apoptosis in vitro and in vivo. Human phosphokinase array data showed that ectopic expression of DUSP4 promotes CREB activation. RNA-sequencing data showed that PRKACB acts as a downstream target gene of DUSP4/CREB and enhances CREB activation through PKA/cAMP signaling. In addition, xenograft model results demonstrated that DUSP4 promotes colorectal tumor progression via PRKACB/CREB activation in vivo.

CONCLUSION

These findings suggest that DUSP4 promotes CRC progression. Therefore, it may be a promising therapeutic target for CRC.

Anti-NSCLC role of SCN4B by negative regulation of the cGMP-PKG pathway: Integrated utilization of bioinformatics analysis and in vitro assay validation

Non-small cell lung cancer (NSCLC) is a malignant tumor with low overall cure and survival rates. Uncovering abnormally expressed genes is significantly important for developing novel targeted therapies in NSCLC. This study aimed to discover new differentially expressed genes (DEGs) of NSCLC. The DEGs of NSCLC were identified in eight data sets from Gene Expression Omnibus (GEO) database. The expression profiles and the prognostic significance of SCN4B in LUAD and LUSC were analyzed using GEPIA database. LinkedOmics was used to identify co-expressed genes with SCN4B, which were further subjected to KEGG pathway enrichment analysis. SCN4B-overexpressing plasmid (pcDNA/SCN4B) was transfected into A549 and NCI-H2170 cells to elevate the expression of SCN4B. MTT and TUNEL assays were performed to evaluate cell viability and apoptosis. Relying on the screened DEGs from GEO database, we identified that SCN4B was significantly downregulated in LUAD and LUSC. We confirmed the downregulation of SCN4B in NSCLC tissues using GEPIA database. SCN4B has a prognostic value in LUAD, but not LUSC. KEGG pathway enrichment analysis of SCN4B-related genes showed that cGMP-PKG signaling pathway might be involved in the role of SCN4B in NSCLC. Overexpression of SCN4B in A549 and NCI-H2170 cells inhibited the cell viability. Besides, SCN4B overexpression induced apoptosis of A549 and NCI-H2170 cells. SCN4B inhibited the expression of PKG1 and p-CREB in NSCLC cells. Moreover, the inhibitory effects of SCN4B on tumor malignancy were attenuated by the activator of PKG. In conclusion, integrated bioinformatical analysis proved that SCN4B was downregulated and had a prognostic significance in NSCLC. In vitro experimental studies demonstrated that SCN4B regulated NSCLC cells viability and apoptosis via inhibiting cGMP-PKG signaling pathway.

Identification of Hub Genes of Keloid Fibroblasts by Coexpression Network Analysis and Degree Algorithm

Background

Keloid is a benign dermal tumor characterized by abnormal proliferation and invasion of fibroblasts. The establishment of biomarkers is essential for the diagnosis and treatment of keloids.

Methods

We systematically identified coexpression modules using the weighted gene coexpression network analysis method (WGCNA). Differential expressed genes (DEGs) in GSE145725 and genes in significant modules were integrated to identify overlapping key genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were then performed, as well as protein-protein interaction (PPI) network construction for hub gene screening.

Results

Using the R package of WGCNA, 22 coexpression modules consisting of different genes were identified from the top 5,000 genes with maximum mean absolute deviation in 19 human fibroblast samples. Blue-green and yellow modules were identified as the most important modules, where genes overlapping with DEGs were identified as key genes. We identified the most critical functions and pathways as extracellular structure organization, vascular smooth muscle contraction, and the cGMP-PKG signaling pathway. Hub genes from key genes as BMP4, MSX1, HAND2, TBX2, SIX1, IRX1, EDN1, DLX5, MEF2C, and DLX2 were identified.

Conclusion

The blue-green and yellow modules may play an important role in the pathogenesis of keloid. 10 hub genes were identified as potential biomarkers and therapeutic targets for keloid.

IGFBP7-AS1 is a p53-responsive long noncoding RNA downregulated by Epstein-Barr virus that contributes to viral tumorigenesis

Epstein-Barr virus (EBV) is closely related to the development of several malignancies, such as B-cell lymphoma (B-CL), by the mechanism through which these malignancies develop remains largely unknown. We previously observed downregulation of the long noncoding RNA (lncRNA) IGFBP7-AS1 in response to EBV infection. However, the role of IGFBP7-AS1 in EBV-associated cancers has not been clarified. Here, we found that expression of IGFBP7-AS1, as well as its sense gene IGFBP7, is decreased in EBV-positive B-CL cells and clinical tissues. IGFBP7-AS1 stabilizes IGFBP7 mRNA by forming a duplex based on their overlapping regions. The tumour suppressor p53 transcriptionally activates IGFBP7-AS1 expression by binding to the promoter region of the lncRNA gene. The IGFBP7-AS1 expression is able to be rescued in EBV-positive cells in wild-type (wt) p53-dependent manner. IGFBP7-AS1 inhibits the proliferation and promotes the apoptosis of B-CL cells. Moreover, tumorigenic properties due to the depletion of IGFBP7-AS1 were restored by exogenous expression of IGFBP7 or wt-p53. Furthermore, the functional p53/IGFBP7-AS1/IGFBP7 axis facilitates apoptosis by suppressing the production and secretion of the NPPB signal peptide and further regulating the cGMP-PKG signalling pathway. This study demonstrates that EBV promotes tumorigenesis, particularly in B-CL progression, by downregulating the novel p53-responsive lncRNA IGFBP7-AS1.

Soluble guanylate cyclase signalling mediates etoposide resistance in progressing small cell lung cancer

Small cell lung cancer (SCLC) has a 5-year survival rate of <7%. Rapid emergence of acquired resistance to standard platinum-etoposide chemotherapy is common and improved therapies are required for this recalcitrant tumour. We exploit six paired pre-treatment and post-chemotherapy circulating tumour cell patient-derived explant (CDX) models from donors with extensive stage SCLC to investigate changes at disease progression after chemotherapy. Soluble guanylate cyclase (sGC) is recurrently upregulated in post-chemotherapy progression CDX models, which correlates with acquired chemoresistance. Expression and activation of sGC is regulated by Notch and nitric oxide (NO) signalling with downstream activation of protein kinase G. Genetic targeting of sGC or pharmacological inhibition of NO synthase re-sensitizes a chemoresistant CDX progression model in vivo, revealing this pathway as a mediator of chemoresistance and potential vulnerability of relapsed SCLC.

The novel ZEB1-upregulated protein PRTG induced by Helicobacter pylori infection promotes gastric carcinogenesis through the cGMP/PKG signaling pathway

Helicobacter pylori (H. pylori) is listed as a class I carcinogen in human gastric cancer; however, the underlying mechanisms are poorly understood. In this study, we identified Protogenin (PRTG) was upregulated in both gastric cancer tissues and H. pylori-infected tissues by analyzing dysregulated genes in TCGA and GEO databases. Importantly, upregulated PRTG predicted poor prognosis of gastric cancer patients and integrative analysis revealed that PRTG served as an oncogenic protein in gastric cancer and was required for H. pylori-mediated tumorigenic activities in in vitro cellular and in vivo tumor-bearing mouse models. Mechanistically, H. pylori infection enhanced PRTG expression by promoting transcriptional factor ZEB1 stabilization and recruitment to the PRTG promoter, and which then activated the sub-following cGMP/PKG signaling pathway in bioinformatic and cellular studies. Cellular studies further confirmed that PRTG depended on activating cGMP/PKG axis to promote proliferation, metastasis, and chemoresistance of gastric cancer cells. The PKG inhibitor KT5823 played synergistic anti-tumor effects with cisplatin and paclitaxel to gastric cancer cells in in vitro cellular and in vivo tumor-bearing mouse models. Taken together, our findings suggested that H. pylori infection depends on ZEB1 to induce PRTG upregulation, and which leading to the development and progression of gastric cancer through activating cGMP/PKG signaling pathway. Blocking PRTG/cGMP/PKG axis, therefore, presents a promising novel therapeutic strategy for gastric cancer.

Dipyridamole induces the phosphorylation of CREB to promote cancer cell proliferation

Dipyridamole, a traditional anti-platelet drug, has been reported to inhibit the proliferation of cancer cells. The present study aimed to investigate the possibility of dipyridamole as an adjuvant of chemotherapy by enhancing the cytotoxicity of an anti-cancer drug. The cytotoxicity of colorectal cancer cells (HCT-8), CD133⁺/CD44⁺ stem-like subpopulation of HCT-8 cells and lymphoma cells (U937) to dipyridamole and/or doxorubicin was evaluated using MTT proliferation and colony forming assays. The expression levels of phosphorylated cAMP-regulatory element-binding protein (pCREB) and poly(ADP-ribose) polymerase-1 (PARP-1) in cells were analyzed via western blotting and immunofluorescence. The present study reported controversial data regarding the anti-cancer effect of dipyridamole. Dipyridamole increased, rather than inhibited, the proliferation of HCT-8 and U937 cells in a dose-dependent manner. Furthermore, it was found that dipyridamole significantly increased the expression levels of pCREB and PARP-1. However, the combined usage of dipyridamole significantly enhanced the cytotoxicity of doxorubicin to HCT-8 cells at particular doses. Based on the current findings, dipyridamole likely induces the phosphorylation of CREB to promote the proliferation of cancer cells, but may enhance the cytotoxicity of anti-cancer drugs at particular doses.

Abiraterone Acetate Induces CREB1 Phosphorylation and Enhances the Function of the CBP-p300 Complex, Leading to Resistance in Prostate Cancer Cells

PURPOSE

Abiraterone acetate (AA), an inhibitor of cytochrome P450 17alpha-hydroxylase/17, 20 lyase, is an FDA-approved drug for advanced prostate cancer. However, not all patients respond to AA, and AA resistance ultimately develops in patients who initially respond. We aimed to identify AA resistance mechanisms in prostate cancer cells.

EXPERIMENTAL DESIGN

We established several AA-resistant cell lines and performed a comprehensive study on mechanisms involved in AA resistance development. RNA sequencing and phospho-kinase array screenings were performed to discover that the cAMP-response element CRE binding protein 1 (CREB1) was a critical molecule in AA resistance development.

RESULTS

The drug-resistant cell lines are phenotypically stable without drug selection, and exhibit permanent global gene expression changes. The phosphorylated CREB1 (pCREB1) is increased in AA-resistant cell lines and is critical in controlling global gene expression. Upregulation of pCREB1 desensitized prostate cancer cells to AA, while blocking CREB1 phosphorylation resensitized AA-resistant cells to AA. AA treatment increases intracellular cyclic AMP (cAMP) levels, induces kinases activity, and leads to the phosphorylation of CREB1, which may subsequently augment the essential role of the CBP/p300 complex in AA-resistant cells because AA-resistant cells exhibit a relatively higher sensitivity to CBP/p300 inhibitors. Further pharmacokinetics studies demonstrated that AA significantly synergizes with CBP/p300 inhibitors in limiting the growth of prostate cancer cells.

CONCLUSIONS

Our studies suggest that AA treatment upregulates pCREB1, which enhances CBP/p300 activity, leading to global gene expression alterations, subsequently resulting in drug resistance development. Combining AA with therapies targeting resistance mechanisms may provide a more effective treatment strategy.

Tumor necrosis factor-α induces claudin-3 upregulation in kidney tubular epithelial cells through NF-κB and CREB1

Claudins are essential for tight junction formation and paracellular transport, and they affect key cellular events including proliferation and migration. The properties of tight junctions are dynamically modulated by a variety of inputs. We previously showed that the inflammatory cytokine tumor necrosis factor-α (TNFα), a major pathogenic factor in kidney disease, alters epithelial permeability by affecting the expression of claudin-1, -2, and -4 in kidney tubular cells. Here, we explored the effect of TNFα on claudin-3 (Cldn-3), a ubiquitous barrier-forming protein. We found that TNFα elevated Cldn-3 protein expression in tubular epithelial cells (LLC-PK1 and IMCD3) as early as 3 h post treatment. Bafilomycin A and bortezomib, inhibitors of lysosomal and proteasomes, respectively, reduced Cldn-3 degradation. However, TNFα caused a strong upregulation of Cldn-3 in the presence of bafilomycin, suggesting an effect independent from lysosomes. Blocking protein synthesis using cycloheximide prevented Cldn-3 upregulation by TNFα, verifying the contribution of de novo Cldn-3 synthesis. Indeed, TNFα elevated Cldn-3 mRNA levels at early time points. Using pharmacological inhibitors and siRNA-mediated silencing, we determined that the effect of TNFα on Cldn-3 was mediated by extracellular signal regulated kinase (ERK)-dependent activation of NF-κB and PKA-induced activation of CREB1. These two pathways were turned on by TNFα in parallel and both were required for the upregulation of Cldn-3. Because Cldn-3 was suggested to modulate cell migration and epithelial-mesenchymal transition (EMT), and TNFα was shown to affect these processes, Cldn-3 upregulation may modulate regeneration of the tubules following injury.

Crustacean hyperglycemic hormone (CHH) regulates the ammonia excretion and metabolism in white shrimp, Litopenaeus vannamei under ammonia-N stress

To understand the adaptation of Litopenaeus vannamei to high environmental ammonia-N, RNA interference was used to investigate the function of crustacean hyperglycemic hormone (CHH) in the physiological process of neuroendocrine signaling transduction, and ammonia excretion and metabolism. The shrimp were exposed to 25 mg/L NH₄Cl and injected with 20 μg/shrimp CHH dsRNA for 72 h. The results showed that hemolymph ammonia content increased under ammonia-N stress and further increased after CHH knockdown, suggesting that CHH can promote ammonia excretion. Moreover, after CHH knockdown, the levels of CHH, DA, and Wnts decreased significantly, the expression of receptor GC, DA1R, Frizzled and LRP 5/6 also decreased, while DA4R increased remarkably. Moreover, PKA and PKG decreased, while PKC markedly increased, and nuclear transcription factors (CREB and TCF) as well as effector proteins (β-catenin, FXYD2, and 14-3-3) were significantly downregulated. Furthermore, ammonia transporters Na⁺/K⁺-ATPase (NKA), K⁺channel, Rh protein, AQP, V-ATPase, and VAMP decreased significantly, while Na⁺/H⁺ exchangers (NHE) and Na⁺/K⁺/2Cl^- cotransporter (NKCC) increased significantly. These results suggest that CHH regulates ammonia excretion in three ways: 1) by mainly regulating ion channels via PKA, PKC, and PKG signaling pathways; 2) by activating related proteins primarily through Wnt signaling pathway; and 3) by exocytosis, mostly induced by the PKA signaling pathway. In addition, the levels of Gln, uric acid, and urea increased in accordance with the activities of GDH/GS, XDH, and arginase, respectively, suggesting that ammonia excretion was inhibited but ammonia metabolism was slightly enhanced. This study deepens our understanding of the mechanism by which crustaceans respond to high environmental ammonia-N.

Identification of lung cancer gene markers through kernel maximum mean discrepancy and information entropy

BACKGROUND

The early diagnosis of lung cancer has been a critical problem in clinical practice for a long time and identifying differentially expressed gene as disease marker is a promising solution. However, the most existing gene differential expression analysis (DEA) methods have two main drawbacks: First, these methods are based on fixed statistical hypotheses and not always effective; Second, these methods can not identify a certain expression level boundary when there is no obvious expression level gap between control and experiment groups.

METHODS

This paper proposed a novel approach to identify marker genes and gene expression level boundary for lung cancer. By calculating a kernel maximum mean discrepancy, our method can evaluate the expression differences between normal, normal adjacent to tumor (NAT) and tumor samples. For the potential marker genes, the expression level boundaries among different groups are defined with the information entropy method.

RESULTS

Compared with two conventional methods t-test and fold change, the top average ranked genes selected by our method can achieve better performance under all metrics in the 10-fold cross-validation. Then GO and KEGG enrichment analysis are conducted to explore the biological function of the top 100 ranked genes. At last, we choose the top 10 average ranked genes as lung cancer markers and their expression boundaries are calculated and reported.

CONCLUSION

The proposed approach is effective to identify gene markers for lung cancer diagnosis. It is not only more accurate than conventional DEA methods but also provides a reliable method to identify the gene expression level boundaries.

A perspective profile of ADCY1 in cAMP signaling with drug-resistance in lung cancer

Adenylate cyclase 1 (ADCY1 or AC1) is a member of ADCY superfamily and was primarily found to be expressed in the brain. ADCY1 is responsible for catalyzing ATP to cyclic AMP (cAMP). As a secondary messenger, cAMP can regulate plenty of cellular activities. cAMP can perform its regulation in cellular transport through the binding to cAMP dependent protein kinases (PKAs), cAMP-activated guanine exchange factors (EPACs) and cyclic nucleotide-gated channels functioning in transduction of sensory signals (CNGs). Lung cancer is one of the leading factors of cancer-related death worldwide. Platinum-based chemotherapy is the first-line treatment for advanced lung cancer patients. In addition, surgical treatment, radiation treatment, and molecular targeted therapy are also therapeutic options for lung cancer patients in clinical settings. However, drug resistance and toxicity are the major obstacles that affect chemotherapy outcome and prognosis of lung cancer patients. And the therapeutic efficiency and adverse effects are varying with each individual. In recent years, investigations based on genetic sequencing have revealed the emerging role of ADCY1 mutations in affecting drug efficiency in various cancers such as lung cancer, esophageal cancer and colorectal cancer. The potential function of ADCY1 in chemotherapy resistance is of great importance to be noticed and investigated.

Comprehensive analysis of microarray expression profiles of circRNAs and lncRNAs with associated co-expression networks in human colorectal cancer

Increasing data demonstrate that circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs) play important roles in tumorigenesis. However, the mechanisms in colorectal cancer (CRC) remain unclear. Here, hundreds of significantly expressed circRNAs, and thousands of lncRNAs as well as mRNAs were identified. By qRT-PCR, one abnormal circRNA, lncRNA, and three mRNAs were verified in 24 pairs of tissues and blood samples, respectively. Then, by GO analysis, we found that the gene expression profile of linear counterparts of upregulated circRNAs in human CRC tissues preferred positive regulation of GTPase activity, cellular protein metabolic process, and protein binding, while that of downregulated circRNAs of CRC preferred positive regulation of cellular metabolic process, acetyl-CoA metabolic process, and protein kinase C activity. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that p53 signaling pathway was an important pathway in upregulated protein-coding genes, whereas cyclic guanosine monophosphate-protein kinase G (cGMP-PKG) signaling pathway was the top enriched KEGG pathway for downregulated transcripts. Furthermore, lncRNA-mRNA co-expression analysis demonstrated that downregulated lncRNA uc001tma.3 was negatively with CDC45 and positively with ELOVL4, BVES, FLNA, and HSPB8, while upregulated lncRNA NR_110882 was positively with FZD2. In addition, lncRNA-transcription factor (TF) co-expression analysis showed that the most relevant TFs were forkhead box protein A1 (FOXA1), transcription initiation factor TFIID submint 7 (TAF7), and adenovirus early region 1A(E1A)-associated protein p300 (EP300). Our findings offer a fresh view on circRNAs and lncRNAs and provide the foundation for further study on the potential roles of circRNAs and lncRNAs in colorectal cancer.

cGMP/PKG-I Pathway-Mediated GLUT1/4 Regulation by NO in Female Rat Granulosa Cells

Nitric oxide (NO) is a multifunctional gaseous molecule that plays important roles in mammalian reproductive functions, including follicular growth and development. Although our previous study showed that NO mediated 3,5,3'-triiodothyronine and follicle-stimulating hormone-induced granulosa cell development via upregulation of glucose transporter protein (GLUT)1 and GLUT4 in granulosa cells, little is known about the precise mechanisms regulating ovarian development via glucose. The objective of the present study was to determine the cellular and molecular mechanism by which NO regulates GLUT expression and glucose uptake in granulosa cells. Our results indicated that NO increased GLUT1/GLUT4 expression and translocation in cells, as well as glucose uptake. These changes were accompanied by upregulation of cyclic guanosine monophosphate (cGMP) level and cGMP-dependent protein kinase (PKG)-I protein content. The results of small interfering RNA (siRNA) analysis showed that knockdown of PKG-I significantly attenuated gene expression, translocation, and glucose uptake. Moreover, the PKG-I inhibitor also blocked the above processes. Furthermore, NO induced cyclic adenosine monophosphate response element binding factor (CREB) phosphorylation, and CREB siRNA attenuated NO-induced GLUT expression, translocation, and glucose uptake in granulosa cells. These findings suggest that NO increases cellular glucose uptake via GLUT upregulation and translocation, which are mediated through the activation of the cGMP/PKG pathway. Meanwhile, the activated CREB is also involved in the regulation. These findings indicate that NO has an important influence on the glucose uptake of granulosa cells.

Identification of the functional alteration signatures across different cancer types with support vector machine and feature analysis

Cancers are regarded as malignant proliferations of tumor cells present in many tissues and organs, which can severely curtail the quality of human life. The potential of using plasma DNA for cancer detection has been widely recognized, leading to the need of mapping the tissue-of-origin through the identification of somatic mutations. With cutting-edge technologies, such as next-generation sequencing, numerous somatic mutations have been identified, and the mutation signatures have been uncovered across different cancer types. However, somatic mutations are not independent events in carcinogenesis but exert functional effects. In this study, we applied a pan-cancer analysis to five types of cancers: (I) breast cancer (BRCA), (II) colorectal adenocarcinoma (COADREAD), (III) head and neck squamous cell carcinoma (HNSC), (IV) kidney renal clear cell carcinoma (KIRC), and (V) ovarian cancer (OV). Based on the mutated genes of patients suffering from one of the aforementioned cancer types, patients they were encoded into a large number of numerical values based upon the enrichment theory of gene ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. We analyzed these features with the Monte-Carlo Feature Selection (MCFS) method, followed by the incremental feature selection (IFS) method to identify functional alteration features that could be used to build the support vector machine (SVM)-based classifier for distinguishing the five types of cancers. Our results showed that the optimal classifier with the selected 344 features had the highest Matthews correlation coefficient value of 0.523. Sixteen decision rules produced by the MCFS method can yield an overall accuracy of 0.498 for the classification of the five cancer types. Further analysis indicated that some of these features and rules were supported by previous experiments. This study not only presents a new approach to mapping the tissue-of-origin for cancer detection but also unveils the specific functional alterations of each cancer type, providing insight into cancer-specific functional aberrations as potential therapeutic targets. This article is part of a Special Issue entitled: Accelerating Precision Medicine through Genetic and Genomic Big Data Analysis edited by Yudong Cai & Tao Huang.

Identification of a Novel 1,2,3,4-Tetrahydrobenzo[b][1,6]naphthyridine Analogue as a Potent Phosphodiesterase 5 Inhibitor with Improved Aqueous Solubility for the Treatment of Alzheimer's Disease

Phosphodiesterase 5 (PDE5) hydrolyzes cyclic guanosine monophosphate (cGMP) leading to increased levels of the cAMP response element binding protein (CREB), a transcriptional factor involved with learning and memory processes. We previously reported potent quinoline-based PDE5 inhibitors (PDE5Is) for the treatment of Alzheimer's disease (AD). However, the low aqueous solubility rendered them undesirable drug candidates. Here we report a series of novel PDE5Is with two new scaffolds, 1,2,3,4-tetrahydrobenzo[b][1,6]naphthyridine and 2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-one. Among them, compound 6c, 2-acetyl-10-((3-chloro-4-methoxybenzyl)amino)-1,2,3,4-tetrahydrobenzo[b][1,6]naphthyridine-8-carbonitrile, the most potent compound, has an excellent in vitro IC₅₀ (0.056 nM) and improved aqueous solubility as well as good efficacy in a mouse model of AD. Furthermore, we are proposing two plausible binding modes obtained through in silico docking, which provide insights into the structural basis of the activity of the two series of compounds reported herein.

CT45A1 siRNA silencing suppresses the proliferation, metastasis and invasion of lung cancer cells by downregulating the ERK/CREB signaling pathway

The aim of the present study was to investigate the role of the cancer-testis antigen family 45 member A1 (CT45A1) in the proliferation, apoptosis, invasion and metastasis of lung cancer cells, and the associated molecular mechanisms. Western blotting determined that the expression of CT45A1 in normal lung cells was far lower than that observed in lung cancer cells. Following the transfection of CT45A1 small (or short) interfering (si)RNA and its negative control into A549 cells using Lipofectamine 2000, the CT45A1 protein and mRNA levels were determined further by western blotting and reverse transcription-polymerase chain reaction. Following CT45A1 siRNA transfection, the levels of CT45A1 in lung cancer cells were markedly reduced (P<0.01). Then, cell viability and apoptosis were investigated with a methyl thiazolyl tetrazolium assay and Annexin V-FITC/propidium iodide staining, respectively. Transwell assays were employed to evaluate the migration and invasion of A549 cells. When compared with the negative control, the viability, migration and invasion of lung cancer cells treated with CT45A1 siRNA were suppressed and apoptosis was promoted (all P<0.01). In addition, the levels of B-cell lymphoma-2 (Bcl-2), Bcl-2 associated X (Bax), survivin, matrix metalloproteinase 2 (MMP2), MMP9, extracellular signal-regulated kinase 1/2 (ERK1/2), phosphorylated ERK1/2 (p-ERK1/2), cyclic AMP response element binding protein (CREB) and p-CREB were assessed by western blotting. Following CT45A1 silencing, the expressions of Bcl-2, survivin, MMP2, MMP9, p-ERK1/2 and p-CREB were downregulated and the expression of Bax was upregulated (all P<0.01). It was concluded that CT45A1 siRNA silencing suppressed the proliferation, metastasis and invasion of lung cancer cells by downregulating the ERK/CREB signalling pathway.

Pancreatic-β-cell survival and proliferation are promoted by protein kinase G type Iα and downstream regulation of AKT/FOXO1

Early studies showed nitric oxide as a pro-inflammatory-cytokine-induced toxin involved in pancreatic β-cell destruction during pathogenesis of type-1 diabetes. However, nitric oxide has both cytotoxic and cytoprotective effects on mammalian cells, depending on concentration and micro-environmental surroundings. Our studies have shown that low/physiological-level nitric oxide selectively activates protein kinase G type Iα isoform, promoting cytoprotective/pro-cell-survival effects in many cell types. In bone marrow-derived stromal/mesenchymal stem cells, protein kinase G type Iα mediates autocrine effects of nitric oxide and atrial natriuretic peptide, promoting DNA-synthesis/proliferation and cell survival. In this study, endothelial nitric oxide synthase/neuronal nitric oxide synthase inhibitor L-NIO (L-N(5)-(1-iminoethyl)ornithine), soluble guanylyl cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3,-a] quinoxalin-1-one), atrial natriuretic peptide-receptor inhibitor A71915 and protein kinase G type Iα kinase activity inhibitor DT-2 all increased apoptosis and decreased insulin secretion in RINm5F pancreatic β-cells, suggesting autocrine regulatory role for endogenous nitric oxide- and atrial natriuretic peptide-induced activation of protein kinase G type Iα. In four pancreatic β-cell lines, Beta-TC-6, RINm5F, INS-1 and 1.1B4, protein kinase G type Iα small-interfering RNA decreased phospho-serine-239-VASP (indicator of endogenous protein kinase G type Iα kinase activity), increased apoptosis and decreased proliferation. In protein kinase G type Iα-knockdown β-cell lines, expressions of phospho-protein kinase B (PKB/AKT) (AKT), phospho-Forkhead box protein O1 (FOXO1) (transcriptional repressor of pancreas duodenum homobox-1) and pancreas duodenum homobox-1 were decreased, suppressing proliferation and survival in pancreatic β-cells. The data suggest autocrine nitric oxide/atrial natriuretic peptide-induced activation of protein kinase G type Iα/p-AKT/p-FOXO1 promotes survival and proliferation in pancreatic β-cells, providing therapeutic implications for development of new therapeutic agents for diabetes.

Type II cGMP‑dependent protein kinase inhibits the migration, invasion and proliferation of several types of human cancer cells

Previous studies have indicated that type II cyclic guanosine monophosphate (cGMP)‑dependent protein kinase (PKG II) could inhibit the proliferation and migration of gastric cancer cells. However, the effects of PKG II on the biological functions of other types of cancer cells remain to be elucidated. Therefore, the aim of the present study was to investigate the effects of PKG II on cancer cells derived from various types of human tissues, including A549 lung, HepG2 hepatic, OS‑RC‑2 renal, SW480 colon cancer cells and U251 glioma cells. Cancer cells were infected with adenoviral constructs coding PKG II (Ad‑PKG II) to up‑regulate PKG II expression, and treated with 8‑(4‑chlorophenylthio) (8‑pCPT)‑cGMP to activate the kinase. A Cell Counting kit 8 assay was used to detect cell proliferation. Cell migration was measured using a Transwell assay, whereas a terminal deoxynucleotidyl transferase 2'‑deoxyuridine, 5'‑triphosphate nick‑end labeling assay was used to detect cell apoptosis. A pull‑down assay was used to investigate the activation of Ras‑related C3 botulinum toxin substrate (Rac) 1 and western blotting was used to detect the expression of proteins of interest. The present results demonstrated that EGF (100 ng/ml, 24 h) promoted the proliferation and migration of cancer cells, and it suppressed their apoptosis. In addition, treatment with EGF enhanced the activation of Rac1, and up‑regulated the protein expression of proliferating cell nuclear antigen, matrix metalloproteinase (MMP)2, MMP7 and B‑cell lymphoma (Bcl)‑2, whereas it down‑regulated the expression of Bcl‑2‑associated X protein. Transfection of cancer cells with Ad‑PKG II, and PKG II activation with 8‑pCPT‑cGMP, was identified to counteract the effects triggered by EGF. The present results suggested that PKG II may exert inhibitory effects on the proliferation and migration of various types of cancer cells.

Chronic hypoxia attenuates the vasodilator efficacy of protein kinase G in fetal and adult ovine cerebral arteries

Long-term hypoxia (LTH) attenuates nitric oxide-induced vasorelaxation in ovine middle cerebral arteries. Because cGMP-dependent protein kinase (PKG) is an important mediator of NO signaling in vascular smooth muscle, we tested the hypothesis that LTH diminishes the ability of PKG to interact with target proteins and cause vasorelaxation. Prominent among proteins that regulate vascular tone is the large-conductance Ca²⁺-sensitive K⁺ (BK) channel, which is a substrate for PKG and is responsive to phosphorylation on multiple serine/threonine residues. Given the influence of these proteins, we also examined whether LTH attenuates PKG and BK channel protein abundances and PKG activity. Middle cerebral arteries were harvested from normoxic and hypoxic (altitude of 3,820 m for 110 days) fetal and adult sheep. These arteries were denuded and equilibrated with 95% O₂-5% CO₂ in the presence of N-nitro-l-arginine methyl ester (l-NAME) to inhibit potential confounding influences of events upstream from PKG. Expression and activity of PKG-I were not significantly affected by chronic hypoxia in either fetal or adult arteries. Pretreatment with the BK inhibitor iberiotoxin attenuated vasorelaxation induced by 8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate in normoxic but not LTH arteries. The spatial proximities of PKG with BK channel α- and β1-proteins were examined using confocal microscopy, which revealed a strong dissociation of PKG with these proteins after LTH. These results support our hypothesis that hypoxia reduces the ability of PKG to attenuate vasoconstriction in part through suppression of the ability of PKG to associate with and thereby activate BK channels in arterial smooth muscle.NEW & NOTEWORTHY Using measurements of contractility, protein abundance, kinase activity, and confocal colocalization in fetal and adult ovine cerebral arteries, the present study demonstrates that long-term hypoxia diminishes the ability of cGMP-dependent protein kinase (PKG) to cause vasorelaxation through suppression of its colocalization and interaction with large-conductance Ca²⁺-sensitive K⁺ (BK) channel proteins in cerebrovascular smooth muscle. These experiments are among the first to demonstrate hypoxic changes in BK subunit abundances in fetal cerebral arteries and also introduce the use of advanced methods of confocal colocalization to study interaction between PKG and its targets.

Role of NO/VASP Signaling Pathway against Obesity-Related Inflammation and Insulin Resistance

Obesity has quickly become a worldwide pandemic, causing major adverse health outcomes such as dyslipidemia, type 2 diabetes mellitus, cardiovascular disease and cancers. Obesity-induced insulin resistance is the key for developing these metabolic disorders, and investigation to understand the molecular mechanisms involved has been vibrant for the past few decades. Of these, low-grade chronic inflammation is suggested as a critical concept in the development of obesity-induced insulin resistance, and the anti-inflammatory effect of nitric oxide (NO) signaling has been reported to be linked to improvement of insulin resistance in multiple organs involved in glucose metabolism. Recently, a body of evidence suggested that vasodilatory-stimulated phosphoprotein (VASP), a downstream mediator of NO signaling plays a crucial role in the anti-inflammatory effect and improvement of peripheral insulin resistance. These preclinical studies suggest that NO/VASP signaling could be an ideal therapeutic target in the treatment of obesity-related metabolic dysfunction. In this review, we introduce studies that investigated the protective role of NO/VASP signaling against obesity-related inflammation and insulin resistance in various tissues.

Soluble guanylate cyclase stimulators increase sensitivity to cisplatin in head and neck squamous cell carcinoma cells

Head and neck squamous cell carcinoma (HNSCC) is an aggressive and often fatal disease. Cisplatin is the most common chemotherapeutic drug in the treatment of HNSCC, but intrinsic and acquired resistance are frequent, and severe side effects occur at high doses. The second messenger cyclic GMP (cGMP) is produced by soluble guanylate cyclase (sGC). We previously reported that activation of the cGMP signaling cascade caused apoptosis in HNSCC cells, while others found that this pathway enhances cisplatin efficacy in some cell types. Here we found that sGC stimulators reduced HNSCC cell viability synergistically with cisplatin, and enhanced apoptosis by cisplatin. Moreover, the sGC stimulators effectively reduced viability in cells with acquired cisplatin resistance, and were synergistic with cisplatin. The sGC stimulator BAY 41-2272 reduced expression of the survival proteins EGFR and β-catenin, and increased pro-apoptotic Bax, suggesting a potential mechanism for the anti-tumorigenic effects of these drugs. The sGC stimulator Riociguat is FDA-approved to treat pulmonary hypertension, and others are being studied for therapeutic use in several diseases. These drugs could provide valuable addition or alternative to cisplatin in the treatment of HNSCC.

Synthesis and Characterization of 8-Nitroguanosine 3',5'-Cyclic Monophosphorothioate Rp-Isomer as a Potent Inhibitor of Protein Kinase G1α

Guanosine 3',5'-cyclic monophosphate (cGMP)-dependent protein kinases (PKG) are kinases regulating diverse physiological functions including vascular smooth muscle relaxation, neuronal synaptic plasticity, and platelet activities. Certain PKG inhibitors, such as Rp-diastereomers of derivatives of guanosine 3',5'-cyclic monophosphorothioate (Rp-cGMPS), have been designed and used to study PKG-regulated cell signaling. 8-Nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) is an endogenous cGMP derivative formed as a result of excess production of reactive oxygen species and nitric oxide. 8-Nitro-cGMP causes persistent activation of PKG1α through covalent attachment of cGMP moieties to cysteine residues of the enzyme (i.e., the process called protein S-guanylation). In this study, we synthesized a nitrated analogue of Rp-cGMPS, 8-nitroguanosine 3',5'-cyclic monophosphorothioate Rp-isomer (Rp-8-nitro-cGMPS), and investigated its effects on PKG1α activity. We synthesized Rp-8-nitro-cGMPS by reacting Rp-8-bromoguanosine 3',5'-cyclic monophosphorothioate (Rp-8-bromo-cGMPS) with sodium nitrite. Rp-8-Nitro-cGMPS reacted with the thiol compounds cysteine and glutathione to form Rp-8-thioalkoxy-cGMPS adducts to a similar extent as did 8-nitro-cGMP. As an important finding, a protein S-guanylation-like modification was clearly observed, by using Western blotting, in the reaction between recombinant PKG1α and Rp-8-nitro-cGMPS. Rp-8-Nitro-cGMPS inhibited PKG1α activity with an inhibitory constant of 22 µM in a competitive manner. An organ bath assay with mouse aorta demonstrated that Rp-8-nitro-cGMPS inhibited vascular relaxation induced by acetylcholine or 8-bromo-cGMP more than Rp-8-bromo-cGMPS did. These findings suggest that Rp-8-nitro-cGMPS inhibits PKG through induction of an S-guanylation-like modification by attaching the Rp-cGMPS moiety to the enzyme. Additional study is warranted to explore the potential application of Rp-8-nitro-cGMPS to biochemical and therapeutic research involving PKG1α activation.

PKG-1α mediates GATA4 transcriptional activity

GATA4, a zinc-finger transcription factor, is central for cardiac development and diseases. Here we show that GATA4 transcriptional activity is mediated by cell signaling via cGMP dependent PKG-1α activity. Protein kinase G (PKG), a serine/tyrosine specific kinase is the major effector of cGMP signaling. We observed enhanced transcriptional activity elicited by co-expressed GATA4 and PKG-1α. Phosphorylation of GATA4 by PKG-1α was detected on serine 261 (S261), while the C-terminal activation domain of GATA4 associated with PKG-1α. GATA4's DNA binding activity was enhanced by PKG-1α via by both phosphorylation and physical association. More importantly, a number of human disease-linked GATA4 mutants exhibited impaired S261 phosphorylation, pointing to defective S261 phosphorylation in the elaboration of human heart diseases. We showed S261 phosphorylation was favored by PKG-1α but not by PKA, and several other kinase signaling pathways such as MAPK and PKC. Our observations demonstrate that cGMP-PKG signaling mediates transcriptional activity of GATA4 and links defective GATA4 and PKG-1α mutations to the development of human heart disease.

Drug repositioning for non-small cell lung cancer by using machine learning algorithms and topological graph theory

Background

Non-small cell lung cancer (NSCLC) is one of the leading causes of death globally, and research into NSCLC has been accumulating steadily over several years. Drug repositioning is the current trend in the pharmaceutical industry for identifying potential new uses for existing drugs and accelerating the development process of drugs, as well as reducing side effects.

Results

This work integrates two approaches - machine learning algorithms and topological parameter-based classification - to develop a novel pipeline of drug repositioning to analyze four lung cancer microarray datasets, enriched biological processes, potential therapeutic drugs and targeted genes for NSCLC treatments. A total of 7 (8) and 11 (12) promising drugs (targeted genes) were discovered for treating early- and late-stage NSCLC, respectively. The effectiveness of these drugs is supported by the literature, experimentally determined in-vitro IC₅₀ and clinical trials. This work provides better drug prediction accuracy than competitive research according to IC₅₀ measurements.

Conclusions

With the novel pipeline of drug repositioning, the discovery of enriched pathways and potential drugs related to NSCLC can provide insight into the key regulators of tumorigenesis and the treatment of NSCLC. Based on the verified effectiveness of the targeted drugs predicted by this pipeline, we suggest that our drug-finding pipeline is effective for repositioning drugs.

The cyclic GMP/protein kinase G pathway as a therapeutic target in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is an aggressive disease with high mortality. Treatments, which can result in significant morbidity, have not substantially changed in three decades. The second messenger cyclic GMP (cGMP), which targets protein kinase G (PKG), is generated by guanylate cyclases (GCs), and is rapidly hydrolyzed by phosphodiesterases (PDEs). Activation of the cGMP/PKG pathway is antineoplastic in several cancer types, but its impact on HNSCC has not been fully exploited. We found differential expression of critical components of this pathway in four HNSCC cell lines. Several activators of soluble GC (sGC), as well as inhibitors of PDE5, increased intracellular cGMP, reduced cell viability, and induced apoptosis in HNSCC cells. The apoptotic effects of the sGC activator BAY 41-2272 and the PDE5 inhibitor Tadalafil (Cialis) were mediated by PKG. Furthermore, Tadalafil substantially reduced the growth of CAL27-derived tumors in athymic mice. Several drugs which either activate sGC or inhibit PDE5 are approved for treatment of nonmalignant conditions. These drugs could be repurposed as novel and effective therapeutics in patients with head and neck cancer.

Scutellarin's Cardiovascular Endothelium Protective Mechanism: Important Role of PKG-Iα

Scutellarin (SCU), a flavonoid glycoside compound, has been successfully used in clinic for treatment of ischemic diseases in China. In this report, we checked the effects of SCU on endothelium dysfunction (ED) of coronary artery (CA) against myocardial ischemia reperfusion (MIR) injury in vivo. The involvement of PKG-Iα was further studied using cultured endothelial cells subjected to hypoxia reoxygenation (HR) injury in vitro. In rat MIR model, SCU (45 and 90 mg/kg, iv) significantly reduced ischemic size and restored the endothelium-dependent vasodilation of isolated CA rings. PKG inhibitor Rp-8-Br-cGMP (50 μg/kg, iv) could ameliorate the protective effects of SCU. Increase in phosphorylation of vasodilator-stimulated phosphoprotein (VASP), a main substrate of PKG, at Ser 239 was observed in both heart tissue and serum of SCU-treated animals. In cultured human cardiac microvascular endothelial cells (HCMECs), SCU (1 and 10 μM) dose-dependently protected cell viability and increased the mRNA and protein level of PKG-Iα against HR injury. The activity of PKG was also increased by SCU treatment. The activation of PKG–1α was then studied using targeted proteomic analysis (MRM-MS) checking the phosphorylation state of the autophosphorylation domain (aa42-94). Significant decrease in phosphorylation of PKG-Iα at Ser50, Ser72, Ser89 was induced by HR injury while SCU treatment significantly increased the phosphorylation of PKG-Iα, not only at Ser50, Ser72 and Ser89, but also at Ser44 and Thr58 (two novel phosphorylation domains). Our results demonstrate PKG-Iα might play an important role in the protective effects of SCU on ED against MIR injury.

Hydrogen peroxide - production, fate and role in redox signaling of tumor cells

Hydrogen peroxide (H₂O₂) is involved in various signal transduction pathways and cell fate decisions. The mechanism of the so called “redox signaling” includes the H₂O₂-mediated reversible oxidation of redox sensitive cysteine residues in enzymes and transcription factors thereby altering their activities. Depending on its intracellular concentration and localization, H₂O₂ exhibits either pro- or anti-apoptotic activities. In comparison to normal cells, cancer cells are characterized by an increased H₂O₂ production rate and an impaired redox balance thereby affecting the microenvironment as well as the anti-tumoral immune response. This article reviews the current knowledge about the intracellular production of H₂O₂ along with redox signaling pathways mediating either the growth or apoptosis of tumor cells. In addition it will be discussed how the targeting of H₂O₂-linked sources and/or signaling components involved in tumor progression and survival might lead to novel therapeutic targets.

Capillary Isoelectric Focusing Immunoassay for Fat Cell Differentiation Proteomics

Profiling cellular proteome is critical to understanding signal integration during cell fate determination. In this study, the capability of capillary isoelectric focusing (cIEF) immunoassays to detect post-translational modifications (PTM) of protein isoforms is demonstrated. cIEF immunoassays exhibit protein detection sensitivity at up to 5 orders of magnitude higher than traditional methods. This detection ultra-sensitivity permits proteomic profiling of several nanograms of tissue samples. cIEF immunoassays are employed to simultaneously profile three protein kinases during fat cell differentiation: cGMP-dependent protein kinase type I (PKG-I) of the nitric oxide (NO) signaling pathway, protein kinase B (Akt) of the insulin signaling pathway, and extracellular signal-regulated kinase (ERK) of the mitogen-activated protein kinase (MAPK) signaling pathway. Interestingly, a switch in the expression level of PKG- isoforms is observed during fat cell differentiation. While both PKG-Iα and PKG-Iβ isoforms are present in preadipocytes, only PKG-Iβ isoform is expressed in adipocytes. On the other hand, the phosphorylation level increases for Akt while decreases for ERK1 and ERK2 following the maturation of preadipocytes into adipocytes. Taken together, cIEF immunoassay provides a highly sensitive means to study fat cell differentiation proteomics. cIEF immunoassay should be a powerful proteomics tool to study complex protein signal integration in biological systems.

Hyperglycemia down-regulates cGMP-dependent protein kinase I expression in first trimester cytotrophoblast cells

Diabetes in pregnancy is associated with microvascular complications and a higher incidence of preeclampsia. The regulatory signaling pathways involving nitric oxide, cGMP, and cGMP-dependent protein kinase (PKG) have been shown to be down-regulated under diabetic conditions and contribute to the pathogenesis of vascular complications in diabetes. The present study was undertaken to investigate how high glucose concentrations regulate PKG expression in cytotrophoblast cells (CTBs). Human CTBs (Sw. 71) were treated with 45, 135, 225, 495, or 945 mg/dL glucose for 48 h. Some cells were pretreated with a p38 inhibitor (10 μM SB203580) or 10 μM rosiglitazone. After treatment, the cell lysates were subjected to measure the expression of protein kinase G1α (PKG1α), protein kinase G1β (PKG1β), soluble guanylate cyclase 1α (sGC1α), and soluble guanylate cyclase 1 β (sGC1β) by Western blot. Statistical comparisons were performed using analysis of variance with Duncan's post hoc test. The expressions of PKG1α, PKG1β, sGC1α, and sGC1β were significantly down-regulated (p < 0.05) in CTBs treated with >135 mg/dL glucose compared to basal (45 mg/dL). The hyperglycemia-induced down-regulation of cGMP and cGMP-dependent PKG were attenuated by the SB203580 or rosiglitazone pretreatment. Exposure of CTBs to excess glucose down-regulates cGMP and cGMP-dependent PKG, contributing to the development of vascular complications in diabetic mothers during pregnancy. The attenuation of hyperglycemia-induced down-regulation of PKG proteins by SB203580 or rosiglitazone pretreatment further suggests the involvement of stress signaling mechanisms in this process.

Synaptic therapy in Alzheimer's disease: a CREB-centric approach

Therapeutic attempts to cure Alzheimer's disease (AD) have failed, and new strategies are desperately needed. Motivated by this reality, many laboratories (including our own) have focused on synaptic dysfunction in AD because synaptic changes are highly correlated with the severity of clinical dementia. In particular, memory formation is accompanied by altered synaptic strength, and this phenomenon (and its dysfunction in AD) has been a recent focus for many laboratories. The molecule cyclic adenosine monophosphate response element-binding protein (CREB) is at a central converging point of pathways and mechanisms activated during the processes of synaptic strengthening and memory formation, as CREB phosphorylation leads to transcription of memory-associated genes. Disruption of these mechanisms in AD results in a reduction of CREB activation with accompanying memory impairment. Thus, it is likely that strategies aimed at these mechanisms will lead to future therapies for AD. In this review, we will summarize literature that investigates 5 possible therapeutic pathways for rescuing synaptic dysfunction in AD: 4 enzymatic pathways that lead to CREB phosphorylation (the cyclic adenosine monophosphate cascade, the serine/threonine kinases extracellular regulated kinases 1 and 2, the nitric oxide cascade, and the calpains), as well as histone acetyltransferases and histone deacetylases (2 enzymes that regulate the histone acetylation necessary for gene transcription).

Nitric oxide confers cisplatin resistance in human lung cancer cells through upregulation of aldo-keto reductase 1B10 and proteasome

In this study, we show that exposure of human lung cancer A549 cells to cisplatin (cis-diamminedichloroplatinum, CDDP) promotes production of nitric oxide (NO) through generation of reactive oxygen species (ROS) and resulting upregulation of inducible NO synthase (iNOS). The incubation of the cells with a NO donor, diethylenetriamine NONOate, not only reduced the CDDP-induced cell death and apoptotic alterations (induction of CCAAT-enhancer-binding protein homologous protein and caspase-3 activation), but also elevated proteolytic activity of 26S proteasome, suggesting that the activation of proteasome function contributes to the reduction of CDDP sensitivity by NO. Monitoring expression levels of six aldo-keto reductases (AKRs) (1A1, 1B1, 1B10, 1C1, 1C2, and 1C3) during the treatment with the NO donor and subsequent CDDP sensitivity test using the specific inhibitors also proposed that upregulation of AKR1B10 by NO is a key process for acquiring the CDDP resistance in A549 cells. Treatment with CDDP and NO increased amounts of nitrotyrosine protein adducts, indicative of peroxynitrite formation, and promoted the induction of AKR1B10, inferring a relationship between peroxynitrite formation and the enzyme upregulation in the cells. The treatment with CDDP or a ROS-related lipid aldehyde, 4-hydroxy-2-nonenal, facilitated the iNOS upregulation, which was restored by increasing the AKR1B10 expression. In contrast, the facilitation of NO production by CDDP treatment was hardly observed in AKR1B10-overexpressing A549 cells and established CDDP-resistant cancer cells (A549, LoVo, and PC3). Collectively, these results suggest the NO functions as a key regulator controlling AKR1B10 expression and 26S proteasome function leading to gain of the CDDP resistance.

Bimodal oscillations of cyclic nucleotide concentrations in the circadian system of the Madeira cockroach Rhyparobia maderae

Pigment-dispersing factor (PDF) is the most important coupling factor of the circadian system in insects, comparable to its functional ortholog vasoactive intestinal polypeptide of the mammalian circadian clock. In Drosophila melanogaster, PDF signals via activation of adenylyl cyclases, controlling circadian locomotor activity rhythms at dusk and dawn. In addition, PDF mediates circadian rhythms of the visual system and is involved in entrainment to different photoperiods. We examined whether PDF daytime-dependently elevates cAMP levels in the Madeira cockroach Rhyparobia maderae and whether cAMP mimics PDF effects on locomotor activity rhythms. To determine time windows of PDF release, we searched for circadian rhythms in concentrations of cAMP and its functional opponent cGMP in the accessory medulla (AMe), the insect circadian pacemaker controlling locomotor activity rhythms, and in the optic lobes, as the major input and output area of the circadian clock. Enzyme-linked immunosorbent assays detected PDF-dependent increases of cAMP in optic lobes and daytime-dependent oscillations of cAMP and cGMP baseline levels in the AMe, both with maxima at dusk and dawn. Although these rhythms disappeared at the first day in constant conditions (DD1), cAMP but not cGMP oscillations returned at the second day in constant conditions (DD2). Whereas in light-dark cycles the cAMP baseline level remained constant in other optic lobe neuropils, it oscillated in phase with the AMe at DD2. To determine whether cAMP and cGMP mimic PDF-dependent control of locomotor activity rhythms, both cyclic nucleotides were injected at different times of the circadian day using running-wheel assays. Whereas cAMP injections generated delays at dusk and advances at dawn, cGMP only delayed locomotor activity at dusk. For the first time we found PDF-dependent phase advances at dawn in addition to previously described phase delays at dusk. Thus, we hypothesize that PDF release at dusk and dawn controls locomotor activity rhythms and visual system processing cAMP-dependently.

Interlude of cGMP and cGMP/protein kinase G type 1 in pancreatic adenocarcinoma cells

OBJECTIVE

cAMP and cGMP signaling is important both for normal and cancer cells. This signaling is controlled by adenylyl and guanylyl cyclases and cyclic nucleotide phosphodiesterases. One of the direct targets for cGMP is protein kinase G (PKG). The main aim of this work was to investigate cGMP and PKG signaling in pancreatic adenocarcinoma (PDAC) cells.

METHODS

The PKG activity, cGMP, and calcium level were measured with the CycLex Cyclic GMP dependent protein kinase (cGK) Assay Kit, the DetectX Cyclic GMP Colorimetric EIA Kit, and the Fluo-4 NW Calcium Assay Kit, respectively. The Proteome Profiler Array was done using Human Phospho-Kinase Array and Human Phospho-MAPK Array Kits.

RESULTS

This study shows for the first time that functional PKG1 is expressed in PDAC cells. It demonstrates that the specific PKG1 inhibitor, DT3, induces cytotoxicity through necrosis and reduces proliferation and migration of PDAC cells. Moreover, ERK1/2 and p38 can be considered as potential targets for PKG1 in PDAC cells. In addition, the study shows that phosphodiesterases and nitric oxide-guanylyl cyclases regulate the cGMP level in PDAC cells, affecting the proliferation of the cells.

CONCLUSIONS

The cGMP and PKG signaling may be a target for developing new therapeutic approaches for PDAC.

cGMP signaling as a target for the prevention and treatment of breast cancer

One in eight women in the United States will be diagnosed with invasive breast cancer in her lifetime. Advances in therapeutic strategies, diagnosis, and improved awareness have resulted in a significant reduction in breast cancer related mortality. However, there is a continued need for more effective and less toxic drugs for both the prevention and the treatment of breast cancer in order to see a continued decline in the morbidity and mortality associated with this disease. Recent studies suggest that the cGMP signaling pathway may be aberrantly regulated in breast cancer. As such, this pathway may serve as a source of novel targets for future breast cancer drug discovery efforts. This review provides an overview of cGMP signaling in normal physiology and in breast cancer as well as current strategies being investigated for targeting this pathway in breast cancer.

The role of cyclic nucleotide signaling pathways in cancer: targets for prevention and treatment

For more than four decades, the cyclic nucleotides cyclic AMP (cAMP) and cyclic GMP (cGMP) have been recognized as important signaling molecules within cells. Under normal physiological conditions, cyclic nucleotides regulate a myriad of biological processes such as cell growth and adhesion, energy homeostasis, neuronal signaling, and muscle relaxation. In addition, altered cyclic nucleotide signaling has been observed in a number of pathophysiological conditions, including cancer. While the distinct molecular alterations responsible for these effects vary depending on the specific cancer type, several studies have demonstrated that activation of cyclic nucleotide signaling through one of three mechanisms-induction of cyclic nucleotide synthesis, inhibition of cyclic nucleotide degradation, or activation of cyclic nucleotide receptors-is sufficient to inhibit proliferation and activate apoptosis in many types of cancer cells. These findings suggest that targeting cyclic nucleotide signaling can provide a strategy for the discovery of novel agents for the prevention and/or treatment of selected cancers.

Induction of chemoresistance by all-trans retinoic acid via a noncanonical signaling in multiple myeloma cells

Despite the successful application of all-trans retinoic acid (ATRA) in multiple myeloma treatment, ATRA-induced chemoresistance in the myeloma patients is very common in clinic. In this study, we evaluated the effect of ATRA on the expression of apurinic endonuclease/redox factor-1 (Ape/Ref-1) in the U266 and RPMI-8226 myeloma cells to explore the chemoresistance mechanism involved. ATRA treatment induced upregulation of Ape/Ref-1 via a noncanonical signaling pathway, leading to enhanced pro-survival activity counteracting melphalan (an alkylating agent). ATRA rapidly activated p38-MSK (mitogen- and stress activated protein kinase) cascade to phosphorylate cAMP response element-binding protein (CREB). Phosphorylated CREB was recruited to the Ape/Ref-1 promoter to evoke the gene expression. The stimulation of ATRA on Ape/Ref-1 expression was attenuated by either p38-MSK inhibitors or overexpression of dominant-negative MSK1 mutants. Moreover, ATRA-mediated Ape/Ref-1 upregulation was correlated with histone modification and activation of CBP/p300, an important cofactors for CREB transcriptional activity. C646, a competitive CBP/p300 inhibitor, abolished the upregulation of Ape/Ref-1 induced by ATRA. Intriguingly, CBP rather than p300 played a dominant role in the expression of Ape/Ref-1. Hence, our study suggests the existence of a noncanonical mechanism involving p38-MSK-CREB cascade and CBP induction to mediate ATRA-induced Ape/Ref-1 expression and acquired chemoresistance in myeloma cells.

Protective effect of survivin in Doxorubicin-induced cell death in h9c2 cardiac myocytes

BACKGROUND AND OBJECTIVES

Apoptosis has been known to be an important mechanism of doxorubicin-induced cardiotoxicity. Survivin, which belongs to the inhibitor of apoptosis protein family, is associated with apoptosis and alteration of the cardiac myocyte molecular pathways. Therefore, we investigated the anti-apoptotic effect and cellular mechanisms of survivin using a protein delivery system in a doxorubicin-induced cardiac myocyte injury model.

MATERIALS AND METHODS

We constructed a recombinant survivin which was fused to the protein transduction domain derived from HIV-TAT protein. In cultured H9c2 cardiac myocytes, TAT-survivin (1 µM) was added for 1 hour prior to doxorubicin (1 µM) treatment for 24 hours. Cell viability and apoptosis were evaluated by 2-(4,5-dimethyltriazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, caspase-3 activity, and terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling assay. We measured the expression levels of several apoptosis-related signal proteins.

RESULTS

The survivin level was significantly reduced in a dose dependent manner up to 1 µM of doxorubicin in concentration. Purified recombinant TAT-survivin protein was efficiently delivered to H9c2 cardiac myocytes, and its transduction showed an anti-apoptotic effect, demonstrated by reduced caspase-3 activity and the apoptotic index, concomitantly with increased cell viability against doxorubicin injury. The phosphorylation of p38 mitogen-activated protein (MAP) kinase and the release of Smac from mitochondria were suppressed and the expression levels of Bcl-2 and cAMP response element-binding protein (CREB), the transcription factor of Bcl-2, were recovered following TAT-survivin transduction, indicating that survivin had an anti-apoptotic effect against doxorubicin injury.

CONCLUSION

Our results suggest that survivin has a potentially cytoprotective effect against doxorubicin-induced cardiac myocyte apoptosis through mechanisms that involve a decrease in the phosphorylation of p38 MAP kinase, mitochondrial Smac release, and increased expression of Bcl-2 and CREB.

Lipoxin A(4) activates alveolar epithelial sodium channel, Na,K-ATPase, and increases alveolar fluid clearance

Edema fluid resorption is critical for gas exchange, and both alveolar epithelial sodium channel (ENaC) and Na,K-ATPase are accredited with key roles in the resolution of pulmonary edema. Alveolar fluid clearance (AFC) was measured in in situ ventilated lungs by instilling isosmolar 5% BSA solution with Evans Blue-labeled albumin tracer (5 ml/kg) and measuring the change in Evans Blue-labeled albumin concentration over time. Treatment with lipoxin A4 and lipoxin receptor agonist (5(S), 6(R)-7-trihydroxymethyl 17 heptanoate) significantly stimulated AFC in oleic acid (OA)-induced lung injury, with the outcome of decreased pulmonary edema. Lipoxin A4 and 5(S), 6(R)-7-trihydroxymethyl 17 heptanoate not only up-regulated the ENaC α and ENaC γ subunits protein expression, but also increased Na,K-ATPase α1 subunit protein expression and Na,K-ATPase activity in lung tissues. There was no significant difference of intracellular cAMP level between the lipoxin A4 treatment and OA group. However, the intracellular cGMP level was significantly decreased after lipoxin A4 treatment. The beneficial effects of lipoxin A4 were abrogated by butoxycarbonyl-Phe-Leu-Phe-Leu-Ph (lipoxin A4 receptor antagonist) in OA-induced lung injury. In primary rat alveolar type II epithelial cells stimulated with LPS, lipoxin A4 increased ENaC α and ENaC γ subunits protein expression and Na,K-ATPase activity. Lipoxin A4 stimulated AFC through activation of alveolar epithelial ENaC and Na,K-ATPase.

cGMP-dependent protein kinase Iβ regulates breast cancer cell migration and invasion via interaction with the actin/myosin-associated protein caldesmon

The two isoforms of type I cGMP-dependent protein kinase (PKGIα and PKGIβ) differ in their first ∼100 amino acids, giving each isoform unique dimerization and autoinhibitory domains. The dimerization domains form coiled-coil structures and serve as platforms for isoform-specific protein-protein interactions. Using the PKGIβ dimerization domain as an affinity probe in a proteomic screen, we identified the actin/myosin-associated protein caldesmon (CaD) as a PKGIβ-specific binding protein. PKGIβ phosphorylated human CaD on serine 12 in vitro and in intact cells. Phosphorylation on serine 12 or mutation of serine 12 to glutamic acid (S12E) reduced the interaction between CaD and myosin IIA. Because CaD inhibits myosin ATPase activity and regulates cell motility, we examined the effects of PKGIβ and CaD on cell migration and invasion. Inhibition of the NO/cGMP/PKG pathway reduced migration and invasion of human breast cancer cells, whereas PKG activation enhanced their motility and invasion. siRNA-mediated knockdown of endogenous CaD had pro-migratory and pro-invasive effects in human breast cancer cells. Reconstituting cells with wild-type CaD slowed migration and invasion; however, CaD containing a phospho-mimetic S12E mutation failed to reverse the pro-migratory and pro-invasive activity of CaD depletion. Our data suggest that PKGIβ enhances breast cancer cell motility and invasive capacity, at least in part, by phosphorylating CaD. These findings identify a pro-migratory and pro-invasive function for PKGIβ in human breast cancer cells, suggesting that PKGIβ is a potential target for breast cancer treatment.

cGMP-Dependent Protein Kinase Inhibitors in Health and Disease

cGMP-dependent protein kinases (PKG) exhibit diverse physiological functions in the mammalian system e.g., in vascular and gastrointestinal smooth muscles, in platelets, in kidney, in bone growth, nociception and in the central nervous system. Furthermore, PKG were found in insects and in the malaria parasite Plasmodium falciparum. Two different genes of PKG exist: a) the PKG-I gene that is expressed as cytosolic PKG-Iα or PKG-Iβ isoform, and b) the PKG-II gene, which expresses the membrane associated PKG-II protein. The enzyme kinetics, the localization and the substrates of these PKG enzymes differ utilizing different physiological functions. Various inhibitors of PKG were developed directed against diverse functional regions of the kinase. These inhibitors of PKG have been used to analyse the specific functions of these enzymes. The review article will summarize these different inhibitors regarding their specificity and their present applications in vitro and in vivo. Furthermore, it will be discussed that the distinct inhibition of the PKG enzymes could be used as a valuable pharmacological target e.g., in the treatment of cardiovascular diseases, diarrhea, cancer or malaria.