Cyclic AMP and cyclic GMP phosphodiesterase activities in Hodgkin's disease lymphocytes

Germline Variants in Phosphodiesterase Genes and Genetic Predisposition to Pediatric Adrenocortical Tumors

Phosphodiesterases (PDEs) form a superfamily of enzymes that catalyze the hydrolysis of cyclic nucleotides adenosine 3′5′-cyclic monophosphate (cAMP) and guanosine 3′5′-cyclic monophosphate (cGMP) to their inactive 5′ monophosphates. cAMP plays a critical role as a second messenger in endocrine tissues, and activation of cAMP signaling has been reported in endocrine tumors. Germline variants in PDEs have been associated with benign cortisol-secreting adrenocortical adenomas and testicular germ cell cancer but not adrenocortical carcinoma. We performed whole genome sequencing (WGS) and whole exome sequencing (WES) of paired blood and tumor samples from 37 pediatric adrenocortical tumors (ACTs). Germline inactivating variants in PDEs were observed in 9 of 37 (24%) patients. Tumor DNA analysis revealed loss of heterozygosity, with maintenance of the mutated allele in all cases. Our results suggest that germline variants in PDEs and other regulators of the cAMP-signaling pathway may contribute to pediatric adrenocortical tumorigenesis, perhaps by cooperating with germline hypomorphic mutant TP53 alleles and uniparental disomy of chromosome 11p15 (Beckwith–Wiedemann syndrome).

DHA induces apoptosis of human malignant breast cancer tissues by the TLR-4/PPAR-α pathways

Docosahexaenoic acid (DHA) oil is an important polyunsaturated fatty acid for the human body. Evidence has demonstrated that DHA is beneficial for inhibiting mammary carcinogenesis. However, the mechanisms of DHA mediating apoptosis induction have not been fully elucidated. Thus, in the present study, the activity levels of total-superoxide dismutase (t-SOD), catalase (CAT), glutathione-peroxidase (GSH-PX) and the concentration of malondialdehyde (MDA) were determined in DHA oil-treated human malignant breast tissues. The results revealed that compared with control, DHA significantly increased the main antioxidant enzymes levels, including t-SOD, CAT, and GSH-PX, but decreased the MDA concentration in the DHA oil treated breast cancer tissues. Furthermore, DHA significantly increased the ratio of cyclic (c)AMP/cGMP levels and promoted the expression of Toll-like receptor 4 (TLR-4) and peroxisome proliferator activated receptor (PPAR)-α, thus DHA induced breast cancer cell apoptosis. We hypothesized that the levels of TLR-4 and PPAR-α are involved in the antitumorigenesis properties of DHA in breast cancer. The results of the present study hold significance for the further clinical development of DHA oil in breast cancer treatment.

Therapeutic potentials of natural compounds acting on cyclic nucleotide phosphodiesterase families

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

Effects of tobacco constituents and psychological stress on the beta-adrenergic regulation of non-small cell lung cancer and pancreatic cancer: implications for intervention

This review summarizes current preclinical and clinical evidence in support of the hypothesis that smoking and psychological stress have significant cancer promoting effects on non small cell lung cancer and pancreatic cancer via direct and indirect effects on nicotinic receptor-regulated beta-adrenergic signaling. Evidence is provided that targeted pharmacological interference with the resulting hyperactive cAMP-dependent signaling by beta-blockers or by γ-aminobutyric acid as well as positive psychological influences may be highly effective in preventing and improving clinical outcomes of these cancers, provided that appropriate diagnostic protocols are followed to monitor systemic levels of stress neurotransmitters and cAMP.

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.

t(4;8)(q27;q24) in Hodgkin lymphoma cells targets phosphodiesterase PDE5A and homeobox gene ZHX2

Hodgkin/Reed-Sternberg (HRS) cells represent the malignant fraction of infiltrated lymph nodes in Hodgkin lymphoma (HL). Although HRS cells display multiple chromosomal aberrations, few are recurrent and the targeted genes unknown. However, understanding the pathology of HL and developing rational therapies may well require identifying putative deregulated genes. Here, we analyzed the karyotype of the well-defined HL cell line L-1236 by spectral karyotyping and identified multiple abnormalities, therein, notably t(4;8)(q27;q24) which includes two breakpoint regions previously highlighted in HL. Target genes at 4q27 and 8q24 were shortlisted by high density genomic arrays and fluorescence in situ hybridization. Expression analysis of candidate target genes revealed conspicuous activation of phosphodiesterase PDE5A at 4q27 and inhibition of homeobox gene ZHX2 at 8q24. Treatment of L-1236 with PDE5A-inhibitor sildenafil or with siRNA directed against PDE5A and concomitant stimulation with cyclic guanosine monophosphate (cGMP) resulted in enhanced apoptosis, indicating PDE5A as an oncogene. Expression profiling of L-1236 cells following siRNA-mediated knockdown of ZHX2 showed inhibition of genes regulating differentiation and apoptosis, suggesting tumor suppressor activity of ZHX2. Downstream genes included STAT1 and several STAT1-target genes, indicating activation of STAT1-signaling by ZHX2 as analyzed by RQ-PCR and western blot. Taken together, we have identified a novel aberration with recurrent breakpoints in HL, t(4;8)(q27;q24), which activate PDE5A and repress ZHX2, deregulating apoptosis, differentiation, and STAT1-signaling in HL cells.

Novel protein inhibitor of calmodulin-dependent cyclic nucleotide phosphodiesterase from glioblastoma multiforme

Previous investigations from our laboratory have demonstrated a significant reduction in the catalytic function of the 60 kDa and 63 kDa isozymes of calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) when comparing human cerebral tissue that was free of tumor and glioblastoma multiforme (GBM) and gliosarcoma [Lal S., Raju R. V. S., Macaulay R. B. J., and Sharma R. K. (1996) Can. J. Neurol. Sci., 23, 245-250]. The results suggested the possibility of an endogenously produced inhibitor of CaMPDE expressed in these tumors. Further investigation has initially characterized the presence of a heat-labile, protein inhibitor of both the 60 kDa and 63 kDa isozymes of CaMPDE. Sephacryl S-200 gel filtration column chromatography indicated that the inhibitor has an apparent molecular weight of 22 kDa and experimental evidence demonstrates that this inhibitor protein may act independently of calmodulin, and is therefore a novel CaMPDE inhibitor. Previous work on non-CNS tumors has shown high levels of CaMPDE activity and absence of an inhibitor. This suggests that a different mechanism may exist for the proliferation of these subsets of tumors.

Calmodulin-dependent cyclic nucleotide phosphodiesterase in human cerebral cortex and glioblastoma multiforme

BACKGROUND

Calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) has been extensively studied and characterized in normal mammalian tissues; however very little is known about this enzyme in human brain tumors. It has been established that high levels of this enzyme exist in non-central nervous system tumors, PDE inhibitors or cAMP analogues have been used to treat them. This study has examined the levels of CaMPDE in glioblastoma multiforme from six patients and has compared these to the levels of CaMPDE in four patients with normal cerebral tissue. In addition, an enzyme immune assay method (EIA) was developed in this study for the detection of CaMPDE in human cerebral tissue. This method is proposed to be used as an adjunct to the spectrophotometric method presently utilized. This would be beneficial in cases where small tissue samples, for example in stereotactic biopsy, are available.

METHODS

The CaMPDE activity and corresponding levels of expression in cerebral tissue from temporal lobectomies and both surgical extraction or stereotactic biopsy in patients with primary tumors were determined by spectrophotometric and EIA, respectively. The EIA was developed from the production of a polyclonal antibody against bovine brain 60 kDa CaMPDE isozyme. Cross reactivity of the antibody with human was confirmed using transblot and immunohistochemistry.

RESULTS

Utilising the EIA, there was found to be significant reduction in both catalytic activity (p < 0.001) and in quantitative protein expression (p < 0.001) in glioblastoma multiforme from patients when compared to normal cerebral cortex. Immunoblotting experiments and immunohistochemistry demonstrated that CaMPDE in glioblastoma multiforme failed to react with a polyclonal antibody raised against bovine brain 60 kDa CaMPDE isozyme, whereas the enzyme from normal tissue reacted with antibody.

CONCLUSIONS

Contrary to other studies on non-CNS tumors, the catalytic activity and the protein expression of CaMPDE is reduced in glioblastoma multiforme. The EIA method is a more sensitive in detecting CaMPDE than in the spectrophotometric method, especially when a small amount of tissue is available. Immunohistochemistry and the EIA may be useful in the future to use as markers for other types of brain tumors and not for glioblastoma multiforme as demonstrated.

Characterization of cyclic nucleotide phosphodiesterases from cultured bovine aortic endothelial cells

Experiments were carried out in order to isolate and characterize the cyclic nucleotide phosphodiesterase activities in primary and low passages of cultured bovine aortic endothelial cells. The subcellular characterization of the cyclic nucleotide hydrolytic activity showed that both cAMP and cGMP hydrolytic activities were predominant in the cytosolic rather than the particulate fraction of the endothelial cell homogenate. At a low substrate concentration (0.25 microM), the major hydrolytic activity was for cAMP while at a high concentration (20 microM) it was for both cAMP and cGMP. Both cAMP and cGMP hydrolytic activities were insensitive to calmodulin. Cytosolic cyclic nucleotide phosphodiesterase activity was resolved into two distinct phosphodiesterase forms using HPLC. The first eluted form was designated cGS-PDE: it hydrolysed both cAMP and cGMP and its cAMP hydrolytic activity was markedly enhanced by the presence of cGMP. The second form was designated cAMP-PDE: it selectively hydrolysed cAMP. The cytosolic cAMP-PDE was inhibited by micromolar concentrations of cAMP-PDE inhibitors such as trequinsin, rolipram, dipyridamole or papaverine. The cGS-PDE was inhibited by micromolar concentrations of trequinsin, dipyridamole and papaverine and was insensitive to rolipram, except for the hydrolysis of cAMP which was inhibited in the micromolar range. Both the cAMP-PDE and the cGS-PDE were relatively insensitive to the selective cGMP-PDE inhibitor, zaprinast which was about 750-fold less potent on endothelial PDEs than on smooth muscle cGMP-PDE. The identification of selective and specific PDE inhibitors of the different PDE forms may allow a better understanding of the regulation and the role of cyclic nucleotides in endothelial cells.