PRUNE1 and NME/NDPK family proteins influence energy metabolism and signaling in cancer metastases.

We describe here the molecular basis of the complex formation of PRUNE1 with the tumor metastasis suppressors NME1 and NME2, two isoforms appertaining to the nucleoside diphosphate kinase (NDPK) enzyme family, and how this complex regulates signaling the immune system and energy metabolism, thereby shaping the tumor microenvironment (TME). Disrupting the interaction between NME1/2 and PRUNE1, as suggested, holds the potential to be an excellent therapeutic target for the treatment of cancer and the inhibition of metastasis dissemination. Furthermore, we postulate an interaction and regulation of the other Class I NME proteins, NME3 and NME4 proteins, with PRUNE1 and discuss potential functions. Class I NME1-4 proteins are NTP/NDP transphosphorylases required for balancing the intracellular pools of nucleotide diphosphates and triphosphates. They regulate different cellular functions by interacting with a large variety of other proteins, and in cancer and metastasis processes, they can exert pro- and anti-oncogenic properties depending on the cellular context. In this review, we therefore additionally discuss general aspects of class1 NME and PRUNE1 molecular structures as well as their posttranslational modifications and subcellular localization. The current knowledge on the contributions of PRUNE1 as well as NME proteins to signaling cascades is summarized with a special regard to cancer and metastasis.

Mechanistic Insights into Substrate Recognition of Human Nucleoside Diphosphate Kinase C Based on Nucleotide-Induced Structural Changes.

Nucleoside diphosphate kinases (NDPKs) are encoded by nme genes and exist in various isoforms. Based on interactions with other proteins, they are involved in signal transduction, development and pathological processes such as tumorigenesis, metastasis and heart failure. In this study, we report a 1.25 Å resolution structure of human homohexameric NDPK-C bound to ADP and describe the yet unknown complexes formed with GDP, UDP and cAMP, all obtained at a high resolution via X-ray crystallography. Each nucleotide represents a distinct group of mono- or diphosphate purine or pyrimidine bases. We analyzed different NDPK-C nucleotide complexes in the presence and absence of Mg2+ and explain how this ion plays an essential role in NDPKs' phosphotransferase activity. By analyzing a nucleotide-depleted NDPK-C structure, we detected conformational changes upon substrate binding and identify flexible regions in the substrate binding site. A comparison of NDPK-C with other human isoforms revealed a strong similarity in the overall composition with regard to the 3D structure, but significant differences in the charge and hydrophobicity of the isoforms' surfaces. This may play a role in isoform-specific NDPK interactions with ligands and/or important complex partners like other NDPK isoforms, as well as monomeric and heterotrimeric G proteins. Considering the recently discovered role of NDPK-C in different pathologies, these high-resolution structures thus might provide a basis for interaction studies with other proteins or small ligands, like activators or inhibitors.

Sufficient Cav-1 levels in the endothelium are critical for the maintenance of the neurovascular unit in the retina.

BACKGROUND: Caveolin-1 (Cav-1) is a pivotal protein in the plasma membrane. Studies on homozygous Cav-1 deficient mice revealed that Cav-1 is essential for endothelial function and angiogenesis in the retina. However, whether a reduction in Cav-1 content hampers the neurovascular unit (NVU) in the retina is unclear. Thus, this study examines the NVU in the retinas of heterozygous Cav-1 deficient (Cav-1+/-) mice and analyzes possible underlying mechanisms. METHODS: The vascular, glial and neuronal components in the retina were evaluated using retinal morphometry, whole mount retinal immunofluorescence staining, histological analysis and optical coherence tomography. In addition, immunoblotting and immunofluorescence staining, subcellular fractionation, biotin labeling of cell surface proteins, and proximity ligation assay were employed to detect expression and localization of proteins in the retina or endothelial cells (ECs) upon knockdown of Cav-1 with Cav-1 siRNA. RESULTS: Cav-1+/- retinas showed a significant reduction in pericyte coverage along with an increase in acellular capillaries compared to controls at 8 months of age, but not at 1 month. A significant loss and obvious morphological abnormalities of smooth muscle cells were observed in 8-month-old Cav-1+/- retinal arterioles. Macroglial and microglial cells were activated in the Cav-1+/- retinas. A transient significant delay in retinal angiogenesis was detected in Cav-1+/- retinas at p5, which was however no longer detectable at p10. The Cav-1+/- retinas displayed increased vascular permeability and a notable reduction in VEGFR2 content at 8 months. In vitro, siRNA-mediated knockdown experiments in ECs revealed that the loss of Cav-1 in ECs resulted in decreased levels of VEGFR2, VE-Cadherin and their interaction at the plasma membrane as well. CONCLUSION: Our results indicate that a sufficient Cav-1 level over 50% of its normal abundance is vital for the proper localization of VEGFR2 and VE-cadherin, likely in a complex, at the plasma membrane, which is essential for the maintenance of normal NVU in the retina.

Chemical Tools for Studying Phosphohistidine: Generation of Selective τ-Phosphohistidine and π-Phosphohistidine Antibodies.

Nonhydrolysable stable analogues of τ-phosphohistidine (τ-pHis) and π-pHis have been designed, aided by electrostatic surface potential calculations, and subsequently synthesized. The τ-pHis and π-pHis analogues (phosphopyrazole 8 and pyridyl amino amide 13, respectively) were used as haptens to generate pHis polyclonal antibodies. Both τ-pHis and π-pHis conjugates in the form of BSA-glutaraldehyde-τ-pHis and BSA-glutaraldehyde-π-pHis were synthesized and characterized by 31 P NMR spectroscopy. Commercially available τ-pHis (SC56-2) and π-pHis (SC1-1; SC50-3) monoclonal antibodies were used to show that the BSA-G-τ-pHis and BSA-G-π-pHis conjugates could be used to assess the selectivity of pHis antibodies in a competitive ELISA. Subsequently, the selectivity of the pHis antibodies generated by using phosphopyrazole 8 and pyridyl amino amide 13 as haptens was assessed by competitive ELISA against His, pSer, pThr, pTyr, τ-pHis and π-pHis. Antibodies generated by using phosphopyrazole 8 as a hapten were found to be selective for τ-pHis, and antibodies generated by using pyridyl amino amide 13 were found to be selective for π-pHis. Both τ- and π-pHis antibodies were shown to be effective in immunological experiments, including ELISA, western blot, and immunofluorescence. The τ-pHis antibody was also shown to be useful in the immunoprecipitation of proteins containing pHis.

The orphan receptor GPRC5B activates pro-inflammatory signaling in the vascular wall via Fyn and NFκB.

BACKGROUND AND AIMS: Atherosclerosis is driven by an inflammatory process of the vascular wall. The novel orphan G-protein coupled receptor 5B of family C (GPRC5B) is involved in drosophila sugar and lipid metabolism as well as mice adipose tissue inflammation. Here, we investigated the role of GPRC5B in the pro-atherogenic mechanisms of hyperglycemia and vascular inflammation. METHODS: Immortalized and primary endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) were used for stimulation with high glucose or different cytokines. Adenoviral- or plasmid-driven GPRC5B overexpression and siRNA-mediated knockdown were performed in these cells to analyze functional and mechanistic pathways of GPRC5B. RESULTS: In ECs and VSMCs, stimulation with high glucose, TNFα or LPS induced a significant upregulation of endogenous GPRC5B mRNA and protein levels. GPRC5B overexpression and knockdown increased and attenuated, respectively, the expression of the pro-inflammatory cytokines TNFα, IL-1ß, IL-6 as well as the pro-atherogenic vascular adhesion molecules ICAM-1 and VCAM-1. Furthermore, the expression and activity of the metalloproteinase MMP-9, a component of atherosclerotic plaque stabilization, were significantly enhanced by GPRC5B overexpression. Mechanistically, GPRC5B increased the phosphorylation of ERK1/2 and activated NFκB through a direct interaction with the tyrosine kinase Fyn. CONCLUSIONS: Our findings demonstrate that GPRC5B is upregulated in response to high glucose and pro-inflammatory signaling. GPRC5B functionally modulates the inflammatory activity in cells of the vascular wall, suggesting a pro-atherogenic GPRC5B-dependent positive feedback loop via Fyn and NFκB. Thus, GPRC5B warrants further attention as a novel pharmacological target for the treatment of vascular inflammation and possibly atherogenesis.

Chronic isoprenaline/phenylephrine vs. exclusive isoprenaline stimulation in mice: critical contribution of alpha1-adrenoceptors to early cardiac stress responses.

Hyperactivity of the sympathetic nervous system is a major driver of cardiac remodeling, exerting its effects through both α-, and ß-adrenoceptors (α-, ß-ARs). As the relative contribution of subtype α1-AR to cardiac stress responses remains poorly investigated, we subjected mice to either subcutaneous perfusion with the ß-AR agonist isoprenaline (ISO, 30 mg/kg × day) or to a combination of ISO and the stable α1-AR agonist phenylephrine (ISO/PE, 30 mg/kg × day each). Telemetry analysis revealed similar hemodynamic responses under both ISO and ISO/PE treatment i.e., permanently increased heart rates and only transient decreases in mean blood pressure during the first 24 h. Echocardiography and single cell analysis after 1 week of exposure showed that ISO/PE-, but not ISO-treated animals established α1-AR-mediated inotropic responsiveness to acute adrenergic stimulation. Morphologically, additional PE perfusion limited concentric cardiomyocyte growth and enhanced cardiac collagen deposition during 7 days of treatment. Time-course analysis demonstrated a diverging development in transcriptional patterns at day 4 of treatment i.e., increased expression of selected marker genes Xirp2, Nppa, Tgfb1, Col1a1, Postn under chronic ISO/PE treatment which was either less pronounced or absent in the ISO group. Transcriptome analyses at day 4 via RNA sequencing demonstrated that additional PE treatment caused a marked upregulation of genes allocated to extracellular matrix and fiber organization along with a more pronounced downregulation of genes involved in metabolic processes, muscle adaptation and cardiac electrophysiology. Consistently, transcriptome changes under ISO/PE challenge more effectively recapitulated early transcriptional alterations in pressure overload-induced experimental heart failure and in human hypertrophic cardiomyopathy.

RGS3L allows for an M2 muscarinic receptor-mediated RhoA-dependent inotropy in cardiomyocytes.

The role and outcome of the muscarinic M2 acetylcholine receptor (M2R) signaling in healthy and diseased cardiomyocytes is still a matter of debate. Here, we report that the long isoform of the regulator of G protein signaling 3 (RGS3L) functions as a switch in the muscarinic signaling, most likely of the M2R, in primary cardiomyocytes. High levels of RGS3L, as found in heart failure, redirect the Gi-mediated Rac1 activation into a Gi-mediated RhoA/ROCK activation. Functionally, this switch resulted in a reduced production of reactive oxygen species (- 50%) in cardiomyocytes and an inotropic response (+ 18%) in transduced engineered heart tissues. Importantly, we could show that an adeno-associated virus 9-mediated overexpression of RGS3L in rats in vivo, increased the contractility of ventricular strips by maximally about twofold. Mechanistically, we demonstrate that this switch is mediated by a complex formation of RGS3L with the GTPase-activating protein p190RhoGAP, which balances the activity of RhoA and Rac1 by altering its substrate preference in cardiomyocytes. Enhancement of this complex formation could open new possibilities in the regulation of the contractility of the diseased heart.

Antitumor Activity of Larotrectinib in Esophageal Carcinoma with NTRK Gene Amplification.

BACKGROUND: Increasing knowledge about the genomic changes underpinning cancer development and growth has led to a rapidly expanding number of individualized therapies that specifically target these changes in a patient's tumor. Here we present a case report of a patient with metastatic esophageal carcinoma whose tumor harbored NTRK1 gene amplification and who received targeted systemic therapy with larotrectinib. At initial diagnosis, the patient presented with tumor obstruction of the middle esophagus, simultaneous liver and lung metastases, UICC IV and WHO performance status 3. MATERIALS AND METHODS: The solid tumor genomic profiling test FoundationOne CDx (F1CDx) was used to detect clinically relevant genomic alterations that, in turn, might identify a targeted therapeutic approach if suggested by the findings. The patient was then treated with larotrectinib and had subsequent follow-up biopsies. RESULTS: Simultaneous biopsies of the primary tumor and liver lesions identified a metastatic squamous cell esophageal carcinoma. Comprehensive genomic profiling obtained from liver metastases identified numerous genomic alterations including amplification of NTRK1. Owing to the reduced performance status of the patient, chemotherapy could not be applied and was denied. Although larotrectinib is only approved for the treatment of cancers with NTRK gene fusions, treatment was started and led to a shrinkage of the primary tumor as well as the liver and lung metastases within 6 weeks according to RECIST criteria accompanied by tumor marker decrease. The NTRK1 gene amplification was below the limit of detection in a subsequent liver biopsy. CONCLUSION: The use of comprehensive genomic profiling, specifically F1CDx, enabled the selection of a targeted therapy that led to a rapid reduction of the tumor and its metastases according to RECIST criteria. This case suggests that larotrectinib is not only effective in NTRK fusions but may be efficacious in cases with gene amplification. KEY POINTS: Advances in precision medicine have revolutionized the treatment of cancer and have allowed oncologists to perform more individualized therapy. This case shows that larotrectinib could also be effective in cases of NTRK amplification of cancer. Today, there is only limited knowledge about NTRK alterations in squamous epithelial carcinoma of the esophagus. Longitudinal tumor sequencing during the course of the disease may allow for the detection of a molecular genetic cause once the tumor progresses. Additional actionable gene alterations may then be identified, which may provide the rationale for a therapy switch.

Quantification and discovery of sequence determinants of protein-per-mRNA amount in 29 human tissues.

Despite their importance in determining protein abundance, a comprehensive catalogue of sequence features controlling protein-to-mRNA (PTR) ratios and a quantification of their effects are still lacking. Here, we quantified PTR ratios for 11,575 proteins across 29 human tissues using matched transcriptomes and proteomes. We estimated by regression the contribution of known sequence determinants of protein synthesis and degradation in addition to 45 mRNA and 3 protein sequence motifs that we found by association testing. While PTR ratios span more than 2 orders of magnitude, our integrative model predicts PTR ratios at a median precision of 3.2-fold. A reporter assay provided functional support for two novel UTR motifs, and an immobilized mRNA affinity competition-binding assay identified motif-specific bound proteins for one motif. Moreover, our integrative model led to a new metric of codon optimality that captures the effects of codon frequency on protein synthesis and degradation. Altogether, this study shows that a large fraction of PTR ratio variation in human tissues can be predicted from sequence, and it identifies many new candidate post-transcriptional regulatory elements.

A deep proteome and transcriptome abundance atlas of 29 healthy human tissues.

Genome-, transcriptome- and proteome-wide measurements provide insights into how biological systems are regulated. However, fundamental aspects relating to which human proteins exist, where they are expressed and in which quantities are not fully understood. Therefore, we generated a quantitative proteome and transcriptome abundance atlas of 29 paired healthy human tissues from the Human Protein Atlas project representing human genes by 18,072 transcripts and 13,640 proteins including 37 without prior protein-level evidence. The analysis revealed that hundreds of proteins, particularly in testis, could not be detected even for highly expressed mRNAs, that few proteins show tissue-specific expression, that strong differences between mRNA and protein quantities within and across tissues exist and that protein expression is often more stable across tissues than that of transcripts. Only 238 of 9,848 amino acid variants found by exome sequencing could be confidently detected at the protein level showing that proteogenomics remains challenging, needs better computational methods and requires rigorous validation. Many uses of this resource can be envisaged including the study of gene/protein expression regulation and biomarker specificity evaluation.

Bacillus anthracis' PA63 Delivers the Tumor Metastasis Suppressor Protein NDPK-A/NME1 into Breast Cancer Cells.

Some highly metastatic types of breast cancer show decreased intracellular levels of the tumor suppressor protein NME1, also known as nm23-H1 or nucleoside diphosphate kinase A (NDPK-A), which decreases cancer cell motility and metastasis. Since its activity is directly correlated with the overall outcome in patients, increasing the cytosolic levels of NDPK-A/NME1 in such cancer cells should represent an attractive starting point for novel therapeutic approaches to reduce tumor cell motility and decrease metastasis. Here, we established the Bacillus anthracis protein toxins' transport component PA63 as transporter for the delivery of His-tagged human NDPK-A into the cytosol of cultured cells including human MDA-MB-231 breast cancer cells. The specifically delivered His6-tagged NDPK-A was detected in MDA-MB-231 cells via Western blotting and immunofluorescence microscopy. The PA63-mediated delivery of His6-NDPK-A resulted in reduced migration of MDA-MB-231 cells, as determined by a wound-healing assay. In conclusion, PA63 serves for the transport of the tumor metastasis suppressor NDPK-A/NME1 into the cytosol of human breast cancer cells in vitro, which reduced the migratory activity of these cells. This approach might lead to development of novel therapeutic options.

Role of the Ang2-Tie2 Axis in Vascular Damage Driven by High Glucose or Nucleoside Diphosphate Kinase B Deficiency.

Ablation of nucleoside diphosphate kinase B (NDPK-B) in mice causes a breakdown of the neurovascular unit in the retina, mimicking diabetic retinopathy. The NDPK-B deficiency-induced vascular damage is mediated by excessive angiopoietin 2 (Ang2). Herein, the potential involvement of its receptor, Tie2, was investigated. NDPK-B-deficient mouse retinas showed an upregulation of Tie2, specifically in the deep capillary layer. A similar upregulation of Tie2 was observed in cultured endothelial cells (ECs) from different origins upon NDPK-B depletion, whereas high glucose (HG) treatment did not alter Tie2 expression. Immunofluorescence staining and subcellular fractionation showed that the majority of Tie2 upregulation occurred at the plasma membrane. Similar to HG, however, NDPK-B depletion reduced Tie2 tyrosine phosphorylation. Compared to HG, a stronger increase of Ang2 was observed in NDPK-B depleted ECs. Treatment of ECs with soluble Tie2 or siRNA-mediated Tie2 knockdown attenuated NDPK-B depletion- but not HG-induced Ang2 upregulation. Like NDPK-B depletion, overexpression of recombinant Ang2 in ECs enhanced Ang2 secretion and concomitantly promoted the upregulation of Tie2. Thus, we identified a new mechanism showing that after reaching a threshold level of secretion, Ang2 sustains its own expression and secretion by a Tie2-dependent positive feedback loop.

Rare Variants in MME, Encoding Metalloprotease Neprilysin, Are Linked to Late-Onset Autosomal-Dominant Axonal Polyneuropathies.

Axonal polyneuropathies are a frequent cause of progressive disability in the elderly. Common etiologies comprise diabetes mellitus, paraproteinaemia, and inflammatory disorders, but often the underlying causes remain elusive. Late-onset axonal Charcot-Marie-Tooth neuropathy (CMT2) is an autosomal-dominantly inherited condition that manifests in the second half of life and is genetically largely unexplained. We assumed age-dependent penetrance of mutations in a so far unknown gene causing late-onset CMT2. We screened 51 index case subjects with late-onset CMT2 for mutations by whole-exome (WES) and Sanger sequencing and subsequently queried WES repositories for further case subjects carrying mutations in the identified candidate gene. We studied nerve pathology and tissue levels and function of the abnormal protein in order to explore consequences of the mutations. Altogether, we observed heterozygous rare loss-of-function and missense mutations in MME encoding the metalloprotease neprilysin in 19 index case subjects diagnosed with axonal polyneuropathies or neurodegenerative conditions involving the peripheral nervous system. MME mutations segregated in an autosomal-dominant fashion with age-related incomplete penetrance and some affected individuals were isolated case subjects. We also found that MME mutations resulted in strongly decreased tissue availability of neprilysin and impaired enzymatic activity. Although neprilysin is known to degrade ß-amyloid, we observed no increased amyloid deposition or increased incidence of dementia in individuals with MME mutations. Detection of MME mutations is expected to increase the diagnostic yield in late-onset polyneuropathies, and it will be tempting to explore whether substances that can elevate neprilysin activity could be a rational option for treatment.

The orphan receptor GPRC5B modulates inflammatory and fibrotic pathways in cardiac fibroblasts and mice hearts.

Inflammation is a major driver of cardiac remodeling. Cardiac fibroblasts play an integral role in cardiac inflammation, fibrosis and remodeling. The orphan G-protein-coupled-receptor 5B of family C (GPRC5B) has recently been shown to have pro-inflammatory effects in adipocytes via the NFκB-signaling-pathway. Here, we investigated whether GPRC5B is involved in myocardial inflammation and fibrosis. Using neonatal rat cardiac fibroblasts (NRCF) we show that the transcription and the expression of endogenous GPRC5B is induced by stimulation with TNFα and LPS as well as through cyclic mechanical stretch, while the principle pro-fibrotic factor TGFß has no effect on the GPRC5B expression. Furthermore, we demonstrate that adenoviral overexpression and siRNA-mediated knockdown of GPRC5B in NRCF significantly alters the transcription level of the pro-inflammatory and pro-fibrotic cytokines TNFα, IL-1ß, IL-6 and MCP-1, and extracellular matrix-degrading MMP-9 in vitro. Additionally, in adult GPRC5B-transgenic mice the protein expression of collagen-1A1 is decreased and the production of MMP-9 is increased, indicating remodeling of the extracellular matrix in vivo. Our data show that GPRC5B is up-regulated by inflammatory signals and mechanical stress in NRCF, while GPRC5B modulates the inflammatory response of cardiac fibroblasts and the degradation of extracellular matrix-proteins in the mice heart. Thus, our findings are the first to report a novel role of the orphan receptor GPRC5B in fibroblast-driven myocardial inflammation and cardiac remodeling.

Hypertension-evoked RhoA activity in vascular smooth muscle cells requires RGS5.

G protein-mediated signaling plays a decisive role in blood pressure regulation and the phenotype of vascular smooth muscle cells (VSMCs); however, the relevance of proteins that restrict G protein activity is not well characterized in this context. Here, we investigated the influence of regulator of G protein signaling 5 (RGS5), an inhibitor of Gαq/11 and Gαi/o activity, on blood pressure and the VSMC phenotype during experimental hypertension. In mice, loss of RGS5 did not affect baseline blood pressure, but prevented hypertension-induced structural remodeling. RGS5-deficient arterial VSMCs did not acquire a synthetic phenotype as evidenced by their inability to decrease the abundance of contractile markers-α-smooth muscle actin and smooth muscle-myosin heavy chain-or to proliferate under these conditions. Mechanistically, hypertensive pressure levels or biomechanical stretch are sufficient to increase the expression of RGS5. Loss of RGS5 severely impairs the activation of RhoA and stress fiber formation. In stretch-exposed VSMCs, RhoA activity was amplified upon inhibition of PKC, which mimics the downstream effects evoked by RGS5-mediated inhibition of Gαq/11 signaling. Collectively, our findings underline that RhoA activation may depend on the restriction of G protein activity and identify RGS5 as a mechanosensitive regulatory protein that is required to promote the synthetic VSMC phenotype as a prerequisite for structural renovation of the arterial wall during hypertension.-Arnold, C., Demirel, E., Feldner, A., Genové, G., Zhang, H., Sticht, C., Wieland, T., Hecker, M., Heximer, S., Korff, T. Hypertension-evoked RhoA activity in vascular smooth muscle cells requires RGS5.

Phosphodiesterase 2 Protects Against Catecholamine-Induced Arrhythmia and Preserves Contractile Function After Myocardial Infarction.

RATIONALE: Phosphodiesterase 2 is a dual substrate esterase, which has the unique property to be stimulated by cGMP, but primarily hydrolyzes cAMP. Myocardial phosphodiesterase 2 is upregulated in human heart failure, but its role in the heart is unknown. OBJECTIVE: To explore the role of phosphodiesterase 2 in cardiac function, propensity to arrhythmia, and myocardial infarction. METHODS AND RESULTS: Pharmacological inhibition of phosphodiesterase 2 (BAY 60-7550, BAY) led to a significant positive chronotropic effect on top of maximal ß-adrenoceptor activation in healthy mice. Under pathological conditions induced by chronic catecholamine infusions, BAY reversed both the attenuated ß-adrenoceptor-mediated inotropy and chronotropy. Conversely, ECG telemetry in heart-specific phosphodiesterase 2-transgenic (TG) mice showed a marked reduction in resting and in maximal heart rate, whereas cardiac output was completely preserved because of greater cardiac contraction. This well-tolerated phenotype persisted in elderly TG with no indications of cardiac pathology or premature death. During arrhythmia provocation induced by catecholamine injections, TG animals were resistant to triggered ventricular arrhythmias. Accordingly, Ca2+-spark analysis in isolated TG cardiomyocytes revealed remarkably reduced Ca2+ leakage and lower basal phosphorylation levels of Ca2+-cycling proteins including ryanodine receptor type 2. Moreover, TG demonstrated improved cardiac function after myocardial infarction. CONCLUSIONS: Endogenous phosphodiesterase 2 contributes to heart rate regulation. Greater phosphodiesterase 2 abundance protects against arrhythmias and improves contraction force after severe ischemic insult. Activating myocardial phosphodiesterase 2 may, thus, represent a novel intracellular antiadrenergic therapeutic strategy protecting the heart from arrhythmia and contractile dysfunction.

A cellular model of Brugada syndrome with SCN10A variants using human-induced pluripotent stem cell-derived cardiomyocytes.

AIMS: Brugada syndrome (BrS) is associated with a pronounced risk to develop sudden cardiac death (SCD). Up to 21% of patients are related to mutations in SCN5A. Studies identified SCN10A as a contributor of BrS. However, the investigation of the human cellular phenotype of BrS in the presence of SCN10A mutations remains lacking. The objective of this study was to establish a cellular model of BrS in presence of SCN10A mutations using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). METHODS AND RESULTS: Dermal fibroblasts obtained from a BrS patient suffering from SCD harbouring the SCN10A double variants (c.3803G>A and c.3749G>A) and three independent healthy control subjects were reprogrammed to hiPSCs. Human-induced pluripotent stem cells were differentiated into cardiomyocytes (hiPSC-CMs).The hiPSC-CMs from the BrS patient showed a significantly reduced peak sodium channel current (INa) and a significantly reduced ATX II (sea anemone toxin, an enhancer of late INa) sensitive as well as A-887826 (a blocker of SCN10A channel) sensitive late sodium channel current (INa) when compared with the healthy control hiPSC-CMs, indicating loss-of-function of sodium channels. Consistent with reduced INa the action potential amplitude and upstroke velocity (Vmax) were significantly reduced, which may contribute to arrhythmogenesis of BrS. Moreover, Ajmaline effects on action potentials were stronger in BrS-hiPSC-CMs than in healthy control cells. This is in agreement with the higher susceptibility of patients to sodium channel blocking drugs in unmasking BrS. CONCLUSION: Patient-specific hiPSC-CMs are able to recapitulate single-cell phenotype features of BrS with SCN10A mutations and may provide novel opportunities to further elucidate the cellular disease mechanism.

Transcriptome and genome sequencing uncovers functional variation in humans.

Genome sequencing projects are discovering millions of genetic variants in humans, and interpretation of their functional effects is essential for understanding the genetic basis of variation in human traits. Here we report sequencing and deep analysis of messenger RNA and microRNA from lymphoblastoid cell lines of 462 individuals from the 1000 Genomes Project--the first uniformly processed high-throughput RNA-sequencing data from multiple human populations with high-quality genome sequences. We discover extremely widespread genetic variation affecting the regulation of most genes, with transcript structure and expression level variation being equally common but genetically largely independent. Our characterization of causal regulatory variation sheds light on the cellular mechanisms of regulatory and loss-of-function variation, and allows us to infer putative causal variants for dozens of disease-associated loci. Altogether, this study provides a deep understanding of the cellular mechanisms of transcriptome variation and of the landscape of functional variants in the human genome.

Nucleoside Diphosphate Kinase-C Suppresses cAMP Formation in Human Heart Failure.

BACKGROUND: Chronic heart failure (HF) is associated with altered signal transduction via ß-adrenoceptors and G proteins and with reduced cAMP formation. Nucleoside diphosphate kinases (NDPKs) are enriched at the plasma membrane of patients with end-stage HF, but the functional consequences of this are largely unknown, particularly for NDPK-C. Here, we investigated the potential role of NDPK-C in cardiac cAMP formation and contractility. METHODS: Real-time polymerase chain reaction, (far) Western blot, immunoprecipitation, and immunocytochemistry were used to study the expression, interaction with G proteins, and localization of NDPKs. cAMP levels were determined with immunoassays or fluorescent resonance energy transfer, and contractility was determined in cardiomyocytes (cell shortening) and in vivo (fractional shortening). RESULTS: NDPK-C was essential for the formation of an NDPK-B/G protein complex. Protein and mRNA levels of NDPK-C were upregulated in end-stage human HF, in rats after long-term isoprenaline stimulation through osmotic minipumps, and after incubation of rat neonatal cardiomyocytes with isoprenaline. Isoprenaline also promoted translocation of NDPK-C to the plasma membrane. Overexpression of NDPK-C in cardiomyocytes increased cAMP levels and sensitized cardiomyocytes to isoprenaline-induced augmentation of contractility, whereas NDPK-C knockdown decreased cAMP levels. In vivo, depletion of NDPK-C in zebrafish embryos caused cardiac edema and ventricular dysfunction. NDPK-B knockout mice had unaltered NDPK-C expression but showed contractile dysfunction and exacerbated cardiac remodeling during long-term isoprenaline stimulation. In human end-stage HF, the complex formation between NDPK-C and Gαi2 was increased whereas the NDPK-C/Gαs interaction was decreased, producing a switch that may contribute to an NDPK-C-dependent cAMP reduction in HF. CONCLUSIONS: Our findings identify NDPK-C as an essential requirement for both the interaction between NDPK isoforms and between NDPK isoforms and G proteins. NDPK-C is a novel critical regulator of ß-adrenoceptor/cAMP signaling and cardiac contractility. By switching from Gαs to Gαi2 activation, NDPK-C may contribute to lower cAMP levels and the related contractile dysfunction in HF.

Regulation of heterotrimeric G-protein signaling by NDPK/NME proteins and caveolins: an update.

Heterotrimeric G proteins are pivotal mediators of cellular signal transduction in eukaryotic cells and abnormal G-protein signaling plays an important role in numerous diseases. During the last two decades it has become evident that the activation status of heterotrimeric G proteins is both highly localized and strongly regulated by a number of factors, including a receptor-independent activation pathway of heterotrimeric G proteins that does not involve the classical GDP/GTP exchange and relies on nucleoside diphosphate kinases (NDPKs). NDPKs are NTP/NDP transphosphorylases encoded by the nme/nm23 genes that are involved in a variety of cellular events such as proliferation, migration, and apoptosis. They therefore contribute, for example, to tumor metastasis, angiogenesis, retinopathy, and heart failure. Interestingly, NDPKs are translocated and/or upregulated in human heart failure. Here we describe recent advances in the current understanding of NDPK functions and how they have an impact on local regulation of G-protein signaling.