Epidemiological description and trajectories of patients with prostate cancer in Denmark: an observational study of 7448 patients

OBJECTIVE

Identification of patients at high risk of aggressive prostate cancer is a major clinical challenge. With the view of developing artificial intelligence-based methods for identification of these patients, we are constructing a comprehensive clinical database including 7448 prostate cancer (PCa) Danish patients. In this paper we provide an epidemiological description and patients' trajectories of this retrospective observational population, to contribute to the understanding of the characteristics and pathways of PCa patients in Denmark.

RESULTS

Individuals receiving a PCa diagnosis during 2008-2014 in Region Southern Denmark were identified, and all diagnoses, operations, investigations, and biochemistry analyses, from 4 years prior, to 5 years after PCa diagnosis were obtained. About 85.1% were not diagnosed with metastatic PCa during the study period (unaggressive PCa); 9.2% were simultaneously diagnosed with PCa and metastasis (aggressive-advanced PCa), while 5.7% were not diagnosed with metastatic PCa at first, but they were diagnosed with metastasis at some point during the 5 years follow-up (aggressive-not advanced PCa). Patients with unaggressive PCa had more clinical investigations directly related to PCa detection (prostate ultrasounds and biopsies) during the 4 years prior to PCa diagnosis, compared to patients with aggressive PCa, which may have contributed to the early detection of PCa.

Isolation of Adipose Derived Regenerative Cells for the Treatment of Erectile Dysfunction Following Radical Prostatectomy

Stem cells are used in many research areas within regenerative medicine in part because these treatments can be curative rather than symptomatic. Stem cells can be obtained from different tissues and several methods for isolation have been described. The presented method for the isolation of adipose-derived regenerative cells (ADRCs) can be used within many therapeutic areas because the method is a general procedure and, therefore, not limited to erectile dysfunction (ED) therapy. ED is a common and serious side effect to radical prostatectomy (RP) since ED often is not well treated with conventional therapy. Using ADRC's as treatment for ED has attracted great interest due to the initial positive results after a single injection of cells into the corpora cavernosum. The method used for the isolation of ADRC's is a simple, automated process, that is reproducible and ensures a uniform product. Furthermore, the sterility of the isolated product is ensured because the entire process takes place in a closed system. It is important to minimize the risk of contamination and infection since the stem cells are used for injection in humans. The whole procedure can be done within 2.5-3.5 hours and does not require a classified laboratory which eliminates the need for shipping tissue to an off-site. However, the procedure has some limitations since the minimum amount of drained lipoaspirate for the isolation device to function is 100 g.

MESP1 knock-down in human iPSC attenuates early vascular progenitor cell differentiation after completed primitive streak specification

MESP1 is a key transcription factor in development of early cardiovascular tissue and it is required for induction of the cardiomyocyte (CM) gene expression program, but its role in vascular development is unclear. Here, we used inducible CRISPRi knock-down of MESP1 to analyze the molecular processes of the early differentiation stages of human induced pluripotent stem cells into mesoderm and subsequently vascular progenitor cells. We found that expression of the mesodermal marker, BRACHYURY (encoded by T) was unaffected in MESP1 knock-down cells as compared to wild type cells suggesting timely movement through the primitive streak whereas another mesodermal marker MIXL1 was slightly, but significantly decreased. In contrast, the expression of the vascular cell surface marker KDR was decreased and CD31 and CD34 expression were substantially reduced in MESP1 knock-down cells supporting inhibition or delay of vascular specification. In addition, mRNA microarray data revealed several other altered gene expressions including the EMT regulating transcription factors SNAI1 and TWIST1, which were both significantly decreased indicating that MESP1 knock-down cells are less likely to undergo EMT during vascular progenitor differentiation. Our study demonstrates that while leaving primitive streak markers unaffected, MESP1 expression is required for timely vascular progenitor specification. Thus, MESP1 expression is essential for the molecular features of early CM, EC and VSMC lineage specification.

Human induced pluripotent stem cell-derived vascular smooth muscle cells: differentiation and therapeutic potential

Cardiovascular diseases remain the leading cause of death worldwide and current treatment strategies have limited effect of disease progression. It would be desirable to have better models to study developmental and pathological processes and model vascular diseases in laboratory settings. To this end, human induced pluripotent stem cells (hiPSCs) have generated great enthusiasm, and have been a driving force for development of novel strategies in drug discovery and regenerative cell-therapy for the last decade. Hence, investigating the mechanisms underlying the differentiation of hiPSCs into specialized cell types such as cardiomyocytes, endothelial cells, and vascular smooth muscle cells (VSMCs) may lead to a better understanding of developmental cardiovascular processes and potentiate progress of safe autologous regenerative therapies in pathological conditions. In this review, we summarize the latest trends on differentiation protocols of hiPSC-derived VSMCs and their potential application in vascular research and regenerative therapy.

Antibody-based inhibition of circulating DLK1 protects from estrogen deficiency-induced bone loss in mice

Soluble delta-like 1 homolog (DLK1) is a circulating protein that belongs to the Notch/Serrate/delta family, which regulates many differentiation processes including osteogenesis and adipogenesis. We have previously demonstrated an inhibitory effect of DLK1 on bone mass via stimulation of bone resorption and inhibition of bone formation. Further, serum DLK1 levels are elevated and positively correlated to bone turnover markers in estrogen (E)-deficient rodents and women. In this report, we examined whether inhibition of serum DLK1 activity using a neutralizing monoclonal antibody protects from E deficiency-associated bone loss in mice. Thus, we generated mouse monoclonal anti-mouse DLK1 antibodies (MAb DLK1) that enabled us to reduce and also quantitate the levels of bioavailable serum DLK1 in vivo. Ovariectomized (ovx) mice were injected intraperitoneally twice weekly with MAb DLK1 over a period of one month. DEXA-, microCT scanning, and bone histomorphometric analyses were performed. Compared to controls, MAb DLK1 treated ovx mice were protected against ovx-induced bone loss, as revealed by significantly increased total bone mass (BMD) due to increased trabecular bone volume fraction (BV/TV) and inhibition of bone resorption. No significant changes were observed in total fat mass or in the number of bone marrow adipocytes. These results support the potential use of anti-DLK1 antibody therapy as a novel intervention to protect from E deficiency associated bone loss.

Neonatal epicardial-derived progenitors aquire myogenic traits in skeletal muscle, but not cardiac muscle

BACKGROUND/OBJECTIVES

Epicardium-derived progenitor cells (EPDCs) differentiate into all heart cell types in the embryonic heart, yet their differentiation into cardiomyocytes in the adult heart is limited and poorly described. This may be due to EPDCs lacking myogenic potential or the inert adult heart missing regenerative signals essential for directed differentiation of EPDCs. Herein, we aimed to evaluate the myogenic potential of neonatal EPDCs in adult and neonatal mouse myocardium, as well as in skeletal muscle. The two latter tissues have an intrinsic capability to develop and regenerate, in contrast to the adult heart.

METHODS

Highly purified mouse EPDCs were transplanted into damaged neonatal and adult myocardium as well as regenerating skeletal muscle. Co-cultures with skeletal myoblasts were used to distinguish fusion independent myogenic conversion.

RESULTS

No donor EPDC-derived cardiomyocytes were observed in hearts. In contrast, a remarkable contribution of EPDCs to skeletal muscle myofiber formation was evident in vivo. Furthermore, co-cultures of EPDCs with myoblasts showed that EPDCs became part of multinucleated fibers and appeared to acquire myogenic traits independent of a fusion event. Fluorescence activated cell sorting of EPDCs co-cultured with and without myoblasts and subsequent qRT-PCR of 64 transcripts established that the myogenic phenotype conversion was accomplished through induction of a transcriptional myogenic program.

CONCLUSION

These results suggest that EPDCs may be more myogenic than previously anticipated. But, the heart may lack factors for induction of myogenesis of EPDCs, a scenario that should be taken into consideration when aiming for repair of damaged myocardium by stem cell transplantation.

CRISPR Interference Efficiently Induces Specific and Reversible Gene Silencing in Human iPSCs

Developing technologies for efficient and scalable disruption of gene expression will provide powerful tools for studying gene function, developmental pathways, and disease mechanisms. Here, we develop clustered regularly interspaced short palindromic repeat interference (CRISPRi) to repress gene expression in human induced pluripotent stem cells (iPSCs). CRISPRi, in which a doxycycline-inducible deactivated Cas9 is fused to a KRAB repression domain, can specifically and reversibly inhibit gene expression in iPSCs and iPSC-derived cardiac progenitors, cardiomyocytes, and T lymphocytes. This gene repression system is tunable and has the potential to silence single alleles. Compared with CRISPR nuclease (CRISPRn), CRISPRi gene repression is more efficient and homogenous across cell populations. The CRISPRi system in iPSCs provides a powerful platform to perform genome-scale screens in a wide range of iPSC-derived cell types, dissect developmental pathways, and model disease.

Evidence of non-canonical NOTCH signaling: Delta-like 1 homolog (DLK1) directly interacts with the NOTCH1 receptor in mammals

Canonical NOTCH signaling, known to be essential for tissue development, requires the Delta-Serrate-LAG2 (DSL) domain for NOTCH to interact with its ligand. However, despite lacking DSL, Delta-like 1 homolog (DLK1), a protein that plays a significant role in mammalian development, has been suggested to interact with NOTCH1 and act as an antagonist. This non-canonical interaction is, however controversial, and evidence for a direct interaction, still lacking in mammals. In this study, we elucidated the putative DLK1-NOTCH1 interaction in a mammalian context. Taking a global approach and using Dlk1(+/+) and Dlk1(-/-) mouse tissues at E16.5, we demonstrated that several NOTCH signaling pathways indeed are affected by DLK1 during tissue development, and this was supported by a lower activation of NOTCH1 protein in Dlk1(+/+) embryos. Likewise, but using a distinct Dlk1-manipulated (siRNA) setup in a mammalian cell line, NOTCH signaling was substantially inhibited by DLK1. Using a mammalian two-hybrid system, we firmly established that the effect of DLK1 on NOTCH signaling was due to a direct interaction between DLK1 and NOTCH1. By careful dissection of this mechanism, we found this interaction to occur between EGF domains 5 and 6 of DLK1 and EGF domains 10-15 of NOTCH1. Thus, our data provide the first evidence for a direct interaction between DLK1 and NOTCH1 in mammals, and substantiate that non-canonical NOTCH ligands exist, adding to the complexity of NOTCH signaling.

Inhibition of 14q32 MicroRNAs miR-329, miR-487b, miR-494, and miR-495 Increases Neovascularization and Blood Flow Recovery After Ischemia

Rationale:

Effective neovascularization is crucial for recovery after cardiovascular events.

Objective:

Because microRNAs regulate expression of up to several hundred target genes, we set out to identify microRNAs that target genes in all pathways of the multifactorial neovascularization process. Using www.targetscan.org , we performed a reverse target prediction analysis on a set of 197 genes involved in neovascularization. We found enrichment of binding sites for 27 microRNAs in a single microRNA gene cluster. Microarray analyses showed upregulation of 14q32 microRNAs during neovascularization in mice after single femoral artery ligation.

Methods and Results:

Gene silencing oligonucleotides (GSOs) were used to inhibit 4 14q32 microRNAs, miR-329, miR-487b, miR-494, and miR-495, 1 day before double femoral artery ligation. Blood flow recovery was followed by laser Doppler perfusion imaging. All 4 GSOs clearly improved blood flow recovery after ischemia. Mice treated with GSO-495 or GSO-329 showed increased perfusion already after 3 days (30% perfusion versus 15% in control), and those treated with GSO-329 showed a full recovery of perfusion after 7 days (versus 60% in control). Increased collateral artery diameters (arteriogenesis) were observed in adductor muscles of GSO-treated mice, as well as increased capillary densities (angiogenesis) in the ischemic soleus muscle. In vitro, treatment with GSOs led to increased sprout formation and increased arterial endothelial cell proliferation, as well as to increased arterial myofibroblast proliferation.

Conclusions:

The 14q32 microRNA gene cluster is highly involved in neovascularization. Inhibition of 14q32 microRNAs miR-329, miR-487b, miR-494, and miR-495 provides a promising tool for future therapeutic neovascularization.

The microRNA-132/212 family fine-tunes multiple targets in Angiotensin II signalling in cardiac fibroblasts

INTRODUCTION

MicroRNAs (miRNAs) are emerging as key regulators of cardiovascular development and disease; however, the cardiac miRNA target molecules are not well understood. We and others have described the Angiotensin II (AngII)-induced miR-132/212 family as novel regulators of cardiovascular function including regulation of cardiac hypertrophy, heart failure and blood pressure possibly through AT1R signalling. However, the miR-132/212 targets in the heart remain unknown.

MATERIALS AND METHODS

To understand the role of these miRNAs in cardiac signalling networks, we undertook comprehensive in silico and in vitro experiments to identify miR-132/212 molecular targets in primary rat cardiac fibroblasts.

RESULTS

MiR-132/212 overexpression increased fibroblast cell size and mRNA arrays detected several hundred genes that were differentially expressed, including a wide panel of receptors, signalling molecules and transcription factors. Subsequent comprehensive in silico analysis identified 24 target genes, of which 22 genes were qPCR validated. We identified seven genes involved in AngII signalling pathways.

CONCLUSION

We here report novel insight of an extensive network of molecular pathways that fine-tuned by miR-132/212, suggesting a role for this miRNA family as master signalling switches in cardiac fibroblasts. Our data underscore the potential for miRNA tools to manipulate a large array of molecules and thereby control biological function.

Preadipocytes proliferate and differentiate under the guidance of Delta-like 1 homolog (DLK1)

Obesity occurs when an excessive dietary fat intake leads to expansion of adipose tissue, which mainly consists of adipocytes that arise from proliferating and differentiating adipose stem cells, the preadipocytes. Obesity is a consequence of both adipocyte hypertrophy and hyperplasia. Knowledge about preadipocyte differentiation is relatively well established, whereas the mechanism responsible for preadipocyte proliferation is incompletely understood and only in the early stage of comprehension. In this regard, we have recently identified that Delta-like 1 homolog (Dlk1) (also known as Preadipocyte factor 1 [Pref-1]) inhibits preadipocyte proliferation by regulating their entry into G1/S-phase. This novel disclosure, adding to the previous published data on Dlk1 repression of preadipocyte differentiation, has given us the chance to firmly place Dlk1 as a master regulator of preadipocyte homeostasis and adipose tissue expansion. Dlk1 manipulation may, therefore, open new perspectives in obesity treatments.

Functional enhancement of AT1R potency in the presence of the TPαR is revealed by a comprehensive 7TM receptor co-expression screen

Background

Functional cross-talk between seven transmembrane (7TM) receptors can dramatically alter their pharmacological properties, both in vitro and in vivo. This represents an opportunity for the development of novel therapeutics that potentially target more specific biological effects while causing fewer adverse events. Although several studies convincingly have established the existence of 7TM receptor cross-talk, little is known about the frequencey and biological significance of this phenomenon.

Methodology/Principal Findings

To evaluate the extent of synergism in 7TM receptor signaling, we took a comprehensive approach and co-expressed 123 different 7TM receptors together with the angiotensin II type 1 receptor (AT1R) and analyzed how each receptor affected the angiotensin II (AngII) response. To monitor the effect we used integrative receptor activation/signaling assay called Receptor Selection and Amplification Technology (R-SAT). In this screen the thromboxane A2α receptor (TPαR) was the only receptor which significantly enhanced the AngII-mediated response. The TPαR-mediated enhancement of AngII signaling was significantly reduced when a signaling deficient receptor mutant (TPαR R130V) was co-expressed instead of the wild-type TPαR, and was completely blocked both by TPαR antagonists and COX inhibitors inhibiting formation of thromboxane A₂ (TXA₂).

Conclusions/Significance

We found a functional enhancement of AT1R only when co-expressed with TPαR, but not with 122 other 7TM receptors. In addition, the TPαR must be functionally active, indicating the AT1R enhancement is mediated by a paracrine mechanism. Since we only found one receptor enhancing AT1R potency, our results suggest that functional augmentation through 7TM receptor cross-talk is a rare event that may require specific conditions to occur.

Membrane-tethered delta-like 1 homolog (DLK1) restricts adipose tissue size by inhibiting preadipocyte proliferation

Adipocyte renewal from preadipocytes has been shown to occur throughout life and to contribute to obesity, yet very little is known about the molecular circuits that control preadipocyte expansion. The soluble form of the preadipocyte factor (also known as pref-1) delta-like 1 homolog (DLK1(S)) is known to inhibit adipogenic differentiation; however, the impact of DLK1 isoforms on preadipocyte proliferation remains to be determined. We generated preadipocytes with different levels of DLK1 and examined differentially affected gene pathways, which were functionally tested in vitro and confirmed in vivo. Here, we demonstrate for the first time that only membrane-bound DLK1 (DLK1(M)) exhibits a substantial repression effect on preadipocyte proliferation. Thus, by independently manipulating DLK1 isoform levels, we established that DLK1(M) inhibits G1-to-S-phase cell cycle progression and thereby strongly inhibits preadipocyte proliferation in vitro. Adult DLK1-null mice exhibit higher fat amounts than wild-type controls, and our in vivo analysis demonstrates that this may be explained by a marked increase in preadipocyte replication. Together, these data imply a major dual inhibitory function of DLK1 on adipogenesis, which places DLK1 as a master regulator of preadipocyte homeostasis, suggesting that DLK1 manipulation may open new avenues in obesity treatment.

SNPs in microRNA binding sites in 3'-UTRs of RAAS genes influence arterial blood pressure and risk of myocardial infarction

BACKGROUND

We hypothesized that single nucleotide polymorphisms (SNPs) located in microRNA (miR) binding sites in genes of the renin angiotensin aldosterone system (RAAS) can influence blood pressure and risk of myocardial infarction.

METHODS

Using online databases dbSNP and TargetScan, we identified 10 SNPs in potential miR binding sites in eight RAAS-related genes, common in Caucasians. We genotyped a large case-control study on myocardial infarctions, the Study of Myocardial Infarctions LEiden (SMILE) for these 10 SNPs and found nine SNPs, in seven genes, to be prevalent. Functionality of each SNP in interfering with mRNA/miR binding was tested using a dual luciferase reporter gene system.

RESULTS

Of these nine SNPs, four SNPs, located in the arginine vasopressin 1A receptor (AVPR1A), bradykinin 2 receptor (BDKRB2), and thromboxane A2 receptor (TBXA2R) genes were associated with blood pressure. The rare allele of the AVPR1A SNP rs11174811, was associated with increased blood pressure whereas the rare alleles of the two linked BDKRB2 SNPs rs5225 and rs2069591 and of the TBXA2R SNP rs13306046 were associated with decreased blood pressure. Although not associated with blood pressure, the rare allele of the mineralocorticoid receptor (NR3C2) SNP rs5534, was associated with a twofold increased risk of myocardial infarction in men younger than 50 years. For all of these five SNPs, except rs2069591, we could demonstrate a reduction in miR-induced repression of gene expression.

CONCLUSIONS

Common SNPs in miR binding sites of RAAS-related genes can influence both blood pressure and risk of myocardial infarction. These results may imply an important role for SNPs in miR target sites in human disease.

AT(1) receptor Gαq protein-independent signalling transcriptionally activates only a few genes directly, but robustly potentiates gene regulation from the β2-adrenergic receptor

The angiotensin II type 1 receptor (AT(1)R) is known to signal through heterotrimeric G proteins, and Gαq protein-independent signalling has only recently gained appreciation for profound impact on a diverse range of biological functions. β-Arrestins, among other central mediators of Gαq protein-independent signalling from the AT(1)R interact with transcriptional regulators and promote phosphorylation of nuclear proteins. However, the relative contribution of Gαq protein-independent signalling in AT(1)R mediated transcriptional regulation remains elusive. We here present a comprehensive comparative analysis of Gαq protein-dependent and -independent regulation of AT(1)R mediated gene expression. We found angiotensin II to regulate 212 genes, whereas Gαq-independent signalling obtained with the biased agonist, SII angiotensin II only regulated few genes. Interestingly, SII angiotensin II, like Ang II vastly potentiated β2-adrenergic receptor-stimulated gene expression. These novel findings indicate that the Gαq protein-independent signalling mainly modifies the transcriptional response governed by other signalling pathways, while direct induction of gene expression by the AT(1)R is dependent on classical Gαq protein activation.

Functional variation in the arginine vasopressin 2 receptor as a modifier of human plasma von Willebrand factor levels

SUMMARY OBJECTIVES

Stimulation of arginine vasopressin 2 receptor (V2R) with arginine vasopressin (AVP) results in a rise in von Willebrand factor (VWF) and factor VIII plasma levels. We hypothesized that gain-of-function variations in the V2R gene (AVPR2) would lead to higher plasma levels of VWF and FVIII.

METHODS AND RESULTS

We genotyped the control populations of two population-based studies for four AVPR2 variations: a-245c, G12E, L309L, and S331S. Rare alleles of a-245c, G12E, and S331S, which were in linkage disequilibrium, were associated with higher VWF propeptide, VWF and FVIII levels. The functionality of the G12E variant was studied in stably transfected MDCKII cells, expressing constructs of either 12G-V2R or 12E-V2R. Both V2R variants were fully glycosylated and expressed on the basolateral membrane. The binding affinity of V2R for AVP was increased three-fold in 12E-V2R-green fluorescent protein (GFP) cells, which is in accordance with increased levels of VWF propeptide associated with the 12E variant. The dissociation constant (K(D)) was 4.5 nm [95% confidence interval (CI) 3.6-5.4] for 12E-V2R-GFP and 16.5 nm (95% CI 10.1-22.9) for 12G-V2R-GFP. AVP-induced cAMP generation was enhanced in 12E-V2R-GFP cells.

CONCLUSIONS

The 12E-V2R variant has increased binding affinity for AVP, resulting in increased signal transduction, and is associated with increased levels of VWF propeptide, VWF, and FVIII.

Identification of a core set of genes that signifies pathways underlying cardiac hypertrophy

Although the molecular signals underlying cardiac hypertrophy have been the subject of intense investigation, the extent of common and distinct gene regulation between different forms of cardiac hypertrophy remains unclear. We hypothesized that a general and comparative analysis of hypertrophic gene expression, using microarray technology in multiple models of cardiac hypertrophy, including aortic banding, myocardial infarction, an arteriovenous shunt and pharmacologically induced hypertrophy, would uncover networks of conserved hypertrophy-specific genes and identify novel genes involved in hypertrophic signalling. From gene expression analyses (8740 probe sets, n = 46) of rat ventricular RNA, we identified a core set of 139 genes with consistent differential expression in all hypertrophy models as compared to their controls, including 78 genes not previously associated with hypertrophy and 61 genes whose altered expression had previously been reported. We identified a single common gene program underlying hypertrophic remodelling, regardless of how the hypertrophy was induced. These genes constitute the molecular basis for the existence of one main form of cardiac hypertrophy and may be useful for prediction of a common therapeutic approach. Supplementary material for this article can be found at: http://www.interscience.wiley.com/jpages/1531-6912/suppmat

MicroRNA-15a fine-tunes the level of Delta-like 1 homolog (DLK1) in proliferating 3T3-L1 preadipocytes

Delta like 1 homolog (Dlk1) exists in both transmembrane and soluble molecular forms, and is implicated in cellular growth and plays multiple roles in development, tissue regeneration, and cancer. Thus, DLK1 levels are critical for cell function, and abnormal DLK1 expression can be lethal; however, little is known about the underlying mechanisms. We here report that miR-15a modulates DLK1 levels in preadipocytes thus providing a mechanism for DLK1 regulation that further links it to cell cycle arrest and cancer since miR-15a is deregulated in these processes. In preadipocytes, miR-15a increases with cell density, and peaks at the same stage where membrane DLK1(M) and soluble DLK1(S) are found at maximum levels. Remarkably, miR-15a represses the amount of all Dlk1 variants at the mRNA level but also the level of DLK1(M) protein while it increases the amount of DLK1(S) supporting a direct repression of DLK1 and a parallel effect on the protease that cleaves off the DLK1 from the membrane. In agreement with previous studies, we found that miR-15a represses cell numbers, but additionally, we report that miR-15a also increases cell size. Conversely, anti-miR-15a treatment decreases cell size while increasing cell numbers, scenarios that were completely rescued by addition of purified DLK1(S). Our data thus imply that miR-15a regulates cell size and proliferation by fine-tuning Dlk1 among others, and further emphasize miR-15a and DLK1 levels to play important roles in growth signaling networks.

Quantitative phosphoproteomics dissection of seven-transmembrane receptor signaling using full and biased agonists

Seven-transmembrane receptors (7TMRs) signal through the well described heterotrimeric G proteins but can also activate G protein-independent signaling pathways of which the impact and complexity are less understood. The angiotensin II type 1 receptor (AT(1)R) is a prototypical 7TMR and an important drug target in cardiovascular diseases. "Biased agonists" with intrinsic "functional selectivity" that simultaneously blocks Galpha(q) protein activity and activates G protein-independent pathways of the AT(1)R confer important perspectives in treatment of cardiovascular diseases. In this study, we performed a global quantitative phosphoproteomics analysis of the AT(1)R signaling network. We analyzed ligand-stimulated SILAC (stable isotope labeling by amino acids in cell culture) cells by high resolution (LTQ-Orbitrap) MS and compared the phosphoproteomes of the AT(1)R agonist angiotensin II and the biased agonist [Sar(1),Ile(4),Ile(8)]angiotensin II (SII angiotensin II), which only activates the Galpha(q) protein-independent signaling. We quantified more than 10,000 phosphorylation sites of which 1183 were regulated by angiotensin II or its analogue SII angiotensin II. 36% of the AT(1)R-regulated phosphorylations were regulated by SII angiotensin II. Analysis of phosphorylation site patterns showed a striking distinction between protein kinases activated by Galpha(q) protein-dependent and -independent mechanisms, and we now place protein kinase D as a key protein involved in both Galpha(q)-dependent and -independent AT(1)R signaling. This study provides substantial novel insight into angiotensin II signal transduction and is the first study dissecting the differences between a full agonist and a biased agonist from a 7TMR on a systems-wide scale. Importantly, it reveals a previously unappreciated diversity and quantity of Galpha(q) protein-independent signaling and uncovers novel signaling pathways. We foresee that the amount and diversity of G protein-independent signaling may be more pronounced than previously recognized for other 7TMRs as well. Quantitative mass spectrometry is a promising tool for evaluation of the signaling properties of biased agonists to other receptors in the future.

An angiotensin II type 1 receptor activation switch patch revealed through evolutionary trace analysis

Seven transmembrane (7TM) or G protein-coupled receptors constitute a large superfamily of cell surface receptors sharing a structural motif of seven transmembrane spanning alpha helices. Their activation mechanism most likely involves concerted movements of the transmembrane helices, but remains to be completely resolved. Evolutionary Trace (ET) analysis is a computational method, which identifies clusters of functionally important residues by integrating information on evolutionary important residue variations with receptor structure. Combined with known mutational data, ET predicted a patch of residues in the cytoplasmic parts of TM2, TM3, and TM6 to form an activation switch that is common to all family A 7TM receptors. We tested this hypothesis in the rat Angiotensin II (Ang II) type 1a (AT1a) receptor. The receptor has important roles in the cardiovascular system, but has also frequently been applied as a model for 7TM receptor activation and signaling. Six mutations: F66A, L67R, L70R, L119R, D125A, and I245F were targeted to the putative switch and assayed for changes in activation state by their ligand binding, signaling, and trafficking properties. All but one receptor mutant (that was not expressed well) displayed phenotypes associated with changed activation state, such as increased agonist affinity or basal activity, promiscuous activation, or constitutive internalization highlighting the importance of testing different signaling pathways. We conclude that this evolutionary important patch mediates interactions important for maintaining the inactive state. More broadly, these observations in the AT1 receptor are consistent with computational predictions of a generic role for this patch in 7TM receptor activation.

Normal levels of cerebrospinal fluid hypocretin-1 and daytime sleepiness during attacks of relapsing-remitting multiple sclerosis and monosymptomatic optic neuritis

There is emerging evidence that multiple sclerosis (MS), the hypothalamic sleep-wake regulating neuropeptide hypocretin-1 (hcrt-1) and the sleep disorder narcolepsy may be connected. Thus, the major pathophysiological component of narcolepsy is lack of hcrt-1. Dysfunction of the hypocretin system has been reported in MS case reports with attacks of hypothalamic lesions, undetectable cerebrospinal fluid (CSF) hcrt-1 and hypersomnia, but not found during remission in small samples. Finally, daytime sleepiness, the major symptom of narcolepsy, is reported in several MS populations, and there are case reports of co-existent narcolepsy and MS. However, it is unknown whether hcrt-1 and daytime sleepiness generally change during MS attacks. We therefore analyzed whether daytime sleepiness (using the Epworth Sleepiness Scale (ESS)) and CSF hcrt-1 levels differed between MS attack and remission, in 48 consecutively referred patients with relapsing–remitting MS (RRMS) or monosymptomatic optic neuritis (MON). Twenty-seven patients were in attack and 21 in remission. ESS was normal both during attacks (5.4 ± 3.0) and remission (5.8 ± 2.6), and mean CSF hcrt-1 was normal (456 ± 41 pg/ml). No statistically significant differences were found between attack and remission. MRI scans revealed no hypothalamic lesions. The results show that the hypocretin system is intact and sleepiness is not typical in RRMS and MON without hypothalamic lesions on MRI.

S100A4: a common mediator of epithelial-mesenchymal transition, fibrosis and regeneration in diseases?

Multiple reports have focused on S100A4's role in cancer progression, specifically its ability to enhance metastasis. However, recent studies have linked S100A4 to several diseases besides cancer, including kidney fibrosis, cirrhosis, pulmonary disease, cardiac hypertrophy and fibrosis, arthritis and neuronal injuries. Common to all these diseases is the involvement of fibrotic and inflammatory processes, i.e. processes greatly dependent on tissue remodelling, cell motility and epithelial-mesenchymal transition. Therefore, the basic biological mechanisms behind S100A4's effects are emerging. S100A4 belongs to the S100 family of proteins that contain two Ca2+-binding sites including a canonical EF-hand motif. S100A4 is involved in the regulation of a wide range of biological effects including cell motility, survival, differentiation and contractility. S100A4 has both intracellular and extracellular effects. Hence, S100A4 interacts with cytoskeletal proteins and enhances metastasis of several types of cancer cells. In addition, S100A4 is secreted by unknown mechanisms, thus, paracrinely stimulating a variety of cellular responses, including angiogenesis and neuronal growth. Although many cellular effects of S100A4 are well described, the molecular mechanisms whereby S100A4 elicits these responses remain largely unknown. However, it is likely that the intracellular and the extracellular effects involve distinct mechanisms. In this review, we explore the possible roles of S100A4 in non-cancer diseases and employ this knowledge to describe underlying biological mechanisms including a change in cellular phenotype towards less tightly adherent cells and activation of fibrotic processes that may explain this protein's involvement in multiple pathologies.

Differential extracellular signal-regulated kinases 1 and 2 activation by the angiotensin type 1 receptor supports distinct phenotypes of cardiac myocytes

The angiotensin II (AngII) type 1 receptor (AT(1)R) is a seven-transmembrane receptor well established to activate extracellular signal-regulated kinases 1 and 2 (ERK1/2) by discrete G protein-dependent and beta-arrestin2-dependent pathways. The biological importance of this, however, remains obscure. Application of the modified analogue [Sar(1), Ile(4), Ile(8)]-AngII ([SII] AngII) allowed us to dissect the two pathways of ERK1/2 activation in native cardiac myocytes. Although cytosol-retained, the beta-arrestin2-bound pool of ERK1/2 represents an active signalling component that phosphorylates p90 Ribosomal S6 Kinase, a ubiquitous and versatile mediator of ERK1/2 signal transduction. Moreover, the beta-arrestin2-dependent ERK1/2 signal supports intact proliferation of cardiac myocytes. In contrast to G(q)-activated ERK1/2, and in keeping with its failure to translocate to the nucleus, the beta-arrestin2-scaffolded pool of ERK1/2 does not phosphorylate the transcription factor Elk-1, induces no increased transcription of the immediate-early gene c-Fos, and does not entail myocyte hypertrophy. These results clearly demonstrate the biological significance of differential signalling by the AT(1)R. The opportunity to separate desirable cardiac myocyte division from detrimental hypertrophy holds promise that novel pharmacological approaches will allow targeting of pathway-specific actions.

The angiotensin type 1 receptor activates extracellular signal-regulated kinases 1 and 2 by G protein-dependent and -independent pathways in cardiac myocytes and langendorff-perfused hearts

The angiotensin II (AngII) type 1 receptor (AT(1)R) has been shown to activate extracellular signal-regulated kinases 1 and 2 (ERK1/2) through G proteins or G protein-independently through beta-arrestin2 in cellular expression systems. As activation mechanisms may greatly influence the biological effects of ERK1/2 activity, differential activation of the AT(1)R in its native cellular context could have important biological and pharmacological implications. To examine if AT(1)R activates ERK1/2 by G protein-independent mechanisms in the heart, we used the [Sar(1), Ile(4), Ile(8)]-AngII ([SII] AngII) analogue in native preparations of cardiac myocytes and beating hearts. We found that [SII] AngII does not activate G(q)-coupling, yet stimulates the beta-arrestin2-dependent ERK1/2. The G(q)-activated pool of ERK1/2 rapidly translocates to the nucleus, while the beta-arrestin2-scaffolded pool remains in the cytosol. Similar biased agonism was achieved in Langendorff-perfused hearts, where both agonists elicit ERK1/2 phosphorylation, but [SII] AngII induces neither inotropic nor chronotropic effects.

S100A4 is upregulated in injured myocardium and promotes growth and survival of cardiac myocytes

OBJECTIVE

The multifunctional Ca2+-binding protein S100A4 (also known as Mts1 and Fsp1) is involved in fibrosis and tissue remodeling in several diseases including cancer, kidney fibrosis, central nervous system injury, and pulmonary vascular disease. We previously reported that S100A4 mRNA expression was increased in hypertrophic rat hearts and that it has pro-cardiomyogenic effects in embryonic stem cell-derived embryoid bodies. We therefore hypothesized that S100A4 could play a supportive role in the injured heart.

METHODS AND RESULTS

Here we verify by quantitative real-time PCR and immunoblotting that S100A4 mRNA and protein is upregulated in hypertrophic rat and human hearts and show by way of confocal microscopy that S100A4 protein, but not mRNA, appears in cardiac myocytes only in the border zone after an acute ischemic event in rat and human hearts. In normal rat and human hearts, S100A4 expression primarily colocalizes with markers of fibroblasts. In hypertrophy elicited by aortic banding/stenosis or myocardial infarction, this expression is increased. Moreover, invading macrophages and leucocytes stain strongly for S100A4, further increasing cardiac levels of S100A4 protein after injury. Promisingly, recombinant S100A4 protein elicited a robust hypertrophic response and increased the number of viable cells in cardiac myocyte cultures by inhibiting apoptosis. We also found that ERK1/2 activation was necessary for both the hypertrophy and survival effects of S100A4 in vitro.

CONCLUSIONS

Along with proposed angiogenic and cell motility stimulating effects of S100A4, these findings suggest that S100A4 can act as a novel cardiac growth and survival factor and may have regenerative effects in injured myocardium.

Cardiac regeneration by resident stem and progenitor cells in the adult heart

Two main pieces of data have created a new field in cardiac research. First, the traditional view on the heart as a postmitotic organ has been challenged by the finding of small dividing cells in the heart expressing cardiac contractile proteins with stem cell properties and, second, cellular therapy of the diseased heart using a variety of different cells has shown encouraging effects on cardiac function. These findings immediately raise questions like "what is the identity and origin of the cardiac progenitor cells?","which molecular factors are involved in their mobilization and differentiation?", and "can these cells repair the damaged heart?" This review will address the state of current answers to these questions. Emerging evidence suggests that several subpopulations of cardiac stem or progenitor cells (CPCs) reside within the adult heart. CPCs with the ability to differentiate into all the constituent cells in the adult heart including cardiac myocytes, vascular smooth muscle and endothelial cells have been identified. Valuable knowledge has been obtained from the large number of animal studies and a number of small clinical trials that have utilized a variety of adult stem cells for regenerating infarcted hearts. However, contradictory reports on the regenerative potential of the CPCs exist, and the mechanisms behind the reported hemodynamic effects are intensely debated. Besides directly replenishing cardiac tissue, CPCs could also function by stimulating angiogenesis and improving survival of existing cells by secretion of paracrine factors. With this review we suggest that a better understanding of CPC biology will be pivotal for progressing therapeutic cardiac regeneration. This includes an extended knowledge of the molecular mechanisms behind their mobilization, differentiation, survival and integration in the myocardium.

Role of G-protein-coupled receptor kinase 2 in the heart--do regulatory mechanisms open novel therapeutic perspectives?

G-protein-coupled receptor kinase (GRK) 2 regulates a plethora of cellular processes, including cardiac expression and function of key seven-transmembrane receptors (7TM receptors) such as the beta-adrenergic and angiotensin receptors (Penela P, Murga C, Ribas C, et al.: 2006. Mechanisms of regulation of G-protein-coupled receptor kinases [GRKs] and cardiovascular disease. Cardiovasc Res 69:46-56, Rockman HA, Koch WJ, Lefkowitz RJ: 2002. Seven-transmembrane-spanning receptors and heart function. Nature 415:206-212). Interestingly, these two G-protein-coupled receptor systems are targeted by modern heart failure treatment including beta-adrenergic blockers, angiotensin-converting enzyme inhibitors, and angiotensin receptor blockers. Although GRK2 is ubiquitously expressed, its particular importance in the heart has been demonstrated by interesting phenotypes of genetically altered mice that suggest GRK2 inhibition can ameliorate heart failure. In essence, this work suggests GRK2 could be an endogenous receptor blocker targeting both the beta-adrenergic and angiotensin receptors in the heart. This notion immediately suggests it is important to understand the molecular mechanisms that regulate GRK2 activity in the heart. In this review, we provide a detailed presentation of the tight regulation of GRK2 expression levels and protein activity, and we discuss the cardiovascular GRK2 functions and possible therapeutic perspectives.

Constitutive homo- and hetero-oligomerization of TbetaRII-B, an alternatively spliced variant of the mouse TGF-beta type II receptor

Transforming growth factor (TGF)-beta ligands signal through transmembrane type I and type II serine/threonine kinase receptors, which form heteromeric signalling complexes upon ligand binding. Type II TGF-beta receptors (TbetaRII) are reported to exist as homodimers at the cell surface, but the oligomerization pattern and dynamics of TbetaRII splice variants in live cells has not been demonstrated thus far. Using co-immunoprecipitation and bioluminescence resonance energy transfer (BRET), we demonstrate that the mouse TbetaRII receptor splice variant TbetaRII-B is capable of forming ligand-independent homodimers and heterodimers with TbetaRII. The homomeric interaction of mouse (m)TbetaRII-B isoforms, however, is less robust than the heteromeric interactions of mTbetaRII-B with wild-type TbetaRII, which indicates that these receptors may be more likely to heterodimerize when both receptors are expressed. Moreover, we demonstrate that mTbetaRII-B is a signalling receptor with ubiquitous tissue expression. Our study thus demonstrates previously unappreciated complex formation of TGF-beta type II receptors, and suggests that mTbetaRII-B can direct TGF-beta-induced signalling in vitro and in vivo.

Extracellular calcium sensing in rat aortic vascular smooth muscle cells

Extracellular calcium (Ca(2+)(o)) can act as a first messenger in many cell types through a G protein-coupled receptor, calcium-sensing receptor (CaR). It is still debated whether the CaR is expressed in vascular smooth muscle cells (VSMCs). Here, we report the expression of CaR mRNA and protein in rat aortic VSMCs and show that Ca(2+)(o) stimulates proliferation of the cells. The effects of Ca(2+)(o) were attenuated by pre-treatment with MAPK kinase 1 (MEK1) inhibitor, as well as an allosteric modulator, NPS 2390. Furthermore, stimulation of the VSMCs with Ca(2+)(o)-induced phosphorylation of ERK1/2, but surprisingly did not cause inositol phosphate accumulation. We were not able to conclusively state that the CaR mediates Ca(2+)(o)-induced cell proliferation. Rather, an additional calcium-sensing mechanism may exist. Our findings may be of importance with regard to atherosclerosis, an inflammatory disease characterized by abnormal proliferation of VSMCs and high local levels of calcium.

Parietal endoderm secreted S100A4 promotes early cardiomyogenesis in embryoid bodies

Cardiomyogenesis is influenced by factors secreted by anterior-lateral and extra-embryonic endoderm. Differentiation of embryonic stem cells in embryoid bodies allows to study the influence of growth factors on cardiomyogenesis. By these means SPARC was identified as a new factor enhancing cardiomyogenesis [M. Stary, W. Pasteiner, A. Summer, A. Hrdina, A. Eger, G. Weitzer, Parietal endoderm secreted SPARC promotes early cardiomyogenesis in vitro, Exp. Cell Res. 310 (2005) 331-341]. Here we report a similar and new function for S100A4, a calcium-binding protein of the EF-hand type. S100A4 is secreted by parietal endoderm and promotes early differentiation and proliferation of cardiomyocytes. Oligomeric S100A4 supports cardiomyogenesis in a concentration-dependent manner, whereas inhibition of autocrine S100A4 severely attenuates cardiomyogenesis. S100A4 specifically influences transcription in differentiating cardiomyocytes, as evident from increased expression of cardiac transcription factor genes nkx2.5 and mef2C. These data suggest that S100A4, like SPARC, plays a supportive role in early in vitro cardiomyogenesis.

Family C 7TM Receptor Dimerization and Activation

The family C seven transmembrane (7TM) receptors constitutes a small and especially well characterized subfamily of the large 7TM receptor superfamily. Approximately 50% of current prescription drugs target 7TM receptors, this biologically important family represents the largest class of drug-targets today. It is well established that family C 7TM receptors form homo- or hetero-dimers on the cell surface of living cells. The large extra-cellular domains (ECD) have been crystallized as a dimer in the presence and absence of agonist. Upon agonist binding, the dimeric ECD undergoes large conformational changes that lead to receptor activation. Despite extensive studies of the receptor transmembrane domain, several key features, including the exact organization of the complete receptor dimer, the sequence of events leading to receptor activation, and the functional significance of dimerization, have yet to be fully defined. This review presents the biochemical support for family C 7TM receptor dimerization and discusses its importance for receptor biosynthesis, surface expression, ligand binding and activation, since lessons learnt here may well be applicable to the whole superfamily of 7TM receptors.

Expression profiling reveals differences in metabolic gene expression between exercise-induced cardiac effects and maladaptive cardiac hypertrophy

While cardiac hypertrophy elicited by pathological stimuli eventually leads to cardiac dysfunction, exercise-induced hypertrophy does not. This suggests that a beneficial hypertrophic phenotype exists. In search of an underlying molecular substrate we used microarray technology to identify cardiac gene expression in response to exercise. Rats exercised for seven weeks on a treadmill were characterized by invasive blood pressure measurements and echocardiography. RNA was isolated from the left ventricle and analysed on DNA microarrays containing 8740 genes. Selected genes were analysed by quantitative PCR. The exercise program resulted in cardiac hypertrophy without impaired cardiac function. Principal component analysis identified an exercise-induced change in gene expression that was distinct from the program observed in maladaptive hypertrophy. Statistical analysis identified 267 upregulated genes and 62 downregulated genes in response to exercise. Expression changes in genes encoding extracellular matrix proteins, cytoskeletal elements, signalling factors and ribosomal proteins mimicked changes previously described in maladaptive hypertrophy. Our most striking observation was that expression changes of genes involved in beta-oxidation of fatty acids and glucose metabolism differentiate adaptive from maladaptive hypertrophy. Direct comparison to maladaptive hypertrophy was enabled by quantitative PCR of key metabolic enzymes including uncoupling protein 2 (UCP2) and fatty acid translocase (CD36). DNA microarray analysis of gene expression changes in exercise-induced cardiac hypertrophy suggests that a set of genes involved in fatty acid and glucose metabolism could be fundamental to the beneficial phenotype of exercise-induced hypertrophy, as these changes are absent or reversed in maladaptive hypertrophy.

MAP kinase protects G protein-coupled receptor kinase 2 from proteasomal degradation

The G protein-coupled receptor kinase 2 (GRK2) phosphorylates and shuts down signaling from 7-transmembrane receptors (7TMs). Although, receptor activity controls GRK2 expression levels, the underlying molecular mechanisms are poorly understood. We have previously shown that extracellular signal-regulated kinase (ERK1/2) activation increases GRK2 expression [J. Theilade, J. Lerche Hansen, S. Haunso, S.P. Sheikh, Extracellular signal-regulated kinases control expression of G protein-coupled receptor kinase 2 (GRK2), FEBS Lett. 518 (2002) 195-199]. In the present study, we found that ERK1/2 regulates GRK2 degradation rather than synthesis. ERK1/2 blockade using PD98059 decreased GRK2 cellular levels to 0.25-fold of control in Cos7 cells. This effect was due to enhanced degradation of the GRK2 protein, since proteasome blockade prevented down-regulation of GRK2 protein levels in the presence of PD98059. Further, ERK blockade had no effect on GRK2 synthesis as probed using a reporter construct carrying the GRK2 promoter upstream of the luciferase gene. We predict ERK1/2 mediated GRK2 protection could be a general phenomenon as proteasome inhibition increased GRK2 expression in two other cell lines, HEK293 and NIH3T3.

Functional consequences of 7TM receptor dimerization

7TM receptors work as signaling platforms that activate multiple signalling systems at the intracellular face of the plasma membrane. It is an emerging concept that 7TM receptors form homo- and hetero-dimers or -oligomers in vitro and in vivo. Numerous studies suggest dimerization is important for receptor function including agonist/antagonist affinity, efficacy, trafficking, and specificity of signal transduction, yet it remains unknown whether dimerization is a prerequisite for 7TM receptor signaling. The current review provides an overview of the biochemical support for 7TM homodimerization, followed by a discussion of the characteristics of homodimerization, with focus on dimer organization, and the functional consequences of dimerization. Heterodimerization will not generally be discussed in this review although we have included a few examples to illustrate specific points, and a table that summarises the current literature on this subject.

Oligomerization of Wild Type and Nonfunctional Mutant Angiotensin II Type I Receptors Inhibits Gαq Protein Signaling but Not ERK Activation

The 7-transmembrane or G protein-coupled receptors relay signals from hormones and sensory stimuli to multiple signaling systems at the intracellular face of the plasma membrane including heterotrimeric G proteins, ERK1/2, and arrestins. It is an emerging concept that 7-transmembrane receptors form oligomers; however, it is not well understood which roles oligomerization plays in receptor activation of different signaling systems. To begin to address this question, we used the angiotensin II type 1 (AT(1)) receptor, a key regulator of blood pressure and fluid homeostasis that in specific context has been described to activate ERKs without activating G proteins. By using bioluminescence resonance energy transfer, we demonstrate that AT(1) receptors exist as oligomers in transfected COS-7 cells. AT(1) oligomerization was both constitutive and receptor-specific as neither agonist, antagonist, nor co-expression with three other receptors affected the bioluminescence resonance energy transfer 2 signal. Furthermore, the oligomerization occurs early in biosynthesis before surface expression, because we could control AT(1) receptor export from the endoplasmic reticulum or Golgi by using regulated secretion/aggregation technology (RPD trade mark ). Co-expression studies of wild type AT(1) and AT(1) receptor mutants, defective in either ligand binding or G protein and ERK activation, yielded an interesting result. The mutant receptors specifically exerted a dominant negative effect on Galpha(q) activation, whereas ERK activation was preserved. These data suggest that distinctly active conformations of AT(1) oligomers can couple to each of these signaling systems and imply that oligomerization plays an active role in supporting these distinctly active conformations of AT(1) receptors.

Loss-of-function polymorphic variants of the human angiotensin II type 1 receptor

The angiotensin II type 1 (AT1) receptor is the primary effector for angiotensin II (Ang II), a key peptide regulator of blood pressure and fluid homeostasis. AT1 receptors are involved in the pathogenesis of several cardiovascular diseases, including hypertension, cardiac hypertrophy, and congestive heart failure, which are characterized by significant interindividual variation in disease risk, progression, and response to pharmacotherapy. Such variation could arise from genomic polymorphisms in the AT1 receptor. To pursue this notion, we have pharmacologically characterized seven known and putative nonsynonymous AT1 receptor variants. Functional analysis using the cell-based assay receptor selection and amplification technology (R-SAT) revealed that three variants (AT1-G45R, AT1-F204S, and AT1-C289W) displayed altered responses to Ang II and other AT1 receptor agonists and antagonists. Agonist responses to Ang II were absent for AT1-G45R and significantly reduced in potency for AT1-C289W (11-fold) and AT1-F204S (57-fold) compared with the wild-type (WT) receptor. AT1-F204S also displayed reduced relative efficacy (57%). Quantitatively similar results were obtained in two additional functional assays, phosphatidyl inositol hydrolysis and extracellular signal-regulated kinase activation. Radioligand binding studies revealed that AT1-G45R failed to bind Ang II, whereas cell surface staining clearly showed that it trafficked to the cell surface. AT1-C289W and AT1-F204S displayed reduced binding affinities of 3- and 5-fold and reduced cell surface expression of 43 and 60% of that observed for the WT receptor, respectively. These data demonstrate that polymorphic variation in the human AT1 receptor induces loss of functional phenotypes, which may constitute the molecular basis of variability of AT1 receptor-mediated physiological responses.

Multiprotein bridging factor 1 cooperates with c-Jun and is necessary for cardiac hypertrophy in vitro

Cardiac hypertrophy is induced by a number of stimuli and can lead to cardiomyopathy and heart failure. Cardiomyocyte hypertrophy is characterized by increased cell size and altered gene expression. By differential-display polymerase chain reaction and Western blotting we found that the transcriptional coactivator MBF1 was upregulated during hypertrophy in cardiomyocyte cultures. Furthermore, MBF1 protein level increased in two animal models of hypertrophy, angiotensin II treatment and aortic banding. MBF1 antisense oligodeoxynuclotides blocked phenylephrine-induced hypertrophy, suggesting MBF1 plays a key role in hypertrophic growth. In contrast, overexpression of MBF1 potentiated the hormone-induced response of the atrial natriuretic peptide promoter. MBF1 overexpressed by transient transfection cooperated with the transcription factor c-Jun in activation of transcription but not with GATA4. MBF1 and c-Jun induced the activity of a transiently transfected atrial natriuretic peptide promoter, whereas neither MBF1 nor c-Jun could induce the promoter alone. Moreover, MBF1 bound to c-Jun in vitro. These data suggest that MBF1 is a transcriptional coactivator of c-Jun regulating hypertrophic gene expression. Inhibitor studies suggested that MBF1 activates the atrial natriuretic peptide promoter independently of the calcineurin and CaMK signaling pathways. Our results indicate that MBF1 participates in hormone-induced cardiomyocyte hypertrophy and activates hypertrophic gene expression as a coactivator of c-Jun.

Differential G protein receptor kinase 2 expression in compensated hypertrophy and heart failure after myocardial infarction in the rat

The onset of heart failure is associated with characteristic changes in myocardial expression of G protein receptor kinase 2 (GRK2). Although, GRK2 significantly contributes to the regulation of myocardial function in the failing heart, the GRK2 expression during cardiac hypertrophy without heart failure remains to be explored. We here report a differential expression of GRK2 in cardiac hypertrophy with or without heart failure in response to a myocardial infarction in the rat. Postmyocardial infarction animals were divided into two groups depending on the absence or presence of pulmonary edema, which is a manifestation of heart failure. Remarkably, cardiac GRK2 expression and activity were inhibited in animals with cardiac hypertrophy without heart failure, whereas animals with heart failure had elevated GRK2. Thus, three weeks after the infarction cardiac GRK2 expression in animals with hypertrophy alone was decreased to 0.34 of control, whereas in the group of animals with heart failure GRK2 expression was 1.89-fold higher than in sham-operated animals. GRK2 activity was affected in a similar way, three and nine weeks after the infarction cardiac GRK2 activity was reduced to 0.58 and 0.62 in animals with hypertrophy without heart failure when compared to sham operated animals. By contrast, GRK2 activity was increased by 1.32- and 1.21-fold three and nine weeks postinfarction in animals with heart failure when compared to sham animals. These data suggest that GRK2 expression is differentially regulated in hypertrophic, non-failing and hypertrophic, failing hearts.

Probing intermolecular protein-protein interactions in the calcium-sensing receptor homodimer using bioluminescence resonance energy transfer (BRET)

The calcium-sensing receptor (CaR) belongs to family C of the G-protein coupled receptor superfamily. The receptor is believed to exist as a homodimer due to covalent and non-covalent interactions between the two amino terminal domains (ATDs). It is well established that agonist binding to family C receptors takes place at the ATD and that this causes the ATD dimer to twist. However, very little is known about the translation of the ATD dimer twist into G-protein coupling to the 7 transmembrane moieties (7TMs) of these receptor dimers. In this study we have attempted to delineate the agonist-induced intermolecular movements in the CaR homodimer using the new bioluminescence resonance energy transfer technique, BRET2, which is based on the transference of energy from Renilla luciferase (Rluc) to the green fluorescent protein mutant GFP2. We tagged CaR with Rluc and GFP2 at different intracellular locations. Stable and highly receptor-specific BRET signals were obtained in tsA cells transfected with Rluc- and GFP2-tagged CaRs under basal conditions, indicating that CaR is constitutively dimerized. However, the signals were not enhanced by the presence of agonist. These results could indicate that at least parts of the two 7TMs of the CaR homodimer are in close proximity in the inactivated state of the receptor and do not move much relative to one another upon agonist activation. However, we cannot exclude the possibility that the BRET technology is unable to register putative conformational changes in the CaR homodimer induced by agonist binding because of the bulk sizes of the Rluc and GFP2 molecules.

Involvement of cyclin D activity in left ventricle hypertrophy in vivo and in vitro

OBJECTIVE

Cardiac hypertrophy is induced by a number of stimuli and can lead to cardiomyopathy and heart failure. Present knowledge suggests that cell-cycle regulatory proteins take part in hypertrophy. We have investigated if the D-type cyclins are involved in cardiac hypertrophy.

METHODS

The expression and activity of the D-type cyclins and associated kinases in cardiomyocytes were studied during angiotensin II- and pressure overload-induced hypertrophy in rats (Rattus norvegicus) and in isolated, neonatal cardiomyocytes. Expression of the D-type cyclins was manipulated pharmacologically and genetically in neonatal myocytes.

RESULTS

In the left ventricle, there was a low, constitutive expression of the D-type cyclins, which may have a biological role in normal, adult myocytes. The protein level and the associated kinase activity of the D-type cyclins were up-regulated during hypertrophic growth. The increase in cyclin D expression could be mimicked in vitro in neonatal cardiac myocytes. Interestingly, the cyclin Ds were up-regulated by hypertrophic elicitors that stimulate different signalling pathways, suggesting that cyclin D expression is an inherent part of cardiac hypertrophy. Treatment of myocytes with the compound differentiation inducing factor 1 inhibited expression of the D-type cyclins and impaired hypertrophic growth induced by angiotensin II, phenylephrine and serum. The response to hypertrophic elicitors could be restored in differentiation inducing factor 1-treated myocytes by expressing cyclin D2 from a heterologous promoter.

CONCLUSION

Our results point to the D-type cyclins as important regulators of cardiac hypertrophy. This supports the notion that cell-cycle regulatory proteins regulate hypertrophic growth.

Extracellular signal-regulated kinases control expression of G protein-coupled receptor kinase 2 (GRK2)

G protein-coupled receptor kinase 2 (GRK2) phosphorylates G protein-coupled receptors resulting in uncoupling from G proteins. Receptors modulate GRK2 expression, however the mechanistic basis for this effect is largely unknown. Here we report a novel mechanism by which receptors use the extracellular signal-regulated kinase (ERK) cascade to regulate GRK2 cellular levels. ERK activation by receptor stimulation elevated endogenous GRK2 while antagonist treatment decreased cellular GRK2. Activating ERK by overexpressing constitutive active MEK-1 or Ras elevated GRK2 protein levels while blocking ERK using PD98059 or dominant negative Ras abolished this effect. These data suggest ERK is a critical regulator of GRK2 levels.

G protein-coupled receptor kinase 2--a feedback regulator of Gq pathway signalling

G protein coupled receptors or serpentine receptors work as signalling switches that turn extracellular signals into activation of multiple molecules at the intracellular face of the plasma membrane. Serpentine receptors are the targets of around 70% of all current drugs in clinical medicine. We suggest that these receptors can be pharmacologically targeted by modification of their unique internal inhibitors the G protein coupled receptor kinases (GRKs). The GRKs constitute a family of serine/threonine kinases that specifically bind to and phosphorylate agonist-activated serpentine receptors. The phosphorylated receptors are recognized by arrestins that bind to the receptor and uncouple them from attached G proteins thereby terminating G protein signalling. This review focuses on a ubiquitously expressed GRK family member dubbed GRK2 (previously called beta-adrenergic receptor kinase 1) that regulates cellular signalling at multiple levels. In Gq-coupled signalling modules GRK2 may function as a feedback inhibitor molecule that monitors, inhibits and re-directs the information flow. GRK2 acts as a negative feedback protein by interacting with at least six key signalling molecules in the Gq pathway including; receptors, free G beta gamma subunits, activated G alpha q subunits, phosphatidylinositol-4, 5-bisphosphate (PIP2), protein kinase C (PKC) and calmodulin (CaM). GRK signalling is important for immune, endocrine and cardiovascular function manifesting itself in disorders such as heart failure and lymphocyte activation especially in chronic inflammation. This review summarizes the advances made in understanding the many actions of GRKs and addresses their potential as novel therapeutic targets.

Functional reconstitution of the angiotensin II type 2 receptor and G(i) activation

On the basis of the patterns of conserved amino acid sequence, the angiotensin II type 2 (AT(2)) receptor belongs to the family of serpentine receptors, which relay signals from extracellular stimuli to heterotrimeric G proteins. However, the AT(2) receptor signal transduction mechanisms are poorly understood. We have measured AT(2)-triggered activation of purified heterotrimeric proteins in urea-extracted membranes from cultured COS-7 cells expressing the recombinant receptor. This procedure removes contaminating GTP-binding proteins without inactivating the serpentine receptor. Binding studies using [(125)I] angiotensin (Ang) II revealed a single binding site with a K(d)=0.45 and a capacity of 627 fmol/mg protein in the extracted membranes. The AT(2) receptor caused a rapid activation of alpha(i) and alpha(o) but not of alpha(q) and alpha(s), as measured by radioactive guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) binding. Activation required the presence of activated receptors, betagamma, and alpha subunits. As a first step aimed at developing an in vitro assay to examine AT(2) receptor pharmacology, we tested a battery of Ang II-related ligands for their ability to promote AT(1) or AT(2) receptor-catalyzed G(i) activation. Two proteolytic fragments of Ang II, Ang III and Ang1-7, also promoted activation of alpha(i) through the AT(2) receptor. Furthermore, we found that [Sar(1),Ala(8)]Ang II is an antagonist for both AT(1) and AT(2) receptors and that CPG42112 behaves as a partial agonist for the AT(2) receptor. In combination with previous observations, these results show that the AT(2) receptor is fully capable of activating G(i) and provides a new tool for exploring AT(2) receptor pharmacology and interactions with G-protein trimers.

Effect of glucagon-like peptide 1(7-36)amide in insulin-treated patients with diabetes mellitus secondary to chronic pancreatitis

Diabetes mellitus secondary to chronic pancreatitis is characterized by a progressive destruction of the pancreas, including loss of the islet cells, leading to a form of diabetes that can mimic both type 1 and type 2 diabetes. Glucagon-like peptide 1(7-36)amide (GLP-1), an intestinally derived insulinotropic hormone, represents a potential therapeutic agent for type 2 diabetes, because exogenous GLP-1 has been shown to increase the insulin and reduce the glucagon concentrations in these patients, and thus induce lower blood glucose, but without causing hypoglycemia. Ten patients with diabetes mellitus secondary to chronic pancreatitis and five normal subjects were studied. Nine patients were treated with insulin and one patient with sulfonylurea. In the fasting state, saline or GLP-1 in doses of 0.4 or 1.2 pmol/min/kg body weight were infused intravenously for 4 hours. Blood glucose was reduced in all patients with both doses of GLP-1; plasma C-peptide increased (p<0.02), and plasma glucagon decreased (p<0.02) compared with basal levels, also in three patients with normoglycemia and high levels of presumably exogenous insulin. Similar results were obtained in the normal subjects. In conclusion, GLP-1 treatment may be considered in patients with diabetes mellitus secondary to chronic pancreatitis, provided that a certain amount of alpha- and beta-cell secretory capacity is still present.

Similar structures and shared switch mechanisms of the beta2-adrenoceptor and the parathyroid hormone receptor. Zn(II) bridges between helices III and VI block activation

The seven transmembrane helices of serpentine receptors comprise a conserved switch that relays signals from extracellular stimuli to heterotrimeric G proteins on the cytoplasmic face of the membrane. By substituting histidines for residues at the cytoplasmic ends of helices III and VI in retinal rhodopsin, we engineered a metal-binding site whose occupancy by Zn(II) prevented the receptor from activating a retinal G protein, Gt (Sheikh, S. P., Zvyaga, T. A. , Lichtarge, O., Sakmar, T. P., and Bourne, H. R. (1996) Nature 383, 347-350). Now we report engineering of metal-binding sites bridging the cytoplasmic ends of these two helices in two other serpentine receptors, the beta2-adrenoreceptor and the parathyroid hormone receptor; occupancy of the metal-binding site by Zn(II) markedly impairs the ability of each receptor to mediate ligand-dependent activation of Gs, the stimulatory regulator of adenylyl cyclase. We infer that these two receptors share with rhodopsin a common three-dimensional architecture and an activation switch that requires movement, relative to one another, of helices III and VI; these inferences are surprising in the case of the parathyroid hormone receptor, a receptor that contains seven stretches of hydrophobic sequence but whose amino acid sequence otherwise shows no apparent similarity to those of receptors in the rhodopsin family. These findings highlight the evolutionary conservation of the switch mechanism of serpentine receptors and help to constrain models of how the switch works.

C5a receptor activation. Genetic identification of critical residues in four transmembrane helices

Hormones and sensory stimuli activate serpentine receptors, transmembrane switches that relay signals to heterotrimeric guanine nucleotide-binding proteins (G proteins). To understand the switch mechanism, we subjected 93 amino acids in transmembrane helices III, V, VI, and VII of the human chemoattractant C5a receptor to random saturation mutagenesis. A yeast selection identified 121 functioning mutant receptors, containing a total of 523 amino acid substitutions. Conserved hydrophobic residues are located on helix surfaces that face other helices in a modeled seven-helix bundle (Baldwin, J. M., Schertler, G. F., and Unger, V. M. (1997) J. Mol. Biol. 272, 144-164), whereas surfaces predicted to contact the surrounding lipid tolerate many substitutions. Our analysis identified 25 amino acid positions resistant to nonconservative substitutions. These appear to comprise two distinct components of the receptor switch, a surface at or near the extracellular membrane interface and a core cluster in the cytoplasmic half of the bundle. Twenty-one of the 121 mutant receptors exhibit constitutive activity. Amino acids substitutions in these activated receptors predominate in helices III and VI; other activating mutations truncate the receptor near the extracellular end of helix VI. These results identify key elements of a general mechanism for the serpentine receptor switch.