The different facets of organelle interplay-an overview of organelle interactions

Membrane-bound organelles such as mitochondria, peroxisomes, or the endoplasmic reticulum (ER) create distinct environments to promote specific cellular tasks such as ATP production, lipid breakdown, or protein export. During recent years, it has become evident that organelles are integrated into cellular networks regulating metabolism, intracellular signaling, cellular maintenance, cell fate decision, and pathogen defence. In order to facilitate such signaling events, specialized membrane regions between apposing organelles bear distinct sets of proteins to enable tethering and exchange of metabolites and signaling molecules. Such membrane associations between the mitochondria and a specialized site of the ER, the mitochondria associated-membrane (MAM), as well as between the ER and the plasma membrane (PAM) have been partially characterized at the molecular level. However, historical and recent observations imply that other organelles like peroxisomes, lysosomes, and lipid droplets might also be involved in the formation of such apposing membrane contact sites. Alternatively, reports on so-called mitochondria derived-vesicles (MDV) suggest alternative mechanisms of organelle interaction. Moreover, maintenance of cellular homeostasis requires the precise removal of aged organelles by autophagy—a process which involves the detection of ubiquitinated organelle proteins by the autophagosome membrane, representing another site of membrane associated-signaling. This review will summarize the available data on the existence and composition of organelle contact sites and the molecular specializations each site uses in order to provide a timely overview on the potential functions of organelle interaction.

Oxytocin Regulates Stress-Induced Crf Gene Transcription through CREB-Regulated Transcription Coactivator 3

The major regulator of the neuroendocrine stress response in the brain is corticotropin releasing factor (CRF), whose transcription is controlled by CREB and its cofactors CRTC2/3 (TORC2/3). Phosphorylated CRTCs are sequestered in the cytoplasm, but rapidly dephosphorylated and translocated into the nucleus following a stressful stimulus. As the stress response is attenuated by oxytocin (OT), we tested whether OT interferes with CRTC translocation and, thereby, Crf expression. OT (1 nmol, i.c.v.) delayed the stress-induced increase of nuclear CRTC3 and Crf hnRNA levels in the paraventricular nucleus of male rats and mice, but did not affect either parameter in the absence of the stressor. The increase in Crf hnRNA levels at later time points was parallel to elevated nuclear CRTC2/3 levels. A direct effect of Thr(4) Gly(7)-OT (TGOT) on CRTC3 translocation and Crf expression was found in rat primary hypothalamic neurons, amygdaloid (Ar-5), hypothalamic (H32), and human neuroblastoma (Be(2)M17) cell lines. CRTC3, but not CRCT2, knockdown using siRNA in Be(2)M17 cells prevented the effect of TGOT on Crf hnRNA levels. Chromatin-immunoprecipitation demonstrated that TGOT reduced CRTC3, but not CRTC2, binding to the Crf promoter after 10 min of forskolin stimulation. Together, the results indicate that OT modulates CRTC3 translocation, the binding of CRTC3 to the Crf promoter and, ultimately, transcription of the Crf gene.

SIGNIFICANCE STATEMENT

The neuropeptide oxytocin has been proposed to reduce hypothalamic-pituitary-adrenal (HPA) axis activation during stress. The underlying mechanisms are, however, elusive. In this study we show that activation of the oxytocin receptor in the paraventricular nucleus delays transcription of the gene encoding corticotropin releasing factor (Crf), the main regulator of the stress response. It does so by sequestering the coactivator of the transcription factor CREB, CRTC3, in the cytosol, resulting in reduced binding of CRTC3 to the Crf gene promoter and subsequent Crf gene expression. This novel oxytocin receptor-mediated intracellular mechanism might provide a basis for the treatment of exaggerated stress responses in the future.

Effects of small platform catheter-based left ventricular assist device support on regional myocardial signal transduction

OBJECTIVES

Left ventricular (LV) assist device (LVAD) support reduces pathological loading. However, load-induced adaptive responses may be suppressed. Pathological loading dysregulates cardiac G protein-coupled receptor (GPCR) signaling. Signaling through G proteins is deleterious, whereas beta (β)-arrestin-mediated signaling is cardioprotective. We examined the effects of pathological LV loading/LV dysfunction and treatment via LVAD, on β-arrestin-mediated signaling, and genetic networks downstream of load.

METHODS

An ovine myocardial infarction (MI) model was used. Sheep underwent sham thoracotomy (n = 3), mid-left anterior descending coronary artery ligation to produce MI (n = 3), or MI with placement of a small-platform catheter-based LVAD (n = 3). LVAD support was continued for 2 weeks. Animals were maintained for a total of 12 weeks. Myocardial specimens were harvested and analyzed.

RESULTS

MI induced β-arrestin activation. Increased interactions between epidermal growth factor receptor and β-arrestins were observed. LVAD support inhibited these responses to MI (P < .05). LVAD support inhibited the activation of cardioprotective signaling effectors Akt (P < .05), and, to a lesser extent, extracellular regulated kinase 1/2 (P not significant); however, MI resulted in regional activation of load-induced GPCR signaling via G proteins, as assessed by the induction of atrial natriuretic peptide mRNA expression in the MI-adjacent zone relative to the MI-remote zone (P < .05). MI-adjacent zone atrial natriuretic peptide expression was renormalized with LVAD support.

CONCLUSIONS

LVAD support inhibited cardioprotective β-arrestin-mediated signaling. However, net benefits of normalization of load-induced GPCR signaling were observed in the MI-adjacent zone. These findings may have implications for the optimal extent and duration of unloading, and for the development of adjunctive medical therapies.

Phase I study of the anti-IGF1R antibody cixutumumab with everolimus and octreotide in advanced well-differentiated neuroendocrine tumors

Preclinical data suggest multiple roles for the IGF1 receptor (IGF1R) in neuroendocrine tumors (NETs), including mediating resistance to mammalian target of rapamycin (mTOR) inhibitors. Everolimus, an oral mTOR inhibitor, and octreotide long-acting repeatable (LAR) are approved for subgroups of well-differentiated NET. The primary objective of the present study was to establish the safety and recommended phase II dose (RP2D) of cixutumumab, a monoclonal antibody (MAB) against IGF1R, with everolimus and octreotide LAR. Patients with well-differentiated NET were treated with 10  mg everolimus p.o. daily, 20  mg octreotide LAR i.m. every 21 days, and escalating doses of cixutumumab. An expansion cohort was enrolled at RP2D. Correlative studies included the evaluation of mTOR pathway inhibition in paired tumor biopsies and the effects of this combination on metabolism via indirect calorimetry. Nineteen patients with progressive disease were enrolled, including nine to the expansion portion. Two patients had dose-limiting toxicities of grade 3 mucositis at 15  mg/kg cixutumumab. Long-term tolerance at RP2D was problematic, and the most common ≥grade 3 adverse event was fatigue. One patient with metastatic insulinoma had a confirmed partial response, whereas 17 had stable disease. The median progression-free survival was 43.6 weeks, and the median overall survival was 25.5 months. The RP2D of this combination per the predefined study protocol of 10  mg/kg cixutumumab i.v., 20  mg octreotide LAR i.m. every 21 days plus 10  mg everolimus p.o. daily is associated with non-dose-limiting toxicities that limit long-term tolerance. Although a signal of activity was noted in the present study, this will need to be reconciled with limited tolerance of the combination and data from larger studies of anti-IGF1R MABs in NET that have been disappointing.

Targeting unfolded protein response in cancer and diabetes

The maturation of secretory and membrane proteins in the endoplasmic reticulum (ER) is tightly regulated by the unfolded protein response (UPR), a signal transduction pathway maintaining ER protein folding homeostasis. However, certain ER states are incompatible with cell survival and therefore the UPR may choose to eliminate severely disrupted cells by apoptosis. This is accomplished primarily through the activation of the transcription factor CCAAT-enhancer-binding protein homologous protein (CHOP). In the April 2015 issue of Endocrine-Related Cancer, researchers from the universities of South Carolina and Athens (Greece) suggested a novel mechanism of CHOP-mediated apoptosis connected with the suppression of a prominent cell cycle regulator with anti-apoptotic activity, p21. These findings and suggested clinical applications, such as potentiation of cancer chemotherapy and a novel therapeutic approach for type 2 diabetes, are discussed in the context of UPR.

Down-regulation of Immune-related Genes by PSCA in Gallbladder Cancer Cells Implanted into Mice

BACKGROUND/AIM

In previous work, we found that prostate stem cell antigen (PSCA) gene, encoding a glycosylphosphatidylinositol-anchored protein, is a presumable tumor suppressor in gastric cancer and gallbladder cancer (GBC). The introduction of PSCA cDNA into GBC cell lines significantly suppressed tumorigenecity of cells in mice. The PSCA protein is thought to be involved in some form of intracellular signaling that remains to be elucidated.

MATERIALS AND METHODS

Using microarrays, we conducted gene-expression profiling on tumors generated by a GBC cell line TGBC-1TKB, with and without expression of PSCA, which was implanted into mice. Genes whose expression was down-regulated by PSCA were selected, and their down-regulation was confirmed by real-time PCR.

RESULTS

We identified several immune-related genes down-regulated by PSCA, including interleukin 8 (IL8), IL1 receptor antagonist (IL1RN) and S100 calcium-binding proteins A8 (S100A8) and A9 (S100A9).

CONCLUSION

PSCA signaling may suppress tumor growth in vivo by modulating immunological characteristics of GBC cells.

Ligand-Binding Affinity at the Insulin Receptor Isoform-A and Subsequent IR-A Tyrosine Phosphorylation Kinetics are Important Determinants of Mitogenic Biological Outcomes

The insulin receptor (IR) is a tyrosine kinase receptor that can mediate both metabolic and mitogenic biological actions. The IR isoform-A (IR-A) arises from alternative splicing of exon 11 and has different ligand binding and signaling properties compared to the IR isoform-B. The IR-A not only binds insulin but also insulin-like growth factor-II (IGF-II) with high affinity. IGF-II acting through the IR-A promotes cancer cell proliferation, survival, and migration by activating some unique signaling molecules compared to those activated by insulin. This observation led us to investigate whether the different IR-A signaling outcomes in response to IGF-II and insulin could be attributed to phosphorylation of a different subset of IR-A tyrosine residues or to the phosphorylation kinetics. We correlated IR-A phosphorylation to activation of molecules involved in mitogenic and metabolic signaling (MAPK and Akt) and receptor internalization rates (related to mitogenic signaling). We also extended this study to incorporate two ligands that are known to promote predominantly mitogenic [(His(4), Tyr(15), Thr(49), Ile(51)) IGF-I, qIGF-I] or metabolic (S597 peptide) biological actions, to see if common mechanisms can be used to define mitogenic or metabolic signaling through the IR-A. The threefold lower mitogenic action of IGF-II compared to insulin was associated with a decreased potency in activation of Y960, Y1146, Y1150, Y1151, Y1316, and Y1322, in MAPK phosphorylation and in IR-A internalization. With the poorly mitogenic S597 peptide, it was a decreased rate of tyrosine phosphorylation rather than potency that was associated with a low mitogenic potential. We conclude that both decreased affinity of IR-A binding and kinetics of IR-A phosphorylation can independently lead to a lower mitogenic activity. None of the studied parameters could account for the lower metabolic activity of qIGF-I.

The unfolded protein response: the dawn of a new field

Originating from cancer research in mammalian cultured cells, the entirely new field of the unfolded protein response (UPR) was born in 1988. The UPR is a transcriptional induction program coupled with intracellular signaling from the endoplasmic reticulum (ER) to the nucleus to maintain the homeostasis of the ER, an organelle which controls the quality of proteins destined for the secretory pathway. Extremely competitive analyses using the budding yeast Saccharomyces cerevisiae revealed that although signaling from both the ER and cell surface is initiated by activation of a transmembrane protein kinase, the mechanism downstream of ER-resident Ire1p, a sensor molecule of the UPR, is unique. Thus, unconventional spliceosome-independent mRNA splicing is utilized to produce the highly active transcription factor Hac1p. This is the autobiographical story of how a young and not yet independent scientist competed with a very famous full professor in the early days of UPR research, which ultimately lead to their sharing Lasker Basic Medical Research Award in 2014.

Clues to the signals for chloroplast photo-relocation from the lifetimes of accumulation and avoidance responses

Chloroplast photo-relocation movement is crucial for plant survival; however, the mechanism of this phenomenon is still poorly understood. Especially, the signal that goes from photoreceptor to chloroplast is unknown, although the photoreceptors (phototropin 1 and 2) have been identified and an actin structure (chloroplast actin filaments) has been characterized that is specific for chloroplast movement. Here, in gametophytes of the fern Adiantum capillus-veneris, gametophores of the moss Physcomiterella patens, and leaves of the seed plant Arabidopsis thaliana, we sought to characterize the signaling system by measuring the lifetime of the induced response. Chloroplast movements were induced by microbeam irradiation with high-intensity blue light and recorded. The lifetime of the avoidance state was measured as a lag time between switching off the beam and the loss of avoidance behavior, and that of the accumulation state was measured as the duration of accumulation behavior following the extinction of the beam. The lifetime for the avoidance response state is approximately 3-4 min and that for the accumulation response is 19-28 min. These data suggest that the two responses are based on distinct signals.

Middle Ear and Eustachian Tube Mucosal Immunology

Mucosal immune responses within the middle ear and eustachian tube generally provide an effective and efficient response to the presence of microbial pathogens, with approximately 80% of clinically recognizable middle ear infections resolved within 7 days. Particularly for young children aged less than 3 years of age, the proximity and direct connection of the middle ear, via the eustachian tube, to the nasopharynx provide increased risk of commensal bacteria and upper respiratory tract viruses infecting the middle ear. Mucosal immunological defense in the middle ear and eustachian tube utilizes a number of mechanisms, including physicochemical barriers of mucus and the mucosal epithelial cells and innate immune responses such as inflammation, cellular infiltration, effusion, and antimicrobial protein secretions, in addition to adaptive host immune responses. Recent advances in otopathogen recognition via microbial pattern recognition receptors and elucidation of complex signaling cascades have improved understanding of the coordination and regulation of the middle ear mucosal response. These advances support vaccine development aiming to reduce the risk of otitis media in children.

The molecular machinery of neurotransmitter release (Nobel lecture)

The most important property of synaptic transmission is its speed, which is crucial for the overall workings of the brain. In his Nobel Lecture, T. C. Südhof explains how the synaptic vesicle and the plasma membrane undergo rapid fusion during neurotransmitter release and how this process is spatially organized, such that opening of Ca(2+) -channels allows rapid translation of the entering Ca(2+) signal into a fusion event.

Flavonoids Affect Host-Microbiota Crosstalk through TLR Modulation

Interaction between host cells and microbes is known as crosstalk. Among other mechanisms, this takes place when certain molecules of the micro-organisms are recognized by the toll-like receptors (TLRs) in the body cells, mainly in the intestinal epithelial cells and in the immune cells. TLRs belong to the pattern-recognition receptors and represent the first line of defense against pathogens, playing a pivotal role in both innate and adaptive immunity. Dysregulation in the activity of such receptors can lead to the development of chronic and severe inflammation as well as immunological disorders. Among components present in the diet, flavonoids have been suggested as antioxidant dietary factors able to modulate TLR-mediated signaling pathways. This review focuses on the molecular targets involved in the modulatory action of flavonoids on TLR-mediated signaling pathways, providing an overview of the mechanisms involved in such action. Particular flavonoids have been able to modify the composition of the microbiota, to modulate TLR gene and protein expression, and to regulate the downstream signaling molecules involved in the TLR pathway. These synergistic mechanisms suggest the role of some flavonoids in the preventive effect on certain chronic diseases.

Thymidine phosphorylase participates in platelet signaling and promotes thrombosis

RATIONALE

Platelets contain abundant thymidine phosphorylase (TYMP), which is highly expressed in diseases with high risk of thrombosis, such as atherosclerosis and type II diabetes mellitus.

OBJECTIVE

To test the hypothesis that TYMP participates in platelet signaling and promotes thrombosis.

METHODS AND RESULTS

By using a ferric chloride (FeCl3)-induced carotid artery injury thrombosis model, we found time to blood flow cessation was significantly prolonged in Tymp(-/-) and Tymp(+/-) mice compared with wild-type mice. Bone marrow transplantation and platelet transfusion studies demonstrated that platelet TYMP was responsible for the antithrombotic phenomenon in the TYMP-deficient mice. Collagen-, collagen-related peptide-, adenosine diphosphate-, or thrombin-induced platelet aggregation were significantly attenuated in Tymp(+/-) and Tymp(-/-) platelets, and in wild type or human platelets pretreated with TYMP inhibitor KIN59. Tymp deficiency also significantly decreased agonist-induced P-selectin expression. TYMP contains an N-terminal SH3 domain-binding proline-rich motif and forms a complex with the tyrosine kinases Lyn, Fyn, and Yes in platelets. TYMP-associated Lyn was inactive in resting platelets, and TYMP trapped and diminished active Lyn after collagen stimulation. Tymp/Lyn double haploinsufficiency diminished the antithrombotic phenotype of Tymp(+/-) mice. TYMP deletion or inhibition of TYMP with KIN59 dramatically increased platelet-endothelial cell adhesion molecule 1 tyrosine phosphorylation and diminished collagen-related peptide- or collagen-induced AKT phosphorylation. In vivo administration of KIN59 significantly inhibited FeCl3-induced carotid artery thrombosis without affecting hemostasis.

CONCLUSIONS

TYMP participates in multiple platelet signaling pathways and regulates platelet activation and thrombosis. Targeting TYMP might be a novel antiplatelet and antithrombosis therapy.

Role of G-proteins in the differentiation of epiphyseal chondrocytes

Herein, we review the regulation of differentiation of the growth plate chondrocytes by G-proteins. In connection with this, we summarize the current knowledge regarding each family of G-protein α subunit, specifically, Gα(s), Gα(q/11), Gα(12/13), and Gα(i/o). We discuss different mechanisms involved in chondrocyte differentiation downstream of G-proteins and different G-protein-coupled receptors (GPCRs) activating G-proteins in the epiphyseal chondrocytes. We conclude that among all G-proteins and GPCRs expressed by chondrocytes, Gα(s) has the most important role and prevents premature chondrocyte differentiation. Receptor for parathyroid hormone (PTHR1) appears to be the major activator of Gα(s) in chondrocytes and ablation of either one leads to accelerated chondrocyte differentiation, premature fusion of the postnatal growth plate, and ultimately short stature.

Melanoma upregulates ICAM-1 expression on endothelial cells through engagement of tumor CD44 with endothelial E-selectin and activation of a PKCα-p38-SP-1 pathway

Cancer metastasis involves multistep adhesive interactions between tumor cells (TCs) and endothelial cells (ECs), but the molecular mechanisms of intercellular communication in the tumor microenvironment remain elusive. Using static and flow coculture systems in conjunction with flow cytometry, we discovered that certain receptors on the ECs are upregulated on melanoma cell adhesion. Direct contact but not separate coculture between human umbilical endothelial cells (HUVECs) and a human melanoma cell line (Lu1205) increased intercellular adhesion molecule 1 (ICAM-1) and E-selectin expression on HUVECs by 3- and 1.5-fold, respectively, compared with HUVECs alone. The nonmetastatic cell line WM35 failed to promote ICAM-1 expression changes in HUVECs on contact. Enzyme-linked immunosorbent assay (ELISA) revealed that EC-TC contact has a synergistic effect on the expression of the cytokines interleukin (IL)-8, IL-6, and growth-related oncogene α (Gro-α). By using E-selectin cross-linking and beads coated with CD44 immunopurified from Lu1205 cells, we showed that CD44/selectin ligation was responsible for the ICAM-1 up-regulation on HUVECs. Protein kinase Cα (PKC-α) activation was found to be the downstream target of the CD44/selectin-initiated signaling, as ICAM-1 elevation was inhibited by siRNA targeting PKCα or a dominant negative form of PKCα (PKCα DN). Western blot analysis and electrophoretic mobility shift assays (EMSAs) showed that TC-EC contact mediated p38 phosphorylation and binding of the transcription factor SP-1 to its regulation site. In conclusion, CD44/selectin binding signals ICAM-1 up-regulation on the EC surface through a PKCα-p38-SP-1 pathway, which further enhances melanoma cell adhesion to ECs during metastasis.

1D-3D hybrid modeling-from multi-compartment models to full resolution models in space and time

Investigation of cellular and network dynamics in the brain by means of modeling and simulation has evolved into a highly interdisciplinary field, that uses sophisticated modeling and simulation approaches to understand distinct areas of brain function. Depending on the underlying complexity, these models vary in their level of detail, in order to cope with the attached computational cost. Hence for large network simulations, single neurons are typically reduced to time-dependent signal processors, dismissing the spatial aspect of each cell. For single cell or networks with relatively small numbers of neurons, general purpose simulators allow for space and time-dependent simulations of electrical signal processing, based on the cable equation theory. An emerging field in Computational Neuroscience encompasses a new level of detail by incorporating the full three-dimensional morphology of cells and organelles into three-dimensional, space and time-dependent, simulations. While every approach has its advantages and limitations, such as computational cost, integrated and methods-spanning simulation approaches, depending on the network size could establish new ways to investigate the brain. In this paper we present a hybrid simulation approach, that makes use of reduced 1D-models using e.g., the NEURON simulator—which couples to fully resolved models for simulating cellular and sub-cellular dynamics, including the detailed three-dimensional morphology of neurons and organelles. In order to couple 1D- and 3D-simulations, we present a geometry-, membrane potential- and intracellular concentration mapping framework, with which graph- based morphologies, e.g., in the swc- or hoc-format, are mapped to full surface and volume representations of the neuron and computational data from 1D-simulations can be used as boundary conditions for full 3D simulations and vice versa. Thus, established models and data, based on general purpose 1D-simulators, can be directly coupled to the emerging field of fully resolved, highly detailed 3D-modeling approaches. We present the developed general framework for 1D/3D hybrid modeling and apply it to investigate electrically active neurons and their intracellular spatio-temporal calcium dynamics.

Cortical interneurons require Jnk1 to enter and navigate the developing cerebral cortex

Proper assembly of cortical circuitry relies on the correct migration of cortical interneurons from their place of birth in the ganglionic eminences to their place of terminal differentiation in the cerebral cortex. Although molecular mechanisms mediating cortical interneuron migration have been well studied, intracellular signals directing their migration are largely unknown. Here we illustrate a novel and essential role for c-Jun N-terminal kinase (JNK) signaling in guiding the pioneering population of cortical interneurons into the mouse cerebral cortex. Migrating cortical interneurons express Jnk proteins at the entrance to the cortical rudiment and have enriched expression of Jnk1 relative to noninterneuronal cortical cells. Pharmacological blockade of JNK signaling in ex vivo slice cultures resulted in dose-dependent and highly specific disruption of interneuron migration into the nascent cortex. Time-lapse imaging revealed that JNK-inhibited cortical interneurons advanced slowly and assumed aberrant migratory trajectories while traversing the cortical entry zone. In vivo analyses of JNK-deficient embryos supported our ex vivo pharmacological data. Deficits in interneuron migration were observed in Jnk1 but not Jnk2 single nulls, and those migratory deficits were further exacerbated when homozygous loss of Jnk1 was combined with heterozygous reduction of Jnk2. Finally, genetic ablation of Jnk1 and Jnk2 from cortical interneurons significantly perturbed migration in vivo, but not in vitro, suggesting JNK activity functions to direct their guidance rather than enhance their motility. These data suggest JNK signaling, predominantly mediated by interneuron expressed Jnk1, is required for guiding migration of cortical interneurons into and within the developing cerebral cortex.

Regulation of human neutrophil apoptosis and lifespan in health and disease

Neutrophils (also called polymorphonuclear leukocytes, PMNs) are the most abundant white blood cells in humans and play a central role in innate host defense. Another distinguishing feature of PMNs is their short lifespan. Specifically, these cells survive for less than 24 hours in the bloodstream and are inherently pre-programed to die by constitutive apoptosis. Recent data indicate that this process is regulated by intracellular signaling and changes in gene expression that define an “apoptosis differentiation program.” Infection typically accelerates neutrophil turnover, and as such, phagocytosis-induced cell death (PICD) and subsequent clearance of the corpses by macrophages are essential for control of infection and resolution of the inflammatory response. Herein we reprise recent advances in our understanding of the molecular mechanisms of neutrophil apoptosis with a focus on regulatory factors and pathway intermediates that are specific to this cell type. In addition, we summarize mechanisms whereby perturbation of PMN death contributes directly to the pathogenesis of many infectious and inflammatory disease states.

GH administration patterns differently regulate epidermal growth factor signaling

Current GH administration protocols imply frequent s.c. injections, resulting in suboptimal compliance. Therefore, there is interest in developing delivery systems for sustained release of the hormone. However, GH has different actions depending on its continuous or pulsatile plasma concentration pattern. GH levels and circulating concentration patterns could be involved in the regulation of epidermal growth factor receptor (EGFR) expression in liver. Aberrant expression of this receptor and/or its hyperactivation has been associated with the pathogenesis of different types of carcinoma. Considering that one of the adverse effects associated with GH overexpression and chronic use of GH is the increased incidence of malignancies, the aim of this study was to analyze the effects of GH plasma concentration patterns on EGFR expression and signaling in livers of mice. For this purpose, GH was administered by s.c. daily injections to produce an intermittent plasma pattern or by osmotic pumps to provoke a continuously elevated GH concentration. Intermittent injections of GH induced upregulation of liver EGFR content, augmented the response to EGF, and the induction of proteins involved in promotion of cell proliferation in female mice. In contrast, continuous GH delivery in male mice was associated with diminished EGFR in liver and decreased EGF-induced signaling and expression of early genes. The results indicate that sustained delivery systems that allow continuous GH plasma patterns would be beneficial in terms of treatment safety with regard to the actions of GH on EGFR signaling and its promitogenic activity.

Genomewide RNAi screen identifies protein kinase Cb and new members of mitogen-activated protein kinase pathway as regulators of melanoma cell growth and metastasis

A large-scale RNAi screen was performed for eight different melanoma cell lines using a pooled whole-genome lentiviral shRNA library. shRNAs affecting proliferation of transduced melanoma cells were negatively selected during 10 days of culture. Overall, 617 shRNAs were identified by microarray hybridization. Pathway analyses identified mitogen-activated protein kinase (MAPK) pathway members such as ERK1/2, JNK1/2 and MAP3K7 and protein kinase C β (PKCβ) as candidate genes. Knockdown of PKCβ most consistently reduced cellular proliferation, colony formation and migratory capacity of melanoma cells and was selected for further validation. PKCβ showed enhanced expression in human primary melanomas and distant metastases as compared with benign melanocytic nevi. Moreover, treatment of melanoma cells with PKCβ-specific inhibitor enzastaurin reduced melanoma cell growth but had only small effects on benign fibroblasts. Finally, PKCβ-shRNA significantly reduced lung colonization capacity of stably transduced melanoma cells in mice. Taken together, this study identified new candidate genes for melanoma cell growth and proliferation. PKCβ seems to play an important role in these processes and might serve as a new target for the treatment of metastatic melanoma.

β1-Adrenergic receptor blockade extends the life span of Drosophila and long-lived mice

Chronic treatment with β-adrenergic receptor (βAR) agonists increases mortality and morbidity while βAR antagonists (β-blockers) decrease all-cause mortality for those at risk of cardiac disease. Levels of sympathetic nervous system βAR agonists and βAR activity increase with age, and this increase may hasten the development of age-related mortality. Here, we show that β-blockers extend the life span of healthy metazoans. The β-blockers metoprolol and nebivolol, administered in food daily beginning at 12 months of age, significantly increase the mean and median life span of isocalorically fed, male C3B6F1 mice, by 10 and 6.4%, respectively (P < 0.05). Neither drug affected the weight or food intake of the mice, indicating that induced CR is not responsible for these effects, and that energy absorption and utilization are not altered by the drugs. Both β-blockers were investigated to control for their idiosyncratic, off-target effects. Metoprolol and nebivolol extended Drosophila life span, without affecting food intake or locomotion. Thus, βAR antagonists are capable of directly extending the life span of two widely divergent metazoans, suggesting that these effects are phylogenetically highly conserved. Thus, long-term use of β-blockers, which are generally well-tolerated, may enhance the longevity of healthy humans.

Clinical utility of the oral JAK inhibitor tofacitinib in the treatment of rheumatoid arthritis

Immune/inflammatory cells act in rheumatoid arthritis (RA)-affected patients by synthesizing several inflammatory mediators, including cytokines that initiate intracellular signaling. Recently, small molecule inhibitors of transduction and transcription signals that influence the intracellular pathways (such as the Janus kinase [JAK] family of tyrosine kinases) have been tested for RA treatment. Four members of the JAK family are known: JAK1, JAK2, JAK3, and TyK2. JAK1/JAK3 constitutively binds to the cytoplasmic portion of the cytokine receptor – the common gamma chain – that represents a common subunit of several cytokines involved in T-cell and natural killer cell development, as well as in B-cell activation. Tofacitinib is an oral JAK inhibitor that is now available and effective in RA treatment, as shown in multiple Phase II and Phase III clinical trials. However, long-term safety data and comparisons with other disease-modifying antirheumatic drugs and small molecule inhibitors are necessary to better determine the role of tofacitinib in RA.

Adenosine 2A receptor promotes collagen production by human fibroblasts via pathways involving cyclic AMP and AKT but independent of Smad2/3

Activation of adenosine A2A receptor (A2AR) promotes fibrosis and collagen synthesis. However, the underlying mechanism is still unclear, not least because cAMP, its principal effector, has been found to inhibit TGFβ1-induced collagen synthesis. Here, we show that in primary normal human dermal fibroblasts, A2AR stimulation with CGS21680 elicits a modest cAMP increase (150 ± 12% of control; EC50 54.8 nM), which stimulates collagen1 (Col1) and collagen3 (Col3), but maximal cAMP resulting from direct activation of adenylyl cyclase by forskolin (15,689 ± 7038% of control; EC50 360.7 nM) inhibits Col1 and increases Col3. Similar to Col1 expression, fibroblast proliferation increased following physiological cAMP increases by CGS21680 but was inhibited by cAMP increases beyond the physiological range by forskolin. The A2AR-mediated increase of Col1 and Col3 was mediated by AKT, while Col3, but not Col1, expression was dependent on p38 and repressed by ERK. TGFβ1 induced phosphorylation of Smad2/3 and increased Col3 expression, which was prevented by Smad3 depletion. In contrast, CGS21680 did not activate Smad2/3, and Smad2/3 knockdown did not prevent CGS21680-induced Col1 or Col3 increases. Our results indicate that cAMP is a concentration-dependent switch for collagen production via noncanonical, AKT-dependent, Smad2/3-independent signaling. These observations explain the paradoxical effects of cAMP on collagen expression.

Diminazene aceturate (Berenil) modulates LPS induced pro-inflammatory cytokine production by inhibiting phosphorylation of MAPKs and STAT proteins

Although diminazene aceturate (Berenil) is widely used as a trypanolytic agent in livestock, its mechanisms of action remain poorly understood. We previously showed that Berenil treatment suppresses pro-inflammatory cytokine production by splenic and liver macrophages leading to a concomitant reduction in serum cytokine levels in mice infected with Trypanosoma congolense or challenged with LPS. Here, we investigated the molecular mechanisms through which Berenil alters pro-inflammatory cytokine production by macrophages. We show that pre-treatment of macrophages with Berenil dramatically suppressed IL-6, IL-12 and TNF-α production following LPS, CpG and Poly I:C stimulation without altering the expression of TLRs. Instead, it significantly down-regulated phosphorylation of mitogen-activated protein kinases (p38, extracellular signal-regulated kinase and c-Jun N-terminal kinases), signal transducer and activator of transcription (STAT) proteins (STAT1 and STAT3) and NF-кB p65 activity both in vitro and in vivo. Interestingly, Berenil treatment up-regulated the phosphorylation of STAT5 and the expression of suppressor of cytokine signaling 1 (SOCS1) and SOCS3, which are negative regulators of innate immune responses, including MAPKs and STATs. Collectively, these results show that Berenil down-regulates macrophage pro-inflammatory cytokine production by inhibiting key signaling pathways associated with cytokine production and suggest that this drug may be used to treat conditions caused by excessive production of inflammatory cytokines.

NF-κB inhibitor targeted to activated endothelium demonstrates a critical role of endothelial NF-κB in immune-mediated diseases

Activation of the nuclear transcription factor κB (NF-κB) regulates the expression of inflammatory genes crucially involved in the pathogenesis of inflammatory diseases. NF-κB governs the expression of adhesion molecules that play a pivotal role in leukocyte-endothelium interactions. We uncovered the crucial role of NF-κB activation within endothelial cells in models of immune-mediated diseases using a "sneaking ligand construct" (SLC) selectively inhibiting NF-κB in the activated endothelium. The recombinant SLC1 consists of three modules: (i) an E-selectin targeting domain, (ii) a Pseudomonas exotoxin A translocation domain, and (iii) a NF-κB Essential Modifier-binding effector domain interfering with NF-κB activation. The E-selectin-specific SLC1 inhibited NF-κB by interfering with endothelial IκB kinase 2 activity in vitro and in vivo. In murine experimental peritonitis, the application of SLC1 drastically reduced the extravasation of inflammatory cells. Furthermore, SLC1 treatment significantly ameliorated the disease course in murine models of rheumatoid arthritis. Our data establish that endothelial NF-κB activation is critically involved in the pathogenesis of arthritis and can be selectively inhibited in a cell type- and activation stage-dependent manner by the SLC approach. Moreover, our strategy is applicable to delineating other pathogenic signaling pathways in a cell type-specific manner and enables selective targeting of distinct cell populations to improve effectiveness and risk-benefit ratios of therapeutic interventions.