Amplification of Snake Venom Toxicity by Endogenous Signaling Pathways

The active components of snake venoms encompass a complex and variable mixture of proteins that produce a diverse, but largely stereotypical, range of pharmacologic effects and toxicities. Venom protein diversity and host susceptibilities determine the relative contributions of five main pathologies: neuromuscular dysfunction, inflammation, coagulopathy, cell/organ injury, and disruption of homeostatic mechanisms of normal physiology. In this review, we describe how snakebite is not only a condition mediated directly by venom, but by the amplification of signals dysregulating inflammation, coagulation, neurotransmission, and cell survival. Although venom proteins are diverse, the majority of important pathologic events following envenoming follow from a small group of enzyme-like activities and the actions of small toxic peptides. This review focuses on two of the most important enzymatic activities: snake venom phospholipases (svPLA2) and snake venom metalloproteases (svMP). These two enzyme classes are adept at enabling venom to recruit homologous endogenous signaling systems with sufficient magnitude and duration to produce and amplify cell injury beyond what would be expected from the direct impact of a whole venom dose. This magnification produces many of the most acutely important consequences of envenoming as well as chronic sequelae. Snake venom PLA2s and MPs enzymes recruit prey analogs of similar activity. The transduction mechanisms that recruit endogenous responses include arachidonic acid, intracellular calcium, cytokines, bioactive peptides, and possibly dimerization of venom and prey protein homologs. Despite years of investigation, the precise mechanism of svPLA2-induced neuromuscular paralysis remains incomplete. Based on recent studies, paralysis results from a self-amplifying cycle of endogenous PLA2 activation, arachidonic acid, increases in intracellular Ca2+ and nicotinic receptor deactivation. When prolonged, synaptic suppression supports the degeneration of the synapse. Interaction between endothelium-damaging MPs, sPLA2s and hyaluronidases enhance venom spread, accentuating venom-induced neurotoxicity, inflammation, coagulopathy and tissue injury. Improving snakebite treatment requires new tools to understand direct and indirect effects of envenoming. Homologous PLA2 and MP activities in both venoms and prey/snakebite victim provide molecular targets for non-antibody, small molecule agents for dissecting mechanisms of venom toxicity. Importantly, these tools enable the separation of venom-specific and prey-specific pathological responses to venom.

Considering the Role of Murine Double Minute 2 in the Cardiovascular System?

The E3 ubiquitin ligase Murine double minute 2 (MDM2) is the main negative regulator of the tumor protein p53 (TP53). Extensive studies over more than two decades have confirmed MDM2 oncogenic role through mechanisms both TP53-dependent and TP53-independent oncogenic function. These studies have contributed to designate MDM2 as a therapeutic target of choice for cancer treatment and the number of patents for MDM2 antagonists has increased immensely over the last years. However, the question of the physiological functions of MDM2 has not been fully resolved yet, particularly when expressed and regulated physiologically in healthy tissue. Cardiovascular complications are almost an inescapable side-effect of anti-cancer therapies. While several MDM2 antagonists are entering phase I, II and even III of clinical trials, this review proposes to bring awareness on the physiological role of MDM2 in the cardiovascular system.

Emerging Role of Cellular Prion Protein in the Maintenance and Expansion of Glioma Stem Cells

Cellular prion protein (PrP^C) is a membrane-anchored glycoprotein representing the physiological counterpart of PrP scrapie (PrP^Sc), which plays a pathogenetic role in prion diseases. Relatively little information is however available about physiological role of PrP^C. Although PrP^C ablation in mice does not induce lethal phenotypes, impairment of neuronal and bone marrow plasticity was reported in embryos and adult animals. In neurons, PrP^C stimulates neurite growth, prevents oxidative stress-dependent cell death, and favors antiapoptotic signaling. However, PrP^C activity is not restricted to post-mitotic neurons, but promotes cell proliferation and migration during embryogenesis and tissue regeneration in adult. PrP^C acts as scaffold to stabilize the binding between different membrane receptors, growth factors, and basement proteins, contributing to tumorigenesis. Indeed, ablation of PrP^C expression reduces cancer cell proliferation and migration and restores cell sensitivity to chemotherapy. Conversely, PrP^C overexpression in cancer stem cells (CSCs) from different tumors, including gliomas—the most malignant brain tumors—is predictive for poor prognosis, and correlates with relapses. The mechanisms of the PrP^C role in tumorigenesis and its molecular partners in this activity are the topic of the present review, with a particular focus on PrP^C contribution to glioma CSCs multipotency, invasiveness, and tumorigenicity.

Tracking intra- and inter-organelle signaling of mitochondria

Mitochondria are as highly specialized organelles and masters of the cellular energy metabolism in a constant and dynamic interplay with their cellular environment, providing adenosine triphosphate, buffering Ca²⁺ and fundamentally contributing to various signaling pathways. Hence, such broad field of action within eukaryotic cells requires a high level of structural and functional adaptation. Therefore, mitochondria are constantly moving and undergoing fusion and fission processes, changing their shape and their interaction with other organelles. Moreover, mitochondrial activity gets fine-tuned by intra- and interorganelle H⁺ , K⁺ , Na⁺ , and Ca²⁺ signaling. In this review, we provide an up-to-date overview on mitochondrial strategies to adapt and respond to, as well as affect, their cellular environment. We also present cutting-edge technologies used to track and investigate subcellular signaling, essential to the understanding of various physiological and pathophysiological processes.

Sustained Egr-1 Response via p38 MAP Kinase Signaling Modulates Early Immune Responses of Dendritic Cells Parasitized by Toxoplasma gondii

As a response to a diverse array of external stimuli, early growth response protein 1 (Egr-1) plays important roles in the transcriptional regulation of inflammation and the cellular immune response. However, a number of intracellular pathogens colonize immune cells and the implication of Egr-1 in the host-pathogen interplay has remained elusive. Here, we have characterized the Egr-1 responses of primary murine and human dendritic cells (DCs) upon challenge with the obligate intracellular parasite Toxoplasma gondii. We report that live intracellular parasites induce a sustained high expression of Egr-1 in DCs, different from the immediate-early Egr-1 response to parasite lysates, inactivated parasites or LPS. Moreover, a distinct nuclear localization of elevated amounts of Egr-1 protein was detected in infected DCs, but not in by-stander DCs. The ERK1/2 MAPK signaling pathway mediated the canonical immediate-early Egr-1 response to soluble antigens in a MyD88/TLR-dependent fashion. In contrast, a non-canonical extended Egr-1 response that relied primarily on p38 MAPK signaling was induced by intracellular parasites and was exhibited similarly by MyD88-deficient and wildtype DCs. The extended phase Egr-1 response was dramatically reduced upon challenge of DCs with T. gondii parasites deficient in GRA24, a secreted p38-interacting protein. Further, Egr-1-silenced primary DCs maintained their migratory responses upon T. gondii challenge. Importantly, Egr-1 silencing led to elevated expression of co-stimulatory molecules (CD40, CD80) in Toxoplasma-infected DCs and in LPS-challenged immature DCs, indicating that Egr-1 responses suppressed maturation of DCs. Moreover, the IL-12 and IL-2 responses of Toxoplasma-challenged DCs were modulated in a GRA24-dependent fashion. Jointly, the data show that the Egr-1 responses of DCs to microbial external stimuli and intracellular stimuli can be selectively mediated by ERK1/2 or p38 MAPK signaling, and that Egr-1 can act as an intrinsic negative modulator of maturation in primary DCs.

Role of Heme Oxygenase as a Modulator of Heme-Mediated Pathways

The heme oxygenase (HO) system is essential for heme and iron homeostasis and necessary for adaptation to cell stress. HO degrades heme to biliverdin (BV), carbon monoxide (CO) and ferrous iron. Although mostly beneficial, the HO reaction can also produce deleterious effects, predominantly attributed to excessive product formation. Underrated so far is, however, that HO may exert effects additionally via modulation of the cellular heme levels. Heme, besides being an often-quoted generator of oxidative stress, plays also an important role as a signaling molecule. Heme controls the anti-oxidative defense, circadian rhythms, activity of ion channels, glucose utilization, erythropoiesis, and macrophage function. This broad spectrum of effects depends on its interaction with proteins ranging from transcription factors to enzymes. In degrading heme, HO has the potential to exert effects also via modulation of heme-mediated pathways. In this review, we will discuss the multitude of pathways regulated by heme to enlarge the view on HO and its role in cell physiology. We will further highlight the contribution of HO to pathophysiology, which results from a dysregulated balance between heme and the degradation products formed by HO.

Cannabidiol Regulates the Expression of Keratinocyte Proteins Involved in the Inflammation Process through Transcriptional Regulation

Cannabidiol (CBD), a natural phytocannabinoid without psychoactive effect, is a well-known anti-inflammatory and antioxidant compound. The possibility of its use in cytoprotection of cells from harmful factors, including ultraviolet (UV) radiation, is an area of ongoing investigation. Therefore, the aim of this study was to evaluate the effect of CBD on the regulatory mechanisms associated with the redox balance and inflammation in keratinocytes irradiated with UVA [30 J/cm²] and UVB [60 mJ/cm²]. Spectrophotometric results show that CBD significantly enhances the activity of antioxidant enzymes such as superoxide dismutase and thioredoxin reductase in UV irradiated keratinocytes. Furthermore, despite decreased glutathione peroxidase and reductase activities, CBD prevents lipid peroxidation, which was observed as a decreased level of 4-HNE and 15d-PGJ₂ (measured using GC/MS and LC/MS). Moreover, Western blot analysis of protein levels shows that, under stress conditions, CBD influences interactions of transcription factors Nrf2- NFκB by inhibiting the NFκB pathway, increasing the expression of Nrf2 activators and stimulating the transcription activity of Nrf2. In conclusion, the antioxidant activity of CBD through Nrf2 activation as well as its anti-inflammatory properties as an inhibitor of NFκB should be considered during design of new protective treatments for the skin.

Melanocyte Activation Mechanisms and Rational Therapeutic Treatments of Solar Lentigos

To characterize the pathobiology of solar lentigos (SLs), analyses by semiquantitative RT-PCR, Western blotting, and immunohistochemistry revealed the upregulated expression of endothelin (EDN)-1/endothelin B receptors (EDNBRs), stem cell factor (SCF)/c-KIT, and tumor necrosis factor (TNF)α in the lesional epidermis, which contrasted with the downregulated expression of interleukin (IL) 1α. These findings strongly support the hypothesis that previous repeated UVB exposure triggers keratinocytes to continuously produce TNFα. TNFα then stimulates the secretion of EDNs and the production of SCF in an autocrine fashion, leading to the continuous melanogenic activation of neighboring melanocytes, which causes SLs. A clinical study of 36 patients with SLs for six months treated with an M. Chamomilla extract with a potent ability to abrogate the EDN1-induced increase in DNA synthesis and melanization of human melanocytes in culture revealed a significant improvement in pigment scores and color differences expressed as L values. Another clinical study using a tyrosinase inhibitor L-ascorbate-2-phosphate 3 Na (ASP) demonstrated that L values of test lotion (6% APS)-treated skin significantly increased in SLs and in non-lesional skin with a significantly higher ΔL value in SLs when compared with non-lesional skin. The sum of these findings strongly suggests that combined topical treatment with EDN signaling blockers and tyrosinase inhibitors is a desirable therapeutic choice for SLs.

Intracellular Signaling in Key Pathways Is Induced by Treatment with Ultrasound and Microbubbles in a Leukemia Cell Line, but Not in Healthy Peripheral Blood Mononuclear Cells

Treatment with ultrasound and microbubbles (sonoporation) to enhance therapeutic efficacy in cancer therapy is rapidly expanding, but there is still very little consensus as to why it works. Despite the original assumption that pore formation in the cell membrane is responsible for increased uptake of drugs, the molecular mechanisms behind this phenomenon are largely unknown. We treated cancer cells (MOLM-13) and healthy peripheral blood mononuclear cells (PBMCs) with ultrasound at three acoustic intensities (74, 501, 2079 mW/cm²) ± microbubbles. We subsequently monitored the intracellular response of a number of key signaling pathways using flow cytometry or western blotting 5 min, 30 min and 2 h post-treatment. This was complemented by studies on uptake of a cell impermeable dye (calcein) and investigations of cell viability (cell count, Hoechst staining and colony forming assay). Ultrasound + microbubbles resulted in both early changes (p38 (Arcsinh ratio at high ultrasound + microbubbles: +0.5), ERK1/2 (+0.7), CREB (+1.3), STAT3 (+0.7) and AKT (+0.5)) and late changes (ribosomal protein S6 (Arcsinh ratio at low ultrasound: +0.6) and eIF2α in protein phosphorylation). Observed changes in protein phosphorylation corresponded to changes in sonoporation efficiency and in viability, predominantly in cancer cells. Sonoporation induced protein phosphorylation in healthy cells was pronounced (p38 (+0.03), ERK1/2 (−0.03), CREB (+0.0), STAT3 (−0.1) and AKT (+0.04) and S6 (+0.2)). This supports the hypothesis that sonoporation may enhance therapeutic efficacy of cancer treatment, without causing damage to healthy cells.

Regulation of CD4+ T Cell Signaling and Immunological Synapse by Protein Tyrosine Phosphatases: Molecular Mechanisms in Autoimmunity

T cell activation and effector function is mediated by the formation of a long-lasting interaction established between T cells and antigen-presenting cells (APCs) called immunological synapse (IS). During T cell activation, different signaling molecules as well as the cytoskeleton and the endosomal compartment are polarized to the IS. This molecular dynamics is tightly regulated by phosphorylation networks, which are controlled by protein tyrosine phosphatases (PTPs). While some PTPs are known to be important regulators of adhesion, ligand discrimination or the stimulation threshold, there is still little information about the regulatory role of PTPs in cytoskeleton rearrangements and endosomal compartment dynamics. Besides, spatial and temporal regulation of PTPs and substrates at the IS is only barely known. Consistent with an important role of PTPs in T cell activation, multiple mutations as well as altered expression levels or dynamic behaviors have been associated with autoimmune diseases. However, the precise mechanism for the regulation of T cell activation and effector function by PTPs in health and autoimmunity is not fully understood. Herein, we review the current knowledge about the regulatory role of PTPs in CD4⁺ T cell activation, IS assembly and effector function. The potential molecular mechanisms mediating the action of these enzymes in autoimmune disorders are discussed.

The Lysosome Signaling Platform: Adapting With the Times

Lysosomes are the terminal degradative compartment of autophagy, endocytosis and phagocytosis. What once was viewed as a simple acidic organelle in charge of macromolecular digestion has emerged as a dynamic organelle capable of integrating cellular signals and producing signal outputs. In this review, we focus on the concept that the lysosome surface serves as a platform to assemble major signaling hubs like mTORC1, AMPK, GSK3 and the inflammasome. These molecular assemblies integrate and facilitate cross-talk between signals such as amino acid and energy levels, membrane damage and infection, and ultimately enable responses such as autophagy, cell growth, membrane repair and microbe clearance. In particular, we review how molecular machinery like the vacuolar-ATPase proton pump, sestrins, the GATOR complexes, and the Ragulator, modulate mTORC1, AMPK, GSK3 and inflammation. We then elaborate how these signals control autophagy initiation and resolution, TFEB-mediated lysosome adaptation, lysosome remodeling, antigen presentation, inflammation, membrane damage repair and clearance. Overall, by being at the cross-roads for several membrane pathways, lysosomes have emerged as the ideal surveillance compartment to sense, integrate and elicit cellular behavior and adaptation in response to changing environmental and cellular conditions.

Identification of LPS-Activated Endothelial Subpopulations With Distinct Inflammatory Phenotypes and Regulatory Signaling Mechanisms

Sepsis is a life-threatening condition caused by a dysregulated host response to infection. Endothelial cells (EC) are actively involved in sepsis-associated (micro)vascular disturbances and subsequent organ dysfunction. Lipopolysaccharide (LPS), a Gram-negative bacterial product, can activate EC leading to the expression of pro-inflammatory molecules. This process is molecularly regulated by specific receptors and distinct, yet poorly understood intracellular signaling pathways. LPS-induced expression of endothelial adhesion molecules E-selectin and VCAM-1 in mice was previously shown to be organ- and microvascular-specific. Here we report that also within renal microvascular beds the endothelium expresses different extents of E-selectin and VCAM-1. This heterogeneity was recapitulated in vitro in LPS-activated human umbilical vein EC (HUVEC). Within 2 h after LPS exposure, four distinct HUVEC subpopulations were visible by flow cytometric analysis detecting E-selectin and VCAM-1 protein. These encompassed E-selectin^-/VCAM-1^- (-/-), E-selectin⁺/VCAM-1^- (E-sel+), E-selectin⁺/VCAM-1⁺ (+/+), and E-selectin^-/VCAM-1⁺ (VCAM-1+) subpopulations. The formation of subpopulations was a common response of endothelial cells to LPS challenge. Using fluorescence-activated cell sorting (FACS) we demonstrated that the +/+ subpopulation also expressed the highest levels of inflammatory cytokines and chemokines. The differences in responsiveness of EC subpopulations could not be explained by differential expression of LPS receptors TLR4 and RIG-I. Functional studies, however, demonstrated that the formation of the E-sel+ subpopulation was mainly TLR4-mediated, while the formation of the +/+ subpopulation was mediated by both TLR4 and RIG-I. Pharmacological blockade of NF-κB and p38 MAPK furthermore revealed a prominent role of their signaling cascades in E-sel+ and +/+ subpopulation formation. In contrast, the VCAM-1+ subpopulation was not controlled by any of these signaling pathways. Noteworthy is the existence of a "quiescent" subpopulation that was devoid of the two adhesion molecules and did not express cytokines or chemokines despite LPS exposure. Summarizing, our findings suggest that LPS activates different signaling mechanisms in EC that drive heterogeneous expression of EC inflammatory molecules. Further characterization of the signaling pathways involved will enhance our understanding of endothelial heterogeneous responses to sepsis related stimuli and enable the future design of effective therapeutic strategies to interfere in these processes to counteract sepsis-associated organ dysfunction.

Fendiline Enhances the Cytotoxic Effects of Therapeutic Agents on PDAC Cells by Inhibiting Tumor-Promoting Signaling Events: A Potential Strategy to Combat PDAC

The L-type calcium channel blocker fendiline has been shown to interfere with Ras-dependent signaling in K-Ras mutant cancer cells. Earlier studies from our lab had shown that treatment of pancreatic cancer cells with fendiline causes significant cytotoxicity and interferes with proliferation, survival, migration, invasion and anchorage independent growth. Currently there are no effective therapies to manage PDACs. As fendiline has been approved for treatment of patients with angina, we hypothesized that, if proven effective, combinatorial therapies using this agent would be easily translatable to clinic for testing in PDAC patients. Here we tested combinations of fendiline with gemcitabine, visudyne (a YAP1 inhibitor) or tivantinib (ARQ197, a c-Met inhibitor) for their effectiveness in overcoming growth and oncogenic characteristics of PDAC cells. The Hippo pathway component YAP1 has been shown to bypass K-Ras addiction, and allow tumor growth, in a Ras-null mouse model. Similarly, c-Met expression has been associated with poor prognosis and metastasis in PDAC patients. Our results presented here show that combinations of fendiline with these inhibitors show enhanced anti-tumor activity in Panc1, MiaPaCa2 and CD18/HPAF PDAC cells, as evident from the reduced viability, migration, anchorage-independent growth and self-renewal. Biochemical analysis shows that these agents interfere with various signaling cascades such as the activation of Akt and ERK, as well as the expression of c-Myc and CD44 that are altered in PDACs. These results imply that inclusion of fendiline may improve the efficacy of various chemotherapeutic agents that could potentially benefit PDAC patients.

Physiological levels of chromogranin A prevent doxorubicin-induced cardiotoxicity without impairing its anticancer activity

The clinical use of doxorubicin (Doxo), a widely used anticancer chemotherapeutic drug, is limited by dose-dependent cardiotoxicity. We have investigated whether chromogranin A (CgA), a cardioregulatory protein released in the blood by the neuroendocrine system and by the heart itself, may contribute to regulation of the cardiotoxic and antitumor activities of Doxo. The effects of a physiologic dose of full-length recombinant CgA on Doxo-induced cardiotoxicity and antitumor activity were investigated in rats using in vivo and ex vivo models and in murine models of melanoma, fibrosarcoma, lymphoma, and lung cancer, respectively. The effect of Doxo on circulating levels of CgA was also investigated. In vivo and ex vivo mechanistic studies showed that CgA can prevent Doxo-induced heart inflammation, oxidative stress, apoptosis, fibrosis, and ischemic injury. On the other hand, CgA did not impair the anticancer activity of Doxo in all the murine models investigated. Furthermore, we observed that Doxo can reduce the intracardiac expression and release of CgA in the blood (i.e., an important cardioprotective agent). These findings suggest that administration of low-dose CgA to patients with low levels of endogenous CgA might represent a novel approach to prevent Doxo-induced adverse events without impairing antitumor effects.-Rocca, C., Scavello, F., Colombo, B., Gasparri, A. M., Dallatomasina, A., Granieri, M. C., Amelio, D., Pasqua, T., Cerra, M. C., Tota, B., Corti, A., Angelone, T. Physiological levels of chromogranin A prevent doxorubicin-induced cardiotoxicity without impairing its anticancer activity.

MAPK/ERK Signaling in Regulation of Renal Differentiation

Congenital anomalies of the kidney and urinary tract (CAKUT) are common birth defects derived from abnormalities in renal differentiation during embryogenesis. CAKUT is the major cause of end-stage renal disease and chronic kidney diseases in children, but its genetic causes remain largely unresolved. Here we discuss advances in the understanding of how mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) activity contributes to the regulation of ureteric bud branching morphogenesis, which dictates the final size, shape, and nephron number of the kidney. Recent studies also demonstrate that the MAPK/ERK pathway is directly involved in nephrogenesis, regulating both the maintenance and differentiation of the nephrogenic mesenchyme. Interestingly, aberrant MAPK/ERK signaling is linked to many cancers, and recent studies suggest it also plays a role in the most common pediatric renal cancer, Wilms' tumor.

Evaluation of in vitro Assays to Assess the Modulation of Dendritic Cells Functions by Therapeutic Antibodies and Aggregates

Therapeutic antibodies have the potential to induce immunogenicity leading to the development of anti-drug antibodies (ADA) that consequently may result in reduced serum drug concentrations, a loss of efficacy or potential hypersensitivity reactions. Among other factors, aggregated antibodies have been suggested to promote immunogenicity, thus enhancing ADA production. Dendritic cells (DC) are the most efficient antigen-presenting cell population and are crucial for the initiation of T cell responses and the subsequent generation of an adaptive immune response. This work focuses on the development of predictive in vitro assays that can monitor DC maturation, in order to determine whether drug products have direct DC stimulatory capabilities. To this end, four independent laboratories aligned a common protocol to differentiate human monocyte-derived DC (moDC) that were treated with either native or aggregated preparations of infliximab, natalizumab, adalimumab, or rituximab. These drug products were subjected to different forms of physical stress, heat and shear, resulting in aggregation and the formation of subvisible particles. Each partner developed and optimized assays to monitor diverse end-points of moDC maturation: measuring the upregulation of DC activation markers via flow cytometry, analyzing cytokine, and chemokine production via mRNA and protein quantification and identifying cell signaling pathways via quantification of protein phosphorylation. These study results indicated that infliximab, with the highest propensity to form aggregates when heat-stressed, induced a marked activation of moDC as measured by an increase in CD83 and CD86 surface expression, IL-1β, IL-6, IL-8, IL-12, TNFα, CCL3, and CCL4 transcript upregulation and release of respective proteins, and phosphorylation of the intracellular signaling proteins Syk, ERK1/2, and Akt. In contrast, natalizumab, which does not aggregate under these stress conditions, induced no DC activation in any assay system, whereas adalimumab or rituximab aggregates induced only slight parameter variation. Importantly, the data generated in the different assay systems by each partner site correlated and supported the use of these assays to monitor drug-intrinsic propensities to drive maturation of DC. This moDC assay is also a valuable tool as an in vitro model to assess the intracellular mechanisms that drive DC activation by aggregated therapeutic proteins.

Below the surface: The inner lives of TLR4 and TLR9

TLRs are a class of pattern recognition receptors (PRRs) that detect invading microbes by recognizing pathogen-associated molecular patterns (PAMPs). Upon PAMP engagement, TLRs activate a signaling cascade that leads to the production of inflammatory mediators. The localization of TLRs, either on the plasma membrane or in the endolysosomal compartment, has been considered to be a fundamental aspect to determine to which ligands the receptors bind, and which transduction pathways are induced. However, new observations have challenged this view by identifying complex trafficking events that occur upon TLR-ligand binding. These findings have highlighted the central role that endocytosis and receptor trafficking play in the regulation of the innate immune response. Here, we review the TLR4 and TLR9 transduction pathways and the importance of their different subcellular localization during the inflammatory response. Finally, we discuss the implications of TLR9 subcellular localization in autoimmunity.

The split protein phosphatase system

Reversible phosphorylation of proteins is a post-translational modification that regulates all aspect of life through the antagonistic action of kinases and phosphatases. Protein kinases are well characterized, but protein phosphatases have been relatively neglected. Protein phosphatase 1 (PP1) catalyzes the dephosphorylation of a major fraction of phospho-serines and phospho-threonines in cells and thereby controls a broad range of cellular processes. In this review, I will discuss how phosphatases were discovered, how the view that they were unselective emerged and how recent findings have revealed their exquisite selectivity. Unlike kinases, PP1 phosphatases are obligatory heteromers composed of a catalytic subunit bound to one (or two) non-catalytic subunit(s). Based on an in-depth study of two holophosphatases, I propose the following: selective dephosphorylation depends on the assembly of two components, the catalytic subunit and the non-catalytic subunit, which serves as a high-affinity substrate receptor. Because functional complementation of the two modules is required to produce a selective holophosphatase, one can consider that they are split enzymes. The non-catalytic subunit was often referred to as a regulatory subunit, but it is, in fact, an essential component of the holoenzyme. In this model, a phosphatase and its array of mostly orphan substrate receptors constitute the split protein phosphatase system. The set of potentially generalizable principles outlined in this review may facilitate the study of these poorly understood enzymes and the identification of their physiological substrates.

Semaphorin 3F and Netrin-1: The Novel Function as a Regulator of Tumor Microenvironment

Axon guidance molecules play an important role in regulating proper neuronal networking during neuronal development. They also have non-neuronal properties, which include angiogenesis, inflammation, and tumor development. Semaphorin 3F (SEMA3F), a member of the class 3 semaphorins, was initially identified as an axon guidance factor, that repels axons and collapses growth cones. However, SEMA3F has similar effects on endothelial cells (ECs) and tumor cells. In this review, we discuss the novel molecular mechanisms underlying SEMA3F activity in vascular and tumor biology. Recent evidence suggests that SEMA3F functions as a PI3K-Akt-mTOR inhibitor in mammalian cells, including T cells, ECs, and tumor cells. Therefore, SEMA3F may have broad therapeutic implications. We also discuss the key role of axon guidance molecules as regulators of the tumor microenvironment. Netrin-1, a chemoattractant factor in the neuronal system, promotes tumor progression by enhancing angiogenesis and metastasis. Moreover, our recent studies demonstrate that netrin-1/neogenin interactions augment CD4+ T cell chemokinesis and elicit pro-inflammatory responses, suggesting that netrin-1 plays a key role in modulating the function of a tumor and its surrounding cells in the tumor microenvironment. Overall, this review focuses on SEMA3F and netrin-1 signaling mechanisms to understand the diverse biological functions of axon guidance molecules.

Noradrenaline Sensitivity Is Severely Impaired in Immortalized Adipose-Derived Mesenchymal Stem Cell Line

Primary adipose tissue-derived multipotent stem/stromal cells (adMSCs) demonstrate unusual signaling regulatory mechanisms, i.e., increased of sensitivity to catecholamines in response to noradrenaline. This phenomenon is called “heterologous sensitization”, and was previously found only in embryonic cells. Since further elucidation of the molecular mechanisms that are responsible for such sensitization in primary adMSCs was difficult due to the high heterogeneity in adrenergic receptor expression, we employed immortalized adipose-derived mesenchymal stem cell lines (hTERT-MSCs). Using flow cytometry and immunofluorescence microscopy, we demonstrated that the proportion of cells expressing adrenergic receptor isoforms does not differ significantly in hTERT-MSCs cells compared to the primary adMSCs culture. However, using analysis of Ca²⁺-mobilization in single cells, we found that these cells did not demonstrate the sensitization seen in primary adMSCs. Consistently, these cells did not activate cAMP synthesis in response to noradrenaline. These data indicate that immortalized adipose-derived mesenchymal stem cell lines demonstrated impaired ability to respond to noradrenaline compared to primary adMSCs. These data draw attention to the usage of immortalized cells for MSCs-based regenerative medicine, especially in the field of pharmacology.

Reconstructing phosphorylation signalling networks from quantitative phosphoproteomic data

Cascades of phosphorylation between protein kinases comprise a core mechanism in the integration and propagation of intracellular signals. Although we have accumulated a wealth of knowledge around some such pathways, this is subject to study biases and much remains to be uncovered. Phosphoproteomics, the identification and quantification of phosphorylated proteins on a proteomic scale, provides a high-throughput means of interrogating the state of intracellular phosphorylation, both at the pathway level and at the whole-cell level. In this review, we discuss methods for using human quantitative phosphoproteomic data to reconstruct the underlying signalling networks that generated it. We address several challenges imposed by the data on such analyses and we consider promising advances towards reconstructing unbiased, kinome-scale signalling networks.

Exploring major signaling cascades in melanomagenesis: a rationale route for targetted skin cancer therapy

Although most melanoma cases may be treated by surgical intervention upon early diagnosis, a significant portion of patients can still be refractory, presenting low survival rates within 5 years after the discovery of the illness. As a hallmark, melanomas are highly prone to evolve into metastatic sites. Moreover, melanoma tumors are highly resistant to most available drug therapies and their incidence have increased over the years, therefore leading to public health concerns about the development of novel therapies. Therefore, researches are getting deeper in unveiling the mechanisms by which melanoma initiation can be triggered and sustained. In this context, important progress has been achieved regarding the roles and the impact of cellular signaling pathways in melanoma. This knowledge has provided tools for the development of therapies based on the intervention of signal(s) promoted by these cascades. In this review, we summarize the importance of major signaling pathways (mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)-Akt, Wnt, nuclear factor κ-light-chain-enhancer of activated B cell (NF-κB), Janus kinase (JAK)-signal transducer and activator of transcription (STAT), transforming growth factor β (TGF-β) and Notch) in skin homeostasis and melanoma progression. Available and developing melanoma therapies interfering with these signaling cascades are further discussed.

HoxB8 neutrophils replicate Fcγ receptor and integrin-induced neutrophil signaling and functions

Neutrophils are short‐lived, terminally differentiated leukocytes that form an essential part of host immunity and play a key role in acute and chronic inflammation. The analysis of these important cells is hindered by the fact that neutrophils are not amenable to culture, transfection, or transduction. Conditionally HoxB8‐immortalized mouse hematopoietic progenitors are suitable for in vitro differentiation of a range of myeloid cells, including neutrophils. Integrins and FcγRs are cell surface receptors, the ligation of which is required for a range of neutrophil functions that are important in health and disease. We show here that HoxB8 neutrophils express major neutrophil integrins and FcγRs. They respond to FcγR and integrin stimulation in a manner that is comparable with primary neutrophils, in terms of intracellular signaling. HoxB8 neutrophils also perform a range of FcγR/integrin‐dependent neutrophil functions, including, generation of reactive oxygen species, degranulation, and chemotaxis. Our findings suggest that HoxB8 neutrophils represent a faithful experimental model system for the analysis of Fc and integrin receptor‐dependent neutrophil functions.

Dynamic MAPK/ERK Activity Sustains Nephron Progenitors through Niche Regulation and Primes Precursors for Differentiation

The in vivo niche and basic cellular properties of nephron progenitors are poorly described. Here we studied the cellular organization and function of the MAPK/ERK pathway in nephron progenitors. Live-imaging of ERK activity by a Förster resonance energy transfer biosensor revealed a dynamic activation pattern in progenitors, whereas differentiating precursors exhibited sustained activity. Genetic experiments demonstrate that MAPK/ERK activity controls the thickness, coherence, and integrity of the nephron progenitor niche. Molecularly, MAPK/ERK activity regulates niche organization and communication with extracellular matrix through PAX2 and ITGA8, and is needed for CITED1 expression denoting undifferentiated status. MAPK/ERK activation in nephron precursors propels differentiation by priming cells for distal and proximal fates induced by the Wnt and Notch pathways. Thus, our results demonstrate a mechanism through which MAPK/ERK activity controls both progenitor maintenance and differentiation by regulating a distinct set of targets, which maintain the biomechanical milieu of tissue-residing progenitors and prime precursors for nephrogenesis.

A current view of G protein-coupled receptor - mediated signaling in pulmonary hypertension: finding opportunities for therapeutic intervention

Pathological vascular remodeling is observed in various cardiovascular diseases including pulmonary hypertension (PH), a disease of unknown etiology that has been characterized by pulmonary artery vasoconstriction, right ventricular hypertrophy, vascular inflammation, and abnormal angiogenesis in pulmonary circulation. G protein-coupled receptors (GPCRs) are the largest family in the genome and widely expressed in cardiovascular system. They regulate all aspects of PH pathophysiology and represent therapeutic targets. We overview GPCRs function in vasoconstriction, vasodilation, vascular inflammation-driven remodeling and describe signaling cross talk between GPCR, inflammatory cytokines, and growth factors. Overall, the goal of this review is to emphasize the importance of GPCRs as critical signal transducers and targets for drug development in PH.