Sphingosine-1-phosphate signaling in vasculogenesis and angiogenesis

Blood vessels either form de novo through the process of vasculogenesis or through angiogenesis that involves the sprouting and proliferation of endothelial cells in pre-existing blood vessels. A complex interactive network of signaling cascades downstream from at least three of the nine known G-protein-coupled sphingosine-1-phosphate (S1P) receptors act as a prime effector of neovascularization that occurs in embryonic development and in association with various pathologies. This review focuses on the current knowledge of the roles of S1P signaling in vasculogenesis and angiogenesis, with particular emphasis on vascular cell adhesion and motility responses.

HIV aspartyl protease inhibitors as promising compounds against Candida albicans André Luis Souza dos Santos

Cells of Candida albicans (C. albicans) can invade humans and may lead to mucosal and skin infections or to deep-seated mycoses of almost all inner organs, especially in immunocompromised patients. In this context, both the host immune status and the ability of C. albicans to modulate the expression of its virulence factors are relevant aspects that drive the candidal susceptibility or resistance; in this last case, culminating in the establishment of successful infection known as candidiasis. C. albicans possesses a potent armamentarium consisting of several virulence molecules that help the fungal cells to escape of the host immune responses. There is no doubt that the secretion of aspartyl-type proteases, designated as Saps, are one of the major virulence attributes produced by C. albicans cells, since these hydrolytic enzymes participate in a wide range of fungal physiological processes as well as in different facets of the fungal-host interactions. For these reasons, Saps clearly hold promise as new potential drug targets. Corroborating this hypothesis, the introduction of new anti-human immunodeficiency virus drugs of the aspartyl protease inhibitor-type (HIV PIs) have emerged as new agents for the inhibition of Saps. The introduction of HIV PIs has revolutionized the treatment of HIV disease, reducing opportunistic infections, especially candidiasis. The attenuation of candidal infections in HIV-infected individuals might not solely have resulted from improved immunological status, but also as a result of direct inhibition of C. albicans Saps. In this article, we review updates on the beneficial effects of HIV PIs against the human fungal pathogen C. albicans, focusing on the effects of these compounds on Sap activity, growth behavior, morphological architecture, cellular differentiation, fungal adhesion to animal cells and abiotic materials, modulation of virulence factors, experimental candidiasis infection, and their synergistic actions with classical antifungal agents.

Methionine sulfoxide reductase A: Structure, function and role in ocular pathology

Methionine is a highly susceptible amino acid that can be oxidized to S and R diastereomeric forms of methionine sulfoxide by many of the reactive oxygen species generated in biological systems. Methionine sulfoxide reductases (Msrs) are thioredoxin-linked enzymes involved in the enzymatic conversion of methionine sulfoxide to methionine. Although MsrA and MsrB have the same function of methionine reduction, they differ in substrate specificity, active site composition, subcellular localization, and evolution. MsrA has been localized in different ocular regions and is abundantly expressed in the retina and in retinal pigment epithelial (RPE) cells. MsrA protects cells from oxidative stress. Overexpression of MsrA increases resistance to cell death, while silencing or knocking down MsrA decreases cell survival; events that are mediated by mitochondria. MsrA participates in protein-protein interaction with several other cellular proteins. The interaction of MsrA with α-crystallins is of utmost importance given the known functions of the latter in protein folding, neuroprotection, and cell survival. Oxidation of methionine residues in α-crystallins results in loss of chaperone function and possibly its antiapoptotic properties. Recent work from our laboratory has shown that MsrA is co-localized with αA and αB crystallins in the retinal samples of patients with age-related macular degeneration. We have also found that chemically induced hypoxia regulates the expression of MsrA and MsrB2 in human RPE cells. Thus, MsrA is a critical enzyme that participates in cell and tissue protection, and its interaction with other proteins/growth factors may provide a target for therapeutic strategies to prevent degenerative diseases.

Galectin-1-mediated biochemical controls of melanoma and glioma aggressive behavior

Gliomas and melanomas are associated with dismal prognosis because of their marked intrinsic resistance to proapoptotic stimuli, such as conventional chemotherapy and radiotherapy, as well as their ability to escape immune cell attacks. In addition, gliomas and melanomas display pronounced neoangiogenesis. Galectin-1 is a hypoxia-sensitive protein, which is abundantly secreted by glioma and melanoma cells, which displays marked proangiogenic effects. It also provides immune tolerogenic environments to melanoma and glioma cells through the killing of activated T cells that attack these tumor cells. Galectin-1 protects glioma and melanoma cells against cytotoxic insults (including chemotherapy and radiotherapy) through a direct role in the unfolded protein response. Altogether, these facts clearly point to galectin-1 as an important target to be combated in gliomas and melanomas in order to: (1) weaken the defenses of these two types of cancers against radiotherapy, chemotherapy and immunotherapy/vaccine therapy; and (2) reinforce antiangiogenic therapies. In the present article, we review the biochemical and molecular biology-related pathways controlled by galectin-1, which are actually beneficial for melanoma and glioma cells, and therefore detrimental for melanoma and glioma patients.

Epigenetic basis of Alzheimer disease

Alzheimer disease (AD) is the primary form of dementia that occurs spontaneously in older adults. Interestingly, the epigenetic profile of the cells forming the central nervous system changes during aging and may contribute to the progression of some neurodegenerative diseases such as AD. In this review, we present general insights into relevant epigenetic mechanisms and their relationship with aging and AD. The data suggest that some epigenetic changes during aging could be utilized as biomarkers and target molecules for the prevention and control of AD.

Regulation of cancer cell migration and invasion by sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that has been implicated in regulation of a number of cancer cell malignant behaviors, including cell proliferation, survival, chemotherapeutic resistance and angiogenesis. However, the effects of S1P on cancer cell migration, invasion and metastasis, are perhaps its most complex, due to the fact that, depending upon the S1P receptors that mediate its responses and the crosstalk with other signaling pathways, S1P can either positively or negatively regulate invasion. This review summarizes the effects of S1P on cancer cell invasion and the mechanisms by which it affects this important aspect of cancer cell behavior.

Alcoholic liver disease: Current insights into cellular mechanisms

Alcoholic liver disease (ALD) due to chronic alcohol consumption is a significant global disease burden and a leading cause of mortality. Alcohol abuse induces a myriad of aberrant changes in hepatocytes at both the cellular and molecular level. Although the disease spectrum of ALD is widely recognized, the precise triggers for disease progression are still to be fully elucidated. Oxidative stress, mitochondrial dysfunction, gut dysbiosis and altered immune system response plays an important role in disease pathogenesis, triggering the activation of inflammatory pathways and apoptosis. Despite many recent clinical studies treatment options for ALD are limited, especially at the alcoholic hepatitis stage. We have therefore reviewed some of the key pathways involved in the pathogenesis of ALD and highlighted current trials for treating patients.

High-density lipoprotein endocytosis in endothelial cells

AIM: To describe the way stations of high-density lipoprotein (HDL) uptake and its lipid exchange in endothelial cells in vitro and in vivo.

METHODS: A combination of fluorescence microscopy using novel fluorescent cholesterol surrogates and electron microscopy was used to analyze HDL endocytosis in great detail in primary human endothelial cells. Further, HDL uptake was quantified using radio-labeled HDL particles. To validate the in vitro findings mice were injected with fluorescently labeled HDL and particle uptake in the liver was analyzed using fluorescence microscopy.

RESULTS: HDL uptake occurred via clathrin-coated pits, tubular endosomes and multivesicular bodies in human umbilical vein endothelial cells. During uptake and resecretion, HDL-derived cholesterol was exchanged at a faster rate than cholesteryl oleate, resembling the HDL particle pathway seen in hepatic cells. In addition, lysosomes were not involved in this process and thus HDL degradation was not detectable. In vivo, we found HDL mainly localized in mouse hepatic endothelial cells. HDL was not detected in parenchymal liver cells, indicating that lipid transfer from HDL to hepatocytes occurs primarily via scavenger receptor, class B, type I mediated selective uptake without concomitant HDL endocytosis.

CONCLUSION: HDL endocytosis occurs via clathrin-coated pits, tubular endosomes and multivesicular bodies in human endothelial cells. Mouse endothelial cells showed a similar HDL uptake pattern in vivo indicating that the endothelium is one major site of HDL endocytosis and transcytosis.

Why the discovery of adherent-invasive Escherichia coli molecular markers is so challenging?

Adherent-invasive Escherichia coli (AIEC) strains have been extensively related to Crohn’s disease (CD) etiopathogenesis. Higher AIEC prevalence in CD patients versus controls has been reported, and its mechanisms of pathogenicity have been linked to CD physiopathology. In CD, the therapeutic armamentarium remains limited and non-curative; hence, the necessity to better understand AIEC as a putative instigator or propagator of the disease is certain. Nonetheless, AIEC identification is currently challenging because it relies on phenotypic assays based on infected cell cultures which are highly time-consuming, laborious and non-standardizable. To address this issue, AIEC molecular mechanisms and virulence genes have been studied; however, a specific and widely distributed genetic AIEC marker is still missing. The finding of molecular tools to easily identify AIEC could be useful in the identification of AIEC carriers who could profit from personalized treatment. Also, it would significantly promote AIEC epidemiological studies. Here, we reviewed the existing data regarding AIEC genetics and presented those molecular markers that could assist with AIEC identification. Finally, we highlighted the problems behind the discovery of exclusive AIEC biomarkers and proposed strategies to facilitate the search of AIEC signature sequences.

Important relationships between Rab and MICAL proteins in endocytic trafficking

The internalization of essential nutrients, lipids and receptors is a crucial process for all eukaryotic cells. Accordingly, endocytosis is highly conserved across cell types and species. Once internalized, small cargo-containing vesicles fuse with early endosomes (also known as sorting endosomes), where they undergo segregation to distinct membrane regions and are sorted and transported on through the endocytic pathway. Although the mechanisms that regulate this sorting are still poorly understood, some receptors are directed to late endosomes and lysosomes for degradation, whereas other receptors are recycled back to the plasma membrane; either directly or through recycling endosomes. The Rab family of small GTP-binding proteins plays crucial roles in regulating these trafficking pathways. Rabs cycle from inactive GDP-bound cytoplasmic proteins to active GTP-bound membrane-associated proteins, as a consequence of the activity of multiple specific GTPase-activating proteins (GAPs) and GTP exchange factors (GEFs). Once bound to GTP, Rabs interact with a multitude of effector proteins that carry out Rab-specific functions. Recent studies have shown that some of these effectors are also interaction partners for the C-terminal Eps15 homology (EHD) proteins, which are also intimately involved in endocytic regulation. A particularly interesting example of common Rab-EHD interaction partners is the MICAL-like protein, MICAL-L1. MICAL-L1 and its homolog, MICAL-L2, belong to the larger MICAL family of proteins, and both have been directly implicated in regulating endocytic recycling of cell surface receptors and junctional proteins, as well as controlling cytoskeletal rearrangement and neurite outgrowth. In this review, we summarize the functional roles of MICAL and Rab proteins, and focus on the significance of their interactions and the implications for endocytic transport.

Caspase-1 activation and mature interleukin-1β release are uncoupled events in monocytes

AIM: To investigate whether caspase-1 activation/intracellular processing of pro-interleukin-1β (pro-IL-1β) and extracellular release of mature IL-1β from activated monocytes are separable events.

METHODS: All experiments were performed on fresh or overnight cultured human peripheral blood monocytes (PBMCs) that were isolated from healthy donors. PBMCs were activated by lipopolysaccharide (LPS) stimulation before being treated with Adenosine triphosphate (ATP, 1 mmol/L), human α-defensin-5 (HD-5, 50 μg/mL), and/or nigericin (Nig, 30 μmol/L). For each experiment, the culture supernatants were collected separately from the cells. Cell lysates and supernatants were both subject to immunoprecipitation with anti-IL-1β antibodies followed by western blot analysis with anti-caspase-1 and anti-IL-1β antibodies.

RESULTS: We found that pro-IL-1β was processed to mature IL-1β in LPS-activated fresh and overnight cultured human monocytes in response to ATP stimulation. In the presence of HD-5, this release of IL-1β, but not the processing of pro-IL-1β to IL-1β, was completely inhibited. Similarly, in the presence of HD-5, the release of IL-1β, but not the processing of IL-1β, was significantly inhibited from LPS-activated monocytes stimulated with Nig. Finally, we treated LPS-activated monocytes with ATP and Nig and collected the supernatants. We found that both ATP and Nig stimulation could activate and release cleaved caspase-1 from the monocytes. Interestingly, and contrary to IL-1β processing and release, caspase-1 cleavage and release was not blocked by HD-5. All images are representative of three independent experiments.

CONCLUSION: These data suggest that caspase-1 activation/processing of pro-IL-1β by caspase-1 and the release of mature IL-1β from human monocytes are distinct and separable events.

Frontier of therapeutic antibody discovery: The challenges and how to face them

Therapeutic monoclonal antibodies have become an important class of modern medicines. The established technologies for therapeutic antibody discovery such as humanization of mouse antibodies, phage display of human antibody libraries and transgenic animals harboring human IgG genes have been practiced successfully so far, and many incremental improvements are being made constantly. These methodologies are responsible for currently marketed therapeutic antibodies and for the biopharma industry pipeline which are concentrated on only a few dozen targets. A key challenge for wider application of biotherapeutic approaches is the paucity of truly validated targets for biotherapeutic intervention. The efforts to expand the target space include taking the pathway approach to study the disease correlation. Since many new targets are multi-spanning and multimeric membrane proteins there is a need to develop more effective methods to generate antibodies against these difficult targets. The pharmaceutical properties of therapeutic antibodies are an active area for study concentrating on biophysical characteristics such as thermal stability and aggregation propensity. The immunogenicity of biotherapeutics in humans is a very complex issue and there are no truly predictive animal models to rely on. The in silico and T-cell response approaches identify the potential for immunogenicity; however, one needs contingency plans for emergence of anti-product antibody response for clinical trials.

Challenges in the chemotherapy of Chagas disease: Looking for possibilities related to the differences and similarities between the parasite and host

Almost 110 years after the first studies by Dr. Carlos Chagas describing an infectious disease that was named for him, Chagas disease remains a neglected illness and a death sentence for infected people in poor countries. This short review highlights the enormous need for new studies aimed at the development of novel and more specific drugs to treat chagasic patients. The primary tool for facing this challenge is deep knowledge about the similarities and differences between the parasite and its human host.

Lack of new antiinfective agents: Passing into the pre-antibiotic age?

The lack of newly developed antibiotics, together with the increase in multi-resistance of relevant pathogenic bacteria in the last decades, represents an alarming signal for human health care worldwide. The number of severely infected persons increases not only in developing but also in highly industrialized countries. This relates in first line to the most severe form of a bacterial infection, sepsis and the septic shock syndrome, with high mortality on critical care units. No particular anti-sepsis drug is available, and the therapy with conventional antibiotics more and more fails to provide a survival benefit. Due to the fact that the pharmaceutical industry has withdrawn to a high degree from the development of anti-infectious agents, a huge challenge for health care is approaching in the 21^st century. In this article, these problems are outlined and possible alternatives are presented which may be helpful to solve the problem.

Autophagy and cancer

Autophagy is a homeostatic and evolutionarily conserved mechanism of self-digestion by which the cells degrade and recycle long-lived proteins and excess or damaged organelles. Autophagy is activated in response to both physiological and pathological stimuli including growth factor depletion, energy deficiency or the upregulation of Bcl-2 protein expression. A novel role of autophagy in various cancers has been proposed. Interestingly, evidence that supports both a positive and negative role of autophagy in the pathogenesis of cancer has been reported. As a tumor suppression mechanism, autophagy maintains genome stability, induces senescence and possibly autophagic cell death. On the other hand, autophagy participates in tumor growth and maintenance by supplying metabolic substrate, limiting oxidative stress, and maintaining cancer stem cell population. It has been proposed that the differential roles of autophagy in cancer are disease type and stage specific. In addition, substrate selectivity might be involved in carrying out the specific effect of autophagy in cancer, and represents one of the potential directions for future studies.

Biocommunication and natural genome editing

The biocommunicative approach investigates communication processes within and among cells, tissues, organs and organisms as sign-mediated interactions, and nucleotide sequences as code, i.e. language-like text, which follows in parallel three kinds of rules: combinatorial (syntactic), context-sensitive (pragmatic), and content-specific (semantic). Natural genome editing from a biocommunicative perspective is competent agent-driven generation and integration of meaningful nucleotide sequences into pre-existing genomic content arrangements and the ability to (re-)combine and (re-)regulate them according to context-dependent (i.e. adaptational) purposes of the host organism.

Shuffling the cards in signal transduction: Calcium, arachidonic acid and mechanosensitivity

Cell signaling is a very complex network of biochemical reactions triggered by a huge number of stimuli coming from the external medium. The function of any single signaling component depends not only on its own structure but also on its connections with other biomolecules. During prokaryotic-eukaryotic transition, the rearrangement of cell organization in terms of diffusional compartmentalization exerts a deep change in cell signaling functional potentiality. In this review I briefly introduce an intriguing ancient relationship between pathways involved in cell responses to chemical agonists (growth factors, nutrients, hormones) as well as to mechanical forces (stretch, osmotic changes). Some biomolecules (ion channels and enzymes) act as “hubs”, thanks to their ability to be directly or indirectly chemically/mechanically co-regulated. In particular calcium signaling machinery and arachidonic acid metabolism are very ancient networks, already present before eukaryotic appearance. A number of molecular “hubs”, including phospholipase A2 and some calcium channels, appear tightly interconnected in a cross regulation leading to the cellular response to chemical and mechanical stimulations.

CARMA3: A novel scaffold protein in regulation of NF-κB activation and diseases

CARD recruited membrane associated protein 3 (CARMA3) is a novel scaffold protein. It belongs to the CARMA protein family, and is known to activate nuclear factor (NF)-κB. However, it is still unknown which receptor functions upstream of CARMA3 to trigger NF-κB activation. Recently, several studies have demonstrated that CARMA3 serves as an indispensable adaptor protein in NF-κB signaling under some G protein-coupled receptors (GPCRs), such as lysophosphatidic acid (LPA) receptor and angiotensin (Ang) II receptor. Mechanistically, CARMA3 recruits its essential downstream molecules Bcl10 and MALT1 to form the CBM (CARMA3-Bcl10-MALT1) signalosome whereby it triggers NF-κB activation. GPCRs and NF-κB play pivotal roles in the regulation of various cellular functions, therefore, aberrant regulation of the GPCR/NF-κB signaling axis leads to the development of many types of diseases, such as cancer and atherogenesis. Recently, the GPCR/CARMA3/NF-κB signaling axis has been confirmed in these specific diseases and it plays crucial roles in the pathogenesis of disease progression. In ovarian cancer cell lines, knockdown of CARMA3 abolishes LPA receptor-induced NF-κB activation, and reduces LPA-induced ovarian cancer invasion. In vascular smooth cells, downregulation of CARMA3 substantially impairs Ang-II-receptor-induced NF-κB activation, and in vivo studies have confirmed that Bcl10-deficient mice are protected from developing Ang-II-receptor-induced atherosclerosis and aortic aneurysms. In this review, we summarize the biology of CARMA3, describe the role of the GPCR/CARMA3/NF-κB signaling axis in ovarian cancer and atherogenesis, and speculate about the potential roles of this signaling axis in other types of cancer and diseases. With a significant increase in the identification of LPA- and Ang-II-like ligands, such as endothelin-1, which also activates NF-κB via CARMA3 and contributes to the development of many diseases, CARMA3 is emerging as a novel therapeutic target for various types of cancer and other diseases.

Role of sphingosine kinase and sphingosine-1-phosphate in inflammatory arthritis

The importance of sphingosine kinase (SphK) and sphingosine-1-phosphate (S1P) in inflammation has been extensively demonstrated. As an intracellular second messenger, S1P plays an important role in calcium signaling and mobilization, and cell proliferation and survival. Activation of various plasma membrane receptors, such as the formyl methionyl leucyl phenylalanine receptor, C5a receptor, and tumor necrosis factor α receptor, leads to a rapid increase in intracellular S1P level via SphK stimulation. SphK and S1P are implicated in various chronic autoimmune conditions such as rheumatoid arthritis, primary Sjögren’s syndrome, and inflammatory bowel disease. Recent studies have demonstrated the important role of SphK and S1P in the development of arthritis by regulating the pro-inflammatory responses. These novel pathways represent exciting potential therapeutic targets.

L-carnitine protects C2C12 cells against mitochondrial superoxide overproduction and cell death

AIM

To identify and characterize the protective effect that L-carnitine exerted against an oxidative stress in C2C12 cells.

METHODS

Myoblastic C2C12 cells were treated with menadione, a vitamin K analog that engenders oxidative stress, and the protective effect of L-carnitine (a nutrient involved in fatty acid metabolism and the control of the oxidative process), was assessed by monitoring various parameters related to the oxidative stress, autophagy and cell death.

RESULTS

Associated with its physiological function, a muscle cell metabolism is highly dependent on oxygen and may produce reactive oxygen species (ROS), especially under pathological conditions. High levels of ROS are known to induce injuries in cell structure as they interact at many levels in cell function. In C2C12 cells, a treatment with menadione induced a loss of transmembrane mitochondrial potential, an increase in mitochondrial production of ROS; it also induces autophagy and was able to provoke cell death. Pre-treatment of the cells with L-carnitine reduced ROS production, diminished autophagy and protected C2C12 cells against menadione-induced deleterious effects.

CONCLUSION

In conclusion, L-carnitine limits the oxidative stress in these cells and prevents cell death.

Modulation of the matrix redox signaling by mitochondrial Ca2+

Mitochondria sense, shape and integrate signals, and thus function as central players in cellular signal transduction. Ca²⁺ waves and redox reactions are two such intracellular signals modulated by mitochondria. Mitochondrial Ca²⁺ transport is of utmost physio-pathological relevance with a strong impact on metabolism and cell fate. Despite its importance, the molecular nature of the proteins involved in mitochondrial Ca²⁺ transport has been revealed only recently. Mitochondrial Ca²⁺ promotes energy metabolism through the activation of matrix dehydrogenases and down-stream stimulation of the respiratory chain. These changes also alter the mitochondrial NAD(P)H/NAD(P)⁺ ratio, but at the same time will increase reactive oxygen species (ROS) production. Reducing equivalents and ROS are having opposite effects on the mitochondrial redox state, which are hard to dissect. With the recent development of genetically encoded mitochondrial-targeted redox-sensitive sensors, real-time monitoring of matrix thiol redox dynamics has become possible. The discoveries of the molecular nature of mitochondrial transporters of Ca²⁺ combined with the utilization of the novel redox sensors is shedding light on the complex relation between mitochondrial Ca²⁺ and redox signals and their impact on cell function. In this review, we describe mitochondrial Ca²⁺ handling, focusing on a number of newly identified proteins involved in mitochondrial Ca²⁺ uptake and release. We further discuss our recent findings, revealing how mitochondrial Ca²⁺ influences the matrix redox state. As a result, mitochondrial Ca²⁺ is able to modulate the many mitochondrial redox-regulated processes linked to normal physiology and disease.

Multiple implications of 3-phosphoinositide-dependent protein kinase 1 in human cancer

3-phosphoinositide-dependent protein kinase-1 (PDK1) is a central mediator of cellular signaling between phosphoinositide-3 kinase and various intracellular serine/threonine kinases, including protein kinase B, p70 ribosomal S6 kinase, serum and glucocorticoid-inducible kinase, and protein kinase C. PDK1 activates members of the AGC family of protein kinases by phosphorylating serine/threonine residues in the activation loop. Here, we review the regulatory mechanisms of PDK1 and its roles in cancer. PDK1 is activated by autophosphorylation in the activation loop and other serine residues, as well as by phosphorylation of Tyr-9 and Tyr-373/376. Src appears to recognize PDK1 following tyrosine phosphorylation. The role of heat shock protein 90 in regulating PDK1 stability and PDK1-Src complex formation are also discussed. Furthermore, we summarize the subcellular distribution of PDK1. Finally, an important role for PDK1 in cancer chemotherapy is proposed. In conclusion, a better understanding of its molecular regulatory mechanisms in various signaling pathways will help to explain how PDK1 acts as an oncogenic kinase in various cancers, and will contribute to the development of novel cancer chemotherapies.

RNA-binding proteins related to stress response and differentiation in protozoa

RNA-binding proteins (RBPs) are key regulators of gene expression. There are several distinct families of RBPs and they are involved in the cellular response to environmental changes, cell differentiation and cell death. The RBPs can differentially combine with RNA molecules and form ribonucleoprotein (RNP) complexes, defining the function and fate of RNA molecules in the cell. RBPs display diverse domains that allow them to be categorized into distinct families. They play important roles in the cellular response to physiological stress, in cell differentiation, and, it is believed, in the cellular localization of certain mRNAs. In several protozoa, a physiological stress (nutritional, temperature or pH) triggers differentiation to a distinct developmental stage. Most of the RBPs characterized in protozoa arise from trypanosomatids. In these protozoa gene expression regulation is mostly post-transcriptional, which suggests that some RBPs might display regulatory functions distinct from those described for other eukaryotes. mRNA stability can be altered as a response to stress. Transcripts are sequestered to RNA granules that ultimately modulate their availability to the translation machinery, storage or degradation, depending on the associated proteins. These aggregates of mRNPs containing mRNAs that are not being translated colocalize in cytoplasmic foci, and their numbers and size vary according to cell conditions such as oxidative stress, nutritional status and treatment with drugs that inhibit translation.

To stay or to leave: Stem cells and progenitor cells navigating the S1P gradient

Most hematopoietic stem progenitor cells (HSPCs) reside in bone marrow (BM), but a small amount of HSPCs have been found to circulate between BM and tissues through blood and lymph. Several lines of evidence suggest that sphingosine-1-phosphate (S1P) gradient triggers HSPC egression to blood circulation after mobilization from BM stem cell niches. Stem cells also visit certain tissues. After a temporary 36 h short stay in local tissues, HSPCs go to lymph in response to S1P gradient between lymph and tissue and eventually enter the blood circulation. S1P also has a role in the guidance of the primitive HSPCs homing to BM in vivo, as S1P analogue FTY720 treatment can improve HSPC BM homing and engraftment. In stress conditions, various stem cells or progenitor cells can be attracted to local injured tissues and participate in local tissue cell differentiation and tissue rebuilding through modulation the expression level of S1P(1), S1P(2) or S1P(3) receptors. Hence, S1P is important for stem cells circulation in blood system to accomplish its role in body surveillance and injury recovery.

Plasma membrane calcium pump regulation by metabolic stress

The plasma membrane Ca²⁺-ATPase (PMCA) is an ATP-driven pump that is critical for the maintenance of low resting [Ca²⁺]_i in all eukaryotic cells. Metabolic stress, either due to inhibition of mitochondrial or glycolytic metabolism, has the capacity to cause ATP depletion and thus inhibit PMCA activity. This has potentially fatal consequences, particularly for non-excitable cells in which the PMCA is the major Ca²⁺ efflux pathway. This is because inhibition of the PMCA inevitably leads to cytosolic Ca²⁺ overload and the consequent cell death. However, the relationship between metabolic stress, ATP depletion and inhibition of the PMCA is not as simple as one would have originally predicted. There is increasing evidence that metabolic stress can lead to the inhibition of PMCA activity independent of ATP or prior to substantial ATP depletion. In particular, there is evidence that the PMCA has its own glycolytic ATP supply that can fuel the PMCA in the face of impaired mitochondrial function. Moreover, membrane phospholipids, mitochondrial membrane potential, caspase/calpain cleavage and oxidative stress have all been implicated in metabolic stress-induced inhibition of the PMCA. The major focus of this review is to challenge the conventional view of ATP-dependent regulation of the PMCA and bring together some of the alternative or additional mechanisms by which metabolic stress impairs PMCA activity resulting in cytosolic Ca²⁺ overload and cytotoxicity.