N-terminal Slit2 inhibits HIV-1 replication by regulating the actin cytoskeleton

Emerging roles of deubiquitinating enzymes in actin cytoskeleton and tumor metastasis

BACKGROUND

Metastasis accounts for the majority of cancer-related deaths. Actin dynamics and actin-based cell migration and invasion are important factors in cancer metastasis. Metastasis is characterized by actin polymerization and depolymerization, which are precisely regulated by molecular changes involving a plethora of actin regulators, including actin-binding proteins (ABPs) and signalling pathways, that enable cancer cell dissemination from the primary tumour. Research on deubiquitinating enzymes (DUBs) has revealed their vital roles in actin dynamics and actin-based migration and invasion during cancer metastasis.

CONCLUSION

Here, we review how DUBs drive tumour metastasis by participating in actin rearrangement and actin-based migration and invasion. We summarize the well-characterized and essential actin cytoskeleton signalling molecules related to DUBs, including Rho GTPases, Src kinases, and ABPs such as cofilin and cortactin. Other DUBs that modulate actin-based migration signalling pathways are also discussed. Finally, we discuss and address therapeutic opportunities and ongoing challenges related to DUBs with respect to actin dynamics.

Fibroblast-derived CXCL12 increases vascular permeability in a 3-D microfluidic model independent of extracellular matrix contractility

Cancer-associated fibroblasts (CAFs) play an active role in remodeling the local tumor stroma to support tumor initiation, growth, invasion, metastasis, and therapeutic resistance. The CAF-secreted chemokine, CXCL12, has been directly implicated in the tumorigenic progression of carcinomas, including breast cancer. Using a 3-D in vitro microfluidic-based microtissue model, we demonstrate that stromal CXCL12 secreted by CAFs has a potent effect on increasing the vascular permeability of local blood microvessel analogues through paracrine signaling. Moreover, genetic deletion of fibroblast-specific CXCL12 significantly reduced vessel permeability compared to CXCL12 secreting CAFs within the recapitulated tumor microenvironment (TME). We suspected that fibroblast-mediated extracellular matrix (ECM) remodeling and contraction indirectly accounted for this change in vessel permeability. To this end, we investigated the autocrine effects of CXCL12 on fibroblast contractility and determined that antagonistic blocking of CXCL12 did not have a substantial effect on ECM contraction. Our findings indicate that fibroblast-secreted CXCL12 has a significant role in promoting a leakier endothelium hospitable to angiogenesis and tumor cell intravasation; however, autocrine CXCL12 is not the primary upstream trigger of CAF contractility.

SLIT2/ROBO1-signaling inhibits macropinocytosis by opposing cortical cytoskeletal remodeling

Macropinocytosis is essential for myeloid cells to survey their environment and for growth of RAS-transformed cancer cells. Several growth factors and inflammatory stimuli are known to induce macropinocytosis, but its endogenous inhibitors have remained elusive. Stimulation of Roundabout receptors by Slit ligands inhibits directional migration of many cell types, including immune cells and cancer cells. We report that SLIT2 inhibits macropinocytosis in vitro and in vivo by inducing cytoskeletal changes in macrophages. In mice, SLIT2 attenuates the uptake of muramyl dipeptide, thereby preventing NOD2-dependent activation of NF-κB and consequent secretion of pro-inflammatory chemokine, CXCL1. Conversely, blocking the action of endogenous SLIT2 enhances CXCL1 secretion. SLIT2 also inhibits macropinocytosis in RAS-transformed cancer cells, thereby decreasing their survival in nutrient-deficient conditions which resemble tumor microenvironment. Our results identify SLIT2 as a physiological inhibitor of macropinocytosis and challenge the conventional notion that signals that enhance macropinocytosis negatively regulate cell migration, and vice versa.

Inhibitory Effect of Slit2-N on VEGF165-induced proliferation of vascular endothelia via Slit2-N-Robo4-Akt pathway in choroidal neovascularization

Researches have been focusing on the role of Slit2 in angiogenesis, specifically in cell migration and vessel permeability. Nevertheless, the role of Slit2-N, the bioactive fragment of Slit2, in the proliferation of vascular endothelia in choroidal neovascularization and some related mechanisms have not been studied yet. Thus, our study aimed to explore the role of Slit2-N in proliferation of vascular endothelia and the related mechanisms in choroidal neovascularization. Fluorescein isothiocyanate perfusion and HE staining were performed to evaluate volumes of choroidal neovascularization lesions. The effect of Slit2-N on VEGF165-induced cell proliferation and some related mechanisms were detected by CCK8 assay, flow cytometry, siRNA transfection, and western blotting. We found that Slit2-N reduced volumes of laser-induced choroidal neovascularization networks in vivo. Results of the in vitro study showed Slit2-N reduced VEGF165-induced cell proliferation of both human umbilical vascular endothelial cells and human microvascular endothelial cells possibly via activation of AKT rather than that of ERK1/2. Additionally, Robo4, one of the receptors binding to Slit2-N, was involved in the inhibitory effect of Slit2-N. Generally, our findings revealed the inhibitory role of Slit2-N in proliferation of vascular endothelia and some related mechanisms, and presented some potential targets, molecules along Slit2-N-Robo4-AKT axis, to choroidal neovascularization therapy.

Chemokines and Chemokine Receptors: Accomplices for Human Immunodeficiency Virus Infection and Latency

Chemokines are small chemotactic cytokines that are involved in the regulation of immune cell migration. Multiple functional properties of chemokines, such as pro-inflammation, immune regulation, and promotion of cell growth, angiogenesis, and apoptosis, have been identified in many pathological and physiological contexts. Human immunodeficiency virus (HIV) infection is characterized by persistent inflammation and immune activation during both acute and chronic phases, and the "cytokine storm" is one of the hallmarks of HIV infection. Along with immune activation after HIV infection, an extensive range of chemokines and other cytokines are elevated, thereby generating the so-called "cytokine storm." In this review, the effects of the upregulated chemokines and chemokine receptors on the processes of HIV infection are discussed. The objective of this review was to focus on the main chemokines and chemokine receptors that have been found to be associated with HIV infection and latency. Elevated chemokines and chemokine receptors have been shown to play important roles in the HIV life cycle, disease progression, and HIV reservoir establishment. Thus, targeting these chemokines and receptors and the other proteins of related signaling pathways might provide novel therapeutic strategies, and the evidence indicates a promising future regarding the development of a functional cure for HIV.

Peptide regulation of cofilin activity in the CNS: A novel therapeutic approach for treatment of multiple neurological disorders

Cofilin is a ubiquitous protein which cooperates with many other actin-binding proteins in regulating actin dynamics. Cofilin has essential functions in nervous system development including neuritogenesis, neurite elongation, growth cone pathfinding, dendritic spine formation, and the regulation of neurotransmission and spine function, components of synaptic plasticity essential for learning and memory. Cofilin's phosphoregulation is a downstream target of many transmembrane signaling processes, and its misregulation in neurons has been linked in rodent models to many different neurodegenerative and neurological disorders including Alzheimer disease (AD), aggression due to neonatal isolation, autism, manic/bipolar disorder, and sleep deprivation. Cognitive and behavioral deficits of these rodent models have been largely abrogated by modulation of cofilin activity using viral-mediated, genetic, and/or small molecule or peptide therapeutic approaches. Neuropathic pain in rats from sciatic nerve compression has also been reduced by modulating the cofilin pathway within neurons of the dorsal root ganglia. Neuroinflammation, which occurs following cerebral ischemia/reperfusion, but which also accompanies many other neurodegenerative syndromes, is markedly reduced by peptides targeting specific chemokine receptors, which also modulate cofilin activity. Thus, peptide therapeutics offer potential for cost-effective treatment of a wide variety of neurological disorders. Here we discuss some recent results from rodent models using therapeutic peptides with a surprising ability to cross the rodent blood brain barrier and alter cofilin activity in brain. We also offer suggestions as to how neuronal-specific cofilin regulation might be achieved.

Renal endothelial injury and microvascular dysfunction in acute kidney injury

The kidney is comprised of heterogeneous cell populations that function together to perform a number of tightly controlled, complex and interdependent processes. Renal endothelial cells contribute to vascular tone, regulation of blood flow to local tissue beds, modulation of coagulation and inflammation, and vascular permeability. Both ischemia and sepsis have profound effects on the renal endothelium, resulting in microvascular dysregulation resulting in continued ischemia and further injury. In recent years, the concept of the vascular endothelium as an organ that is both the source of and target for inflammatory injury has become widely appreciated. Here we revisit the renal endothelium in the light of ever evolving molecular advances.

Slit2N Inhibits Transmission of HIV-1 from Dendritic Cells to T-cells by Modulating Novel Cytoskeletal Elements

Dendritic cells are among the first cells to encounter sexually acquired human immunodeficiency virus (HIV-1), in the mucosa, and they can transmit HIV-1 to CD4(+) T-cells via an infectious synapse. Recent studies reveal that actin-rich membrane extensions establish direct contact between cells at this synapse and facilitate virus transmission. Genesis of these contacts involves signaling through c-Src and Cdc42, which modulate actin polymerization and filopodia formation via the Arp2/3 complex and Diaphanous 2 (Diaph2). We found that Slit2N, a ligand for the Roundabout (Robo) receptors, blocked HIV-1-induced signaling through Arp2/3 and Diaph2, decreased filopodial extensions on dendritic cells, and inhibited cell-to-cell transmission of HIV-1 in a Robo1-dependent manner. Employing proteomic analysis, we identified Flightless-1 as a novel, Robo1-interacting protein. Treatment with shRNAs reduced levels of Flightless-1 and demonstrated its role in efficient cell-to-cell transfer of HIV-1. These results suggest a novel strategy to limit viral infection in the host by targeting the Slit/Robo pathway with modulation of cytoskeletal elements previously unrecognized in HIV-1 transmission.

The Neurorepellent Slit2 Inhibits Postadhesion Stabilization of Monocytes Tethered to Vascular Endothelial Cells

The secreted neurorepellent Slit2, acting through its transmembrane receptor, Roundabout (Robo)-1, inhibits chemotaxis of varied cell types, including leukocytes, endothelial cells, and vascular smooth muscle cells, toward diverse attractants. The role of Slit2 in regulating the steps involved in recruitment of monocytes in vascular inflammation is not well understood. In this study, we showed that Slit2 inhibited adhesion of monocytic cells to activated human endothelial cells, as well as to immobilized ICAM-1 and VCAM-1. Microfluidic live cell imaging showed that Slit2 inhibited the ability of monocytes tethered to endothelial cells to stabilize their actin-associated anchors and to resist detachment in response to increasing shear forces. Transfection of constitutively active plasmids revealed that Slit2 inhibited postadhesion stabilization of monocytes on endothelial cells by preventing activation of Rac1. We further found that Slit2 inhibited chemotaxis of monocytes toward CXCL12 and CCL2. To determine whether Slit2 and Robo-1 modulate pathologic monocyte recruitment associated with vascular inflammation and cardiovascular disease, we tested PBMC from patients with coronary artery disease. PBMC from these patients had reduced surface levels of Robo-1 compared with healthy age- and sex-matched subjects, and Slit2 failed to inhibit chemotaxis of PBMC of affected patients, but not healthy control subjects, toward CCL2. Furthermore, administration of Slit2 to atherosclerosis-prone LDL receptor-deficient mice inhibited monocyte recruitment to nascent atherosclerotic lesions. These results demonstrate that Slit2 inhibits chemotaxis of monocytes, as well as their ability to stabilize adhesions and resist detachment forces. Slit2 may represent a powerful new tool to inhibit pathologic monocyte recruitment in vascular inflammation and atherosclerosis.

Cataloguing of Potential HIV Susceptibility Factors during the Menstrual Cycle of Pig-Tailed Macaques by Using a Systems Biology Approach

Our earlier studies with pig-tailed macaques demonstrated various simian-human immunodeficiency virus (SHIV) susceptibilities during the menstrual cycle, likely caused by cyclic variations in immune responses in the female genital tract. There is concern that high-dose, long-lasting, injectable progestin-based contraception could mimic the high-progesterone luteal phase and predispose women to human immunodeficiency type 1 (HIV-1) acquisition and transmission. In this study, we adopted a systems biology approach employing proteomics (tandem mass spectrometry), transcriptomics (RNA microarray hybridization), and other specific protein assays (enzyme-linked immunosorbent assays and multiplex chemokine and cytokine measurements) to characterize the effects of hormonal changes on the expression of innate factors and secreted proteins in the macaque vagina. Several antiviral factors and pathways (including acute-phase response signaling and complement system) were overexpressed in the follicular phase. Conversely, during the luteal phase there were factors overexpressed (including moesins, syndecans, and integrins, among others) that could play direct or indirect roles in enhancing HIV-1 infection. Thus, our study showed that specific pathways and proteins or genes might work in tandem to regulate innate immunity, thus fostering further investigation and future design of approaches to help counter HIV-1 acquisition in the female genital tract.

IMPORTANCE

HIV infection in women is poorly understood. High levels of the hormone progesterone may make women more vulnerable to infection. This could be the case during the menstrual cycle, when using hormone-based birth control, or during pregnancy. The biological basis for increased HIV vulnerability is not known. We used an animal model with high risk for infection during periods of high progesterone. Genital secretions and tissues during the menstrual cycle were studied. Our goal was to identify biological factors upregulated at high progesterone levels, and we indeed show an upregulation of genes and proteins which enhance the ability of HIV to infect when progesterone is high. In contrast, during low-progesterone periods, we found more HIV inhibitory factors. This study contributes to our understanding of mechanisms that may regulate HIV infection in females under hormonal influences. Such knowledge is needed for the development of novel prevention strategies.

Pathogenic microbes manipulate cofilin activity to subvert actin cytoskeleton

Actin-depolymerizing factor (ADF)/cofilin proteins are key players in controlling the temporal and spatial extent of actin dynamics, which is crucial for mediating host-pathogen interactions. Pathogenic microbes have evolved molecular mechanisms to manipulate cofilin activity to subvert the actin cytoskeletal system in host cells, promoting their internalization into the target cells, modifying the replication niche and facilitating their intracellular and intercellular dissemination. The study of how these pathogens exploit cofilin pathways is crucial for understanding infectious disease and providing potential targets for drug therapies.

miR-29b defines the pro-/anti-proliferative effects of S100A7 in breast cancer

INTRODUCTION

S100A7 (Psoriasin) is an inflammatory protein known to be upregulated in breast cancer. However, the role of S100A7 in breast cancer has been elusive, since both pro- and anti-proliferative roles have been reported in different types of breast cancer cells and animal models. To date, the mechanism by which S100A7 differentially regulates breast cancer cell proliferation is still not clear.

METHODS

We used Gene Functional Enrichment Analysis to search for the determining factor of S100A7 differential regulation. We confirmed the factor and elaborated its regulating mechanism using in vitro cell culture. We further verified the findings using xenografts of human breast cancer cells in nude mice.

RESULTS

In the present study, we show that S100A7 significantly upregulates the expression of miR-29b in Estrogen Receptor (ER)-positive breast cancer cells (represented by MCF7), and significantly downregulates miR-29b in ER-negative cells (represented by MDA-MB-231) [Corrected]. The differential regulation of miR-29b by S100A7 in ER-positive and ER-negative breast cancer is supported by the gene expression analysis of TCGA invasive breast cancer dataset. miR-29b transcription is inhibited by NF-κB, and NF-κB activation is differentially regulated by S100A7 in ER-positive and ER-negative breast cancer cells. This further leads to differential regulation of PI3K p85α and CDC42 expression, p53 activation and p53-associated anti-proliferative pathways. Reversing the S100A7-caused changes of miR-29b expression by transfecting exogenous miR-29b or miR-29b-Decoy can inhibit the effects of S100A7 on in vitro cell proliferation and tumor growth in nude mice.

CONCLUSIONS

The distinct modulations of the NF-κB - miR-29b - p53 pathway make S100A7 an oncogene in ER-negative and a cancer-suppressing gene in ER-positive breast cancer cells, with miR-29b being the determining regulatory factor.

Distinct requirements for HIV-cell fusion and HIV-mediated cell-cell fusion

Whether HIV-1 enters cells by fusing with the plasma membrane or with endosomes is a subject of active debate. The ability of HIV-1 to mediate fusion between adjacent cells, a process referred to as "fusion-from-without" (FFWO), shows that this virus can fuse with the plasma membrane. To compare FFWO occurring at the cell surface with HIV-cell fusion through a conventional entry route, we designed an experimental approach that enabled the measurements of both processes in the same sample. The following key differences were observed. First, a very small fraction of viruses fusing with target cells participated in FFWO. Second, whereas HIV-1 fusion with adherent cells was insensitive to actin inhibitors, post-CD4/coreceptor binding steps during FFWO were abrogated. A partial dependence of HIV-cell fusion on actin remodeling was observed in CD4(+) T cells, but this effect appeared to be due to the actin dependence of virus uptake. Third, deletion of the cytoplasmic tail of HIV-1 gp41 dramatically enhanced the ability of the virus to promote FFWO, while having a modest effect on virus-cell fusion. Distinct efficiencies and actin dependences of FFWO versus HIV-cell fusion are consistent with the notion that, except for a minor fraction of particles that mediate fusion between the plasma membranes of adjacent cells, HIV-1 enters through an endocytic pathway. We surmise, however, that cell-cell contacts enabling HIV-1 fusion with the plasma membrane could be favored at the sites of high density of target cells, such as lymph nodes.

Design of novel leads: ligand based computational modeling studies on non-nucleoside reverse transcriptase inhibitors (NNRTIs) of HIV-1

Researchers are on the constant lookout for new antiviral agents for the treatment of AIDS. In the present work, ligand based modeling studies are performed on analogues of substituted phenyl-thio-thymines, which act as non-nucleoside reverse transcriptase inhibitors (NNRTIs) and novel leads are extracted. Using alignment-dependent descriptors, based on group center overlap (SALL, HDALL, HAALL and RALL), an alignment-independent descriptor (S log P), a topological descriptor (Balaban index (J)) and a 3D descriptor dipole moment (μ) and shape based descriptors (Kappa 2 index ((2)κ)), a correlation is derived with inhibitory activity. Linear and non-linear techniques have been used to achieve the goal. Support Vector Machine (SVM, R = 0.929, R(2) = 0.863) and Back Propagation Neural Network (BPNN, R = 0.928, R(2) = 0.861) methods yielded near similar results and outperformed Multiple Linear Regression (MLR, R = 0.915, R(2) = 0.837). The predictive ability of the models are cross-validated using a test dataset (SVM: R = 0.846, R(2) = 0.716, BPNN: R = 0.841, R(2) = 0.707 and MLR: R = 0.833, R(2) = 0.694). It is concluded that the hydrophobicity (S log P) and the polarity (μ) of a ligand and the presence of hydrogen donor (HDALL) moieties are the deciding factors in improving antiviral activity and pharmaco-therapeutic properties. Based on the above findings, a virtual dataset is created to extract probable leads with reasonable antiviral activity as well as better pharmacophoric properties.

Targeting strategies for delivery of anti-HIV drugs

Human Immunodeficiency Virus (HIV) infection remains a significant cause of mortality globally. Though antiretroviral therapy has significantly reduced AIDS-related morbidity and mortality, there are several drawbacks in the current therapy, including toxicity, drug–drug interactions, development of drug resistance, necessity for long-term drug therapy, poor bio-availability and lack of access to tissues and reservoirs. To circumvent these problems, recent anti-HIV therapeutic research has focused on improving drug delivery systems through drug delivery targeted specifically to host cells infected with HIV or could potentially get infected with HIV. In this regard, several surface molecules of both viral and host cell origin have been described in recent years, that would enable targeted drug delivery in HIV infection. In the present review, we provide a comprehensive overview of the need for novel drug delivery systems, and the successes and challenges in the identification of novel viral and host-cell molecules for the targeted drug delivery of anti-HIV drugs. Such targeted anti-retroviral drug delivery approaches could pave the way for effective treatment and eradication of HIV from the body.

Novel anti-HIV therapeutics targeting chemokine receptors and actin regulatory pathways

The human immunodeficiency virus-1 (HIV-1) infects helper CD4(+) T cells, and causes CD4(+) T-cell depletion and immunodeficiency. In the past 30 years, significant progress has been made in antiretroviral therapy, and the disease has become manageable. Nevertheless, an effective vaccine is still nowhere in sight, and a cure or a functional cure awaits discovery. Among possible curative therapies, traditional antiretroviral therapy, mostly targeting viral proteins, has been proven ineffective. It is possible that targeting HIV-dependent host cofactors may offer alternatives, both for preventing HIV transmission and for forestalling disease progression. Recently, the actin cytoskeleton and its regulators in blood CD4(+) T cells have emerged as major host cofactors that could be targeted. The novel concept that the cortical actin is a barrier to viral entry and early post-entry migration has led to the nascent model of virus-host interaction at the cortical actin layer. Deciphering the cellular regulatory pathways has manifested exciting prospects for future therapeutics. In this review, we describe the study of HIV interactions with actin cytoskeleton. We also examine potential pharmacological targets that emerge from this interaction. In addition, we briefly discuss several actin pathway-based anti-HIV drugs that are currently in development or testing.

Regulatory T Cells Diminish HIV Infection in Dendritic Cells - Conventional CD4(+) T Cell Clusters

Formation of immunological synapses (IS) between dendritic cells (DCs) and conventional CD4(+) T cells (Tcon) is critical for productive immune responses. However, when DCs are HIV-infected such synapses are critical to establish HIV infection. As regulatory T cells (Treg) control DC-Tcon interactions, we inquired whether Treg might interfere with DC to Tcon HIV infection. We developed a model, using monocyte-derived DC infected with R5-HIV, and cultured with Tcon in the presence or absence of autologous Treg, using the physiological ratio of 1 Treg for 10 Tcon. Cultures containing Treg significantly decreased HIV infection in DC:T cell clusters. Notably, Treg appear to have an effect on the quality of the IS, as Treg decreased actin polymerization and DC maturation. Importantly, Treg decreased the trafficking of HIV punctate to the IS. Further, CD152 and cyclic adenosine monophosphate were critical Treg effector molecules, as their individual or simultaneous blockade abolished Treg activity, however no additive effect was found. Together, these data suggest that Treg can reduce HIV dissemination, which may be beneficial to the host in the early stages of infection.

Slit2N and Robo4 regulate lymphangiogenesis through the VEGF-C/VEGFR-3 pathway

Background

Signaling through vascular endothelial growth factor C (VEGF–C) and VEGF receptor 3 (VEGFR-3) plays a central role in lymphangiogenesis and the metastasis of several cancers via the lymphatics. Recently, the Slit2/Robo4 pathway has been recognized as a modulator of vascular permeability and integrity. Signaling via the Robo receptor inhibits VEGF-mediated effects; however, its effects on lymphatic endothelial cell function have not been well characterized.

Results

We found that pretreatment with Slit2N, an active fragment of Slit2, inhibited VEGF-C-mediated lung-derived lymphatic endothelial cell (L-LEC) proliferation, migration, and in vitro tube formation. Slit2N induced the internalization of VEGFR-3, which blocked its activation, and inhibited the activation of the PI3K/Akt pathway by VEGF-C in L-LECs. Moreover, we found that inhibition of VEGF-C-induced effects by Slit2N was Robo4-dependent.

Conclusion

These results indicate that Slit2N/Robo4 modulates several key cellular functions, which contribute to lymphangiogenesis, and identify this ligand-receptor pair as a potential therapeutic target to inhibit lymphatic metastasis of VEGF-C-overexpressing cancers and manage lymphatic dysfunctions characterized by VEGF-C/VEGFR-3 activation.

Roundabout receptors

Roundabout receptors (Robo) and their Slit ligands were discovered in the 1990s and found to be key players in axon guidance. Slit was initially described s an extracellular matrix protein that was expressed by midline glia in Drosophila. A few years later, it was shown that, in vertebrates and invertebrates, Slits acted as chemorepellents for axons crossing the midline. Robo proteins were originally discovered in Drosophila in a mutant screen for genes involved in the regulation of midline crossing. This ligand-receptor pair has since been implicated in a variety of other neuronal and non-neuronal processes ranging from cell migration to angiogenesis, tumourigenesis and even organogenesis of tissues such as kidneys, lungs and breasts.

Slit2-Robo4 pathway modulates lipopolysaccharide-induced endothelial inflammation and its expression is dysregulated during endotoxemia

The secretory protein Slit2 and its receptors Robo1 and Robo4 are considered to regulate mobility and permeability of endothelial cells and other cell types. However, the roles of Slit2 and its two receptors in endothelial inflammatory responses remain to be clarified. In this study, we show that, in primary HUVECs, Slit2 represses LPS-induced secretion of certain inflammatory cytokines/chemokines, cell adhesion molecule ICAM-1 upregulation, and monocyte adhesion. Slit2's anti-inflammatory effect is mediated by its dominant endothelial-specific receptor Robo4. However, the minor receptor Robo1 has proinflammatory properties and is downregulated by Slit2 via targeting of miR-218. Elucidation of molecular mechanism reveals that Slit2 represses inflammatory responses by inhibiting the Pyk2-NF-κB pathway downstream of LPS-TLR4. Further studies reveal that LPS enhances endothelial inflammation by downregulating the anti-inflammatory Slit2 and Robo4 in HUVECs in vitro, as well as in arterial endothelial cells and liver in vivo during endotoxemia. These results suggest that Slit2-Robo4 signaling is important in regulating LPS-induced endothelial inflammation, and LPS, in turn, enhances inflammation by interfering with the expression of the anti-inflammatory Slit2-Robo4 during the disease state. This implies that Slit2-Robo4 is a key regulator of endothelial inflammation, and its dysregulation during endotoxemia is a novel mechanism for LPS-induced vascular pathogenesis.

Emerging therapeutic strategies to prevent infection-related microvascular endothelial activation and dysfunction

Recent evidence suggests that loss of endothelial barrier function and resulting microvascular leak play important mechanistic roles in the pathogenesis of infection-related end-organ dysfunction and failure. Several distinct therapeutic strategies, designed to prevent or limit infection-related microvascular endothelial activation and permeability, thereby mitigating end-organ injury/dysfunction, have recently been investigated in pre-clinical models. In this review, these potential therapeutic strategies, namely, VEGFR2/Src antagonists, sphingosine-1-phosphate agonists, fibrinopeptide Bβ_15–42, slit2N, secinH3, angiopoietin-1/tie-2 agonists, angiopoietin-2 antagonists, statins, atrial natriuretic peptide, and mesenchymal stromal (stem) cells, are discussed in terms of their translational potential for the management of clinical infectious diseases.

Genistein interferes with SDF-1- and HIV-mediated actin dynamics and inhibits HIV infection of resting CD4 T cells

Background

Binding of HIV to the chemokine coreceptor CXCR4 mediates viral fusion and signal transduction that promotes actin dynamics critical for HIV infection of blood resting CD4 T cells. It has been suggested that this gp120-mediated actin activity resembles the chemotactic actin dynamics mediated by chemokines such as SDF-1. To determine whether inhibiting SDF-1-mediated chemotactic activity can also inhibit HIV infection, we screened several inhibitors known to reduce SDF-1-mediated chemotaxis of T cells.

Results

We found that a tyrosine kinase inhibitor, genistein, inhibited both SDF-1-mediated chemotaxis and HIV infection of resting CD4 T cells. Genistein was also found to interfere with SDF-1- and HIV-mediated actin dynamics in CD4 T cells. This reduction in actin activity correlates with genistein-mediated inhibition of viral DNA accumulation in resting CD4 T cells. In addition, we also tested two other tyrosine kinase inhibitors, sunitinib and AG1478. Sunitinib, but not AG1478, inhibited HIV infection of resting CD4 T cells. We further tested the safety of genistein in 3 Chinese rhesus macaques (Macaca mulatta), and each animal was given a monotherapy of genistein at 10 mg/kg orally for 12 weeks. No adverse drug effects were observed in these animals.

Conclusions

Our results suggest that novel therapeutic strategies can be developed based on targeting cellular proteins involved in HIV-dependent signaling. This approach can interfere with HIV-mediated actin dynamics and inhibit HIV infection.

HIV restriction in quiescent CD4⁺ T cells

The restriction of the Human Immunodeficiency Virus (HIV) infection in quiescent CD4⁺ T cells has been an area of active investigation. Early studies have suggested that this T cell subset is refractory to infection by the virus. Subsequently it was demonstrated that quiescent cells could be infected at low levels; nevertheless these observations supported the earlier assertions of debilitating defects in the viral life cycle. This phenomenon raised hopes that identification of the block in quiescent cells could lead to the development of new therapies against HIV. As limiting levels of raw cellular factors such as nucleotides did not account for the block to infection, a number of groups pursued the identification of cellular proteins whose presence or absence may impact the permissiveness of quiescent T cells to HIV infection. A series of studies in the past few years have identified a number of host factors implicated in the block to infection. In this review, we will present the progress made, other avenues of investigation and the potential impact these studies have in the development of more effective therapies against HIV.