Enhanced transgene expression in cord blood CD34(+)-derived hematopoietic cells, including developing T cells and NOD/SCID mouse repopulating cells, following transduction with modified trip lentiviral vectors

Proteomic landscape of tunneling nanotubes reveals CD9 and CD81 tetraspanins as key regulators

Tunneling nanotubes (TNTs) are open actin- and membrane-based channels, connecting remote cells and allowing direct transfer of cellular material (e.g. vesicles, mRNAs, protein aggregates) from the cytoplasm to the cytoplasm. Although they are important especially, in pathological conditions (e.g. cancers, neurodegenerative diseases), their precise composition and their regulation were still poorly described. Here, using a biochemical approach allowing to separate TNTs from cell bodies and from extracellular vesicles and particles (EVPs), we obtained the full composition of TNTs compared to EVPs. We then focused on two major components of our proteomic data, the CD9 and CD81 tetraspanins, and further investigated their specific roles in TNT formation and function. We show that these two tetraspanins have distinct non-redundant functions: CD9 participates in stabilizing TNTs, whereas CD81 expression is required to allow the functional transfer of vesicles in the newly formed TNTs, possibly by regulating docking to or fusion with the opposing cell.

Sphingolipid paracrine signaling impairs keratinocyte adhesion to promote melanoma invasion

Melanoma is the deadliest form of skin cancer due to its propensity to metastasize. It arises from melanocytes, which are attached to keratinocytes within the basal epidermis. Here, we hypothesize that, in addition to melanocyte-intrinsic modifications, dysregulation of keratinocyte functions could initiate early-stage melanoma cell invasion. We identified the lysolipid sphingosine 1-phosphate (S1P) as a tumor paracrine signal from melanoma cells that modifies the keratinocyte transcriptome and reduces their adhesive properties, leading to tumor invasion. Mechanistically, tumor cell-derived S1P reduced E-cadherin expression in keratinocytes via S1P receptor dependent Snail and Slug activation. All of these effects were blocked by S1P2/3 antagonists. Importantly, we showed that epidermal E-cadherin expression was inversely correlated with the expression of the S1P-producing enzyme in neighboring tumors and the Breslow thickness in patients with early-stage melanoma. These findings support the notion that E-cadherin loss in the epidermis initiates the metastatic cascade in melanoma.

Tetraspanin Tspan8 restrains interferon signaling to stabilize intestinal epithelium by directing endocytosis of interferon receptor

Inflammation can impair intestinal barrier, while increased epithelial permeability can lead to inflammation. In this study, we found that the expression of Tspan8, a tetraspanin expressed specifically in epithelial cells, is downregulated in mouse model of ulcerative disease (UC) but correlated with those of cell-cell junction components, such as claudins and E-cadherin, suggesting that Tspan8 supports intestinal epithelial barrier. Tspan8 removal increases intestinal epithelial permeability and upregulates IFN-γ-Stat1 signaling. We also demonstrated that Tspan8 coalesces with lipid rafts and facilitates IFNγ-R1 localization at or near lipid rafts. As IFN-γ induces its receptor undergoing clathrin- or lipid raft-dependent endocytosis and IFN-γR endocytosis plays an important role in Jak-Stat1 signaling, our analysis on IFN-γR endocytosis revealed that Tspan8 silencing impairs lipid raft-mediated but promotes clathrin-mediated endocytosis of IFN-γR1, leading to increased Stat1 signaling. These changes in IFN-γR1 endocytosis upon Tspan8 silencing correlates with fewer lipid raft component GM1 at the cell surface and more clathrin heavy chain in the cells. Our findings indicate that Tspan8 determines the IFN-γR1 endocytosis route, to restrain Stat1 signaling, stabilize intestine epithelium, and subsequently prevent intestine from inflammation. Our finding also implies that Tspan8 is needed for proper endocytosis through lipid rafts.

An Update on the HIV DNA Vaccine Strategy

In 2020, the global prevalence of human immunodeficiency virus (HIV) infection was estimated to be 38 million, and a total of 690,000 people died from acquired immunodeficiency syndrome (AIDS)–related complications. Notably, around 12.6 million people living with HIIV/AIDS did not have access to life-saving treatment. The advent of the highly active antiretroviral therapy (HAART) in the mid-1990s remarkably enhanced the life expectancy of people living with HIV/AIDS as a result of improved immune functions. However, HAART has several drawbacks, especially when it is not used properly, including a high risk for the development of drug resistance, as well as undesirable side effects such as lipodystrophy and endocrine dysfunctions, which result in HAART intolerability. HAART is also not curative. Furthermore, new HIV infections continue to occur globally at a high rate, with an estimated 1.7 million new infections occurring in 2018 alone. Therefore, there is still an urgent need for an affordable, effective, and readily available preventive vaccine against HIV/AIDS. Despite this urgent need, however, progress toward an effective HIV vaccine has been modest over the last four decades. Reasons for this slow progress are mainly associated with the unique aspects of HIV itself and its ability to rapidly mutate, targeting immune cells and escape host immune responses. Several approaches to an HIV vaccine have been undertaken. However, this review will mainly discuss progress made, including the pre-clinical and clinical trials involving vector-based HIV DNA vaccines and the use of integrating lentiviral vectors in HIV vaccine development. We concluded by recommending particularly the use of integrase-defective lentiviral vectors, owing to their safety profiles, as one of the promising vectors in HIV DNA vaccine strategies both for prophylactic and therapeutic HIV vaccines.

Hematopoietic-Stem-Cell-Targeted Gene-Addition and Gene-Editing Strategies for β-hemoglobinopathies

Sickle cell disease (SCD) is caused by a well-defined point mutation in the β-globin gene and therefore is an optimal target for hematopoietic stem cell (HSC) gene-addition/editing therapy. In HSC gene-addition therapy, a therapeutic β-globin gene is integrated into patient HSCs via lentiviral transduction, resulting in long-term phenotypic correction. State-of-the-art gene-editing technology has made it possible to repair the β-globin mutation in patient HSCs or target genetic loci associated with reactivation of endogenous γ-globin expression. With both approaches showing signs of therapeutic efficacy in patients, we discuss current genetic treatments, challenges, and technical advances in this field.

Hypoxia favors chemoresistance in T-ALL through an HIF1α-mediated mTORC1 inhibition loop

Resistance to chemotherapy, a major therapeutic challenge in the treatment of T-cell acute lymphoblastic leukemia (T-ALL), can be driven by interactions between leukemic cells and the microenvironment that promote survival of leukemic cells. The bone marrow, an important leukemia niche, has low oxygen partial pressures that highly participate in the regulation of normal hematopoiesis. Here we show that hypoxia inhibits T-ALL cell growth by slowing down cell cycle progression, decreasing mitochondria activity, and increasing glycolysis, making them less sensitive to antileukemic drugs and preserving their ability to initiate leukemia after treatment. Activation of the mammalian target of rapamycin (mTOR) was diminished in hypoxic leukemic cells, and treatment of T-ALL with the mTOR inhibitor rapamycin in normoxia mimicked the hypoxia effects, namely decreased cell growth and increased quiescence and drug resistance. Knocking down (KD) hypoxia-induced factor 1α (HIF-1α), a key regulator of the cellular response to hypoxia, antagonized the effects observed in hypoxic T-ALL and restored chemosensitivity. HIF-1α KD also restored mTOR activation in low O2 concentrations, and inhibiting mTOR in HIF1α KD T-ALL protected leukemic cells from chemotherapy. Thus, hypoxic niches play a protective role of T-ALL during treatments. Inhibition of HIF-1α and activation of the mTORC1 pathway may help suppress the drug resistance of T-ALL in hypoxic niches.

Mitotic arrest affects clustering of tumor cells

Background

Cancer cell aggregation is a key process involved in the formation of tumor cell clusters. It has recently been shown that clusters of circulating tumor cells (CTCs) have an increased metastatic potential compared to isolated circulating tumor cells. Several widely used chemotherapeutic agents that target the cytoskeleton microtubules and cause cell cycle arrest at mitosis have been reported to modulate CTC number or the size of CTC clusters.

Results

In this study, we investigated in vitro the impact of mitotic arrest on the ability of breast tumor cells to form clusters. By using live imaging and quantitative image analysis, we found that MCF-7 cancer cell aggregation is compromised upon incubation with paclitaxel or vinorelbine, two chemotherapeutic drugs that target microtubules. In line with these results, we observed that MCF-7 breast cancer cells experimentally synchronized and blocked in metaphase aggregated poorly and formed loose clusters. To monitor clustering at the single-cell scale, we next developed and validated an in vitro assay based on live video-microscopy and custom-designed micro-devices. The study of cluster formation from MCF-7 cells that express the fluorescent marker LifeAct-mCherry using this new assay allowed showing that substrate anchorage-independent clustering of MCF-7 cells was associated with the formation of actin-dependent highly dynamic cell protrusions. Metaphase-synchronized and blocked cells did not display such protrusions, and formed very loose clusters that failed to compact.

Conclusions

Altogether, our results suggest that mitotic arrest induced by microtubule-targeting anticancer drugs prevents cancer cell clustering and therefore, could reduce the metastatic potential of circulating tumor cells.

Canstatin represses glioma growth by inhibiting formation of VM-like structures

Vasculogenic mimicry (VM) is different from classical tumor angiogenesis and does not depend on endothelial cells. VM is closely related to the prognosis of various cancers. Canstatin was first identified as an endogenous angiogenesis inhibitor. In the present study, the inhibitory effect of canstatin on VM formation was evaluated. Human glioblastoma cell lines U87 and U251 were letivirally transduced to overexpress canstatin gene or GFP as control. In vitro assays showed that canstatin overexpression reduced the tube formation of U87 and U251 cells in Matrigel. A xenograft glioma model was created by subcutaneous injection of lentivirally modified U87 cells into nude mice. The results of in vivo experiments showed that canstatin gene introduction inhibited the growth of glioma xenografts. In tumor xenografts overexpressing canstatin, U87-mediated formation of VM-like structures and VM-related VEGF (vascular endothelial growth factor) expression were remarkably reduced. Canstatin overexpression also decreased the phosphorylation of Akt and reduced the expression of Survivin in vitro. In addition, HIF-1α production and MMP-2 secretion were decreased by canstatin overexpression. Therefore, these results suggested a protective role of canstatin during VM-like structure formation of glioma probably via inhibiting signaling pathways inducing vasculogenic mimicry.

Improvement of motor and behavioral activity in Sandhoff mice transplanted with human CD34+ cells transduced with a HexA/HexB expressing lentiviral vector

BACKGROUND

Tay-Sachs and Sandhoff disease are debilitating genetic diseases that affect the central nervous system leading to neurodegeneration through the accumulation of GM2 gangliosides. There are no cures for these diseases and treatments do not alleviate all symptoms. Hematopoietic stem cell gene therapy offers a promising treatment strategy for delivering wild-type enzymes to affected cells. By genetically modifying hematopoietic stem cells to express wild-type HexA and HexB, systemic delivery of functional enzyme can be achieved.

METHODS

Primary human hematopoietic stem/progenitor cells and Tay-Sachs affected cells were used to evaluate the functionality of the vector. An immunodeficient and humanized mouse model of Sandhoff disease was used to evaluate whether the HexA/HexB lentiviral vector transduced cells were able to improve the phenotypes associated with Sandhoff disease. An immunodeficient NOD-RAG1-/-IL2-/- (NRG) mouse model was used to evaluate whether the HexA/HexB vector transduced human CD34+ cells were able to engraft and undergo normal multilineage hematopoiesis.

RESULTS

HexA/HexB lentiviral vector transduced cells demonstrated strong expression of HexA and HexB and restored enzyme activity in Tay-Sachs affected cells. Upon transplantation into a humanized Sandhoff disease mouse model, improved motor and behavioral skills were observed. Decreased GM2 gangliosides were observed in the brains of HexA/HexB vector transduced cell transplanted mice. Increased peripheral blood levels of HexB was also observed in transplanted mice. Normal hematopoiesis in the peripheral blood and various lymphoid organs was also observed in transplanted NRG mice.

CONCLUSIONS

These results highlight the potential use of stem cell gene therapy as a treatment strategy for Tay-Sachs and Sandhoff disease.

BDNF increases synaptic NMDA receptor abundance by enhancing the local translation of Pyk2 in cultured hippocampal neurons

The effects of brain-derived neurotrophic factor (BDNF) in long-term synaptic potentiation (LTP) are thought to underlie learning and memory formation and are partly mediated by local protein synthesis. Here, we investigated the mechanisms that mediate BDNF-induced alterations in the synaptic proteome that are coupled to synaptic strengthening. BDNF induced the synaptic accumulation of GluN2B-containing NMDA receptors (NMDARs) and increased the amplitude of NMDAR-mediated miniature excitatory postsynaptic currents (mEPSCs) in cultured rat hippocampal neurons by a mechanism requiring activation of the protein tyrosine kinase Pyk2 and dependent on cellular protein synthesis. Single-particle tracking using quantum dot imaging revealed that the increase in the abundance of synaptic NMDAR currents correlated with their enhanced stability in the synaptic compartment. Furthermore, BDNF increased the local synthesis of Pyk2 at the synapse, and the observed increase in Pyk2 protein abundance along dendrites of cultured hippocampal neurons was mediated by a mechanism dependent on the ribonucleoprotein hnRNP K, which bound to Pyk2 mRNA and dissociated from it upon BDNF application. Knocking down hnRNP K reduced the BDNF-induced synaptic synthesis of Pyk2 protein, whereas its overexpression enhanced it. Together, these findings indicate that hnRNP K mediates the synaptic distribution of Pyk2 synthesis, and hence the synaptic incorporation of GluN2B-containing NMDARs, induced by BDNF, which may affect LTP and synaptic plasticity.

Clinical use of lentiviral vectors

Viral vectors provide an efficient means for modification of eukaryotic cells, and their use is now commonplace in academic laboratories and industry for both research and clinical gene therapy applications. Lentiviral vectors, derived from the human immunodeficiency virus, have been extensively investigated and optimized over the past two decades. Third-generation, self-inactivating lentiviral vectors have recently been used in multiple clinical trials to introduce genes into hematopoietic stem cells to correct primary immunodeficiencies and hemoglobinopathies. These vectors have also been used to introduce genes into mature T cells to generate immunity to cancer through the delivery of chimeric antigen receptors (CARs) or cloned T-cell receptors. CAR T-cell therapies engineered using lentiviral vectors have demonstrated noteworthy clinical success in patients with B-cell malignancies leading to regulatory approval of the first genetically engineered cellular therapy using lentiviral vectors. In this review, we discuss several aspects of lentiviral vectors that will be of interest to clinicians, including an overview of lentiviral vector development, the current uses of viral vectors as therapy for primary immunodeficiencies and cancers, large-scale manufacturing of lentiviral vectors, and long-term follow-up of patients treated with gene therapy products.

The RNA-Binding Protein hnRNP K Mediates the Effect of BDNF on Dendritic mRNA Metabolism and Regulates Synaptic NMDA Receptors in Hippocampal Neurons

Brain-derived neurotrophic factor (BDNF) is an important mediator of long-term synaptic potentiation (LTP) in the hippocampus. The local effects of BDNF depend on the activation of translation activity, which requires the delivery of transcripts to the synapse. In this work, we found that neuronal activity regulates the dendritic localization of the RNA-binding protein heterogeneous nuclear ribonucleoprotein K (hnRNP K) in cultured rat hippocampal neurons by stimulating BDNF-Trk signaling. Microarray experiments identified a large number of transcripts that are coimmunoprecipitated with hnRNP K, and about 60% of these transcripts are dissociated from the protein upon stimulation of rat hippocampal neurons with BDNF. In vivo studies also showed a role for TrkB signaling in the dissociation of transcripts from hnRNP K upon high-frequency stimulation (HFS) of medial perforant path-granule cell synapses of male rat dentate gyrus (DG). Furthermore, treatment of rat hippocampal synaptoneurosomes with BDNF decreased the coimmunoprecipitation of hnRNP K with mRNAs coding for glutamate receptor subunits, Ca²⁺- and calmodulin-dependent protein kinase IIβ (CaMKIIβ) and BDNF. Downregulation of hnRNP K impaired the BDNF-induced enhancement of NMDA receptor (NMDAR)-mediated mEPSC, and similar results were obtained upon inhibition of protein synthesis with cycloheximide. The results demonstrate that BDNF regulates specific populations of hnRNP-associated mRNAs in neuronal dendrites and suggests an important role of hnRNP K in BDNF-dependent forms of synaptic plasticity.

Assay Development for High Content Quantification of Sod1 Mutant Protein Aggregate Formation in Living Cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that can be caused by inherited mutations in the gene encoding copper-zinc superoxide dismutase 1 (SOD1). The structural instability of SOD1 and the detection of SOD1-positive inclusions in familial-ALS patients supports a potential causal role for misfolded and/or aggregated SOD1 in ALS pathology. In this study, we describe the development of a cell-based assay designed to quantify the dynamics of SOD1 aggregation in living cells by high content screening approaches. Using lentiviral vectors, we generated stable cell lines expressing wild-type and mutant A4V SOD1 tagged with yellow fluorescent protein and found that both proteins were expressed in the cytosol without any sign of aggregation. Interestingly, only SOD1 A4V stably expressed in HEK-293, but not in U2OS or SH-SY5Y cell lines, formed aggregates upon proteasome inhibitor treatment. We show that it is possible to quantify aggregation based on dose-response analysis of various proteasome inhibitors, and to track aggregate-formation kinetics by time-lapse microscopy. Our approach introduces the possibility of quantifying the effect of ALS mutations on the role of SOD1 in aggregate formation as well as screening for small molecules that prevent SOD1 A4V aggregation.

The β-globin Replicator greatly enhances the potential of S/MAR based episomal vectors for gene transfer into human haematopoietic progenitor cells

Specific human chromosomal elements enhance the performance of episomal gene-transfer vectors. S/MAR-based episomal vector pEPI-eGFP transfects CD34+ haematopoietic cells, but only transiently. To address this issue we reinforced (1) transgene transcription by replacing the CMV promoter driving eGFP with the EF1/HTLV or SFFV promoters to produce vectors pEPI-EF1/HTLV and pEPI-SFFV, respectively; and (2) plasmid replication by inserting the replication-Initiation Region (IR) from the β-globin locus into vector pEPI-SFFV to produce vector pEP-IR. All vectors supported stable transfections in K562 cells. Transfections of CD34+ cells from peripheral blood of healthy donors reached 30% efficiency. Upon evaluation of CD34+/eGFP+ cells in colony-forming cell (CFC) assays, vector pEP-IR showed superior performance after 14 days, by fluorescent microscopy: 100% eGFP+-colonies against 0% for pEPI-eGFP, 56.9% for pEPI-SFFV and 49.8% for pEPI-EF1/HTLV; 50% more plasmid copies per cell and 3-fold eGFP expression compared to the latter two constructs, by quantitative (q)PCR and RT-qPCR, respectively. Importantly, the establishment rate in CFC assays was 15% for pEP-IR against 5.5% for pEPI-SFFV and 5% for pEPI-EF1/HTLV. Vector pEP-IR shows extremely low delivery rate but supports eGFP expression in thalassaemic mouse haematopoietic progenitor cells. The IR is a novel human control element for improved episomal gene transfer into progenitor cells.

Efficient Transduction of Human and Rhesus Macaque Primary T Cells by a Modified Human Immunodeficiency Virus Type 1-Based Lentiviral Vector

Human immunodeficiency virus type 1 (HIV-1)-based lentiviral vectors efficiently transduce genes to human, but not rhesus, primary T cells and hematopoietic stem cells (HSCs). The poor transduction of HIV-1 vectors to rhesus cells is mainly due to species-specific restriction factors such as rhesus TRIM5α. Previously, several strategies to modify HIV-1 vectors were developed to overcome rhesus TRIM5α restriction. While the modified HIV-1 vectors efficiently transduce rhesus HSCs, they remain suboptimal for rhesus primary T cells. Recently, HIV-1 variants that encode combinations of LNEIE mutations in capsid (CA) protein and SIVmac239 Vif were found to replicate efficiently in rhesus primary T cells. Thus, the present study tested whether HIV-1 vectors packaged by a packaging construct containing these CA substitutions could efficiently transduce both human and rhesus primary CD4 T cells. To accomplish this, LNEIE mutations were made in the packaging construct CEMΔ8.9, and recombinant HIV-1 vectors packaged by Δ8.9 WT or Δ8.9 LNEIE were generated. Transduction rates, CA stability, and vector integration in CEMss-CCR5 and CEMss-CCR5-rhTRIM5α/green fluorescent protein cells, as well as transduction rates in human and rhesus primary CD4 T cells by Δ8.9 WT or Δ8.9 LNEIE-packaged HIV-1 vectors, were compared. Finally, the influence of rhesus TRIM5α variations in transduction rates to primary CD4 T cells from a cohort of 37 Chinese rhesus macaques was studied. While it maintains efficient transduction for human T-cell line and primary CD4 T cells, Δ8.9 LNEIE-packaged HIV-1 vector overcomes rhesus TRIM5α-mediated CA degradation, resulting in significantly higher transduction efficiency of rhesus primary CD4 T cells than Δ8.9 WT-packaged HIV-1 vector. Rhesus TRIM5α variations strongly influence transduction efficiency of rhesus primary CD4 T cells by both Δ8.9 WT or Δ8.9 LNEIE-packaged HIV-1 vectors. Thus, it is concluded that Δ8.9 LNEIE-packaged HIV-1 vector overcomes rhesus TRIM5α restriction and efficiently transduces both human and rhesus primary T cells.

The Glycosylphosphatidylinositol-Anchored Variable Region of Llama Heavy Chain-Only Antibody JM4 Efficiently Blocks both Cell-Free and T Cell-T Cell Transmission of Human Immunodeficiency Virus Type 1

The variable regions (VHHs) of two heavy chain-only antibodies, JM2 and JM4, from llamas that have been immunized with a trimeric gp140 bound to a CD4 mimic have been recently isolated (here referred to as VHH JM2 and VHH JM4, respectively). JM2 binds the CD4-binding site of gp120 and neutralizes HIV-1 strains from subtypes B, C, and G. JM4 binds gp120 and neutralizes HIV-1 strains from subtypes A, B, C, A/E, and G in a CD4-dependent manner. In the present study, we constructed glycosylphosphatidylinositol (GPI)-anchored VHH JM2 and JM4 along with an E4 control and transduced them into human CD4⁺ cell lines and primary CD4 T cells. We report that by genetically linking the VHHs with a GPI attachment signal, VHHs are targeted to the lipid rafts of the plasma membranes. Expression of GPI-VHH JM4, but not GPI-VHH E4 and JM2, on the surface of transduced TZM.bl cells potently neutralizes multiple subtypes of HIV-1 isolates, including tier 2 or 3 strains, transmitted founders, quasispecies, and soluble single domain antibody (sdAb) JM4-resistant viruses. Moreover, transduction of CEMss-CCR5 cells with GPI-VHH JM4, but not with GPI-VHH E4, confers resistance to both cell-free and T cell-T cell transmission of HIV-1 and HIV-1 envelope-mediated fusion. Finally, GPI-VHH JM4-transduced human primary CD4 T cells efficiently resist both cell-free and T cell-T cell transmission of HIV-1. Thus, we conclude that VHH JM4, when targeted to the lipid rafts of the plasma membrane, efficiently neutralizes HIV-1 infection via both cell-free and T cell-T cell transmission. Our findings should have important implications for GPI-anchored antibody-based therapy against HIV-1.

IMPORTANCE

Lipid rafts are specialized dynamic microdomains of the plasma membrane and have been shown to be gateways for HIV-1 budding as well as entry into T cells and macrophages. In nature, many glycosylphosphatidylinositol (GPI)-anchored proteins localize in the lipid rafts. In the present study, we developed GPI-anchored variable regions (VHHs) of two heavy chain-only antibodies, JM2 and JM4, from immunized llamas. We show that by genetically linking the VHHs with a GPI attachment signal, VHHs are targeted to the lipid rafts of the plasma membranes. GPI-VHH JM4, but not GPI-VHH JM2, in transduced CD4⁺ cell lines and human primary CD4 T cells not only efficiently blocks diverse HIV-1 strains, including tier 2 or 3 strains, transmitted founders, quasispecies, and soluble sdAb JM4-resistant strains, but also efficiently interferes T cell-T cell transmissions of HIV-1 and HIV-1 envelope-mediated fusion. Our findings should have important implications in GPI-anchored antibody-based therapy against HIV-1.

Atg5-dependent autophagy contributes to the development of acute myeloid leukemia in an MLL-AF9-driven mouse model

Acute myeloid leukemia (AML) is a hierarchical hematopoietic malignancy originating from leukemic stem cells (LSCs). Autophagy is a lysosomal degradation pathway that is hypothesized to be important for the maintenance of AML as well as contribute to chemotherapy response. Here we employ a mouse model of AML expressing the fusion oncogene MLL-AF9 and explore the effects of Atg5 deletion, a key autophagy protein, on the malignant transformation and progression of AML. Consistent with a transient decrease in colony-forming potential in vitro, the in vivo deletion of Atg5 in MLL-AF9-transduced bone marrow cells during primary transplantation prolonged the survival of recipient mice, suggesting that autophagy has a role in MLL-AF9-driven leukemia initiation. In contrast, deletion of Atg5 in malignant AML cells during secondary transplantation did not influence the survival or chemotherapeutic response of leukemic mice. Interestingly, autophagy was found to be involved in the survival of differentiated myeloid cells originating from MLL-AF9-driven LSCs. Taken together, our data suggest that Atg5-dependent autophagy may contribute to the development but not chemotherapy sensitivity of murine AML induced by MLL-AF9.

Lentiviral gene rescue of a Bernard-Soulier mouse model to study platelet glycoprotein Ibβ function

Essentials A signaling role of glycoprotein (GP)Ibβ is postulated but not formally demonstrated in platelets. Lentiviral-mediated rescue in knock-out mice can be used to evaluate GPIbβ function in vivo. Transduction of the native subunit corrected the main defects associated with GPIb-IX deficiency Deletion of intracellular 159-170 segment increased thrombosis, 150-160 removal increased bleeding.

SUMMARY

Background The platelet glycoprotein (GP)Ib-V-IX complex is required for normal hemostasis and megakaryopoiesis. A role in GPIb-dependent responses has been ascribed to the less well characterized GPIbβ subunit using a specific antibody and GPIb-IX transfected cells. Objectives Our aim was to evaluate, in vivo, the role of the GPIbβ in hemostasis and thrombosis. Methods GPIbβ(null) Sca-1(+) progenitors transduced with viral particles harboring hGPIbβ were transplanted into lethally irradiated GPIbβ(-/-) recipient mice. Results hGPIbβ transplanted into the bone marrow of GPIbβ(null) mice rescued GPIb-IX expression in 97% of circulating platelets. These platelets efficiently bound von Willebrand factor (VWF) and extended filopodia on a VWF matrix, demonstrating the restoration of GPIb-dependent adhesive and signaling properties. These mice exhibited less severe macrothrombocytopenia and had normal tail bleeding times as compared with GPIbβ(null) mice. This strategy was employed to manipulate and evaluate the role of the GPIbβ intracellular domain. Removal of the membrane proximal segment (Δ(150-160) ) decreased GPIb-IX expression by 43%, confirming its involvement in receptor assembly and biosynthesis, and resulted in increased bleeding times and decreased thrombosis in a mechanical injury model in the aorta. On the other hand, deletion of the C-flanking 159-170 segment allowed normal GPIb-IX expression, VWF-dependent responses and bleeding times, but resulted in enhanced arterial thrombosis. Conclusion This pointed to a repressor role of GPIbβ in thrombus formation in vivo that was not predicted in studies of heterologous cells. These results highlight the utility of this lentiviral strategy for the structure-function evaluation of GPIb-IX in platelets.

Selection of a hepatitis C virus with altered entry factor requirements reveals a genetic interaction between the E1 glycoprotein and claudins

Hepatitis C virus (HCV) cell entry is a complex, multistep process requiring numerous host cell factors, including the tight junction protein claudin-1 (CLDN1). It is not known whether CLDN1 and the HCV glycoproteins physically interact. Therefore, the focus of this work was to study genetic interactions between CLDN1 and HCV. We used CRISPR technology to generate CLDN1 knockout (KO) Huh-7.5 cells, which could not be infected by genotype 2a Jc1 HCV unless CLDN1 expression was restored. Passage of Jc1-transfected CLDN1 KO cells resulted in the selection of a virus that could infect these cells. This virus encoded a single mutation, H316N (numbered relative to the HCV polyprotein), in the E1 glycoprotein. Whereas Jc1 H316N efficiently infected cells lacking CLDN1, such infection was blocked by an antibody targeting CLDN6, another member of the claudin family that is expressed in these cells. Furthermore, HuH6 cells, which express CLDN6, but not CLDN1, were infectable only with the mutant virus. Thus, this mutant virus adapted to the loss of CLDN1 by developing the capacity to utilize other CLDNs. Indeed, CLDN1/CLDN6 double-KO Huh-7.5 cells supported infection by the mutant virus only when CLDN1, CLDN6, or CLDN9 was expressed. Finally, this phenotype was not genotype dependent, given that the H316N mutation rendered a Japanese fulminant hepatitis 1 chimeric HCV genome encoding the genotype 5a glycoproteins able to utilize CLDN6 for host cell entry.

CONCLUSION

These data demonstrate plasticity of HCV virus-host interactions, where a previously CLDN1-dependent virus was capable of evolving to use CLDN6. They also reveal a role for E1 in determining entry factor usage and imply a direct, physical interaction between E1 and CLDNs.

Activin B antagonizes RhoA signaling to stimulate mesenchymal morphology and invasiveness of clear cell renal cell carcinomas

Activin B belongs to the TGFβ family of growth factors and is upregulated in clear cell renal cell carcinoma cells by hypoxia inducible factors. Expression of Activin B is required for tumor growth in vivo and tumor cell invasion in vitro. Here we show that activation of RhoA signaling counteracts Activin B mediated disassembly of actin stress fibers, mesenchymal cell morphology and invasiveness, whereas inhibition of RhoA rescues these effects in Activin B knockdown cells. Conversely, Activin B inhibits RhoA signaling suggesting that there is an antagonistic connection between both pathways. In addition we found that Rac1 plays an opposite role to RhoA, i.e. activation of Rac1 initiates loss of actin stress fibers, promotes a mesenchymal cell morphology and induces invasion in Activin B knockown cells, whereas inhibition of Rac1 abolishes these Activin B effects. Collectively, our data provide evidence that reduction of RhoA signaling by Activin B together with persistent Rac1 activity is a prerequisite for inducing an invasive phenotype in clear cell renal cell carcinoma.

HepG2 cells mount an effective antiviral interferon-lambda based innate immune response to hepatitis C virus infection

Hepatitis C virus (HCV) exposure leads to persistent life-long infections characterized by chronic inflammation often developing into cirrhosis and hepatocellular carcinoma. The mechanism by which HCV remains in the liver while inducing an inflammatory and antiviral response remains unclear. Though the innate immune response to HCV in patients seems to be quite active, HCV has been shown in cell culture to employ a diverse array of innate immune antagonists, which suggests that current model systems to study interactions between HCV and the innate immune system are not representative of what happens in vivo. We recently showed that hepatoma-derived HepG2 cells support the entire HCV life cycle if the liver-specific microRNA, miR-122, is expressed along with the entry factor, CD81 (termed HepG2-HFL cells). We found that there was a striking difference in these cells' ability to sustain HCV infection and spread when compared with Huh-7 and Huh-7.5 cells. Additionally, HepG2-HFL cells exhibited a more robust antiviral response when challenged with other RNA viruses and viral mimetics than Huh-7 and Huh-7.5 cells. HCV infection elicited a potent interferon-lambda (IFN-λ), IFN-stimulated gene, and cytokine response in HepG2-HFL cells, but not in Huh-7 cells, suggesting that HepG2-HFL cells more faithfully recapitulate the innate immune response to HCV infection in vivo. Using this model, we found that blocking the retinoic acid-inducible gene I (RIG-I)-like receptor pathway or the IFN-λ-signaling pathway promoted HCV infection and spread in HepG2-HFL cells.

CONCLUSION

HepG2-HFL cells represent a new system to study the interaction between HCV and the innate immune system, solidifying the importance of IFN-λ in hepatic response to HCV infection and revealing non-redundant roles of RIG-I and melanoma differentiation-associated protein 5 in HCV recognition and repression of infection.

Phosphatidylinositol 5-phosphate regulates invasion through binding and activation of Tiam1

PtdIns5P is a lipid messenger acting as a stress-response mediator in the nucleus, and known to maintain cell activation through traffic alterations upon bacterial infection. Here, we show that PtdIns5P regulates actin dynamics and invasion via recruitment and activation of the exchange factor Tiam1 and Rac1. Restricted Rac1 activation results from the binding of Tiam1 DH-PH domains to PtdIns5P. Using an assay that mimics Rac1 membrane anchoring by using Rac1-His and liposomes containing Ni(2+)-NTA modified lipids, we demonstrate that intrinsic Tiam1 DH-PH activity increases when Rac1 is anchored in a PtdIns5P-enriched environment. This pathway appears to be general since it is valid in different pathophysiological models: receptor tyrosine kinase activation, bacterial phosphatase IpgD expression and the invasive NPM-ALK(+) lymphomas. The discovery that PtdIns5P could be a keystone of GTPases and cytoskeleton spatiotemporal regulation opens important research avenues towards unravelling new strategies counteracting cell invasion.

Hypothalamic apelin/reactive oxygen species signaling controls hepatic glucose metabolism in the onset of diabetes

AIMS

We have previously demonstrated that central apelin is implicated in the control of peripheral glycemia, and its action depends on nutritional (fast versus fed) and physiological (normal versus diabetic) states. An intracerebroventricular (icv) injection of a high dose of apelin, similar to that observed in obese/diabetic mice, increase fasted glycemia, suggesting (i) that apelin contributes to the establishment of a diabetic state, and (ii) the existence of a hypothalamic to liver axis. Using pharmacological, genetic, and nutritional approaches, we aim at unraveling this system of regulation by identifying the hypothalamic molecular actors that trigger the apelin effect on liver glucose metabolism and glycemia.

RESULTS

We show that icv apelin injection stimulates liver glycogenolysis and gluconeogenesis via an over-activation of the sympathetic nervous system (SNS), leading to fasted hyperglycemia. The effect of central apelin on liver function is dependent of an increased production of hypothalamic reactive oxygen species (ROS). These data are strengthened by experiments using lentiviral vector-mediated over-expression of apelin in hypothalamus of mice that present over-activation of SNS associated to an increase in hepatic glucose production. Finally, we report that mice fed a high-fat diet present major alterations of hypothalamic apelin/ROS signaling, leading to activation of glycogenolysis. INNOVATION/CONCLUSION: These data bring compelling evidence that hypothalamic apelin is one master switch that participates in the onset of diabetes by directly acting on liver function. Our data support the idea that hypothalamic apelin is a new potential therapeutic target to treat diabetes.

Transcription factor SCL/TAL1 mediates the phosphorylation of MEK/ERK pathway in umbilical cord blood CD34⁺ stem cells during hematopoietic differentiation

Transcription factor stem cell leukemia (SCL), also known as the T-cell acute lymphocytic leukemia 1 (TAL1), plays a key role in the regulation of hematopoiesis, but the molecular mechanisms are not well understood. The aim of the present study is to elucidate the effects of the epidermal growth factor receptor (EGFR) signal pathways underlying the biologic activity of SCL/TAL1 on normal hematopoietic development. Lentiviral vectors with up or down-regulation of SCL/TAL1 were transfected into umbilical cord blood CD34 stem cells. EGFR signaling pathways (including MEK/ERK and Akt/mTOR) and surface hematopoietic markers were analyzed in the process of hematopoietic differentiation. The data revealed that up or down-regulation of SCL/TAL1 gene was accompanied positively by the expressions of p-MEK and p-ERK1/2 protein, but the changes of Akt/mTOR were unobvious. MEK/ERK inhibitor U0126 and SCL/TAL1 down-regulation showed similar inhibitory effects on erythroid, myeloid, and megakaryoid differentiation. However, Akt/mTOR pathway altered insignificantly. MEK/ERK inhibitor U0126 could not affect the expression of SCL/TAL1 mRNA or protein. Taken together, these findings fully illustrated that SCL/TAL1 is located in the up-stream of MEK/ERK pathway and partially regulates hematopoiesis by modulating the phosphorylation level of the key proteins in MEK/ERK pathway.

Transgene expression in various organs post BM-HSC transplantation

Gene therapy mediated by bone marrow-derived hematopoietic stem cells (BM-HSC) has been widely used in treating genetic deficiencies in both pre-clinical and clinical settings. Using mitotically inactive cell-targeting lentivirus with separate promoters for our gene of interest (the murine MHC class II (MHCII) chaperone, invariant chain (Ii)) and a GFP reporter, we monitored the expression and function of introduced Ii in various types of professional antigen presenting cells (B cells, macrophages and DC) from different organs (spleen, pancreatic lymph nodes (PLN), BM and blood). Ii and GFP were detected. Ii levels correlated with GFP levels only in macrophages and monocytes from spleen, monocytes from PLN and macrophage precursors from blood. By cell type, Ii levels in PLN cells were more similar to those in spleen cells than to those in blood or BM cells. Functionally, Ii expressed in PLN or spleen had more effect on MHCII abundance than Ii expressed in BM or blood. The results have implications for analysis of the outcomes of gene therapy when both therapeutic and reporter genes are introduced. The findings also have implications for understanding the development of immune molecule function.

Hepatic cells derived from induced pluripotent stem cells of pigtail macaques support hepatitis C virus infection

The narrow species tropism of hepatitis C virus (HCV) limits animal studies. We found that pigtail macaque (Macaca nemestrina) hepatic cells derived from induced pluripotent stem cells support the entire HCV life cycle, although infection efficiency was limited by defects in the HCV cell entry process. This block was overcome by either increasing occludin expression, complementing the cells with human CD81, or infecting them with a strain of HCV with less restricted requirements for CD81. Using this system, we can modify viral and host cell genetics to make pigtail macaques a suitable, clinically relevant model for the study of HCV infection.

Dual-color HIV reporters trace a population of latently infected cells and enable their purification

HIV latency constitutes the main barrier for clearing HIV infection from patients. Our inability to recognize and isolate latently infected cells hinders the study of latent HIV. We engineered two HIV-based viral reporters expressing different fluorescent markers: one HIV promoter-dependent marker for productive HIV infection, and a second marker under a constitutive promoter independent of HIV promoter activity. Infection of cells with these viruses allows the identification and separation of latently infected cells from uninfected and productively infected cells. These reporters are sufficiently sensitive and robust for high-throughput screening to identify drugs that reactivate latent HIV. These reporters can be used in primary CD4 T lymphocytes and reveal a rare population of latently infected cells responsive to physiological stimuli. In summary, our HIV-1 reporters enable visualization and purification of latent-cell populations and open up new perspectives for studies of latent HIV infection.

CXCL4L1-fibstatin cooperation inhibits tumor angiogenesis, lymphangiogenesis and metastasis

Anti-angiogenic and anti-lymphangiogenic drugs slow tumor progression and dissemination. However, an important difficulty is that a tumor reacts and compensates to obtain the blood supply needed for tumor growth and lymphatic vessels to escape to distant loci. Therefore, there is a growing consensus on the requirement of multiple anti-(lymph)angiogenic molecules to stop cell invasion efficiently. Here we studied the cooperation between endogenous anti-angiogenic molecules, endostatin and fibstatin, and a chemokine, the Platelet Factor-4 variant 1, CXCL4L1. Anti-angiogenic factors were co-expressed by IRES-based bicistronic vectors and their cooperation was analyzed either by local delivery following transduction of pancreatic adenocarcinoma cells with lentivectors, or by distant delivery resulting from intramuscular administration in vivo of adeno-associated virus derived vectors followed by tumor subcutaneous injection. In this study, fibstatin and CXCL4L1 cooperate to inhibit endothelial cell proliferation, migration and tubulogenesis in vitro. No synergistic effect was found for fibstatin-endostatin combination. Importantly, we demonstrated for the first time that fibstatin and CXCL4L1 not only inhibit in vivo angiogenesis, but also lymphangiogenesis and tumor spread to the lymph nodes, whereas no beneficial effect was found on tumor growth inhibition using molecule combinations compared to molecules alone. These data reveal the synergy of CXCL4L1 and fibstatin in inhibition of tumor angiogenesis, lymphangiogenesis and metastasis and highlight the potential of IRES-based vectors to develop anti-metastasis combined gene therapies.

Temporal analysis of hepatitis C virus cell entry with occludin directed blocking antibodies

Hepatitis C virus (HCV) is a major cause of liver disease worldwide. A better understanding of its life cycle, including the process of host cell entry, is important for the development of HCV therapies and model systems. Based on the requirement for numerous host factors, including the two tight junction proteins claudin-1 (CLDN1) and occludin (OCLN), HCV cell entry has been proposed to be a multi-step process. The lack of OCLN-specific inhibitors has prevented a comprehensive analysis of this process. To study the role of OCLN in HCV cell entry, we created OCLN mutants whose HCV cell entry activities could be inhibited by antibodies. These mutants were expressed in polarized HepG2 cells engineered to support the complete HCV life cycle by CD81 and miR-122 expression and synchronized infection assays were performed to define the kinetics of HCV cell entry. During these studies, OCLN utilization differences between HCV isolates were observed, supporting a model that HCV directly interacts with OCLN. In HepG2 cells, both HCV cell entry and tight junction formation were impaired by OCLN silencing and restored by expression of antibody regulatable OCLN mutant. Synchronized infection assays showed that glycosaminoglycans and SR-BI mediated host cell binding, while CD81, CLDN1 and OCLN all acted sequentially at a post-binding stage prior to endosomal acidification. These results fit a model where the tight junction region is the last to be encountered by the virion prior to internalization.

HCV is a serious public health problem. Although new treatments have recently become available, it is clear that effective therapies will require combinations of inhibitors targeting diverse stages of the viral life cycle. While the HCV cell entry process is considered a suitable antiviral target, a lack of understanding of this process has hampered the development of inhibitors. It is widely accepted that HCV cell entry requires many cellular proteins that are used in a nonredundant and sequential manner. However, a critical piece of information supporting this model – the determination of when OCLN is used during this process – could not be addressed due to a lack of reagents that specifically target this protein. In this study, we derive mutant OCLN proteins whose HCV cell entry activity can be blocked by incubation with an antibody. These mutants allowed us to show that OCLN is used very late in the HCV cell entry process, which fits a model in which tight junction components are required later in the process than more exposed factors. Furthermore, our studies suggest that HCV virions may interact directly with OCLN, which has thus far not been demonstrated experimentally.

Focal adhesion kinase splice variants maintain primitive acute myeloid leukemia cells through altered Wnt signaling

Focal adhesion kinase (FAK) activity contributes to many advanced cancer phenotypes, but little is known about its role in human acute myeloid leukemia (AML). Here, we show that FAK splice variants are abnormally expressed in the primitive leukemic cells of poor prognosis AML patients. In the CD34(+) 38(-) 123(+) long-term culture-initiating cell-enriched leukemic cells of these patients, FAK upregulates expression of Frizzled-4 and phosphorylates Pyk2 to enable the required association of Pyk2 with the Wnt5a/Frizzled-4/LRP5 endocytosis complex and downstream activation of β-catenin, thereby replacing the Wnt3a-controlled canonical pathway used by normal hematopoietic stem cells. Transduction of primitive normal human hematopoietic cells with FAK splice variants induces a marked increase in their clonogenic activity and signaling via the Wnt5a-controlled canonical pathway. Targeting FAK or β-catenin efficiently eradicates primitive leukemic cells in vitro suggesting that FAK could be a useful therapeutic target for improved treatment of poor prognosis AML cases.

Methyltransferase PRMT1 is a binding partner of HBx and a negative regulator of hepatitis B virus transcription

The hepatitis B virus X protein (HBx) is essential for virus replication and has been implicated in the development of liver cancer. HBx is recruited to viral and cellular promoters and activates transcription by interacting with transcription factors and coactivators. Here, we purified HBx-associated factors in nuclear extracts from HepG2 hepatoma cells and identified protein arginine methyltransferase 1 (PRMT1) as a novel HBx-interacting protein. We showed that PRMT1 overexpression reduced the transcription of hepatitis B virus (HBV), and this inhibition was dependent on the methyltransferase function of PRMT1. Conversely, depletion of PRMT1 correlated with increased HBV transcription. Using a quantitative chromatin immunoprecipitation assay, we found that PRMT1 is recruited to HBV DNA, suggesting a direct effect of PRMT1 on the regulation of HBV transcription. Finally, we showed that HBx expression inhibited PRMT1-mediated protein methylation. Downregulation of PRMT1 activity was further observed in HBV-replicating cells in an in vivo animal model. Altogether, our results support the notion that the binding of HBx to PRMT1 might benefit viral replication by relieving the inhibitory activity of PRMT1 on HBV transcription.

Stress produces aversion and potentiates cocaine reward by releasing endogenous dynorphins in the ventral striatum to locally stimulate serotonin reuptake

Activation of the dynorphin/κ-opioid receptor (KOR) system by repeated stress exposure or agonist treatment produces place aversion, social avoidance, and reinstatement of extinguished cocaine place preference behaviors by stimulation of p38α MAPK, which subsequently causes the translocation of the serotonin transporter (SERT, SLC6A4) to the synaptic terminals of serotonergic neurons. In the present study we extend those findings by showing that stress-induced potentiation of cocaine conditioned place preference occurred by a similar mechanism. In addition, SERT knock-out mice did not show KOR-mediated aversion, and selective reexpression of SERT by lentiviral injection into the dorsal raphe restored the prodepressive effects of KOR activation. Kinetic analysis of several neurotransporters demonstrated that repeated swim stress exposure selectively increased the V(max) but not K(m) of SERT without affecting dopamine transport or the high-capacity, low-affinity transporters. Although the serotonergic neurons in the dorsal raphe project throughout the forebrain, a significant stress-induced increase in cell-surface SERT expression was only evident in the ventral striatum, and not in the dorsal striatum, hippocampus, prefrontal cortex, amygdala, or dorsal raphe. Stereotaxic microinjections of the long-lasting KOR antagonist norbinaltorphimine demonstrated that local KOR activation in the nucleus accumbens, but not dorsal raphe, mediated this stress-induced increase in ventral striatal surface SERT expression. Together, these results support the hypothesis that stress-induced activation of the dynorphin/KOR system produces a transient increase in serotonin transport locally in the ventral striatum that may underlie some of the adverse consequences of stress exposure, including the potentiation of the rewarding effects of cocaine.

Oncogenic kit triggers Shp2/Erk1/2 pathway to down-regulate the pro-apoptotic protein Bim and to promote apoptosis resistance in leukemic cells

Oncogenic mutations leading to persistent kinase activities are implicated in various human malignancies. Thereby, signaling pathway-targeted therapies are powerful customized treatment to eradicate cancer cells. In murine and human leukemia cells harboring mutations in Kit, we previously showed that distinct and independent pathways controlled resistance to apoptosis or cell cycle. A treatment with PI3Kinase inhibitors to reduce cell proliferation combined with inhibitors of Erk1/2 activity to promote apoptosis had synergistic effects allowing eradication of leukemia cell growth. We reported here that Bim_EL, a pro-apoptotic member of the Bcl2 family proteins, is the target of Erk1/2 signaling and that its down-regulation is responsible for the apoptosis resistance of murine and human leukemic cells. Downstream of Kit mutant, the tyrosine phosphatase Shp2 maintains Bim_EL expression at a low level, through Erk/2 activation and proteosomal Bim_EL degradation. This process is controlled by Shp2 independently of other signaling pathways activated downstream of oncogenic Kit, demonstrating that Shp2 is a key regulator of Bim expression in the context of an oncogenic signaling. The increase in Bim_EL expression is associated to an increased apoptosis. Moreover, the depletion of Bim overcomes apoptosis associated with Erk1/2 inactivation in UO126-treated leukemic cells, thereby establishing the contribution of Bim to drug-induced apoptosis. These data provide a molecular rationale for using BH3 mimetics in combination with PI3K inhibitors to treat leukemia, especially in the case of an oncogenic signaling refractory to Tyrosine Kinase inhibitors.

Lysosomal-associated transmembrane protein 5 (LAPTM5) is a molecular partner of CD1e

The CD1e protein participates in the presentation of lipid antigens in dendritic cells. Its transmembrane precursor is transported to lysosomes where it is cleaved into an active soluble form. In the presence of bafilomycin, which inhibits vacuolar ATPase and consequently the acidification of endosomal compartments, CD1e associates with a 27 kD protein. In this work, we identified this molecular partner as LAPTM5. The latter protein and CD1e colocalize in trans-Golgi and late endosomal compartments. The quantity of LAPTM5/CD1e complexes increases when the cells are treated with bafilomycin, probably due to the protection of LAPTM5 from lysosomal proteases. Moreover, we could demonstrate that LAPTM5/CD1e association occurs under physiological conditions. Although LAPTM5 was previously shown to act as a platform recruiting ubiquitin ligases and facilitating the transport of receptors to lysosomes, we found no evidence that LATPM5 controls either CD1e ubiquitination or the generation of soluble lysosomal CD1e proteins. Notwithstanding these last observations, the interaction of LAPTM5 with CD1e and their colocalization in antigen processing compartments both suggest that LAPTM5 might influence the role of CD1e in the presentation of lipid antigens.

The p53 isoform, Δ133p53α, stimulates angiogenesis and tumour progression

The tumour suppressor p53, involved in DNA repair, cell cycle arrest and apoptosis, also inhibits blood vessel formation, that is, angiogenesis, a process strongly contributing to tumour development. The p53 gene expresses 12 different proteins (isoforms), including TAp53 (p53 (or p53α), p53β and p53γ) and Δ133p53 isoforms (Δ133p53α, Δ133p53β and Δ133p53γ). The Δ133p53α isoform was shown to modulate p53 transcriptional activity and is overexpressed in various human tumours. However, its role in tumour progression is still unexplored. In the present study, we examined the involvement of Δ133p53 isoforms in tumoural angiogenesis and tumour growth in the highly angiogenic human glioblastoma U87. Our data show that conditioned media from U87 cells depleted for Δ133p53 isoforms block endothelial cell migration and tubulogenesis without affecting endothelial cell proliferation in vitro. The Δ133p53 depletion in U2OS osteosarcoma cells resulted in a similar angiogenesis blockade. Furthermore, using conditioned media from U87 cells ectopically expressing each Δ133p53 isoform, we determined that Δ133p53α and Δ133p53γ but not Δ133p53β, stimulate angiogenesis. Our in vivo data using the chicken chorio-allantoic membrane and mice xenografts establish that angiogenesis and growth of glioblastoma U87 tumours are inhibited upon depletion of Δ133p53 isoforms. By TaqMan low-density array, we show that alteration of expression ratio of Δ133p53 and TAp53 isoforms differentially regulates angiogenic gene expression with Δ133p53 isoforms inducing pro-angiogenic gene expression and repressing anti-angiogenic gene expression.

A common role for various human truncated adenomatous polyposis coli isoforms in the control of beta-catenin activity and cell proliferation

The tumour suppressor gene adenomatous polyposis coli (APC) is mutated in most colorectal cancer cases, leading to the synthesis of truncated APC products and the stabilization of β-catenin. Truncated APC is almost always retained in tumour cells, suggesting that it serves an essential function. Here, RNA interference has been used to down-regulate truncated APC in several colorectal cancer cell lines expressing truncated APCs of different lengths, thereby performing an analysis covering most of the mutation cluster region (MCR). The consequences on proliferation in vitro, tumour formation in vivo and the level and transcriptional activity of β-catenin have been investigated. Down-regulation of truncated APC results in an inhibition of tumour cell population expansion in vitro in 6 cell lines out of 6 and inhibition of tumour outgrowth in vivo as analysed in one of these cell lines, HT29. This provides a general rule explaining the retention of truncated APC in colorectal tumours and defines it as a suitable target for therapeutic intervention. Actually, we also show that it is possible to design a shRNA that targets a specific truncated isoform of APC without altering the expression of wild-type APC. Down-regulation of truncated APC is accompanied by an up-regulation of the transcriptional activity of β-catenin in 5 out of 6 cell lines. Surprisingly, the increased signalling is associated in most cases (4 out of 5) with an up-regulation of β-catenin levels, indicating that truncated APC can still modulate wnt signalling through controlling the level of β-catenin. This control can happen even when truncated APC lacks the β-catenin inhibiting domain (CiD) involved in targeting β-catenin for proteasomal degradation. Thus, truncated APC is an essential component of colorectal cancer cells, required for cell proliferation, possibly by adjusting β-catenin signalling to the “just right” level.

Cotargeting signaling pathways driving survival and cell cycle circumvents resistance to Kit inhibitors in leukemia

Oncogenic mutations leading to persistent kinase activities are associated with malignancies. Therefore, deciphering the signaling networks downstream of these oncogenic stimuli remains a challenge to gather insights into targeted therapy. To elucidate the biochemical networks connecting the Kit mutant to leukemogenesis, in the present study, we performed a global profiling of tyrosine-phosphorylated proteins from mutant Kit-driven murine leukemia proerythroblasts and identified Shp2 and Stat5 as proximal effectors of Kit. Shp2 or Stat5 gene depletion by sh-RNA, combined with pharmacologic inhibition of PI3kinase or Mek/Erk activities, revealed 2 distinct and independent signaling pathways contributing to malignancy. We demonstrate that cell survival is driven by the Kit/Shp2/Ras/Mek/Erk1/2 pathway, whereas the G(1)/S transition during the cell cycle is accelerated by both the Kit/Stat5 and Kit/PI3K/Akt pathways. The combined use of the clinically relevant drugs NVP-BEZ235, which targets the cell cycle, and Obatoclax, which targets survival, demonstrated synergistic effects to inhibit leukemia cell growth. This synergy was confirmed with a human mast leukemia cell line (HMC-1.2) that expresses mutant Kit. The results of the present study using liquid chromatography/tandem mass spectrometry analysis have elucidated signaling networks downstream of an oncogenic kinase, providing a molecular rationale for pathway-targeted therapy to treat cancer cells refractory to tyrosine kinase inhibitors.

A Novel Cellular Model to Study Angiotensin II AT2 Receptor Function in Breast Cancer Cells

Recent studies have highlighted the AT1 receptor as a potential therapeutic target in breast cancer, while the role of the AT2 subtype in this disease has remained largely neglected. The present study describes the generation and characterization of a new cellular model of human invasive breast cancer cells (D3H2LN-AT2) stably expressing high levels of Flag-tagged human AT2 receptor (Flag-hAT2). These cells exhibit high-affinity binding sites for AngII, and total binding can be displaced by the AT2-selective antagonist PD123319 but not by the AT1-selective antagonist losartan. Of interest, high levels of expression of luciferase and green fluorescent protein make these cells suitable for bioluminescence and fluorescence studies in vitro and in vivo. We provide here a novel tool to investigate the AT2 receptor functions in breast cancer cells, independently of AT1 receptor activation.

Transient proteasome inhibition as a strategy to enhance lentiviral transduction of hematopoietic CD34(+) cells and T lymphocytes: implications for the use of low viral doses and large-size vectors

The proteasome system restricts lentiviral transduction of stem cells. We exploited proteasome inhibition as a strategy to enhance transduction of both hematopoietic stem cells (HSC) and T lymphocytes with low dose or large-size lentiviral vectors (LV). HSC showed higher transduction efficiency if transiently exposed to proteasome inhibitor MG132 (41.8% vs 10.7%, p<0.0001). Treatment with MG132 (0.5 μM) retained its beneficial effect with 3 different LV of increasing size up to 10.9 Kb (p<0.01). We extended, for the first time, the application of proteasome inhibition to the transduction of T lymphocytes. A transient exposure to MG132 significantly improved lentiviral T-cell transduction. The mean percentage of transduced T cells progressively increased from 13.5% of untreated cells, to 21% (p=0.3), 30% (p=0.03) and 37% (p=0.01) of T lymphocytes that were pre-treated with MG132 at 0.1, 0.5 and 1 μM, respectively. MG132 did not affect viability or functionality of HSC or T cells, nor significantly increased the number of integrated vector copies. Transient proteasome inhibition appears as a new procedure to safely enhance lentiviral transduction of HSC and T lymphocytes with low viral doses. This approach could be useful in settings where the use of large size vectors may impair optimal viral production.

SCL-mediated regulation of the cell-cycle regulator p21 is critical for murine megakaryopoiesis

Megakaryopoiesis is a complex process that involves major cellular and nuclear changes and relies on controlled coordination of cellular proliferation and differentiation. These mechanisms are orchestrated in part by transcriptional regulators. The key hematopoietic transcription factor stem cell leukemia (SCL)/TAL1 is required in early hematopoietic progenitors for specification of the megakaryocytic lineage. These early functions have, so far, prevented full investigation of its role in megakaryocyte development in loss-of-function studies. Here, we report that SCL critically controls terminal megakaryocyte maturation. In vivo deletion of Scl specifically in the megakaryocytic lineage affects all key attributes of megakaryocyte progenitors (MkPs), namely, proliferation, ploidization, cytoplasmic maturation, and platelet release. Genome-wide expression analysis reveals increased expression of the cell-cycle regulator p21 in Scl-deleted MkPs. Importantly, p21 knockdown-mediated rescue of Scl-mutant MkPs shows full restoration of cell-cycle progression and partial rescue of the nuclear and cytoplasmic maturation defects. Therefore, SCL-mediated transcriptional control of p21 is essential for terminal maturation of MkPs. Our study provides a mechanistic link between a major hematopoietic transcriptional regulator, cell-cycle progression, and megakaryocytic differentiation.

Impact of intra- and interspecies variation of occludin on its function as coreceptor for authentic hepatitis C virus particles

Hepatitis C virus (HCV) is characterized by a narrow host range and high interindividual variability in the clinical course of infection. Both of these traits are thought to be largely due to genetic variation between species and between individual hosts. The tight junction component occludin (OCLN) is essential for HCV entry into host cells, and the differences between human and murine OCLN are thought to account in part for the inability of HCV to infect mice and hence preclude their use as a convenient small-animal model. This study assesses the impact of genetic variation in OCLN on cell culture-grown HCV (HCVcc) using a newly generated and characterized OCLN(low) subclone of the Huh-7.5 cell line (Huh-7.5 subclone in which endogenous OCLN expression has been downregulated by a short hairpin RNA). We report the frequency of coding nonsynonymous single nucleotide polymorphisms, i.e., polymorphisms resulting in amino acid exchanges, present in the human population and determine their ability to function as HCV (co)receptors. Moreover, we show that murine OCLN can sustain HCVcc entry, albeit with about 5-fold reduced efficiency compared to that of human OCLN. This reduction in efficiency is due solely to two amino acid residues previously identified by others using an HCV pseudoparticle approach. Finally, we use the Huh-7.5/OCLN(low) cell line to show that HCV spread between neighboring cells is strictly dependent on OCLN.

Posttranscriptional deregulation of MYC via PTEN constitutes a major alternative pathway of MYC activation in T-cell acute lymphoblastic leukemia

Cumulative evidence indicates that MYC, one of the major downstream effectors of NOTCH1, is a critical component of T-cell acute lymphoblastic leukemia (T-ALL) oncogenesis and a potential candidate for targeted therapy. However, MYC is a complex oncogene, involving both fine protein dosage and cell-context dependency, and detailed understanding of MYC-mediated oncogenesis in T-ALL is still lacking. To better understand how MYC is interspersed in the complex T-ALL oncogenic networks, we performed a thorough molecular and biochemical analysis of MYC activation in a comprehensive collection of primary adult and pediatric patient samples. We find that MYC expression is highly variable, and that high MYC expression levels can be generated in a large number of cases in absence of NOTCH1/FBXW7 mutations, suggesting the occurrence of multiple activation pathways in addition to NOTCH1. Furthermore, we show that posttranscriptional deregulation of MYC constitutes a major alternative pathway of MYC activation in T-ALL, operating partly via the PI3K/AKT axis through down-regulation of PTEN, and that NOTCH1(m) might play a dual transcriptional and posttranscriptional role in this process. Altogether, our data lend further support to the significance of therapeutic targeting of MYC and/or the PTEN/AKT pathways, both in GSI-resistant and identified NOTCH1-independent/MYC-mediated T-ALL patients.

STAT3 is essential for the maintenance of neurosphere-initiating tumor cells in patients with glioblastomas: a potential for targeted therapy?

Glioblastoma (GBM), the highest-grade form of gliomas, is the most frequent and the most aggressive. Recently, a subpopulation of cells with stem cells characteristics, commonly named "tumor-initiating stem cells" (TISCs) or "cancer stem cells" (CSCs) were identified in GBM. These cells were shown to be highly resistant to chemotherapeutic drugs and to ionizing radiations. Consequently, the knowledge of the signals that regulate the functions and survival of TISCs is crucial. In our work, we describe a neurosphere-initiating cell (NS-IC) assay to quantify TISC/CSCs from patients with GBM and show that these cells are tumorigenic in vivo. We demonstrate that the intracellular signal transducer and activator of transcription STAT3 is constitutively activated by phosphorylation preferentially on serine 727 in these cells. Moreover, we demonstrate that the selective inhibition of STAT3 by the chemical compound Stattic or by siRNA STAT3 abrogates TISC/CSC proliferation and NS-IC suggesting that self-renewal of GBM "stem-like" cells depends on the presence of STAT3 for their maintenance. Finally, we show that inhibition of STAT3 by Stattic sensitizes TISC/CSCs to the inhibitory action of Temozolomide with a strong synergistic effect of both drugs. Overall, these results suggest that strategies focused on STAT3 inhibition are efficient at the level of "stem-like" cells and could be of interest for therapeutic purposes in patients with malignant GBM.

Influence of insulators on transgene expression from integrating and non-integrating lentiviral vectors

BACKGROUND

The efficacy and biosafety of lentiviral gene transfer is influenced by the design of the vector. To this end, properties of lentiviral vectors can be modified by using cis-acting elements such as the modification of the U3 region of the LTR, the incorporation of the central flap (cPPT-CTS) element, or post-transcriptional regulatory elements such as the woodchuck post-transcriptional regulatory element (WPRE). Recently, several studies evaluated the influence of the incorporation of insulators into the integrating lentiviral vector genome on transgene expression level and position effects.

METHODS

In the present study, the influence of the matrix attachment region (MAR) of the mouse immunoglobulin-κ (Ig-κ) or the chicken lysozyme (ChL) gene was studied on three types of HIV-1-derived lentiviral vectors: self-inactivating (SIN) lentiviral vectors (LV), double-copy lentiviral vectors (DC) and non-integrating lentiviral vectors (NILVs) in different cell types: HeLa, HEK293T, NIH-3T3, Raji, and T Jurkat cell lines and primary neural progenitors.

RESULTS AND DISCUSSION

Our results demonstrate that the Ig-κ MAR in the context of LV slightly increases transduction efficiency only in Hela, NIH-3T3 and Jurkat cells. In the context of double-copy lentiviral vectors, the Ig-κ MAR has no effect or even negatively influences transduction efficiency. In the same way, in the context of non-integrating lentiviral vectors, the Ig-κ MAR has no effect or even negatively influences transduction efficiency, except in differentiated primary neural progenitor cells.The ChL MAR in the context of integrating and non-integrating lentiviral vectors shows no effect or a decrease of transgene expression in all tested conditions.

CONCLUSIONS

This study demonstrates that MAR sequences not necessarily increase transgene expression and that the effect of these sequences is probably context dependent and/or vector dependent. Thus, this study highlights the importance to consider a MAR sequence in a given context. Moreover, other recent reports pointed out the potential effects of random integration of insulators on the expression level of endogenous genes. Taken together, these results show that the use of an insulator in a vector for gene therapy must be well assessed in the particular therapeutic context that it will be used for, and must be balanced with its potential genotoxic effects.

E-cadherin/p120-catenin and tetraspanin Co-029 cooperate for cell motility control in human colon carcinoma

Tumor invasion and metastasis are major obstacles to clinical treatment that rely on cell migration. Here, we elucidate a mechanism of colon carcinoma cell migration that is supported by the cell surface tetraspanin Co-029 (tspan8), which is known to favor tumor progression and metastasis. This mechanism is unmasked by silencing of E-cadherin or its associated adapter molecule p120-catenin (p120ctn), and it involves a switch in signaling between the collagen-binding integrins α(1)β(1) and α(2)β(1). Direct interaction between E-cadherin and Co-029 was documented by chemical cross-linking and immunohistologic analysis of colon carcinomas. High expression of Co-029 and cytoplasmic delocalization of p120ctn were each associated with poor prognosis. Cell motility was reduced severely by antibody-mediated disruption of Co-029 only when p120ctn was silenced, suggesting that tumor progression may be hindered by Co-029 targeting. Our findings define a function for tetraspanin Co-029 as a modifier of cancer cell motility and reveal an adhesion signaling network implicated in progression and metastasis.

NKX3.1 is a direct TAL1 target gene that mediates proliferation of TAL1-expressing human T cell acute lymphoblastic leukemia

TAL1 (also known as SCL) is expressed in >40% of human T cell acute lymphoblastic leukemias (T-ALLs). TAL1 encodes a basic helix-loop-helix transcription factor that can interfere with the transcriptional activity of E2A and HEB during T cell leukemogenesis; however, the oncogenic pathways directly activated by TAL1 are not characterized. In this study, we show that, in human TAL1–expressing T-ALL cell lines, TAL1 directly activates NKX3.1, a tumor suppressor gene required for prostate stem cell maintenance. In human T-ALL cell lines, NKX3.1 gene activation is mediated by a TAL1–LMO–Ldb1 complex that is recruited by GATA-3 bound to an NKX3.1 gene promoter regulatory sequence. TAL1-induced NKX3.1 activation is associated with suppression of HP1-α (heterochromatin protein 1 α) binding and opening of chromatin on the NKX3.1 gene promoter. NKX3.1 is necessary for T-ALL proliferation, can partially restore proliferation in TAL1 knockdown cells, and directly regulates miR-17-92. In primary human TAL1-expressing leukemic cells, the NKX3.1 gene is expressed independently of the Notch pathway, and its inactivation impairs proliferation. Finally, TAL1 or NKX3.1 knockdown abrogates the ability of human T-ALL cells to efficiently induce leukemia development in mice. These results suggest that tumor suppressor or oncogenic activity of NKX3.1 depends on tissue expression.

Species-specific regions of occludin required by hepatitis C virus for cell entry

Hepatitis C virus (HCV) is a leading cause of liver disease worldwide. As HCV infects only human and chimpanzee cells, antiviral therapy and vaccine development have been hampered by the lack of a convenient small-animal model. In this study we further investigate how the species tropism of HCV is modulated at the level of cell entry. It has been previously determined that the tight junction protein occludin (OCLN) is essential for HCV host cell entry and that human OCLN is more efficient than the mouse ortholog at mediating HCV cell entry. To further investigate the relationship between OCLN sequence and HCV species tropism, we compared OCLN proteins from a range of species for their ability to mediate infection of naturally OCLN-deficient 786-O cells with lentiviral pseudoparticles bearing the HCV glycoproteins. While primate sequences function equivalently to human OCLN, canine, hamster, and rat OCLN had intermediate activities, and guinea pig OCLN was completely nonfunctional. Through analysis of chimeras between these OCLN proteins and alanine scanning mutagenesis of the extracellular domains of OCLN, we identified the second half of the second extracellular loop (EC2) and specific amino acids within this domain to be critical for modulating the HCV cell entry factor activity of this protein. Furthermore, this critical region of EC2 is flanked by two conserved cysteine residues that are essential for HCV cell entry, suggesting that a subdomain of EC2 may be defined by a disulfide bond.