Angiopoietin-2 is a direct transcriptional target of TAL1, LYL1 and LMO2 in endothelial cells

Cytoplasmic LMO2-LDB1 Complex Activates STAT3 Signaling through Interaction with gp130-JAK in Glioma Stem Cells

The oncogenic role of nuclear LIM domain only 2 (LMO2) as a transcriptional regulator is well established, but its function in the cytoplasm is largely unknown. Here, we identified LMO2 as a cytoplasmic activator for signal transducer and activator of transcription 3 (STAT3) signaling in glioma stem cells (GSCs) through biochemical and bioinformatics analyses. LMO2 increases STAT3 phosphorylation by interacting with glycoprotein 130 (gp130) and Janus kinases (JAKs). LMO2-driven activation of STAT3 signaling requires the LDB1 protein and leads to increased expression of an inhibitor of differentiation 1 (ID1), a master regulator of cancer stemness. Our findings indicate that the cytoplasmic LMO2-LDB1 complex plays a crucial role in the activation of the GSC signaling cascade via interaction with gp130 and JAK1/2. Thus, LMO2-LDB1 is a bona fide oncogenic protein complex that activates either the JAK-STAT signaling cascade in the cytoplasm or direct transcriptional regulation in the nucleus.

The transcription factor complex LMO2/TAL1 regulates branching and endothelial cell migration in sprouting angiogenesis

The transcription factor complex, consisting of LMO2, TAL1 or LYL1, and GATA2, plays an important role in capillary sprouting by regulating VEGFR2, DLL4, and angiopoietin 2 in tip cells. Overexpression of the basic helix-loop-helix transcription factor LYL1 in transgenic mice results in shortened tails. This phenotype is associated with vessel hyperbranching and a relative paucity of straight vessels due to DLL4 downregulation in tip cells by forming aberrant complex consisting of LMO2 and LYL1. Knockdown of LMO2 or TAL1 inhibits capillary sprouting in spheroid-based angiogenesis assays, which is associated with decreased angiopoietin 2 secretion. In the same assay using mixed TAL1- and LYL1-expressing endothelial cells, TAL1 was found to be primarily located in tip cells, while LYL1-expressing cells tended to occupy the stalk position in sprouts by upregulating VEGFR1 than TAL1. Thus, the interaction between LMO2 and TAL1 in tip cells plays a key role in angiogenic switch of sprouting angiogenesis.

Homodimeric and Heterodimeric Interactions among Vertebrate Basic Helix-Loop-Helix Transcription Factors

The basic helix–loop–helix transcription factor (bHLH TF) family is involved in tissue development, cell differentiation, and disease. These factors have transcriptionally positive, negative, and inactive functions by combining dimeric interactions among family members. The best known bHLH TFs are the E-protein homodimers and heterodimers with the tissue-specific TFs or ID proteins. These cooperative and dynamic interactions result in a complex transcriptional network that helps define the cell’s fate. Here, the reported dimeric interactions of 67 vertebrate bHLH TFs with other family members are summarized in tables, including specifications of the experimental techniques that defined the dimers. The compilation of these extensive data underscores homodimers of tissue-specific bHLH TFs as a central part of the bHLH regulatory network, with relevant positive and negative transcriptional regulatory roles. Furthermore, some sequence-specific TFs can also form transcriptionally inactive heterodimers with each other. The function, classification, and developmental role for all vertebrate bHLH TFs in four major classes are detailed.

SLUG and Truncated TAL1 Reduce Glioblastoma Stem Cell Growth Downstream of Notch1 and Define Distinct Vascular Subpopulations in Glioblastoma Multiforme

Simple Summary

Glioblastoma multiforme is the most aggressive form of brain tumor and is still incurable. These neoplasms are particularly difficult to treat efficiently because of their highly heterogeneous and resistant characteristics. Advances in genomics have highlighted the complex molecular landscape of these tumors and the need to further develop effective and targeted therapies for each patient. A specific population of cells with enriched stem cell properties within tumors, i.e., glioblastoma stem cells (GSC), drives this cellular heterogeneity and therapeutical resistance, and thus constitutes an attractive target for the design of innovative treatments. However, the signals driving the maintenance and resistance of these cells are still unclear. We provide new findings regarding the expression of two transcription factors in these cells and directly in glioblastoma patient samples. We show that these proteins downregulate GSC growth and ultimately participate in the progression of gliomas. The forthcoming results will contribute to a better understanding of gliomagenesis.

Abstract

Glioblastomas (GBM) are high-grade brain tumors, containing cells with distinct phenotypes and tumorigenic potentials, notably aggressive and treatment-resistant multipotent glioblastoma stem cells (GSC). The molecular mechanisms controlling GSC plasticity and growth have only partly been elucidated. Contact with endothelial cells and the Notch1 pathway control GSC proliferation and fate. We used three GSC cultures and glioma resections to examine the expression, regulation, and role of two transcription factors, SLUG (SNAI2) and TAL1 (SCL), involved in epithelial to mesenchymal transition (EMT), hematopoiesis, vascular identity, and treatment resistance in various cancers. In vitro, SLUG and a truncated isoform of TAL1 (TAL1-PP22) were strongly upregulated upon Notch1 activation in GSC, together with LMO2, a known cofactor of TAL1, which formed a complex with truncated TAL1. SLUG was also upregulated by TGF-β1 treatment and by co-culture with endothelial cells. In patient samples, the full-length isoform TAL1-PP42 was expressed in all glioma grades. In contrast, SLUG and truncated TAL1 were preferentially overexpressed in GBMs. SLUG and TAL1 are expressed in the tumor microenvironment by perivascular and endothelial cells, respectively, and to a minor extent, by a fraction of epidermal growth factor receptor (EGFR) -amplified GBM cells. Mechanistically, both SLUG and truncated TAL1 reduced GSC growth after their respective overexpression. Collectively, this study provides new evidence for the role of SLUG and TAL1 in regulating GSC plasticity and growth.

Dual and opposing roles of the androgen receptor in VETC-dependent and invasion-dependent metastasis of hepatocellular carcinoma

BACKGROUND & AIMS

Contradictory roles of the androgen receptor (AR) in hepatocellular carcinoma (HCC) metastasis have been reported. We have shown that VETC (vessels encapsulating tumor clusters) mediates invasion-independent metastasis, whereas VETC^- HCCs metastasize in an invasion-dependent manner. Herein, we aimed to reveal the roles of AR in HCC metastasis.

METHODS

Mouse xenograft models, clinical samples, and cell models were used.

RESULTS

AR expression was significantly lower in HCCs with a VETC pattern, portal vein tumor thrombus, endothelium-coated microemboli or high recurrence rates. Overexpressing AR in VETC⁺ hepatoma cells suppressed VETC formation and intrahepatic metastasis but promoted pulmonary metastasis of mouse xenografts. AR decreased the transcription of Angiopoietin-2 (Angpt2), a factor essential for VETC formation, by binding to the Angpt2 promoter. The roles of AR in inhibiting VETC formation and intrahepatic metastasis were attenuated by restoring Angpt2 expression, suggesting that AR may repress VETC-dependent intrahepatic metastasis by inhibiting Angpt2 expression and VETC formation. On the other hand, AR upregulated Rac1 expression, promoted lamellipodia formation and increased cell migration/invasion. A Rac1 inhibitor abrogated the AR-mediated promotion of migration/invasion and pulmonary metastasis of VETC⁺ hepatoma cells, but did not affect the AR-mediated inhibition of intrahepatic metastasis. Furthermore, an AR inhibitor decreased Rac1 expression and attenuated both intrahepatic and pulmonary metastasis of VETC^- xenografts, an effect which was abrogated by restoring Rac1 expression. These data indicate that AR may facilitate the lung metastasis of VETC⁺ HCCs and both the liver/lung metastases of VETC^- HCCs by upregulating Rac1 expression and then promoting migration/invasion.

CONCLUSION

AR plays dual and opposing roles in VETC-dependent and invasion-dependent metastasis, which highlights the complex functions of AR and the importance of individualized cancer therapy.

LAY SUMMARY

In this study, we uncovered the dual and opposing roles of the androgen receptor in VETC (vessels encapsulating tumor clusters)-dependent and invasion-dependent metastasis of hepatocellular carcinoma (HCC). We elucidated the underlying mechanisms of these processes, which provided novel insights into the complex regulatory network of the androgen receptor in HCC metastasis and may have important implications for precision medicine.

Gliosarcoma vs. glioblastoma: a retrospective case series using molecular profiling

Background

Gliosarcoma (GS) refers to the presence of mesenchymal differentiation (as seen using light microscopy) in the setting of glioblastoma (GB, an astrocytoma, WHO Grade 4). Although the same approach to treatment is typically adopted for GS and GB, there remains some debate as to whether GS should be considered a discrete pathological entity. Differences between these tumors have not been clearly established at the molecular level.

Methods

Patients with GS (n=48) or GB (n=1229) underwent molecular profiling (MP) with a pan-cancer panel of tests as part of their clinical care. The methods employed included next-generation sequencing (NGS) of DNA and RNA, copy number variation (CNV) of DNA and immunohistochemistry (IHC). The MP comprised 1153 tests in total, although results for each test were not available for every tumor profiled. We analyzed this data retrospectively in order to determine if our results were in keeping with what is known about the pathogenesis of GS by contrast with GB. We also sought novel associations between the MP and GS vs. GB which might improve our understanding of pathogenesis of GS.

Results

Potentially meaningful associations (p<0.1, Fisher’s exact test (FET)) were found for 14 of these tests in GS vs. GB. A novel finding was higher levels of proteins mediating immuno-evasion (PD-1, PD-L1) in GS. All of the differences we observed have been associated with epithelial-to-mesenchymal transition (EMT) in other tumor types. Many of the changes we saw in GS are novel in the setting of glial tumors, including copy number amplification in LYL1 and mutations in PTPN11.

Conclusions

GS shows certain characteristics of EMT, by contrast with GB. Treatments targeting immuno-evasion may be of greater therapeutic value in GS relative to GB.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12883-021-02233-5).

In Lyl1-/- mice, adipose stem cell vascular niche impairment leads to premature development of fat tissues

Lyl1 encodes a hematopoietic‐ and endothelial‐specific bHLH transcription factor. Lyl1‐deficient mice are viable, but they display mild hematopoietic and vascular defects. Specifically, LYL1 is required for the maturation and stabilization of blood vessel endothelial adherens junctions. Here, we report that young adult Lyl1^−/− mice exhibit transient overweight associated with general expansion of adipose tissue, without signs of metabolic disorder and unrelated to food intake. The increased fat tissue development in Lyl1^−/− mice resulted from earlier differentiation of adipose stem cells (ASCs) into adipocytes through noncell autonomous mechanisms. Specifically, we found that in Lyl1^−/− mice, the adipose tissue vascular structures are immature, as indicated by their high permeability, reduced coverage by pericytes, lower recruitment of VE‐cadherin and ZO1 at cell junctions, and more prone to angiogenesis. Together, our data show that in Lyl1^−/− mice, the impaired vascular compartment of the adipose niche promotes ASC differentiation, leading to early adipocyte expansion and premature ASC depletion. Our study highlights the major structural role of the adipose tissue vascular niche in coordinating stem cell self‐renewal and differentiation into adipocytes.

KLF15-Wnt-Dependent Cardiac Reprogramming Up-Regulates SHISA3 in the Mammalian Heart

BACKGROUND

The combination of cardiomyocyte (CM) and vascular cell (VC) fetal reprogramming upon stress culminates in end-stage heart failure (HF) by mechanisms that are not fully understood. Previous studies suggest KLF15 as a key regulator of CM hypertrophy.

OBJECTIVES

This study aimed to characterize the impact of KLF15-dependent cardiac transcriptional networks leading to HF progression, amenable to therapeutic intervention in the adult heart.

METHODS

Transcriptomic bioinformatics, phenotyping of Klf15 knockout mice, Wnt-signaling-modulated hearts, and pressure overload and myocardial ischemia models were applied. Human KLF15 knockout embryonic stem cells and engineered human myocardium, and human samples were used to validate the relevance of the identified mechanisms.

RESULTS

The authors identified a sequential, postnatal transcriptional repression mediated by KLF15 of pathways implicated in pathological tissue remodeling, including distinct Wnt-pathways that control CM fetal reprogramming and VC remodeling. The authors further uncovered a vascular program induced by a cellular crosstalk initiated by CM, characterized by a reduction of KLF15 and a concomitant activation of Wnt-dependent transcriptional signaling. Within this program, a so-far uncharacterized cardiac player, SHISA3, primarily expressed in VCs in fetal hearts and pathological remodeling was identified. Importantly, the KLF15 and Wnt codependent SHISA3 regulation was demonstrated to be conserved in mouse and human models.

CONCLUSIONS

The authors unraveled a network interplay defined by KLF15-Wnt dynamics controlling CM and VC homeostasis in the postnatal heart and demonstrated its potential as a cardiac-specific therapeutic target in HF. Within this network, they identified SHISA3 as a novel, evolutionarily conserved VC marker involved in pathological remodeling in HF.

Transcriptional profiling of lung cell populations in idiopathic pulmonary arterial hypertension

Despite recent improvements in management of idiopathic pulmonary arterial hypertension, mortality remains high. Understanding the alterations in the transcriptome–phenotype of the key lung cells involved could provide insight into the drivers of pathogenesis. In this study, we examined differential gene expression of cell types implicated in idiopathic pulmonary arterial hypertension from lung explants of patients with idiopathic pulmonary arterial hypertension compared to control lungs. After tissue digestion, we analyzed all cells from three idiopathic pulmonary arterial hypertension and six control lungs using droplet-based single cell RNA-sequencing. After dimensional reduction by t-stochastic neighbor embedding, we compared the transcriptomes of endothelial cells, pericyte/smooth muscle cells, fibroblasts, and macrophage clusters, examining differential gene expression and pathways implicated by analysis of Gene Ontology Enrichment. We found that endothelial cells and pericyte/smooth muscle cells had the most differentially expressed gene profile compared to other cell types. Top differentially upregulated genes in endothelial cells included novel genes: ROBO4, APCDD1, NDST1, MMRN2, NOTCH4, and DOCK6, as well as previously reported genes: ENG, ORAI2, TFDP1, KDR, AMOTL2, PDGFB, FGFR1, EDN1, and NOTCH1. Several transcription factors were also found to be upregulated in idiopathic pulmonary arterial hypertension endothelial cells including SOX18, STRA13, LYL1, and ELK, which have known roles in regulating endothelial cell phenotype. In particular, SOX18 was implicated through bioinformatics analyses in regulating the idiopathic pulmonary arterial hypertension endothelial cell transcriptome. Furthermore, idiopathic pulmonary arterial hypertension endothelial cells upregulated expression of FAM60A and HDAC7, potentially affecting epigenetic changes in idiopathic pulmonary arterial hypertension endothelial cells. Pericyte/smooth muscle cells expressed genes implicated in regulation of cellular apoptosis and extracellular matrix organization, and several ligands for genes showing increased expression in endothelial cells. In conclusion, our study represents the first detailed look at the transcriptomic landscape across idiopathic pulmonary arterial hypertension lung cells and provides robust insight into alterations that occur in vivo in idiopathic pulmonary arterial hypertension lungs.

Comparing atmospheric and hypoxic cultured mesenchymal stem cell transcriptome: implication for stem cell therapies targeting intervertebral discs

Background

Mesenchymal stem cells (MSCs) represent an attractive avenue for cellular therapies targeting degenerative diseases. MSC in vitro expansion is required in order to obtain therapeutic numbers during the manufacturing process. It is known that culture conditions impact cellular properties and behavior after in vivo transplantation. In this study, we aimed at evaluating the benefit of hypoxic culturing of human bone marrow derived mesenchymal stem cells on cell fitness and whole genome expression and discussed its implication on cellular therapies targeting orthopedic diseases such as chronic lower back pain.

Methods

Human bone marrow mesenchymal stem cells (hBMMSCs) were isolated from fresh human anticoagulated whole bone marrow and were cultured side by side in atmospheric (20% O₂) and hypoxic (5% O₂) oxygen partial pressure for up to 3 passages. Stem cell fitness was assessed by clonogenic assay, cell surface marker expression and differentiation potential. Whole genome expression was performed by mRNA sequencing. Data from clonogenic assays, cell surface marker by flow cytometry and gene expression by quantitative PCR were analyzed by two-tailed paired Student’s t-test. Data from mRNA sequencing were aligned to hg19 using Tophat-2.0.13 and analyzed using Cufflinks-2.1.1.

Results

Hypoxic culturing of hBMMSCs had positive effects on cell fitness, as evidenced by an increased clonogenicity and improved differentiation potential towards adipocyte and chondrocyte lineages. No difference in osteoblast differentiation or in cell surface markers were observed. Only a small subset of genes (34) were identified by mRNA sequencing to be significantly dysregulated by hypoxia. When clustered by biological function, these genes were associated with chondrogenesis and cartilage metabolism, inflammation and immunomodulation, cellular survival, migration and proliferation, vasculogenesis and angiogenesis.

Conclusions

Hypoxic culturing positively impacted hBMMSCs fitness and transcriptome, potentially improving inherent properties of these cells that are critical for the development of successful cellular therapies. Hypoxic culturing should be considered for the in vitro expansion of hBMMSCs during manufacturing of cellular therapies targeting orthopedic disorders such as lower back pain.

LYL1 gene amplification predicts poor survival of patients with uterine corpus endometrial carcinoma: analysis of the Cancer genome atlas data

BACKGROUND

Somatic amplifications of the LYL1 gene are relatively common occurrences in patients who develop uterine corpus endometrial carcinoma (UCEC) as opposed to other cancers. This study was undertaken to determine whether such genetic alterations affect survival outcomes of UCEC.

METHODS

In 370 patients with UCEC, we analysed clinicopathologic characteristics and corresponding genomic data from The Cancer Genome Atlas database. Patients were stratified according to LYL1 gene status, grouped as amplification or non-amplification. Heightened levels of cancer-related genes expressed in concert with LYL1 amplification were similarly investigated through differentially expressed gene and gene set enrichment analyses. Factors associated with survival outcomes were also identified.

RESULTS

Somatic LYL1 gene amplification was observed in 22 patients (5.9%) with UCEC. Patients displaying amplification (vs. non-amplification) were significantly older at the time of diagnosis and more often were marked by non-endometrioid, high-grade, or advanced disease. In survival analysis, the amplification subset showed poorer progression-free survival (PFS) and overall survival (OS) rates (3-year PFS: 34.4% vs. 79.9%, P = 0.031; 5-year OS: 25.1% vs. 84.9%, P = 0.014). However, multivariate analyses adjusted for tumor histologic type, grade, and stage did not confirm LYL1 gene amplification as an independent prognostic factor for either PFS or OS. Nevertheless, MAPK, WNT, and cell cycle pathways were significantly enriched by LYL1 gene amplification (P < 0.001, P = 0.002, and P = 0.004, respectively).

CONCLUSIONS

Despite not being identified as an independent prognostic factor in UCEC, LYL1 gene amplification is associated with other poor prognostic factors and correlated with upregulation of cancer-related pathways.

Regulation of angiopoietin-2 secretion from human pulmonary microvascular endothelial cells

INTRODUCTION

Sepsis is characterized by dysregulated systemic inflammation and cytokine storm. Angiopoietin-2 (Ang-2) is known to closely correlate with severity of sepsis-related acute lung injury and mortality. The aim of this study was to clarify the mechanisms involved in Ang-2 secretion to better understand the pathophysiology of sepsis.

MATERIALS AND METHODS

The concentration of Ang-2 was assessed in culture medium of pulmonary microvascular endothelial cells in the presence or absence of Gram-positive bacteria cell wall components [lipoteichoic acid (LTA) and peptidoglycan (PGN)] stimulation at different time points ranging from 15 minutes to 24 hours. Constitutive and LTA-PGN-stimulated Ang-2 level changes were also assessed after cells were pretreated with different pathway inhibitors for 1 hour.

RESULTS

Two distinctive mechanisms of Ang-2 secretion, constitutive and stimulated secretion, were identified. Constitutive secretion resulted in slow but continuous increase in Ang-2 in culture medium over time. It was regulated by 3'5'-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-Ca²⁺ and nitric oxide (NO)-3'5'-cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG)-Ca²⁺ pathways and partially regulated by N-ethyl-maleimide-sensitive factor-Ca²⁺ pathways. LTA-PGN stimulation caused rapid and potent increase followed by gradual decrease of Ang-2. It was partially regulated by both Ral A-phospholipase D and NSF-Ca²⁺ pathways.

CONCLUSIONS

We demonstrated characteristics and involved pathways for two distinctive secretory mechanisms, constitutive and stimulated, of Ang-2 in pulmonary microvascular endothelial cells. Considering the close correlation of Ang-2 with sepsis outcomes, our findings provide a better understanding of an important mechanism associated with sepsis pathophysiology and identify possible therapeutic targets to improve outcomes in the potentially lethal disease.

SCL/TAL1 in Hematopoiesis and Cellular Reprogramming

SCL, a transcription factor of the basic helix-loop-helix family, is a master regulator of hematopoiesis. Scl specifies lateral plate mesoderm to a hematopoietic fate and establishes boundaries by inhibiting the cardiac lineage. A combinatorial interaction between Scl and Vegfa/Flk1 sets in motion the first wave of primitive hematopoiesis. Subsequently, definitive hematopoietic stem cells (HSCs) emerge from the embryo proper via an endothelial-to-hematopoietic transition controlled by Runx1, acting with Scl and Gata2. Past this stage, Scl in steady state HSCs is redundant with Lyl1, a highly homologous factor. However, Scl is haploinsufficient in stress response, when a rare subpopulation of HSCs with very long term repopulating capacity is called into action. SCL activates transcription by recruiting a core complex on DNA that necessarily includes E2A/HEB, GATA1-3, LIM-only proteins LMO1/2, LDB1, and an extended complex comprising ETO2, RUNX1, ERG, or FLI1. These interactions confer multifunctionality to a complex that can control cell proliferation in erythroid progenitors or commitment to terminal differentiation through variations in single component. Ectopic SCL and LMO1/2 expression in immature thymocytes activates of a stem cell gene network and reprogram cells with a finite lifespan into self-renewing preleukemic stem cells (pre-LSCs), an initiating event in T-cell acute lymphoblastic leukemias. Interestingly, fate conversion of fibroblasts to hematoendothelial cells requires not only Scl and Lmo2 but also Gata2, Runx1, and Erg, indicating a necessary collaboration between these transcription factors for hematopoietic reprogramming. Nonetheless, full reprogramming into self-renewing multipotent HSCs may require additional factors and most likely, a permissive microenvironment.

MicroRNA-150 Suppression of Angiopoetin-2 Generation and Signaling Is Crucial for Resolving Vascular Injury

OBJECTIVE

Increased vascular permeability is a hallmark of sepsis and acute respiratory distress syndrome. Angiopoietin (Ang2) induces vascular leak, and excess Ang2 generation is associated with patient mortality from these diseases. However, mechanisms dampening Ang2 generation during injury remain unclear. Interestingly, microRNA (miR)-150 levels were decreased in septic patients. miR regulate signaling networks by silencing mRNAs containing complementary sequences. Thus, we hypothesized that miR-150 suppresses Ang2 generation and thereby resolves vascular injury.

APPROACH AND RESULTS

Wild-type or miR-150(-/-) mice or endothelial cells were exposed to lipopolysaccharide or sepsis, and Ang2 levels, adherens junction reannealing, endothelial barrier function, and mortality were determined. Although Ang2 transiently increased during lipopolysaccharide-induced injury in wild-type endothelial cells and lungs, miR-150 expression was elevated only during recovery from injury. Deletion of miR-150 caused a persistent increase in Ang2 levels and impaired adherens junctions reannealing after injury, resulting thereby in an irreversible increase in vascular permeability. Also, miR-150(-/-) mice died rapidly after sepsis. Rescuing miR-150 expression in endothelial cells prevented Ang2 generation, thereby restoring vascular barrier function in miR-150(-/-) mice. miR-150 terminated Ang2 generation by targeting the transcription factor, early growth response 2. Thus, early growth response 2 or Ang2 depletion in miR-150(-/-) endothelial cells restored junctional reannealing and reinstated barrier function. Importantly, upregulating miR-150 expression by injecting a chemically synthesized miR-150 mimic into wild-type mice vasculature decreased early growth response 2 and Ang2 levels and hence mortality from sepsis.

CONCLUSIONS

miR-150 is a novel suppressor of Ang2 generation with a key role in resolving vascular injury and reducing mortality resulting from sepsis.

Human disease modeling reveals integrated transcriptional and epigenetic mechanisms of NOTCH1 haploinsufficiency

The mechanisms by which transcription factor haploinsufficiency alters the epigenetic and transcriptional landscape in human cells to cause disease are unknown. Here, we utilized human induced pluripotent stem cell (iPSC)-derived endothelial cells (ECs) to show that heterozygous nonsense mutations in NOTCH1 that cause aortic valve calcification disrupt the epigenetic architecture, resulting in derepression of latent pro-osteogenic and -inflammatory gene networks. Hemodynamic shear stress, which protects valves from calcification in vivo, activated anti-osteogenic and anti-inflammatory networks in NOTCH1(+/+), but not NOTCH1(+/-), iPSC-derived ECs. NOTCH1 haploinsufficiency altered H3K27ac at NOTCH1-bound enhancers, dysregulating downstream transcription of more than 1,000 genes involved in osteogenesis, inflammation, and oxidative stress. Computational predictions of the disrupted NOTCH1-dependent gene network revealed regulatory nodes that, when modulated, restored the network toward the NOTCH1(+/+) state. Our results highlight how alterations in transcription factor dosage affect gene networks leading to human disease and reveal nodes for potential therapeutic intervention.

The LIM-only transcription factor LMO2 determines tumorigenic and angiogenic traits in glioma stem cells

Glioblastomas (GBMs) maintain their cellular heterogeneity with glioma stem cells (GSCs) producing a variety of tumor cell types. Here we interrogated the oncogenic roles of Lim domain only 2 (LMO2) in GBM and GSCs in mice and human. High expression of LMO2 was found in human patient-derived GSCs compared with the differentiated progeny cells. LMO2 is required for GSC proliferation both in vitro and in vivo, as shRNA-mediated LMO2 silencing attenuated tumor growth derived from human GSCs. Further, LMO2 is sufficient to induce stem cell characteristics (stemness) in mouse premalignant astrocytes, as forced LMO2 expression facilitated in vitro and in vivo growth of astrocytes derived from Ink4a/Arf null mice and acquisition of GSC phenotypes. A subset of mouse and human GSCs converted into vascular endothelial-like tumor cells both in vitro and in vivo, which phenotype was attenuated by LMO2 silencing and promoted by LMO2 overexpression. Mechanistically, the action of LMO2 for induction of glioma stemness is mediated by transcriptional regulation of Jagged1 resulting in activation of the Notch pathway, whereas LMO2 directly occupies the promoter regions of the VE-cadherin gene for a gain of endothelial cellular phenotype. Subsequently, selective ablation of human GSC-derived VE-cadherin-expressing cells attenuated vascular formation in mouse intracranial tumors, thereby significantly prolonging mouse survival. Clinically, LMO2 expression was elevated in GBM tissues and inversely correlated with prognosis of GBM patients. Taken together, our findings describe novel dual roles of LMO2 to induce tumorigenesis and angiogenesis, and provide potential therapeutic targets in GBMs.

SCL, LMO1 and Notch1 reprogram thymocytes into self-renewing cells

The molecular determinants that render specific populations of normal cells susceptible to oncogenic reprogramming into self-renewing cancer stem cells are poorly understood. Here, we exploit T-cell acute lymphoblastic leukemia (T-ALL) as a model to define the critical initiating events in this disease. First, thymocytes that are reprogrammed by the SCL and LMO1 oncogenic transcription factors into self-renewing pre-leukemic stem cells (pre-LSCs) remain non-malignant, as evidenced by their capacities to generate functional T cells. Second, we provide strong genetic evidence that SCL directly interacts with LMO1 to activate the transcription of a self-renewal program coordinated by LYL1. Moreover, LYL1 can substitute for SCL to reprogram thymocytes in concert with LMO1. In contrast, inhibition of E2A was not sufficient to substitute for SCL, indicating that thymocyte reprogramming requires transcription activation by SCL-LMO1. Third, only a specific subset of normal thymic cells, known as DN3 thymocytes, is susceptible to reprogramming. This is because physiological NOTCH1 signals are highest in DN3 cells compared to other thymocyte subsets. Consistent with this, overexpression of a ligand-independent hyperactive NOTCH1 allele in all immature thymocytes is sufficient to sensitize them to SCL-LMO1, thereby increasing the pool of self-renewing cells. Surprisingly, hyperactive NOTCH1 cannot reprogram thymocytes on its own, despite the fact that NOTCH1 is activated by gain of function mutations in more than 55% of T-ALL cases. Rather, elevating NOTCH1 triggers a parallel pathway involving Hes1 and Myc that dramatically enhances the activity of SCL-LMO1 We conclude that the acquisition of self-renewal and the genesis of pre-LSCs from thymocytes with a finite lifespan represent a critical first event in T-ALL. Finally, LYL1 and LMO1 or LMO2 are co-expressed in most human T-ALL samples, except the cortical T subtype. We therefore anticipate that the self-renewal network described here may be relevant to a majority of human T-ALL.

Deciphering the initiating events in lymphoid leukemia is important for the development of new therapeutic strategies. In this manuscript, we define oncogenic reprogramming as the process through which non-self-renewing progenitors are converted into pre-leukemic stem cells with sustained self-renewal capacities. We provide strong genetic evidence that this step is rate-limiting in leukemogenesis and requires the activation of a self-renewal program by oncogenic transcription factors, as exemplified by SCL and LMO1. Furthermore, NOTCH1 is a pathway that drives cell fate in the thymus. We demonstrate that homeostatic NOTCH1 levels that are highest in specific thymocyte subsets determine their susceptibilities to oncogenic reprogramming by SCL and LMO1. Our data provide novel insight into the acquisition of self-renewal as a critical first step in lymphoid cell transformation, requiring the synergistic interaction of oncogenic transcription factors with a cellular context controlled by high physiological NOTCH1.

Lung endothelial barrier disruption in Lyl1-deficient mice

Maturation of newly formed vessels is a multistep phenomenon during which functional endothelial barriers are established. Disruption of vessel integrity is an important feature in many physiological and pathological processes. We previously reported that lymphoblastic leukemia-derived sequence 1 (LYL1) is required for the late stages of postnatal angiogenesis to limit the formation of new blood vessels, notably by regulating the activity of the small GTPase Rap1. In this study, we show that LYL1 is also required during the formation of the mature endothelial barrier in the lungs of adult mice. Specifically, LYL1 knockdown in human endothelial cells downregulated the expression of ARHGAP21 and ARHGAP24, which encode two Rho GTPase-activating proteins, and this was correlated with increased RhoA activity and reorganization of the actin cytoskeleton into stress fibers. Importantly, in lungs of Lyl1-deficient mice, both vascular endothelial (VE)-cadherin and p120-catenin were poorly recruited to endothelial adherens junctions, indicative of defective cell-cell junctions. Consistent with this, higher Evans blue dye extravasation, edema, and leukocyte infiltration in the lung parenchyma of Lyl1-/- mice than in wild-type littermates confirmed that lung vascular permeability is constitutively elevated in Lyl1-/- adult mice. Our data show that LYL1 acts as a stabilizing signal for adherens junction formation by operating upstream of VE-cadherin and of the two GTPases Rap1 and RhoA. As increased vascular permeability is a key feature and a major mechanism of acute respiratory distress syndrome, molecules that regulate LYL1 activity could represent additional tools to modify the endothelial barrier permeability.

LIM domain only-2 (LMO2) induces T-cell leukemia by two distinct pathways

The LMO2 oncogene is deregulated in the majority of human T-cell leukemia cases and in most gene therapy-induced T-cell leukemias. We made transgenic mice with enforced expression of Lmo2 in T-cells by the CD2 promoter/enhancer. These transgenic mice developed highly penetrant T-ALL by two distinct patterns of gene expression: one in which there was concordant activation of Lyl1, Hhex, and Mycn or alternatively, with Notch1 target gene activation. Most strikingly, this gene expression clustering was conserved in human Early T-cell Precursor ALL (ETP-ALL), where LMO2, HHEX, LYL1, and MYCN were most highly expressed. We discovered that HHEX is a direct transcriptional target of LMO2 consistent with its concordant gene expression. Furthermore, conditional inactivation of Hhex in CD2-Lmo2 transgenic mice markedly attenuated T-ALL development, demonstrating that Hhex is a crucial mediator of Lmo2's oncogenic function. The CD2-Lmo2 transgenic mice offer mechanistic insight into concordant oncogene expression and provide a model for the highly treatment-resistant ETP-ALL subtype.

GATA2 and Lmo2 control angiogenesis and lymphangiogenesis via direct transcriptional regulation of neuropilin-2

GATA-binding protein 2 (GATA2) and LIM domain only 2 (Lmo2) form common transcription complexes during hematopoietic differentiation. Here we show that these two transcription factors also play a key role in endothelial cells (EC) and lymphatic EC (LEC) function. Primary EC and tumor-associated blood vessels expressed GATA2 and Lmo2. VEGF-induced sprouting angiogenesis in both differentiating embryonic stem cells (embryoid bodies) and primary EC increased GATA2 and Lmo2 levels. Conversely, silencing of GATA2 and Lmo2 expression in primary EC inhibited VEGF-induced angiogenic activity, including EC migration and sprouting in vitro, two key steps of angiogenesis in vivo. This inhibition of EC function was associated with downregulated expression of neuropilin-2 (NRP2), a co-receptor of VEGFRs for VEGF, at the protein, mRNA and promoter levels. NRP2 overexpression partially rescued the impaired angiogenic sprouting in the GATA2/Lmo2 knockdown EC, confirming that GATA2 and Lmo2 mediated EC function, at least in part, by directly regulating NRP2 gene expression. Furthermore, it was found that primary LEC expressed GATA2 and Lmo2 as well. Silencing of GATA2 and Lmo2 expression in LEC inhibited VEGF-induced LEC sprouting, also in a NRP2-dependent manner. In conclusion, our results demonstrate that GATA2 and Lmo2 cooperatively regulate VEGF-induced angiogenesis and lymphangiogenesis via NRP2.

LIM-domain-only proteins in cancer

LIM-domain proteins are a large family of proteins that are emerging as key molecules in a wide variety of human cancers. In particular, all members of the human LIM-domain-only (LMO) proteins, LMO1-4, which are required for many developmental processes, are implicated in the onset or the progression of several cancers, including T cell leukaemia, breast cancer and neuroblastoma. These small proteins contain two protein-interacting LIM domains but little additional sequence, and they seem to function by nucleating the formation of new transcriptional complexes and/or by disrupting existing transcriptional complexes to modulate gene expression programmes. Through these activities, the LMO proteins have important cellular roles in processes that are relevant to cancer such as self-renewal, cell cycle regulation and metastasis. These functions highlight the therapeutic potential of targeting these proteins in cancer.