Notch1 and IL-7 receptor signalling in early T-cell development and leukaemia

Progression of Notch signaling regulation of B cells under radiation exposure

With the continuous development of nuclear technology, the radiation exposure caused by radiation therapy is a serious health hazard. It is of great significance to further develop effective radiation countermeasures. B cells easily succumb to irradiation exposure along with immunosuppressive response. The approach to ameliorate radiation-induced B cell damage is rarely studied, implying that the underlying mechanisms of B cell damage after exposure are eager to be revealed. Recent studies suggest that Notch signaling plays an important role in B cell-mediated immune response. Notch signaling is a critical regulator for B cells to maintain immune function. Although accumulating studies reported that Notch signaling contributes to the functionality of hematopoietic stem cells and T cells, its role in B cells is scarcely appreciated. Presently, we discussed the regulation of Notch signaling on B cells under radiation exposure to provide a scientific basis to prevent radiation-induced B cell damage.

The Notch1 signaling pathway directly modulates the human RANKL-induced osteoclastogenesis

Notch signaling is an evolutionary conserved pathway with a key role in tissue homeostasis, differentiation and proliferation. It was reported that Notch1 receptor negatively regulates mouse osteoclast development and formation by inhibiting the expression of macrophage colony-stimulating factor in mesenchymal cells. Nonetheless, the involvement of Notch1 pathway in the generation of human osteoclasts is still controversial. Here, we report that the constitutive activation of Notch1 signaling induced a differentiation block in human mononuclear CD14+ cells directly isolated from peripheral blood mononuclear cells (PBMCs) upon in vitro stimulation to osteoclasts. Additionally, using a combined approach of single-cell RNA sequencing (scRNA-Seq) simultaneously with a panel of 31 oligo-conjugated antibodies against cell surface markers (AbSeq assay) as well as unsupervised learning methods, we detected four different cell stages of human RANKL-induced osteoclastogenesis after 5 days in which Notch1 signaling enforces the cell expansion of specific subsets. These cell populations were characterized by distinct gene expression and immunophenotypic profiles and active Notch1, JAK/STAT and WNT signaling pathways. Furthermore, cell-cell communication analyses revealed extrinsic modulators of osteoclast progenitors including the IL7/IL7R and WNT5a/RYK axes. Interestingly, we also report that Interleukin-7 receptor (IL7R) was a downstream effector of Notch1 pathway and that Notch1 and IL7R interplay promoted cell expansion of human RANKL-induced osteoclast progenitors. Taken together, these findings underline a novel cell pattern of human osteoclastogenesis, outlining the key role of Notch1 and IL-7R signaling pathways.

Ectopic expression of a combination of 5 genes detects high risk forms of T-cell acute lymphoblastic leukemia

BACKGROUND

T cell acute lymphoblastic leukemia (T-ALL) defines a group of hematological malignancies with heterogeneous aggressiveness and highly variable outcome, making therapeutic decisions a challenging task. We tried to discover new predictive model for T-ALL before treatment by using a specific pipeline designed to discover aberrantly active gene.

RESULTS

The expression of 18 genes was significantly associated with shorter survival, including ACTRT2, GOT1L1, SPATA45, TOPAZ1 and ZPBP (5-GEC), which were used as a basis to design a prognostic classifier for T-ALL patients. The molecular characterization of the 5-GEC positive T-ALL unveiled specific characteristics inherent to the most aggressive T leukemic cells, including a drastic shut-down of genes located on the mitochondrial genome and an upregulation of histone genes, the latter characterizing high risk forms in adult patients. These cases fail to respond to the induction treatment, since 5-GEC either predicted positive minimal residual disease (MRD) or a short-term relapse in MRD negative patients.

CONCLUSION

Overall, our investigations led to the discovery of a homogenous group of leukemic cells with profound alterations of their biology. It also resulted in an accurate predictive tool that could significantly improve the management of T-ALL patients.

Signaling Crosstalks Drive Generation and Regeneration of the Thymus

Optimal recovery of immune competence after periods of hematopoietic insults or stress is crucial to re-establish patient response to vaccines, pathogens and tumor antigens. This is particularly relevant for patients receiving high doses of chemotherapy or radiotherapy, who experience prolonged periods of lymphopenia, which can be associated with an increased risk of infections, malignant relapse, and adverse clinical outcome. While the thymus represents the primary organ responsible for the generation of a diverse pool of T cells, its function is profoundly impaired by a range of acute insults (including those caused by cytoreductive chemo/radiation therapy, infections and graft-versus-host disease) and by the chronic physiological deterioration associated with aging. Impaired thymic function increases the risk of infections and tumor antigen escape due to a restriction in T-cell receptor diversity and suboptimal immune response. Therapeutic approaches that can promote the renewal of the thymus have the potential to restore immune competence in patients. Previous work has documented the importance of the crosstalk between thymocytes and thymic epithelial cells in establishing correct architecture and function of thymic epithelium. This crosstalk is relevant not only during thymus organogenesis, but also to promote the recovery of its function after injuries. In this review, we will analyze the signals involved in the crosstalk between TECs and hematopoietic cells. We will focus in particular on how signals from T-cells can regulate TEC function and discuss the relevance of these pathways in restoring thymic function and T-cell immunity in experimental models, as well as in the clinical setting.

Immunopathogenesis and immunogenetic variants in COVID-19

Abstract:

Coronavirus disease 2019 (COVID-19) continues to spread globally despite the discovery of vaccines. Many people die due to COVID-19 as a result of catastrophic consequences, such as acute respiratory distress syndrome, pulmonary embolism, and disseminated intravascular coagulation caused by a cytokine storm. Immunopathology and immunogenetic research may assist in diagnosing, predicting, and treating severe COVID-19 and the cytokine storm associated with COVID-19. This paper reviews the immunopathogenesis and immunogenetic variants that play a role in COVID-19. Although various immune-related genetic variants have been investigated in relation to severe COVID-19, the NOD-like receptor protein 3 (NLRP3) and interleukin 18 (IL-18) have not been assessed for their potential significance in the clinical outcome. Here, we a) summarize the current understanding of the immunogenetic etiology and pathophysiology of COVID-19 and the associated cytokine storm; and b) construct and analyze protein-protein interaction (PPI) networks (using enrichment and annotation analysis) based on the NLRP3 and IL18 variants and all genes, which were established in severe COVID-19. Our PPI network and enrichment analyses predict a) useful drug targets to prevent the onset of severe COVID-19 including key antiviral pathways such as Toll-Like-Receptor cascades, NOD-like receptor signaling, RIG-induction of interferon (IFN) α/β, and interleukin (IL)-1, IL-6, IL-12, IL-18, and tumor necrosis factor signaling; and b) SARS-CoV-2 innate immune evasion and the participation of MYD88 and MAVS in the pathophysiology of severe COVID-19. The PPI network genetic variants may be used to predict more severe COVID-19 outcomes, thereby opening the door for targeted preventive treatments.

Docosahexaenoic acid ester of phloridzin reduces inflammation and insulin resistance via AMPK

BACKGROUND

Docosahexaenoic acid-acylated phloridzin (PZ-DHA), a novel polyphenol fatty acid ester derivative, is synthesized through an acylation reaction of phloridzin (PZ) and docosahexaenoic acid (DHA). PZ-DHA is more stable than DHA and exhibits higher cellular uptake and bioavailability than PZ.

OBJECTIVE

To investigate the effects of PZ-DHA on insulin resistance in the skeletal muscle and the related mechanisms, we used palmitic acid (PA)-treated C2C12 myotubes as an insulin resistance model.

RESULTS

We found that PZ-DHA increased the activity of AMP-activated protein kinase (AMPK) and improved glucose uptake and mitochondrial function in an AMPK-dependent manner in untreated C2C12 myotubes. PZ-DHA treatment of the myotubes reversed PA-induced insulin resistance; this was indicated by increases in glucose uptake and the expression of membrane glucose transporter 4 (Glut4) and phosphorylated Akt. Moreover, PZ-DHA treatment reversed PA-induced inflammation and oxidative stress. These effects of PZ-DHA were mediated by AMPK. Furthermore, the increase in AMPK activity, improvement in insulin resistance, and decrease in inflammatory and oxidative responses after PZ-DHA treatment diminished upon co-treatment with a liver kinase B1 (LKB1) inhibitor, suggesting that PZ-DHA improved AMPK activity by regulating its upstream kinase, LKB1.

CONCLUSION

The effects of PZ-DHA on insulin resistance in C2C12 myotubes may be mediated by the LKB1-AMPK signaling pathway. Hence, PZ-DHA is a promising therapeutic agent for insulin resistance in type 2 diabetes.

Notch Signaling in the Bone Marrow Lymphopoietic Niche

Lifelong mammalian hematopoiesis requires continuous generation of mature blood cells that originate from Hematopoietic Stem and Progenitor Cells (HSPCs) situated in the post-natal Bone Marrow (BM). The BM microenvironment is inherently complex and extensive studies have been devoted to identifying the niche that maintains HSPC homeostasis and supports hematopoietic potential. The Notch signaling pathway is required for the emergence of the definitive Hematopoietic Stem Cell (HSC) during embryonic development, but its role in BM HSC homeostasis is convoluted. Recent work has begun to explore novel roles for the Notch signaling pathway in downstream progenitor populations. In this review, we will focus an important role for Notch signaling in the establishment of a T cell primed sub-population of Common Lymphoid Progenitors (CLPs). Given that its activation mechanism relies primarily on cell-to-cell contact, Notch signaling is an ideal means to investigate and define a novel BM lymphopoietic niche. We will discuss how new genetic model systems indicate a pre-thymic, BM-specific role for Notch activation in early T cell development and what this means to the paradigm of lymphoid lineage commitment. Lastly, we will examine how leukemic T-cell acute lymphoblastic leukemia (T-ALL) blasts take advantage of Notch and downstream lymphoid signals in the pathological BM niche.

HES1 and HES4 have non-redundant roles downstream of Notch during early human T-cell development

In both mouse and human, Notch1 activation is the main initial driver to induce T-cell development in hematopoietic progenitor cells. The initiation of this developmental process coincides with Notch1-dependent repression of differentiation towards other hematopoietic lineages. Although well described in mice, the role of the individual Notch1 target genes during these hematopoietic developmental choices is still unclear in human, particularly for HES4 since no orthologous gene is present in the mouse. Here, we investigated the functional capacity of the Notch1 target genes HES1 and HES4 to modulate human Notch1-dependent hematopoietic lineage decisions and their requirement during early T-cell development. We show that both genes are upregulated in a Notch-dependent manner during early T-cell development and that HES1 acts as a repressor of differentiation by maintaining a quiescent stem cell signature in CD34+ hematopoietic progenitor cells. While HES4 can also inhibit natural killer and myeloid cell development like HES1, it acts differently on the T- versus B-cell lineage choice. Surprisingly, HES4 is not capable of repressing B-cell development, the most sensitive hematopoietic lineage with respect to Notch-mediated repression. In contrast to HES1, HES4 promotes initiation of early T-cell development, but ectopic expression of HES4, or HES1 and HES4 combined, is not sufficient to induce T-lineage differentiation. Importantly, knockdown of HES1 or HES4 significantly reduces human T-cell development. Overall, we show that the Notch1 target genes HES1 and HES4 have non-redundant roles during early human T-cell development which may relate to differences in mediating Notch-dependent human hematopoietic lineage decisions.

Pazopanib and Trametinib as a Synergistic Strategy against Osteosarcoma: Preclinical Activity and Molecular Insights

Receptor tyrosine kinases (RTKs) inhibitors’ activity in advanced osteosarcoma is significant but short-lived. To prevent or at least delay drug resistance, we explored a vertical inhibition by combining drugs acting at different levels of the RTK pathways (pazopanib + trametinib). We studied pazopanib + trametinib antitumor activity both in vitro and in vivo (MNNG-HOS and KHOS xenografts in NOD/SCID mice) investigating the molecular mechanisms and potential escapes. The involvement of MAPK-PI3K pathways was validated by Nanostring technology, western blot and by silencing/overexpression experiments. Pazopanib targets were expressed on seven osteosarcoma cell lines and their pathways were activated. Pazopanib + trametinib exhibited synergistic antitumor activity by inducing apoptosis and inhibiting ERK1/2 and Akt. In vivo antitumor activity was shown in osteosarcoma-bearing mice. The drug combination significantly down-modulated RTK Ephrin Type-A Receptor 2 (EphA2) and Interleukin-7 Receptor (IL-7R), whereas induced mitogen-activated protein-kinase kinase (MAPKK) MEK6. EphA2 silencing significantly reduced osteosarcoma cell proliferation and migration, while impeding MEK6 up-regulation in the treated cells significantly increased the antitumor effect of the studied drugs. Moreover, the up-regulation of MEK6 reduced combination activity. Pazopanib + trametinib demonstrated synergistic antitumor effects in osteosarcoma models through ERK and Akt inhibition and EphA2 and IL-7R down-modulation. MEK6 up-regulation might evoke escaping mechanism.

Bone marrow-derived mesenchymal stromal cells promote resistance to tyrosine kinase inhibitors in chronic myeloid leukemia via the IL-7/JAK1/STAT5 pathway

Chronic myeloid leukemia (CML) is caused by the fusion of the BCR activator of RhoGEF and GTPase activating protein (BCR) and ABL proto-oncogene, the nonreceptor tyrosine kinase (ABL) genes. Although the tyrosine kinase inhibitors (TKIs) imatinib (IM) and nilotinib (NI) have remarkable efficacy in managing CML, the malignancies in some patients become TKI-resistant. Here, we isolated bone marrow (BM)-derived mesenchymal stem cells (MSCs) from several CML patients by Ficoll-Hypaque density-gradient centrifugation for coculture with K562 and BV173 cells with or without TKIs. We used real-time quantitative PCR to assess the level of interleukin 7 (IL-7) expression in the MSCs and employed immunoblotting to monitor protein expression in the BCR/ABL, phosphatidylinositol 3-kinase (PI3K)/AKT, and JAK/STAT signaling pathways. We also used a xenograft tumor model to examine the in vivo effect of different MSCs on CML cells. MSCs from patients with IM-resistant CML protected K562 and BV173 cells against IM- or NI-induced cell death, and this protection was due to increased IL-7 secretion from the MSCs. Moreover, IL-7 levels in the BM of patients with IM-resistant CML were significantly higher than in healthy donors or IM-sensitive CML patients. IL-7 elicited IM and NI resistance via BCR/ABL-independent activation of JAK1/STAT5 signaling, but not of JAK3/STAT5 or PI3K/AKT signaling. IL-7 or JAK1 gene knockdown abrogated IL-7-mediated STAT5 phosphorylation and IM resistance in vitro and in vivo Because high IL-7 levels in the BM mediate TKI resistance via BCR/ABL-independent activation of JAK1/STAT5 signaling, combining TKIs with IL-7/JAK1/STAT5 inhibition may have significant utility for managing CML.

The Profile of Immunophenotype and Genotype Aberrations in Subsets of Pediatric T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a biologically heterogeneous malignancy, which reflects distinctive stages of T-cell differentiation arrest. We have revisited a cohort of pediatric T-ALL, in order to test if immunophenotypes associated with molecular alterations would predict the patient's outcome. Genetic mutations, translocations and copy number alterations were identified through Sanger sequencing, RT-PCR, FISH and multiplex ligation-dependent probe amplification (MLPA). We defined 8 immunophenotypic T-ALL subtypes through multiparametric flow cytometry: early T-cell precursor (ETP, n = 27), immature (n = 38), early cortical (n = 15), cortical (n = 50), late cortical (n = 53), CD4/CD8 double negative mature (n = 31), double positive mature (n = 35) and simple positive mature (n = 31) T-ALL. Deletions (del) or amplifications (amp) in at least one gene were observed in 87% of cases. The most frequent gene alterations were CDKN2A/B^del (71.4%), NOTCH1^mut (47.6%) and FBXW7^mut (17%). ETP-ALL had frequent FLT3^mut (22.2%) and SUZ12^del (16.7%) (p < 0.001), while CDKN2A/B^del were rarely found in this subtype (p < 0.001). The early cortical T-ALL subtype had high frequencies of NOTCH1^mut and IL7R^mut (71%, 28.6%, respectively), whereas, mature T-ALL with double positive CD4/CD8 had the highest frequencies of STIL-TAL1 (36.7%), LEF1^del (27.3%) and CASP8AP2^del (22.7%). The co-existence of two groups of T-ALL with NOTCH1^mut/IL7R^mut, and with TLX3/SUZ12^del/NF1^del/IL7R^mut, were characterized with statistical significance (p < 0.05) but only STIL-TAL1 (pOS 47.5%) and NOTCH1^WT/FBXW7^WT (pOS 55.3%) are predictors of poor T-ALL outcomes. In conclusion, we have observed that 8 T-ALL subgroups are characterized by distinct molecular profiles. The mutations in NOTCH1/FBXW7 and STIL-TAL1 rearrangement had a prognostic impact, independent of immunophenotype.

Opinion: Virtual memory CD8 T cells and lymphopenia-induced memory CD8 T cells represent a single subset: Homeostatic memory T cells

It is well established that lymphopenia induces the formation of the memory-phenotype T cells without the exposure to foreign antigens. More recently, the memory-phenotype antigen-inexperienced memory T cells were described in lymphoreplete mice and called virtual memory T cells. In this review, we compare multiple aspects of the biology of lymphopenia-induced memory T cells and virtual memory T cells, including cytokine requirements, the role of T-cell receptor specificity in the differentiation process, gene expression signature, and the immune response. Based on this comparison, we conclude that lymphopenia-induced memory T cells and virtual memory T cells most likely represent a single T-cell subset, for which we propose a term 'homeostatic memory T cells'.

Therapeutic Targeting of mTOR in T-Cell Acute Lymphoblastic Leukemia: An Update

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive blood malignancy that arises from the clonal expansion of transformed T-cell precursors. Although T-ALL prognosis has significantly improved due to the development of intensive chemotherapeutic protocols, primary drug-resistant and relapsed patients still display a dismal outcome. In addition, lifelong irreversible late effects from conventional therapy are a growing problem for leukemia survivors. Therefore, novel targeted therapies are required to improve the prognosis of high-risk patients. The mechanistic target of rapamycin (mTOR) is the kinase subunit of two structurally and functionally distinct multiprotein complexes, which are referred to as mTOR complex 1 (mTORC1) and mTORC2. These two complexes regulate a variety of physiological cellular processes including protein, lipid, and nucleotide synthesis, as well as autophagy in response to external cues. However, mTOR activity is frequently deregulated in cancer, where it plays a key oncogenetic role driving tumor cell proliferation, survival, metabolic transformation, and metastatic potential. Promising preclinical studies using mTOR inhibitors have demonstrated efficacy in many human cancer types, including T-ALL. Here, we highlight our current knowledge of mTOR signaling and inhibitors in T-ALL, with an emphasis on emerging evidence of the superior efficacy of combinations consisting of mTOR inhibitors and either traditional or targeted therapeutics.

Knockout of zebrafish interleukin 7 receptor (IL7R) by the CRISPR/Cas9 system delays retinal neurodevelopment

Interleukin 7 receptor (il7r), a transmembrane receptor, belongs to the type I cytokine receptor family. Il7r is involved in the pathogenesis of neurodegenerative disorders, such as multiple sclerosis. Targeted knockdown of il7r leads to delayed myelination, highlighting the potential role of il7r in the development of the nervous system. Zebrafish is an ideal model for the study of neurogenesis; moreover, the il7r gene is highly conserved between zebrafish and human. The aim of the present study was to investigate the novel function of il7r in neurogenesis. First, an il7r^−/− homozygous mutant line was generated by clustered regularly interspaced short palindromic repeats (CRISPR)-associated 9 (CRISPR/Cas9) technology. Second, the gross development of il7r^−/− mutants revealed remarkably smaller eyes and delayed retinal neurodifferentiation. Third, microarray analysis revealed that genes associated with the phototransduction signalling pathway were strongly down-regulated in il7r^−/− mutants. Finally, the results from behavioural tests indicated that visual function was impaired in il7r^−/− mutant larvae. Overall, our data demonstrate that a lack of il7r retards the development of the retina. Thus, il7r is an essential molecule for maintaining normal retinal development in zebrafish.

The common oncogenomic program of NOTCH1 and NOTCH3 signaling in T-cell acute lymphoblastic leukemia

Notch is a major oncogenic driver in T cell acute lymphoblastic leukemia (T-ALL), in part because it binds to an enhancer that increases expression of MYC. Here, we exploit the capacity of activated NOTCH1 and NOTCH3 to induce T-ALL, despite substantial divergence in their intracellular regions, as a means to elucidate a broad, common Notch-dependent oncogenomic program through systematic comparison of the transcriptomes and Notch-bound genomic regulatory elements of NOTCH1- and NOTCH3-dependent T-ALL cells. ChIP-seq studies show a high concordance of functional NOTCH1 and NOTCH3 genomic binding sites that are enriched in binding motifs for RBPJ, the transcription factor that recruits activated Notch to DNA. The interchangeability of NOTCH1 and NOTCH3 was confirmed by rescue of NOTCH1-dependent T-ALL cells with activated NOTCH3 and vice versa. Despite remarkable overall similarity, there are nuanced differences in chromatin landscapes near critical common Notch target genes, most notably at a Notch-dependent enhancer that regulates MYC, which correlates with responsiveness to Notch pathway inhibitors. Overall, a common oncogenomic program driven by binding of either Notch is sufficient to maintain T-ALL cell growth, whereas cell-context specific differences appear to influence the response of T-ALL cells to Notch inhibition.

Transcriptional regulation of the IL-7Rα gene by dexamethasone and IL-7 in primary human CD8 T cells

Interleukin-7 is essential for the development and maintenance of T cells, and the expression of the IL-7 receptor is tightly regulated at every stage of the T cell's lifespan. In mature CD8 T cells, IL-7 plays important roles in cell survival, peripheral homeostasis, and cytolytic function. The IL-7 receptor alpha-chain (CD127) is expressed at high levels on naïve and memory cells, but it is rapidly downregulated upon IL-7 stimulation. In this study, we illustrate the dynamicity of the CD127 promoter and show that it possesses positive as well as negative regulatory sites involved in upregulating and downregulating CD127 expression, respectively. We cloned the CD127 gene promoter and identified key cis-regulatory elements required for CD127 expression in mature resting primary CD8 T cells. The core promoter necessary for efficient basal transcription is contained within the first 262 bp upstream of the TATA box. Additional positive regulatory elements are located between -1200 and -2406 bp, conferring a further 2- to 4-fold enhancement in gene expression. While transcription of the CD127 gene is increased directly through a glucocorticoid response element located between -2255 and -2269 bp upstream of the TATA box, we identified a suppressive region that lies upstream of 1760 bp from the TATA box, which is likely involved in the IL-7-mediated suppression of CD127 transcription. Finally, we illustrated IL-7 does not bias alternative splicing of CD127 transcripts in primary human CD8 T cells.

IL-18 acts in synergy with IL-7 to promote ex vivo expansion of T lymphoid progenitor cells

Although IL-18 has not previously been shown to promote T lymphopoiesis, results obtained via a novel data mining algorithm (global microarray meta-analysis) led us to explore a predicted role for this cytokine in T cell development. IL-18 is a member of the IL-1 cytokine family that has been extensively characterized as a mediator of inflammatory immune responses. To assess a potential role for IL-18 in T cell development, we sort-purified mouse bone marrow-derived common lymphoid progenitor cells, early thymic progenitors (ETPs), and double-negative 2 thymocytes and cultured these populations on OP9-Delta-like 4 stromal layers in the presence or absence of IL-18 and/or IL-7. After 1 wk of culture, IL-18 promoted proliferation and accelerated differentiation of ETPs to the double-negative 3 stage, similar in efficiency to IL-7. IL-18 showed synergy with IL-7 and enhanced proliferation of both the thymus-derived progenitor cells and the bone marrow-derived common lymphoid progenitor cells. The synergistic effect on the ETP population was further characterized and found to correlate with increased surface expression of c-Kit and IL-7 receptors on the IL-18-treated cells. In summary, we successfully validated the global microarray meta-analysis prediction that IL-18 affects T lymphopoiesis and demonstrated that IL-18 can positively impact bone marrow lymphopoiesis and T cell development, presumably via interaction with the c-Kit and IL-7 signaling axis.

Transcriptome analysis reveals the contribution of thermal and the specific effects in cellular response to millimeter wave exposure

Radiofrequency radiations constitute a new form of environmental pollution. Among them, millimeter waves (MMW) will be widely used in the near future for high speed communication systems. This study aimed therefore to evaluate the biocompatibility of MMW at 60 GHz. For this purpose, we used a whole gene expression approach to assess the effect of acute 60 GHz exposure on primary cultures of human keratinocytes. Controls were performed to dissociate the electromagnetic from the thermal effect of MMW. Microarray data were validated by RT-PCR, in order to ensure the reproducibility of the results. MMW exposure at 20 mW/cm², corresponding to the maximum incident power density authorized for public use (local exposure averaged over 1 cm²), led to an increase of temperature and to a strong modification of keratinocyte gene expression (665 genes differentially expressed). Nevertheless, when temperature is artificially maintained constant, no modification in gene expression was observed after MMW exposure. However, a heat shock control did not mimic exactly the MMW effect, suggesting a slight but specific electromagnetic effect under hyperthermia conditions (34 genes differentially expressed). By RT-PCR, we analyzed the time course of the transcriptomic response and 7 genes have been validated as differentially expressed: ADAMTS6, NOG, IL7R, FADD, JUNB, SNAI2 and HIST1H1A. Our data evidenced a specific electromagnetic effect of MMW, which is associated to the cellular response to hyperthermia. This study raises the question of co-exposures associating radiofrequencies and other environmental sources of cellular stress.

NOTCH1-RBPJ complexes drive target gene expression through dynamic interactions with superenhancers

The main oncogenic driver in T-lymphoblastic leukemia is NOTCH1, which activates genes by forming chromatin-associated Notch transcription complexes. Gamma-secretase-inhibitor treatment prevents NOTCH1 nuclear localization, but most genes with NOTCH1-binding sites are insensitive to gamma-secretase inhibitors. Here, we demonstrate that fewer than 10% of NOTCH1-binding sites show dynamic changes in NOTCH1 occupancy when T-lymphoblastic leukemia cells are toggled between the Notch-on and -off states with gamma-secretase inhibiters. Dynamic NOTCH1 sites are functional, being highly associated with Notch target genes, are located mainly in distal enhancers, and frequently overlap with RUNX1 binding. In line with the latter association, we show that expression of IL7R, a gene with key roles in normal T-cell development and in T-lymphoblastic leukemia, is coordinately regulated by Runx factors and dynamic NOTCH1 binding to distal enhancers. Like IL7R, most Notch target genes and associated dynamic NOTCH1-binding sites cooccupy chromatin domains defined by constitutive binding of CCCTC binding factor, which appears to restrict the regulatory potential of dynamic NOTCH1 sites. More remarkably, the majority of dynamic NOTCH1 sites lie in superenhancers, distal elements with exceptionally broad and high levels of H3K27ac. Changes in Notch occupancy produces dynamic alterations in H3K27ac levels across the entire breadth of superenhancers and in the promoters of Notch target genes. These findings link regulation of superenhancer function to NOTCH1, a master regulatory factor and potent oncoprotein in the context of immature T cells, and delineate a generally applicable roadmap for identifying functional Notch sites in cellular genomes.