T-cell Acute Lymphoblastic Leukemia Cell Growth Research Articles

Suppression of Super-Enhancer-Driven TAL1 Expression By KLF4 in T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy characterized by differentiation arrest and clonal proliferation of immature thymocytes. Many oncogenes in T-ALL are genes encoding transcription factors. TAL bHLH transcription factor 1 ( TAL1) is one of the most frequently dysregulated transcription factors in T-ALL and is ectopically overexpressed in approximately 50% of T-ALL cases, owing to chromosome translocations, SIL (SCL-interrupting locus) -TAL1 fusion, and 5‘ super-enhancer (SE)-generating mutations. TAL1 overexpression caused by 5‘ TAL1 SE is found in 5% of patients with T-ALL and is associated with unfavorable clinical outcomes. However, no clinically available drugs specifically inhibit TAL1 or TAL1 SE components. Kruppel-like factor 4 (KLF4) is a member of the KLF family of transcription factors that exhibits both oncogenic and tumor-suppressive functions in a context-dependent manner. In T-cell malignancies, KLF4 is regarded as a tumor suppressor because KLF4 expression is silenced by promoter methylation, and the induction of KLF4 promotes apoptosis through the BCL-2/BCL-XL pathway. However, whether KLF4 affects the expression of T-ALL-related transcription factors remains unclear. We first analyzed three independent previously reported microarray datasets to explore the essential downstream targets of KLF4 in T-ALL cells. The following groups of genes were extracted: genes upregulated in patients with T-ALL compared to normal thymocytes (GSE46170), genes upregulated in Klf4-deficient T-ALL mice (GSE75663), and genes downregulated in KLF4-overexpressing human T-ALL cells (Li W et al. Mol. Cancer. 2015). Overlapping genes in these groups were identified as potential downstream targets of KLF4. Among these, we focused on TAL1, a well-known oncogenic transcription factor gene in T-ALL. We performed a functional analysis of KLF4 using TAL1-positive T-ALL cell lines (Jurkat, MOLT-3, CCRF-CEM, and RPMI-8402). Genetic induction of KLF4 showed stronger anti-leukemic effects in Jurkat and MOLT-3 cells, 5‘ TAL1 SE-positive T-ALL cell lines, compared with CCRF-CEM and RPMI-8402 cells, SIL-TAL1-positive T-ALL cell lines. KLF4 overexpression significantly reduced mRNA expression levels of TAL1 in Jurkat and MOLT-3 cells but not in CCRF-CEM and RPMI-8402 cells. Thus, we hypothesized that KLF4 specifically suppressed SE-driven TAL1 expression by impairing mutated TAL1 enhancer activity. The luciferase reporter assay confirmed that the activity of the mutated TAL1 enhancer was significantly reduced by the exogenous expression of KLF4, whereas that of the wild-type reporter was not affected. According to previous studies, mutations in TAL1 enhancers in Jurkat and MOLT-3 cells create MYB primary motifs, and MYB binding at this location is essential for the formation of 5‘ TAL1 SE. Therefore, we examined whether KLF4 represses MYB expression. The chromatin immunoprecipitation assay and qPCR analysis revealed that KLF4 bound to the proximal gene promoter of MYB and directly downregulated its expression. The luciferase reporter assay using the MYB promoter showed a significant reduction of reporter activity upon KLF4 overexpression. Finally, we investigated whether pharmacological induction of KLF4 using APTO-253, a small-molecule inducer ofKLF4, could control leukemia. APTO-253 inhibited the growth of all TAL1-positive T-ALL cell lines at nanomolar concentrations. The GI 50 values of APTO-253 for Jurkat and MOLT-3 cells were lower than those for CCRF-CEM and RPMI-8402 cells, which was consistent with the KLF4-overexpression-induced growth inhibition of T-ALL cell lines. APTO-253 induced KLF4 expression and decreased TAL1 and MYB expression in Jurkat and MOLT-3 cells. Furthermore, exogenous MYB expression rescued growth inhibition by APTO-253. Collectively, these results indicated that APTO-253 suppressed the growth of T-ALL cells by targeting SE-driven TAL1 expression via the induction of KLF4. In summary, we revealed that KLF4 suppressed SE-driven TAL1 expression via the direct inhibition of MYB. Moreover, pharmacological induction of KLF4 demonstrated anti-leukemic activity in T-ALL cells. These findings propose a promising strategy for patients with T-ALL and 5' TAL1 SE.

Super Enhancer Regulatory Gene FYB1 Promotes the Progression of T Cell Acute Lymphoblastic Leukemia by Activating IGLL1.

Arising from T progenitor cells, T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignant tumor, accounting for 15% of childhood ALL and 25% of adult ALL. Composing of putative enhancers in close genomic proximity, super enhancer (SE) is critical for cell identity and the pathogenesis of multiple cancers. Belonging to the cytosolute linker protein group, FYB1 is essential for TCR signaling and extensively studied in terms of tumor pathogenesis and metastasis. Dissecting the role of FYN binding protein 1 (FYB1) in T-ALL holds the potential to improve the treatment outcome and prognosis of T-ALL. In this study, SEs were explored using public H3K27ac ChIP-seq data derived from T-ALL cell lines, AML cell lines and hematopoietic stem and progenitor cells (HSPCs). Downstream target of FYB1 gene was identified by RNA-seq. Effects of shRNA-mediated downregulation of FYB1 and immunoglobulin lambda-like polypeptide 1 (IGLL1) on self-renewal of T-ALL cells were evaluated in vitro and/or in vivo. As an SE-driven gene, overexpression of FYB1 was observed in T-ALL, according to the Cancer Cell Line Encyclopedia database. In vitro, knocking down FYB1 led to comprised growth and enhanced apoptosis of T-ALL cells. In vivo, downregulation of FYB1 significantly decreased the disease burden by suppressing tumor growth and improved survival rate. Knocking down FYB1 resulted in significantly decreased expression of IGLL1 that was also an SE-driven gene in T-ALL. As a downstream target of FYB1, IGLL1 exerted similar role as FYB1 in inhibiting growth of T-ALL cells. Our results suggested that FYB1 gene played important role in regulating self-renewal of T-ALL cells by activating IGLL1, representing a promising therapeutic target for T-ALL patients.

Effect of siRNA-mediated silencing of p53R2 gene on sensitivity of T-ALL cellsto Daunorubicin

Introductionp53R2 is a p53-inducible protein that, as one of the subunits of ribonucleotide reductase, plays an important role in providing dNTPs for DNA repair. Although p53R2 is associated with cancer progression, its role in T-cell acute lymphoblastic leukemia (T-ALL) cells is unknown. Therefore, in this study, we evaluated the effect of p53R2 silencing on double-stranded DNA breaks, apoptosis and cell cycle of T-ALL cells treated with Daunorubicin. MethodsTransfection was performed using Polyethyleneimine (PEI). Gene expression was measured using real-time PCR and protein expression was evaluated using Western blotting. Cell metabolic activity and IC50 were calculated using MTT assay, formation of double-stranded DNA breaks was checked using immunohistochemistry for γH2AX, and cell cycle and apoptosis were evaluated using flow cytometry. ResultsWe found that p53 silencing synergistically inhibited the growth of T-ALL cells by Daunorubicin. p53R2 siRNA in combination with Daunorubicin but not alone increases the rate of DNA double-strand breaks in T-ALL cells. In addition, p53R2 siRNA significantly increased Daunorubicin-induced apoptosis. p53R2 siRNA also caused a non-significant increase in cells in G2 phase. ConclusionThe results of the present study showed that silencing of p53R2 using siRNA can significantly increase the antitumor effects of Daunorubicin on T-ALL cells. Therefore, p53R2 siRNA has the potential to be used as an adjuvant therapy in combination with Daunorubicin in T-ALL.

P332: MIR-625-5P IS NOVEL CANDIDATE ONCOMIR IN T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA IMPLICATED IN REGULATION OF APOPTOSIS VIA REPRESSION OF HARAKIRI

Background: T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive subtype of ALL, arising from T-cell precursors. miRNAs are non-coding RNAs, contributing to leukemogenesis by involvement in key cellular functions such as proliferation, apoptosis, and signaling. We previously found in miRNA transcriptome analysis that miR-625-5p is overexpressed in T-ALL patients, thus is a potential oncomiR in T-ALL. Here, we confirm the implication of miR-625-5p in the regulation of apoptosis in T-ALL cells in vitro. We show that it acts via repression of HARAKIRI (HRK). HRK was originally identified as a proapoptotic gene induced by reduced levels of cytokine in hematopoietic cells and repressed by the expression of death-repressor proteins. Although its proapoptotic function is well described, little is known about the post-transcriptional mechanisms that may participate in HRK inactivation. Aims: The aim of this study was to investigate the mechanism of miR-625-5p oncogenic action via unraveling its targetome and functional effects in T-ALL in vitro. Methods: T-ALL JURKAT cells (with high endogenous miR-625-5p level) were transduced for stable inhibition of this miRNA. To evaluate the influence of miR inhibition on growth of T-ALL cells, we used flow cytometry GFP competition assay and CCK8 proliferation assay. To identify the genes mediating the effect of miR-625-5p, we subjected JURKAT cells to Ago2-RIP-seq. We used magnetic beads coated with anti-AGO2 antibody to immunoprecipitate RNA bound to RISC complexes. Ago2-IP and total RNA fractions were sequenced (polyA RNA-seq, 150 bp reads, 60M PE reads/sample, Illumina NovaSeq 6000). Transcripts depleted in Ago2-IP fraction upon miR inhibition were screened for the presence of miR-625-5p binding sites. Luciferase assay was performed to confirm direct interaction between hsa-miR-625-5p and 3’UTR of HRK gene. The changes of HRK protein level upon miR-625-5p inhibition were evaluated via Western Blot. To estimate the apoptosis rate in T-ALL cells we used two flow cytometry assays based on Annexin V and Caspase 3/7 staining. Results: Inhibition of miR-625-5p decreased the growth of JURKAT cells. In RIP-seq analysis we identified 384 transcripts depleted in RISC by at least 20% upon miR-625-5p inhibition and having at least one putative 3’UTR binding site for this miRNA. Overrepresentation analysis performed for these genes indicated their involvement in the apoptotic process. Among transcripts depleted in RIP-seq with predicted binding sites for miR-625-5p, we found HRK gene, previously reported to have proapoptotic activity. We postulate that repression of this gene by overexpressed miR-625-5p contributes to decreased apoptosis and to growth advantage of T-ALL cells. To further confirm that miR-625-5p affects growth of T-ALL cells via negative regulation of apoptosis, we performed apoptotic assays in JURKAT cells and showed that inhibition of this miRNA increased apoptosis rate, in line with our hypothesis on the oncogenic potential of miR-625-5p. We confirmed the direct interaction between miR-625-5p and HRK 3’UTR by luciferase assay. Additionally, in Western blot a subtle (approaching statistical significance) increase of HRK protein upon miR-625-5p inhibition was observed, supporting our notion that this miRNA is indeed a negative regulator of HRK. Image:Summary/Conclusion: miR-625-5p is a novel candidate oncogenic miRNA in T-ALL, implicated in the negative regulation of apoptosis. Post-transcriptional repression of the proapoptotic HRK gene is a putative mechanism contributing to oncogenic properties of this miRNA when overexpressed in T-ALL cells.

CircFBXW7 inhibits the tumorigenesis of T-cell acute lymphoblastic leukemia through modulating miR-494-3p/SOX1 axis

T-cell acute lymphoblastic leukemia (T-ALL) is a type of leukemia with high malignant behaviors, which seriously threatens the health of people. It has been reported that circFBXW7 is downregulated in lymphoblastic leukemia. Nevertheless, the exact role of circFBXW7 in T-ALL remains elusive. MTT assay was used to assess the cell viability. Cell apoptosis was assessed by flow cytometry. In addition, mRNA expressions were assessed by RT-qPCR, and a western blot was applied to investigate the protein levels. Meanwhile, the correlation among circFBXW7, miR-494-3p, and SOX1 was explored by RNA pull-down and dual-luciferase reporter assays. Furthermore, a xenograft mice model was conducted to verify the function of circFBXW7 in T-ALL in vivo. CircFBXW7 was significantly downregulated in T-ALL, of which overexpression inhibited the cell viability and induced the apoptosis of Jurkat cells. Moreover, miR-494-3p was identified to be a functional downstream effector to be involved in circFBXW7-mediated T-ALL cell proliferation. Besides, SOX1 was a direct target of miR-494-3p, and the impact of miR-494-3p mimics on T-ALL cell growth was inhibited in the presence of SOX1 overexpression. Furthermore, overexpression of circFBXW7 dramatically inhibited T-ALL tumor growth. In summary, circFBXW7 attenuated the tumorigenesis of T-ALL through the mediation of the miR-494-3p/SOX1 axis, which might be novel targets for T-ALL treatment.

Novel Compound, ND-17, Regulates the JAK/STAT, PI3K/AKT, and MAPK Pathways and Restrains Human T-lymphoid Leukemia Development.

T cell acute lymphoblastic leukemia (T-ALL) is an invasive hematological malignant disorder of T cell progenitors. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway plays an important role in the development of T-ALL and in the inhibition of the key molecule, JAK2, and could suppress T-ALL cell proliferation. The objective of this study was to investigate the in vitro anti-tumor effects of a novel nilotinib derivative, ND-17, on cancer cell lines via its interactions with JAK2. The effects of ND-17 on cell proliferation and on cell cycle and apoptosis were evaluated using the tetrazolium assay and flow cytometry, respectively. In addition, the ND-17/JAK2 binding interactions were evaluated using surface plasmon resonance and western blot analyses. ND-17 exerted the greatest inhibitory effects on T-ALL cells amongst all hematological cancer cell lines tested. Flow cytometric analysis indicated that ND-17 blocked the cell cycle at the S phase in T-ALL cells. Nilotinib did not significantly inhibit T-ALL cell growth or regulate the cell cycle. Preliminary investigations revealed that the regulation of cyclin-dependent kinases/cyclins was attributed to ND-17-induced cell cycle arrest. Furthermore, ND-17 could bind to JAK2 with strong affinity, and more importantly, ND-17 bound to the ATP pocket of JAK2 in a manner similar to the potent inhibitor. Thus, ND-17 treatment exhibited a prominent effect in inhibiting the phosphorylation of JAK2 in T-ALL cells. An increase in the phosphorylation of JAK2 was observed in interleukin-6- stimulated Jurkat cells, which was reversed by ND-17 treatment. Meanwhile, the combination of TG- 101348 and ND-17 led to further improvement in inhibiting the phosphorylation of JAK2. Moreover, the transfection and knockdown of JAK2 altered the inhibitory effect of ND-17 on Jurkat cell viability. In addition, ND-17 treatment suppressed the JAK/STAT, phosphatidylinositol-3-kinase/protein kinase B/mechanistic target of rapamycin, and mitogen-activated protein kinase/extracellular signal-regulated protein kinases 1 and 2 signaling pathways. These findings suggest that ND-17 could be a promising JAK2 inhibitor for the treatment of T-ALL.

Upregulation of leukemia-induced non-coding activator RNA (LUNAR1) predicts poor outcome in pediatric T-acute lymphoblastic leukemia

T-cell Acute Lymphoblastic Leukemia (T-ALL) accounts for around 10–15% of all lymphoblastic leukemia in children. Previous studies have proven that dysregulation of Leukemia-induced non-coding activator RNA-1 (LUNAR1) expression promotes T-ALL cell growth by enhancing the NOTCH1/IGF-1R signaling pathway. We aimed to investigate the prognostic value of LUNAR1 in pediatric T-ALL, in addition, to find out its association with NOTCH1 and IGF-1R. The LUNAR1, NOTCH1, and IGF-IR gene expression were measured in peripheral blood (PB) samples of l85 children with T-ALL and forty non-leukemic samples as a control group. Cox regression analysis revealed that overexpression of LUNAR1, NOTCH1, and IGF-IR was significantly correlated with poor prognosis, short overall survival, and progression-free survival. We concluded that LUNAR1 could serve as an independent prognostic biomarker for T-ALL in children.

CARMA1 is required for Notch1-induced NF-κB activation in SIL-TAL1-negative T cell acute lymphoblastic leukemia.

The NF-κB signaling pathway is an important downstream pathway of oncogenic Notch1 in T cell acute lymphoblastic leukemia (T-ALL) cells. However, the molecular mechanisms underlying the cascade activation of Notch1 in T-ALL cells are poorly understood. Here, we evaluated the role of CARMA1 in Notch1-induced NF-κB activation in T-ALL cells. CARMA1 was highly and specifically expressed in T-ALL cells and correlated with the prognosis of T-ALL patients. Interestingly, CARMA1 knockdown only inhibited the growth and proliferation of SIL-TAL1 fusion gene-negative T-ALL cells. In addition, CARMA1 knockdown arrested T-ALL cells at the G1 phase. Furthermore, CARMA1 knockdown significantly inhibited the proliferation of T-ALL cells in vivo and prolonged the survival of mice. Mechanistically, CARMA1 deficiency abolished Notch1-induced NF-κB transcriptional activation and significantly reduced expression levels of the NF-κB target genes c-Myc, Bcl-2, and CCR7. Taken together, these results of our study identify CARMA1 as one of the crucial mediators of Notch1-induced transformation of T-All cells, suggesting that CARMA1 is a promising therapeutic target for T-ALL due to its specific expression in lymphocytes. KEY MESSAGES: CARMA1 contributes to cell survival only in SIL-TAL1 negative T-ALL cells. CARMA1 is a crucial mediator of Notch1-induced activation of NF-κB pathway. CARMA1 is a promising therapeutic target for T-ALL.

ARID5B Activates the TAL1-Induced Core Regulatory Circuit and the MYC Oncogene in T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a malignant disorder characterized by the clonal proliferation of T-cell precursors. The most frequent molecular abnormality in T-ALL is the dysregulation of transcription factor genes, including the overexpression of TAL1/SCL . TAL1 induces a stem cell-like transcriptional regulatory program with its regulatory partners (RUNX1, GATA3 and MYB) in T-ALL cells. However, critical factors downstream of the TAL1 complex in T-ALL cells have not been fully characterized. Here, we performed RNA-seq analysis after genetic knockdown of TAL1 and each of its regulatory partners (E2A, HEB, LMO1, GATA3, RUNX1 and MYB) in a T-ALL cell line (Jurkat). We selected genes that were significantly downregulated after the knockdown of all these factors and were also directly bound by TAL1, HEB, GATA3, RUNX1 and MYB based on chromatin immunoprecipitation sequencing (ChIP-seq) analysis. We further filtered genes that were associated with “super-enhancers” based on the enrichment of histone H3 lysine 27 acetylation (H3K27ac). One of identified genes was ARID5B, which has not been previously implicated in T-ALL. ChIP-seq analysis showed DNA binding of the TAL1 transcriptional complex at a putative enhancer upstream of the ARID5B gene. A chromatin-chromatin interaction analysis by paired-end tag sequencing (ChIA-PET) for the cohesin protein demonstrated a cis-regulatory interaction between the putative enhancer and the ARID5B transcriptional start site. The ARID5B enhancer locus is associated with a super-enhancer in multiple T-ALL samples but not in normal thymus, suggesting that this gene is abnormally activated in T-ALL. The shRNA knockdown experiment showed that ARID5B is required for the survival and growth of T-ALL cells in vitro. Using ChIP-seq and RNA-seq analysis for ARID5B, we discovered that ARID5B frequently co-occupies its target genes with TAL1 and co-ordinately controls their expression. Notably, ARID5B positively regulates expression of TAL1 and its regulatory partners (GATA3, RUNX1 and MYB). Additionally, we identified that ARID5B directly binds to the MYC enhancer, which has previously been reported to be activated by NOTCH1 in T-ALL cells, and activates the expression of this oncogene. Finally, transgenic study using zebrafish model indicated that forced expression of ARID5B in immature thymocytes results in thymus retention, radio-resistance and tumor formation in zebrafish. Taken together, our results indicate that ARID5B reinforces the oncogenic transcriptional program by upregulating the core regulatory circuit, the extended circuitry and the MYC oncogene in T-ALL, thereby contributing to T-cell leukemogenesis. DisclosuresNo relevant conflicts of interest to declare.

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

AbstractResistance 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.

MALT1 Inhibition as a Therapeutic Strategy in T-Cell Acute Lymphoblastic Leukemia by Blocking Notch1-Induced NF-κB Activation.

Current treatment of T-cell acute lymphoblastic leukemia (T-ALL) is primarily based on high-intensity combination chemotherapy, which has serious side effects. Therefore, developments of novel targeted therapeutics are urgently needed for treatment of T-ALL. In this study, we found that mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a novel promising therapeutic target for treatment of T-ALL. MALT1 inhibitor MI-2 significantly suppressed the cell growth, proliferation, and colony formation of T-ALL cells. Furthermore, MI-2 induced cell apoptosis of T-ALL via a mitochondrial-dependent pathway. In a T-ALL mouse model, MI-2 significantly reduced leukemic burden and prolonged the survival of leukemia-bearing mice. Mechanistically, MALT1 inhibition effectively blocked both baseline and Notch1-induced activation of nuclear factor κB pathway, which mediates T-ALL cell survival. In conclusion, our results highlight the potential role of MALT1 as an attractive target for treatment of T-ALL and support the potential of MI-2 or other MALT1 inhibitors to clinical trials in T-ALL.

Clinical-Grade Peptide-Based Inhibition of CK2 Blocks Viability and Proliferation of T-ALL Cells and Counteracts IL-7 Stimulation and Stromal Support.

Despite remarkable advances in the treatment of T-cell acute lymphoblastic leukemia (T-ALL), relapsed cases are still a major challenge. Moreover, even successful cases often face long-term treatment-associated toxicities. Targeted therapeutics may overcome these limitations. We have previously demonstrated that casein kinase 2 (CK2)-mediated phosphatase and tensin homologue (PTEN) posttranslational inactivation, and consequent phosphatidylinositol 3-kinase (PI3K)/Akt signaling hyperactivation, leads to increased T-ALL cell survival and proliferation. We also revealed the existence of a crosstalk between CK2 activity and the signaling mediated by interleukin 7 (IL-7), a critical leukemia-supportive cytokine. Here, we evaluated the impact of CIGB-300, a the clinical-grade peptide-based CK2 inhibitor CIGB-300 on T-ALL biology. We demonstrate that CIGB-300 decreases the viability and proliferation of T-ALL cell lines and diagnostic patient samples. Moreover, CIGB-300 overcomes IL-7-mediated T-ALL cell growth and viability, while preventing the positive effects of OP9-delta-like 1 (DL1) stromal support on leukemia cells. Signaling and pull-down experiments indicate that the CK2 substrate nucleophosmin 1 (B23/NPM1) and CK2 itself are the molecular targets for CIGB-300 in T-ALL cells. However, B23/NPM1 silencing only partially recapitulates the anti-leukemia effects of the peptide, suggesting that CIGB-300-mediated direct binding to CK2, and consequent CK2 inactivation, is the mechanism by which CIGB-300 downregulates PTEN S380 phosphorylation and inhibits PI3K/Akt signaling pathway. In the context of IL-7 stimulation, CIGB-300 blocks janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway in T-ALL cells. Altogether, our results strengthen the case for anti-CK2 therapeutic intervention in T-ALL, demonstrating that CIGB-300 (given its ability to circumvent the effects of pro-leukemic microenvironmental cues) may be a valid tool for clinical intervention in this aggressive malignancy.

TET1 promotes growth of T-cell acute lymphoblastic leukemia and can be antagonized via PARP inhibition.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological cancer characterized by skewed epigenetic patterns, raising the possibility of therapeutically targeting epigenetic factors in this disease. Here we report that among different cancer types, epigenetic factor TET1 is highly expressed in T-ALL and is crucial for human T-ALL cell growth in vivo. Knockout of TET1 in mice and knockdown in human T cell did not perturb normal T-cell proliferation, indicating that TET1 expression is dispensable for normal T-cell growth. The promotion of leukemic growth by TET1 was dependent on its catalytic property to maintain global 5-hydroxymethylcytosine (5hmC) marks, thereby regulate cell cycle, DNA repair genes, and T-ALL associated oncogenes. Furthermore, overexpression of the Tet1-catalytic domain was sufficient to augment global 5hmC levels and leukemic growth of T-ALL cells in vivo. We demonstrate that PARP enzymes, which are highly expressed in T-ALL patients, participate in establishing H3K4me3 marks at the TET1 promoter and that PARP1 interacts with the TET1 protein. Importantly, the growth related role of TET1 in T-ALL could be antagonized by the clinically approved PARP inhibitor Olaparib, which abrogated TET1 expression, induced loss of 5hmC marks, and antagonized leukemic growth of T-ALL cells, opening a therapeutic avenue for this disease.

Protein tyrosine phosphatase 4A3 (PTP4A3/PRL-3) drives migration and progression of T-cell acute lymphoblastic leukemia in vitro and in vivo

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive blood cancer. There are no immunotherapies and few molecularly targeted therapeutics available for treatment of this malignancy. The identification and characterization of genes and pathways that drive T-ALL progression are critical for the development of new therapies for T-ALL. Here, we determined that the protein tyrosine phosphatase 4A3 (PTP4A3 or PRL-3) plays a critical role in T-ALL initiation and progression by promoting leukemia cell migration. PRL-3 is highly expressed in patient T-ALL samples at both the mRNA and protein levels compared to normal lymphocytes. Knock-down of PRL-3 expression using short-hairpin RNA (shRNA) in human T-ALL cell lines significantly impeded T-ALL cell migration capacity in vitro and reduced their ability to engraft and proliferate in vivo in xenograft mouse models. Additionally, PRL-3 overexpression in a Myc-induced zebrafish T-ALL model significantly accelerated disease onset and shortened the time needed for cells to enter blood circulation. Reverse-phase protein array (RPPA) and gene set enrichment analysis (GSEA) revealed that the SRC signaling pathway is affected by PRL-3. Immunoblot analyses validated that manipulation of PRL-3 expression in T-ALL cells affected the SRC signaling pathway, which is directly involved in cell migration, although Src was not a direct substrate of PRL-3. More importantly, T-ALL cell growth and migration were inhibited by small molecule inhibition of PRL-3, suggesting that PRL-3 has potential as a therapeutic target in T-ALL. Taken together, our study identifies PRL-3 as an oncogenic driver in T-ALL both in vitro and in vivo and provides a strong rationale for targeted therapies that interfere with PRL-3 function.

New advances in targeting aberrant signaling pathways in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disorder characterized by malignant transformation of immature progenitors primed towards T-cell development. Over the past 15 years, advances in the molecular characterization of T-ALL have uncovered oncogenic key drivers and crucial signaling pathways of this disease, opening new chances for the development of novel therapeutic strategies. Currently, T-ALL patients are still treated with aggressive therapies, consisting of high dose multiagent chemotherapy. To minimize and overcome the unfavorable effects of these regimens, it is critical to identify innovative targets and test selective inhibitors of such targets. Major efforts are being made to develop small molecules against deregulated signaling pathways, which sustain T-ALL cell growth, survival, metabolism, and drug-resistance. This review will focus on recent improvements in the understanding of the signaling pathways involved in the pathogenesis of T-ALL and on the challenging opportunities for T-ALL targeted therapies.

IL-7 Activates a STAT5/PIM1 Axis to Promote T-Cell Acute Lymphoblastic Leukemia Proliferation and Viability in a Bcl-2-Independent Manner

Background: T-cell acute lymphoblastic leukemia (T-ALL) constitutes an aggressive subset of ALL, the most frequent childhood malignancy. Although risk-adjusted chemotherapeutic regimens are currently extremely effective, their efficacy is associated with significant long-term side effects. Moreover, a significant fraction of the patients still relapse despite intensive chemotherapy, prompting the need for a deeper understanding of T-ALL biology in order to develop novel therapies. Interleukin-7 is a cytokine essential for normal T-cell development, where it has a pivotal role in promoting thymocyte survival via Bcl-2 upregulation. In this normal setting, Bcl-2 is under the control of STAT5 mediated signaling. Previously, we have shown that IL-7 promotes T-ALL expansion in vivo and leukemia cell survival and proliferation in vitro by activating PI3K/Akt/mTOR signaling pathway, consequently leading to p27kip1 downregulation and Bcl-2 upregulation. However, it is also known that T-cell lymphomas arising spontaneously in IL-7 transgenic mice depend on STAT5 activity and that leukemias displaying IL7R gain-of-function mutations are sensitive to JAK and STAT5 inhibitors. Thus, we investigated whether STAT5 could also be involved in the IL-7 pro-leukemia effects in human T-ALL cells.Methods: We used an IL-7-dependent leukemia T-cell line (TAIL7), an IL-7-responsive T-ALL cell line (HPB-ALL, with or without shRNA-mediated STAT5 silencing), primary T-ALL samples collected at diagnosis and patient-derived xenografts (PDX) and treated them with inhibitors of STAT5 (N-((4-Oxo-4H-chromen-3-yl) methylene) nicotinohydrazide) and PIM (AZD1208). Analysis of viability, cell size, cell cycle, surface CD71 and Bcl-2 expression was performed by flow cytometry. Signaling pathway activation, STAT5, PIM1, Bcl-xL, Mcl-1 and cell cycle protein expression was performed by immunoblot analysis. Proliferation was assessed by 3H-Thymidine incorporation. STAT5 ChIP-seq and RNA-seq were performed on TAIL7 cells. ChIP-PCR of histone marks H3K4me3, H3K27me, H3K27ac was performed in TAIL7 and HPB-ALL.Results: IL-7 induces JAK/STAT5 pathway activation in T-ALL cells and STAT5 genetic or pharmacological inactivation prevents IL-7-mediated T-ALL cell viability, growth and proliferation. At the molecular level, STAT5 is required for IL-7-induced downregulation of p27kip1, and upregulation of Cyclin A and TfR/CD71. Surprisingly, STAT5 inhibition does not significantly affect IL-7-mediated Bcl-2 upregulation, suggesting that, contrary to normal T-cells, STAT5 promotes leukemia cell survival via a Bcl-2-independent mechanism. In addition, IL-7-mediated increase in transcription of BCL2, BCL2L1 (Bcl-xL) and MCL1 is not affected by STAT5 silencing. To understand how STAT5 mediates the survival effects of IL-7 in T-ALL cells without affecting BCL2 transcription, we performed STAT5 ChIP-seq together with RNA-seq. Data cross-analysis reveal a diverse IL-7-driven STAT5-dependent transcriptional program in T-ALL cells, which includes transcription of the serine/threonine kinase PIM1. PIM1 is involved in cell cycle regulation and apoptosis, thereby constituting a possible alternative to Bcl-2-dependent prevention of apoptosis. We show that STAT5 silencing prevents IL-7-mediated PIM1 expression and the upregulation of active chromatin marks, H3K4me3 and H3K27ac, at the STAT5 binding region in the PIM1 gene. Notably, pharmacological inhibition of PIM kinase abrogates IL-7-mediated T-ALL cell growth and proliferation, however, without affecting cell survival. In agreement, PIM inhibition does not affect expression of Bcl-2 or Bcl-2 family anti-apoptotic members Bcl-xL and MCL1.Conclusion: Here we present evidence that T-ALL cells may have an alternative wiring of signaling networks downstream of IL-7 to that present in normal T-cells. In contrast to healthy lymphoid cells, IL-7-mediated control of survival of T-ALL cells via STAT5 does not rely on modulation of Bcl-2. Moreover, exploration of STAT5 downstream signaling reveals that PIM1 is required for IL-7-mediated proliferation of human T-ALL cells, indicating that strategies involving the use of PIM kinase small molecule inhibitors may have therapeutic potential against leukemias that rely on IL-7R and STAT5 signaling. DisclosuresBarata:Instituto de Medicina Molecular João Lobo Antunes: Patents & Royalties: Patents.

Growth Arrest-Specific 2 Promotes the Growth of T-Cell Acute Lymphoblastic Leukemia Cells Via Its Regulation of CXCR4

Growth arrest-specific 2 (GAS2) has multiple functions including the regulation of cell morphology, cell cycle, apoptosis and calpain activity.GAS2 has a dual function in cancer cells, however its expression and underlying mechanism in human T-cell acute lymphoblastic leukemia (T-ALL) remain unclear.In the present study, qRT-PCR analysis showed that GAS2 has significantly higher expression (155.5-fold, P=0.0048) in CD3+ cells from T-ALL patients (n=25) than healthy donors (n=13). GAS2 was present in Jurkat cells, while absent in MOLT-4 or HPB-ALL cells. A tiny CpG island of GAS2 was almost fully methylated in both MOLT-4 (100%) and HPB-ALL cells (80%), while 40% methylation in Jurkat cells; suggesting that DNA methylation played a subtle role in regulating GAS2 expression.Two independent shRNA sequences were delivered into Jurkat cells with lentiviral vector. GAS2 silencing inhibited the growth and colony-forming cell (CFC) production significantly. Conversely, GAS2 overexpression enhanced the growth and CFC production of both MOLT-4 and HPB-ALL cells. In addition, GAS2 overexpression promoted HPB-ALL cell induced leukemia in a xenoengraftment model (5 mice in each control group). In GAS2 expressed group, the disease latency was shortened, the splenomegaly was more severe than control group (0.35±0.04g vs. 0.27±0.05g), and more leukemic cells were present in bone marrow (85±3% vs. 45±7%).To obtain the molecular insights of how GAS2 acts, RNA-seq data comparing GAS2 silenced Jurkat cells with control cells were generated. Several Notch signaling molecules were inhibited, including NOTCH1, HES1 and HES4. Despite the differential expression of these transcripts was validated in Jurkat cells, GAS2 overexpression did not elevated the expression of these transcripts in MOLT-4 or HPB-ALL cells, suggesting GAS2 did not have a consistent impact on Notch signaling. However, we found that GAS2 silencing reduced CXCR4 protein expression in Jurkat cells and GAS2 overexpression enhanced CXCR4 protein expression in MOLT-4 cells, while CXCR4 transcript was not altered upon GAS2 manipulation. Consequently, GAS2 silencing significantly reduced migration ability of Jurkat cells and GAS2 overexpression enhanced migration ability of MOLT-4 cells. Overexpression of CXCR4 “rescued” the inhibited CFC production and migration upon GAS2 silencing. A truncated GAS2 (Δ171-313) coined as GAS2DN (dominant negative form of GAS2) has been known to inhibit normal function of GAS2. Herein, we showed that GAS2DN inhibited the growth of Jurkat cells and the expression of CXCR4. To delineate the role of calpain1 and calpain2 in GAS2 function, shRNA sequences against calpain1 and calpain2 was delivered into GAS2DN expressed Jurkat cells respectively, the results showed that calpain2 but not calpain1 silencing was able to enhance the cell growth and CXCR4 expression.Taken together, the present study has demonstrated that GAS2 is aberrantly expressed in human T-ALL cells, which promotes the growth of T-ALL cells partially via its post-transcriptional regulation of CXCR4 depending on calpain2 activity. These data provide new insights of the pathogenesis of T-ALL and possibly new clues to improve the management of the disease. DisclosuresNo relevant conflicts of interest to declare.

USP7 Cooperates with NOTCH1 to Drive the Oncogenic Transcriptional Program in T-Cell Leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease, affecting children and adults. Chemotherapy treatments show high response rates but have debilitating effects and carry risk of relapse. Previous work implicated NOTCH1 and other oncogenes. However, direct inhibition of these pathways affects healthy tissues and cancer alike. Our goal in this work has been to identify enzymes active in T-ALL whose activity could be targeted for therapeutic purposes. To identify and characterize new NOTCH1 druggable partners in T-ALL, we coupled studies of the NOTCH1 interactome to expression analysis and a series of functional analyses in cell lines, patient samples, and xenograft models. We demonstrate that ubiquitin-specific protease 7 (USP7) interacts with NOTCH1 and controls leukemia growth by stabilizing the levels of NOTCH1 and JMJD3 histone demethylase. USP7 is highly expressed in T-ALL and is transcriptionally regulated by NOTCH1. In turn, USP7 controls NOTCH1 levels through deubiquitination. USP7 binds oncogenic targets and controls gene expression through stabilization of NOTCH1 and JMJD3 and ultimately H3K27me3 changes. We also show that USP7 and NOTCH1 bind T-ALL superenhancers, and inhibition of USP7 leads to a decrease of the transcriptional levels of NOTCH1 targets and significantly blocks T-ALL cell growth in vitro and in vivo. These results provide a new model for USP7 deubiquitinase activity through recruitment to oncogenic chromatin loci and regulation of both oncogenic transcription factors and chromatin marks to promote leukemia. Our studies also show that targeting USP7 inhibition could be a therapeutic strategy in aggressive leukemia.

Abstract 3336: ARID5B activates the TAL1-induced core regulatory circuit and the oncogene MYC, thereby promoting T-cell leukemogenesis

Abstract The oncogenic transcription factor TAL1/SCL is abnormally expressed in 40-60% cases of T-cell acute lymphoblastic leukemia (T-ALL) cells. It induces an aberrant transcriptional program with its regulatory partners (E-proteins, LMO1/2, GATA3, RUNX1 and MYB) in malignant T cells. However, the critical factors that are directly activated by the TAL1 transcriptional complex and contribute to T-ALL pathogenesis are largely unknown. Here, we identified ARID5B, an AT-rich interactive domain (ARID) family DNA binding protein, as a collaborating oncogenic factor involved in the transcriptional program in T-ALL. Our result indicated that ARID5B expression is downregulated at the CD4, CD8 double negative 2-4 stages in normal thymocytes, while it is activated by the TAL1 complex in human T-ALL cells. The enhancer located approximately 135 kb upstream of the ARID5B gene locus is associated with a super-enhancer in multiple T-ALL samples but not in normal thymus. These data suggested that ARID5B is aberrantly activated in T-ALL cells. Interestingly, ARID5B-bound regions are predominantly associated with active transcription, as shown by the active histone marks (H3K27ac, H3K4me1 and H3K4me3) by ChIP-seq analysis. ARID5B and TAL1 frequently co-occupy target genes and coordinately control their expression. Notably, ARID5B positively regulates the expression of TAL1 and its regulatory partners (GATA3, RUNX1 and MYB). In addition, ARID5B activates the expression of the oncogene MYC. Importantly, ARID5B is required for the survival and growth of T-ALL cells in vitro, and forced expression of ARID5B in immature thymocytes results in thymus retention, radio-resistance and tumor formation in zebrafish. Our results indicate that ARID5B reinforces the oncogenic transcriptional program by positively regulating the core regulatory circuit and the oncogene MYC in T-ALL, thereby contributing to T-cell leukemogenesis. Citation Format: Wei Zhong Leong, Shi Hao Tan, Phuong Cao Thi Ngoc, Stella Amanda, Alice Wei Yee Yam, Wei-Siang Liau, Zhiyuan Gong, Lee N. Lawton, Daniel G. Tenen, Takaomi Sanda. ARID5B activates the TAL1-induced core regulatory circuit and the oncogene MYC, thereby promoting T-cell leukemogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3336.

ARID5B as a critical downstream target of the TAL1 complex that activates the oncogenic transcriptional program and promotes T-cell leukemogenesis.

The oncogenic transcription factor TAL1/SCL induces an aberrant transcriptional program in T-cell acute lymphoblastic leukemia (T-ALL) cells. However, the critical factors that are directly activated by TAL1 and contribute to T-ALL pathogenesis are largely unknown. Here, we identified AT-rich interactive domain 5B (ARID5B) as a collaborating oncogenic factor involved in the transcriptional program in T-ALL. ARID5B expression is down-regulated at the double-negative 2-4 stages in normal thymocytes, while it is induced by the TAL1 complex in human T-ALL cells. The enhancer located 135 kb upstream of the ARID5B gene locus is activated under a superenhancer in T-ALL cells but not in normal T cells. Notably, ARID5B-bound regions are associated predominantly with active transcription. ARID5B and TAL1 frequently co-occupy target genes and coordinately control their expression. ARID5B positively regulates the expression of TAL1 and its regulatory partners. ARID5B also activates the expression of the oncogene MYC Importantly, ARID5B is required for the survival and growth of T-ALL cells, and forced expression of ARID5B in immature thymocytes results in thymus retention, differentiation arrest, radioresistance, and tumor formation in zebrafish. Our results indicate that ARID5B reinforces the oncogenic transcriptional program by positively regulating the TAL1-induced regulatory circuit and MYC in T-ALL, thereby contributing to T-cell leukemogenesis.