Combinatorial ETS1-Dependent Control of Oncogenic NOTCH1 Enhancers in T-cell Leukemia

Abstract

Notch activation is highly prevalent among cancers, in particular T-cell acute lymphoblastic leukemia (T-ALL). However, the use of pan-Notch inhibitors to treat cancers has been hampered by adverse effects, particularly intestinal toxicities. To circumvent this barrier in TALL , we aimed to inhibit ETS1, a developmentally important T-cell transcription factor previously shown to cobind Notch response elements. Using complementary genetic approaches in mouse models, we show that ablation of Ets1 leads to strong Notch-mediated suppressive effects on T-cell development and leukemogenesis but milder intestinal effects than pan-Notch inhibitors. Mechanistically, genome-wide chromatin profiling studies demonstrate that Ets1 inactivation impairs recruitment of multiple Notch-associated factors and Notch-dependent activation of transcriptional elements controlling major Notch-driven oncogenic effector pathways. These results uncover previously unrecognized hierarchical heterogeneity of Notch-controlled genes and point to Ets1-mediated enucleation of Notch-Rbpj transcriptional complexes as a target for developing specific anti-Notch therapies in TALL that circumvent the barriers of pan-Notch inhibition. SigNifiCaNCE: Notch signaling controls developmentally important and tissue-specific activities, raising barriers for developing anti-Notch therapies. Pivoting away from pan-Notch inhibitors, we show antileukemic but less toxic effects of targeting ETS1, a T-cell NOTCH1 cofactor. These results demonstrate the feasibility of context-dependent suppression of NOTCH1 programs for the treatment of TALL .

ETS1 is a novel transcriptional regulator of adult T-cell leukemia/lymphoma of North American descent

“…56,57 In addition to Tax, interactions have been reported between ETS1 and other transcription factors such as Runx1 and Notch to facilitate DNA binding. 33,42 Of note, the RUNX1 motif was also identified in NA-ATLL cell lines suggesting potential for cooperation between ETS1 and RUNX1 in this context. Further work is required to investigate potential interactions between ETS1, HTLV-1 proteins, and other T cell transcription factors, as well as role for other Ets family transcription factors.…”

“…This is consistent with a recent report of CCR4 as an ETS1 target gene in T-cell acute lymphoblastic leukemia. 33 CCR4 is a chemokine receptor for ligands CCL17 and CCL22, expressed primarily on TH2 and Treg cells. CCR4 is frequently expressed in ATL 10 , and is associated with poor prognosis.…”

“…30 ETS1 target genes were defined by the TRANSFAC curated transcription factor targets gene set for ETS1 (Harmonizome 31,32 ) as well as a recently published ETS1 target dataset in T-ALL. 33 Pathway analysis was performed on ETS1 target genes overexpressed in NA-ATLL compared to J-ATLL (fc>0.5) and normal control cells (fc>0.5; p-value<0.1) using Ingenuity Pathway Analysis (IPA; Qiagen) software.…”

E Protein Transcription Factors as Suppressors of T Lymphocyte Acute Lymphoblastic Leukemia

“…Deletion of RUNX1 in DN2/3 thymocytes impairs IL7R expression ( 114 ), and expression of dominant-negative RUNX1 and NOTCH1 inhibitors (RUNT and DN-MAML, respectively) suppressed IL7R mRNA expression ( 60 ). Further, ETS1 binds to multiple NOTCH1 occupied sites in T-ALL ( 89 ). Indeed, mice overexpressing NOTCH1 fail to develop leukemia when lacking functional ETS1 suggesting that both of these factors are required for leukemia initiation.…”

“…ETS1 is frequently over expressed in human T-ALL samples and cell lines indicating that ETS1 may act in concert with NOTCH1 in the human disease as well. Indeed, shRNA–mediated knockdown of ETS1 in human T-ALL lines promoted cell death and significantly down-regulated expression of the oncogenes c- MYC and IGFR1 , as well as other NOTCH1 target genes like HES1 and DELTEX1 ( 89 ). Understanding of the spectrum of genes induced by NOTCH1 and identifying co-regulators may reveal mechanisms that could be targeted for treatment of T-ALL.…”