scholarly journals GFI1 cooperates with IKAROS/IKZF1 to activate gene expression in T-cell acute lymphoblastic leukemia

2021 ◽  
Author(s):  
Wenxiang Sun ◽  
Jingtao Guo ◽  
David McClellan ◽  
Alexandra Poeschla ◽  
Diana Bareyan ◽  
...  
Keyword(s):  
T Cell ◽  
Transcriptional Control ◽  
Protein Complexes ◽  
Lymphoblastic Leukemia ◽  
Transcriptional Profiling ◽  
T Cell Development ◽  
Key Factor ◽  
Full Complement ◽  
Cell Acute Lymphoblastic Leukemia ◽  
Activate Gene

AbstractGrowth factor independence-1 (GFI1) is a transcriptional repressor and master regulator of normal and malignant hematopoiesis. Repression by GFI1 is attributable to recruitment of LSD1-containing protein complexes via its SNAG domain. However, the full complement of GFI1 partners in transcriptional control is not known. We show that in T-ALL cells, GFI1 and IKAROS are transcriptional partners that co-occupy regulatory regions of hallmark T cell development genes. Transcriptional profiling reveals a subset of genes directly transactivated through the GFI1—IKAROS partnership. Among these is NOTCH3, a key factor in T-ALL pathogenesis. Surprisingly, NOTCH3 transactivation by GFI1 and IKAROS requires the GFI1 SNAG domain but occurs independent of SNAG—LSD1 binding. GFI1 variants deficient in LSD1 binding fail to transactivate NOTCH3, but conversely, small molecules that disrupt the SNAG—LSD1 interaction while leaving the SNAG primary structure intact stimulate NOTCH3 expression. These results identify a non-canonical transcriptional control mechanism in T-ALL which supports GFI1-mediated transactivation in partnership with IKAROS and suggest competition between LSD1-containing repressive complexes and others favoring transactivation.

scholarly journals T-cell receptor delta gene rearrangement in childhood T-cell acute lymphoblastic leukemia

Blood ◽  
1989 ◽  
Vol 73 (8) ◽  
pp. 2133-2138
Author(s):  
A Biondi ◽  
E Champagne ◽  
V Rossi ◽  
G Giudici ◽  
A Cantu-Rajnoldi ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Gene Rearrangement ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
Cell Development ◽  
Early Event ◽  
Chain Gene ◽  
Gamma Chain ◽  
Cell Acute Lymphoblastic Leukemia

During the development of functional T lymphocytes, a variety of genes involved in antigen recognition undergo somatic rearrangement. These include the alpha, beta, and gamma chain genes. Recently a fourth rearranging gene, the delta chain gene, embedded in the alpha chain locus, has been described. We have determined the structure of the beta, gamma, and delta chain genes in 15 cases of T-cell acute lymphoblastic leukemia (T-ALL) representing stage I (CD7+, CD1-, CD3-) and stage II (CD7+, CD1+, CD3-) of intrathymic T-cell development. The alpha-delta locus was rearranged in 14 of the 15 cases. In three cases the delta constant region was deleted on both chromosomes, suggesting biallelic V-J alpha rearrangement. A limited pattern of rearrangement of the delta locus was observed in the remaining 11 cases. When the alpha-delta region was rearranged, there was rearrangement of the beta and gamma TcR in all cases except two; in these cases the beta chain was in the germline configuration. These findings support the hypothesis that delta chain gene rearrangement is an early event in T- cell development, possibly contemporary to gamma gene rearrangement, and that the delta locus has a limited repertoire.

scholarly journals miR-22-3p Negatively Affects Tumor Progression in T-Cell Acute Lymphoblastic Leukemia

Cells ◽  
2020 ◽  
Vol 9 (7) ◽  
pp. 1726
Author(s):  
Valentina Saccomani ◽  
Angela Grassi ◽  
Erich Piovan ◽  
Deborah Bongiovanni ◽  
Ludovica Di Martino ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Target Genes ◽  
Cell Transformation ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
Cell Acute Lymphoblastic Leukemia ◽  
Notch1 Signaling Pathway

T-cell acute lymphoblastic leukemia (T-ALL) is a rare, aggressive disease arising from T-cell precursors. NOTCH1 plays an important role both in T-cell development and leukemia progression, and more than 60% of human T-ALLs harbor mutations in components of the NOTCH1 signaling pathway, leading to deregulated cell growth and contributing to cell transformation. Besides multiple NOTCH1 target genes, microRNAs have also been shown to regulate T-ALL initiation and progression. Using an established mouse model of T-ALL induced by NOTCH1 activation, we identified several microRNAs downstream of NOTCH1 activation. In particular, we found that NOTCH1 inhibition can induce miR-22-3p in NOTCH1-dependent tumors and that this regulation is also conserved in human samples. Importantly, miR-22-3p overexpression in T-ALL cells can inhibit colony formation in vitro and leukemia progression in vivo. In addition, miR-22-3p was found to be downregulated in T-ALL specimens, both T-ALL cell lines and primary samples, relative to immature T-cells. Our results suggest that miR-22-3p is a functionally relevant microRNA in T-ALL whose modulation can be exploited for therapeutic purposes to inhibit T-ALL progression.

scholarly journals Therapeutic targeting of the E3 ubiquitin ligase SKP2 in T-ALL

Leukemia ◽  
2019 ◽  
Vol 34 (5) ◽  
pp. 1241-1252 ◽  
Author(s):  
Sonia Rodriguez ◽  
Christina Abundis ◽  
Francesco Boccalatte ◽  
Purvi Mehrotra ◽  
Mark Y. Chiang ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Ubiquitin Ligase ◽  
Kinase Inhibitor ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
E3 Ubiquitin Ligase ◽  
Cell Development ◽  
Cell Acute Lymphoblastic Leukemia

AbstractTimed degradation of the cyclin-dependent kinase inhibitor p27Kip1 by the E3 ubiquitin ligase F-box protein SKP2 is critical for T-cell progression into cell cycle, coordinating proliferation and differentiation processes. SKP2 expression is regulated by mitogenic stimuli and by Notch signaling, a key pathway in T-cell development and in T-cell acute lymphoblastic leukemia (T-ALL); however, it is not known whether SKP2 plays a role in the development of T-ALL. Here, we determined that SKP2 function is relevant for T-ALL leukemogenesis, whereas is dispensable for T-cell development. Targeted inhibition of SKP2 by genetic deletion or pharmacological blockade markedly inhibited proliferation of human T-ALL cells in vitro and antagonized disease in vivo in murine and xenograft leukemia models, with little effect on normal tissues. We also demonstrate a novel feed forward feedback loop by which Notch and IL-7 signaling cooperatively converge on SKP2 induction and cell cycle activation. These studies show that the Notch/SKP2/p27Kip1 pathway plays a unique role in T-ALL development and provide a proof-of-concept for the use of SKP2 as a new therapeutic target in T-cell acute lymphoblastic leukemia (T-ALL).

scholarly journals The BCL11B tumor suppressor is mutated across the major molecular subtypes of T-cell acute lymphoblastic leukemia

Blood ◽  
2011 ◽  
Vol 118 (15) ◽  
pp. 4169-4173 ◽  
Author(s):  
Alejandro Gutierrez ◽  
Alex Kentsis ◽  
Takaomi Sanda ◽  
Linda Holmfeldt ◽  
Shann-Ching Chen ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Tumor Suppressor ◽  
Molecular Subtypes ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
Missense Mutations ◽  
Thymocyte Development ◽  
Cell Acute Lymphoblastic Leukemia

Abstract The BCL11B transcription factor is required for normal T-cell development, and has recently been implicated in the pathogenesis of T-cell acute lymphoblastic leukemia (T-ALL) induced by TLX overexpression or Atm deficiency. To comprehensively assess the contribution of BCL11B inactivation to human T-ALL, we performed DNA copy number and sequencing analyses of T-ALL diagnostic specimens, revealing monoallelic BCL11B deletions or missense mutations in 9% (n = 10 of 117) of cases. Structural homology modeling revealed that several of the BCL11B mutations disrupted the structure of zinc finger domains required for this transcription factor to bind DNA. BCL11B haploinsufficiency occurred across each of the major molecular subtypes of T-ALL, including early T-cell precursor, HOXA-positive, LEF1-inactivated, and TAL1-positive subtypes, which have differentiation arrest at diverse stages of thymocyte development. Our findings provide compelling evidence that BCL11B is a haploinsufficient tumor suppressor that collaborates with all major T-ALL oncogenic lesions in human thymocyte transformation.

Thymocyte Selection-Associated High-Mobility Group Box Protein (TOX) Induces Genomic Instability in T-Cell Acute Lymphoblastic Leukemia

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 475-475
Author(s):  
Riadh Lobbardi ◽  
Jordan Pinder ◽  
Barbara Martinez-Pastor ◽  
Jessica S Blackburn ◽  
Nouran Abdelfattah ◽  
...  
Keyword(s):  
Dna Repair ◽  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Genomic Instability ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
Strand Break ◽  
End Joining ◽  
Cell Acute Lymphoblastic Leukemia ◽  
Non Homologous End Joining

Abstract MYC and NOTCH are major oncogenic drivers in T-cell Acute Lymphoblastic Leukemia (T-ALL), yet additional collaborating genetic lesions likely collaborate to induce frank malignancy. To identify these factors, a large-scale transgenic screen was completed where 38 amplified and over-expressed genes found in human T-ALL were assessed for accelerating leukemia onset in the zebrafish transgenic model. From this analysis, Thymocyte selection-associated homeobox protein (TOX) synergized with both MYC and NOTCH to induce T-ALL. TOX is dynamically regulated in T cell development with peak expression occurring when thymocytes are actively undergoing T cell receptor (TCR) recombination. TOX is best known for regulating the specification of the mature CD4+ T cells. Despite TOX being genomically amplified in a subset of human and mouse T-ALL and being overexpressed in 100% of human T-ALL, a role for TOX in regulating leukemogenesis has not been reported. Characterization of zebrafish T-ALLs revealed that TOX expands the overall number of malignant T-ALL clones and promoted genomic instability as assessed by changes in DNA content. To identify TOX binding partners, antibody immunoprecipitation studies were performed followed by Tandem Mass Spectrometry. TOX was found to interact with KU70/KU80 but not other DNA repair enzymes including LigaseIV, DNA-PKC, or XRCC4. These results were verified by Western blot analysis and reciprocal immunoprecipitation studies using antibodies specific to KU70/KU80 both in the absence and presence of DNAseI treatment. Given that TOX elevated genomic instability in the zebrafish model and bound specifically to KU70/KU80 – the initiating factors required for Non-Homologous End Joining (NHEJ) repair - we hypothesized that TOX is a negative regulator of double-strand break repair. Fluorescent repair assays were completed in 3T3 fibroblasts and confirmed that TOX inhibits Non-Homologous End Joining (NHEJ). Both the nuclear localization signal and HMG-box were required for the ability of TOX to inhibit double-strand break repair. Dynamic real-time imaging studies confirmed that TOX suppresses recruitment of fluorescent-tagged KU70 to DNA breaks. Importantly, TOX loss of function increased NHEJ in human T-ALL cells and reduced time to DNA repair as assessed by fluorescent Traffic Light Reporter assays and quantitative assessment of 53BP1 and γH2A.X foci resolution following irradiation. Given the prominent role TOX has in T cell development and its coordinated regulation during active TCRβ and TCRα rearrangement, it is likely that the normal function of TOX is to transiently suppress the NHEJ pathway during Recombination-Activating Gene (RAG)-mediated recombination. Prolonging the time to DNA repair would likely facilitate long-range repair across VDJ segments. In the setting of T-ALL, TOX is aberrantly re-activated, thereby suppressing KU70/KU80 function to promote genomic instability and ultimately elevating rates at which acquired mutations and rearrangements are amassed in developing pre-malignant T cells. Disclosures No relevant conflicts of interest to declare.

Identification of Candidate Oncogenes and Chromosomal Breakpoint Sequencing By Targeted Locus Amplification in T-Cell Acute Lymphoblastic Leukemia

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 1409-1409
Author(s):  
Eric M Vroegindeweij ◽  
Tim Lammens ◽  
Erik Splinter ◽  
Anne Uyttebroeck ◽  
Kirsten Canté-Barrett ◽  
...  
Keyword(s):  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Transcriptional Control ◽  
Lymphoblastic Leukemia ◽  
Chromosomal Rearrangements ◽  
Chromosomal Translocations ◽  
The Third ◽  
P Gene ◽  
Translocation Breakpoints ◽  
Cell Acute Lymphoblastic Leukemia

Abstract Background: T-cell acute lymphoblastic leukemia is characterized by clonal and mutual exclusive chromosomal rearrangements that recurrently activate TAL1, LMO2, TLX1, NKX2-1, TLX3, HOXA or MEF2C oncogenes. Most of these translocations or chromosomal rearrangements occur as erroneous D-J or V-DJ rearrangement attempts of T-cell receptor beta (TCRB) or TCR alpha/delta (TCRAD) genes, mostly positioning oncogenes under the transcriptional control of TCR enhancer elements. Alternatively, oncogenes can also be activated as consequence of BCL11B chromosomal rearrangements. Although many oncogenes are known in T-ALL, the driving oncogenic lesion in particular T-ALL cases remains unknown. Aims: In this study, we aimed to clone reciprocal breakpoint sequences to elucidate cellular mechanisms that lead to recurrent BCL11B -TLX3 chromosomal translocations. Moreover, we want to identify oncogene candidates in various T-ALL patient samples with BCL11B-, TCRB- or TCRAD-translocations for which the candidate oncogene so far has not been identified. Methods: We used Targeted Locus Amplification procedure, a recently developed method that relies on the crosslinking of DNA in live cells, DNA digestion and re-ligation to allow formation of circular DNA ligation fragments and inverted polymerase chain reaction amplification from specific view-point loci. Amplified DNA fragments are sequenced by next generation sequencing, allowing sequence identification in a region covering 2MB around selected regions of interest, including TLX3, TLX1, TAL1, LMO2, BCL11B, TCRAD (TRAJ61), TCRB (TCRBC2) Results: TLA was successfully performed on 10 T-ALL patients having FISH validated TAL1 translocations (2 patients), LMO2 translocations (3 patients), TLX3 translocations (3 patients), TLX1 translocations (2 patients) or an inversion targeting NKX2.1 (1 patient). Analysis of both TAL1 translocated cases revealed a TAL1-TCRAD genomic fusion due to a classical t(1;14)(q32;q11) in 1 patient, but surprisingly reveal a TAL1-TCF7 genomic fusion due to a t(1;5)(q32;q31.1) chromosomal translocation in the second patient. For the LMO2 translocated cases, two patients showed classical LMO2-TCRAD (t(11;14)(p13;q11)) or LMO2-TCRB (t(7;11)(q35;p13) translocations, whereas the third patient presented with an unusual LMO2-BCL11B genomic fusion due to a t(11;14)(p13;q32). Two out of 3 TLX3-translocated patients had classical t(5;14)(q35;q32) translocations, whereas the TLX3 gene in the third patient was rearranged to the calcyphosine-like gene (CAPSL, which flanks the IL7Ra gene) on chromosomal 5p13.2 due to a t(5;5)( p13.2;q35) or an inv(5). One patient had an inversion on chromosome 14, i.e. inv(14)(q11;q13), that brings the NKX2.1 oncogene under the transcriptional control of the TCRAD enhancer. Finally, one TLX1-rearranged patient had a classical TLX1-TCRAD translocation, whereas the other presented with a chromosomal inversion involving the chromosomal band 10q24 (which included TLX1), but also revealed a novel translocation involving the centromere protein P gene (CENPP) on chromosome 9q22.31 with the TCRAD locus. Summary/Conclusions: Targeted Locus Amplification identification of chromosomal rearrangements and genomic breakpoint sequences reveals novel complex translocations in 3 out of 10 T-ALL cases analyzed thus far, indicating higher complexity of chromosomal translocations of known T-ALL oncogenes as thus far anticipated. It further proved a useful tool to identify novel translocation partners from various loci such as the TCR or BCL11B genes that are recurrently involved in these chromosomal rearrangements in T-ALL. Cloning of molecular translocation breakpoints of diagnostic T-ALL patient samples may further provide excellent minimal residual disease markers for disease monitoring during the course of treatment. Disclosures Splinter: Cergentis BV: Employment. van Min:Cergentis BV: Employment.

scholarly journals MicroRNAs as Modulators of the Immune Response in T-Cell Acute Lymphoblastic Leukemia

2022 ◽  
Vol 23 (2) ◽  
pp. 829
Author(s):  
Martina Del Gaizo ◽  
Ilaria Sergio ◽  
Sara Lazzari ◽  
Samantha Cialfi ◽  
Maria Pelullo ◽  
...  
Keyword(s):  
Immune Response ◽  
T Cell ◽  
Cell Fate ◽  
Lymphoblastic Leukemia ◽  
Suppressor Cells ◽  
Main Role ◽  
Altered Expression ◽  
Key Factor ◽  
Multistep Process ◽  
Cell Acute Lymphoblastic Leukemia

Acute lymphoblastic leukaemia (ALL) is an aggressive haematological tumour driven by the malignant transformation and expansion of B-cell (B-ALL) or T-cell (T-ALL) progenitors. The evolution of T-ALL pathogenesis encompasses different master developmental pathways, including the main role played by Notch in cell fate choices during tissue differentiation. Recently, a growing body of evidence has highlighted epigenetic changes, particularly the altered expression of microRNAs (miRNAs), as a critical molecular mechanism to sustain T-ALL. The immune response is emerging as key factor in the complex multistep process of cancer but the role of miRNAs in anti-leukaemia response remains elusive. In this review we analyse the available literature on miRNAs as tuners of the immune response in T-ALL, focusing on their role in Natural Killer, T, T-regulatory and Myeloid-derived suppressor cells. A better understanding of this molecular crosstalk may provide the basis for the development of potential immunotherapeutic strategies in the leukemia field.

scholarly journals Elevated Enhancer-Oncogene Contacts and Higher Oncogene Expression Levels By Recurrent CTCF inactivating Mutations in T Cell Acute Lymphoblastic Leukemia

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 501-501
Author(s):  
Willem K. Smits ◽  
Carlo Vermeulen ◽  
Rico Hagelaar ◽  
Shunsuke Kimura ◽  
Eric Vroegindeweij ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Research Funding ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
Expression Levels ◽  
Oncogene Expression ◽  
Cell Acute Lymphoblastic Leukemia ◽  
Inactivating Mutations

Abstract Introduction. The CCCTC-binding factor (CTCF) regulates the 3D chromatin architecture by facilitating chromosomal loops and forming the boundaries of structural domains. In addition, CTCF is an important transcription factor and regulator of antigen receptor and T cell receptor recombination events. CTCF inactivating events have been found in various human cancers. Loss-of-heterozygosity (LOH) or inactivating missense mutations in specific zinc- fingers have been identified in many human cancers including sporadic breast cancer, prostate cancer, Wilms-tumors and acute lymphoblastic leukemia (ALL). Heterozygous deletions or point mutations have been identified in over half of the patients with breast cancer or uterine endometrial cancers, deregulating global gene expression by altering methylated genomic states and poor survival. Here, we investigated the functional significance and molecular-cytogenetic associations of CTCF aberrations in T-cell acute lymphoblastic leukemia patients. Methods. Biopsies from a cohort of 181 pediatric T-ALL patients who enrolled on DCOG or COALL protocols and/or their derivative patient-derived xenograft models were screened for alterations in global DNA copy number, methylation status, topologically associating domain organization and CTCF and cohesion binding patterns and changes in local TLX3 and BCL11B promoter enhancer loops using array-comparative genomic hybridization, single molecule Molecular Inversion Probe sequencing, targeted locus amplification, gene expression and DNA methylation microarrays, Hi-C sequencing, Chromatin Immunoprecipitation and/or real-time quantitative PCR. Ctcf f/fl mice 1 were crossed on a the Lck-cre transgenic background 2 to study the impact of Ctcf loss during early T-cell development. Results. We here describe that inactivation of CTCF can drive subtle and local genomic effects that elevate oncogene expression levels from driver chromosomal rearrangements. We find that for T cell acute lymphoblastic leukemia (T-ALL), heterozygous CTCF deletions or inactivating mutations are present in nearly 50 percent of t(5;14)(q35;q32.2) rearranged patients that positions the TLX3 oncogene in the vicinity of the BCL11B enhancer. Functional CTCF loss results in diminished expression of the αβ-lineage commitment factor BCL11B from the non-rearranged allele and γδ-lineage development. Unexpectedly, it also drives higher levels of the TLX3 oncogene from the translocated allele. We demonstrate that heterozygous CTCF aberrations specifically occur in TLX3-rearranged patients with distal breakpoints that preserve CTCF bindings sites in the translocation breakpoint areas in between the BCL11B enhancer and the TLX3 oncogene. We show that these intervening CTCF sites insulate TLX3 from the enhancer by forming competitive loops with TLX3. Upon loss of CTCF, or the deletion of the intervening CTCF sites, these competitive loops are weakened and loops with the BCL11B enhancer are stimulated, boosting TLX3 oncogene expression levels and leukemia burden in these T-ALL patients. Conclusions. CTCF aberrations are especially associated with t(5;14)(q35;q32.2) rearranged T-ALL patients who maintain TLX3-proximal CTCF sites reflects a necessity to neutralize these sites in order to topologically enable the distal BCL11B enhancer to interact with the TLX3 oncogene and to boost its expression. Collectively, this provides direct demonstration of a mechanism in which loss of CTCF result in removal of enhancer insulation that facilitates elevated levels of an oncogene in leukemia. References. 1. Heath H, Ribeiro de Almeida C, Sleutels F, et al. CTCF regulates cell cycle progression of alphabeta T cells in the thymus. EMBO J. 2008;27(21):2839-2850. 2. Lee PP, Fitzpatrick DR, Beard C, et al. A critical role for Dnmt1 and DNA methylation in T cell development, function, and survival. Immunity. 2001;15(5):763-774. Disclosures Splinter: Cergentis BV: Current Employment. Van Eyndhoven: Agilent Technologies Netherland: Current Employment. Van Min: Cergentis BV: Current Employment. Mullighan: Pfizer: Research Funding; Illumina: Membership on an entity's Board of Directors or advisory committees; AbbVie: Research Funding; Amgen: Current equity holder in publicly-traded company.

Developmentally Restricted Protection From Notch1-Induced T Cell Acute Lymphoblastic Leukemia by the Arf Tumor Suppressor.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 143-143
Author(s):  
Emmanuel Volanakis ◽  
Richard T Williams ◽  
Charles J. Sherr
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
Acute Lymphoblastic Leukemia ◽  
T Cell ◽  
Fluorescent Protein ◽  
Lymphoblastic Leukemia ◽  
T Cell Development ◽  
Double Positive ◽  
Donor Cells ◽  
Cell Acute Lymphoblastic Leukemia

Abstract Abstract 143 At presentation, 50% of T cell acute lymphoblastic leukemia (T ALL) cases harbor activating mutations of the NOTCH1 transmembrane receptor, virtually all of which have also sustained deletions of the CDKN2A (INK4A-ARF) locus. Although the concordance of these genetic anomalies has been well documented, its basis remains unclear. The CDKN2A gene cluster encodes two structurally and functionally distinct tumor suppressors, p16INK4A and p14ARF (p19Arf in the mouse), the activation of which modulates the activities of the retinoblastoma protein and p53, respectively, to induce cell cycle arrest and/or apoptosis in response to oncogenic stress. A novel approach for modeling T ALL in the mouse now reveals that the ability of Arf to suppress Notch1-induced tumors is conferred at a specific stage of T cell development. Bone marrow cells or thymocytes transduced with a vector encoding the constitutively active intracellular fragment of NOTCH1 (ICN1) together with green fluorescent protein (GFP) were cultured ex vivo under conditions that support T lymphocyte differentiation and proliferation. These cultures were quickly dominated by early T cell precursors that expressed Thy-1 but not B cell or myeloid markers, and which produced a rapidly fatal CD4+/CD8+ (”double-positive”) T ALL when transferred into healthy, non-irradiated syngeneic mice. A phenotypically identical disease resulted upon infusion of the transduced cells into athymic nude mice, demonstrating that the deregulated ICN1 signal is sufficient to drive T cell development to the CD4+/CD8+ stage without any requirement for input from the thymic microenvironment. In recipients of bone marrow-derived ICN1+, Arf+/+ progenitors, T ALLs arose at high frequency, retained the Arf locus, but universally failed to express p19Arf. In turn, T ALLs initiated with bone marrow-derived ICN1+, Arf-/- donor cells exhibited only a modest acceleration of disease progression. In marked contrast, retention of the intact Arf locus in thymocyte-derived ICN1+ donor cells significantly prolonged disease latency and decreased tumor penetrance, indicating that Arf tumor suppression can be activated in thymic progenitors, but not in their less mature bone marrow precursors. Polycomb complexes epigenetically silence the Ink4a-Arf locus in primitive hematopoietic progenitors and early T cell precursors, preventing p19Arf expression and licensing a robust proliferative response to ICN1 signals. However, the locus is subsequently remodeled before T cells reach the double-positive stage, and its activation enables the Arf-p53 axis to cull T cells exposed to aberrant ICN1-induced oncogenic signals. In order to directly demonstrate that ICN1 overexpression in thymocyte-derived progenitors can induce the Arf locus, thymocytes from a homozygous Arf-GFP “knock-in” mouse were transduced with a vector encoding ICN1 and cherry-fluorescent protein (CFP), cultured short-term, and infused into healthy recipient mice. Notably, the Arf-GFP allele, while functionally null, expresses GFP in lieu of p19Arf when the cellular Arf promoter is induced. Healthy syngeneic recipients of ICN1/CFP, ArfGfp/Gfp donor cells developed CFP-marked T ALLs that co-expressed GFP, providing direct evidence that Arf is induced during thymus-derived leukemogenesis in vivo. Notably, Arf-induction not only provides p53-dependent elimination of incipient tumor cells but also generates a selective pressure for the emergence and survival of rare clones that have sustained Arf deletions. We reason that deletion of INK4A-ARF observed in human NOTCH1-induced CD4+/CD8+ T ALL strongly argues for the obligate induction of the locus at an earlier stage of T cell maturation. Our mouse model recapitulates this requirement, and should provide a useful platform to further elucidate disease mechanisms and potential therapies in T ALLs arising in nonirradiated mice that retain hematopoietic and immune functions. Disclosures: No relevant conflicts of interest to declare.

Sign in / Sign up

Export Citation Format

Share Document