[show abstract][hide abstract] ABSTRACT: Sequencing efforts led to the identification of somatic mutations that could affect the self-renewal and differentiation of cancer-initiating cells. One such recurrent mutation targets the binding pocket of the ubiquitin ligase Fbxw7. Missense FBXW7 mutations are prevalent in various tumors, including T cell acute lymphoblastic leukemia (T-ALL). To study the effects of such lesions, we generated animals carrying regulatable Fbxw7 mutant alleles. Here, we show that these mutations specifically bolster cancer-initiating cell activity in collaboration with Notch1 oncogenes but spare normal hematopoietic stem cell function. We were also able to show that FBXW7 mutations specifically affect the ubiquitylation and half-life of c-Myc protein, a key T-ALL oncogene. Using animals carrying c-Myc fusion alleles, we connected Fbxw7 function to c-Myc abundance and correlated c-Myc expression to leukemia-initiating activity. Finally, we demonstrated that small-molecule-mediated suppression of MYC activity leads to T-ALL remission, suggesting an effective therapeutic strategy.
[show abstract][hide abstract] ABSTRACT: Acute lymphoblastic leukemia (ALL) is an aggressive hematological tumor resulting from the malignant transformation of lymphoid progenitors. Despite intensive chemotherapy, 20% of pediatric patients and over 50% of adult patients with ALL do not achieve a complete remission or relapse after intensified chemotherapy, making disease relapse and resistance to therapy the most substantial challenge in the treatment of this disease. Using whole-exome sequencing, we identify mutations in the cytosolic 5'-nucleotidase II gene (NT5C2), which encodes a 5'-nucleotidase enzyme that is responsible for the inactivation of nucleoside-analog chemotherapy drugs, in 20/103 (19%) relapse T cell ALLs and 1/35 (3%) relapse B-precursor ALLs. NT5C2 mutant proteins show increased nucleotidase activity in vitro and conferred resistance to chemotherapy with 6-mercaptopurine and 6-thioguanine when expressed in ALL lymphoblasts. These results support a prominent role for activating mutations in NT5C2 and increased nucleoside-analog metabolism in disease progression and chemotherapy resistance in ALL.
[show abstract][hide abstract] ABSTRACT: T cell acute lymphoblastic leukemias (T-ALLs) arise from the malignant transformation of hematopoietic progenitors primed toward T cell development, as result of a multistep oncogenic process involving constitutive activation of NOTCH signaling and genetic alterations in transcription factors, signaling oncogenes, and tumor suppressors. Notably, these genetic alterations define distinct molecular groups of T-ALL with specific gene expression signatures and clinicobiological features. This review summarizes recent advances in our understanding of the molecular genetics of T-ALL.
The Journal of clinical investigation 10/2012; 122(10):3398-406. · 15.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Constitutive phosphoinositide 3-kinase (PI3K)/Akt activation is common in T cell acute lymphoblastic leukemia (T-ALL). Although four distinct class I PI3K isoforms (α, β, γ, δ) could participate in T-ALL pathogenesis, none has been implicated in this process. We report that in the absence of PTEN phosphatase tumor suppressor function, PI3Kγ or PI3Kδ alone can support leukemogenesis, whereas inactivation of both isoforms suppressed tumor formation. The reliance of PTEN null T-ALL on the combined activities of PI3Kγ/δ was further demonstrated by the ability of a dual inhibitor to reduce disease burden and prolong survival in mice as well as prevent proliferation and promote activation of proapoptotic pathways in human tumors. These results support combined inhibition of PI3Kγ/δ as therapy for T-ALL.
Cancer cell 04/2012; 21(4):459-72. · 25.29 Impact Factor
[show abstract][hide abstract] ABSTRACT: Oncogenic activating mutations in NOTCH1 occur in more than 50% of T-cell acute lymphoblastic leukemias (T-ALLs). In the present study, we describe a novel mechanism of NOTCH1 activation in T-ALL in which a deletion removing the 5' portion of NOTCH1 abolishes the negative regulatory control of the extracellular domain and leads to constitutively active NOTCH1 signaling. Polypeptides translated from truncated transcripts encoded by the NOTCH1 deletion allele retain the transmembrane domain of the receptor and are constitutively cleaved by the γ-secretase complex, resulting in high levels of NOTCH1 signaling that can be effectively blocked by γ-secretase inhibitors. Our results expand the spectrum of oncogenic lesions activating NOTCH1 signaling in human T-ALL.
[show abstract][hide abstract] ABSTRACT: T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic tumor resulting from the malignant transformation of immature T-cell progenitors. Originally associated with a dismal prognosis, the outcome of T-ALL patients has improved remarkably over the last two decades as a result of the introduction of intensified chemotherapy protocols. However, these treatments are associated with significant acute and long-term toxicities, and the treatment of patients presenting with primary resistant disease or those relapsing after a transient response remains challenging. T-ALL is a genetically heterogeneous disease in which numerous chromosomal and genetic alterations cooperate to promote the aberrant proliferation and survival of leukemic lymphoblasts. However, the identification of activating mutations in the NOTCH1 gene in over 50% of T-ALL cases has come to define aberrant NOTCH signaling as a central player in this disease. Therefore, the NOTCH pathway represents an important potential therapeutic target. In this review, we will update our current understanding of the molecular basis of T-ALL, with a particular focus on the role of the NOTCH1 oncogene and the development of anti-NOTCH1 targeted therapies for the treatment of this disease.
[show abstract][hide abstract] ABSTRACT: Hematopoietic stem cell (HSC) differentiation is regulated by cell-intrinsic and cell-extrinsic cues. In addition to transcriptional regulation, post-translational regulation may also control HSC differentiation. To test this hypothesis, we visualized the ubiquitin-regulated protein stability of a single transcription factor, c-Myc. The stability of c-Myc protein was indicative of HSC quiescence, and c-Myc protein abundance was controlled by the ubiquitin ligase Fbw7. Fine changes in the stability of c-Myc protein regulated the HSC gene-expression signature. Using whole-genome genomic approaches, we identified specific regulators of HSC function directly controlled by c-Myc binding; however, adult HSCs and embryonic stem cells sensed and interpreted c-Myc-regulated gene expression in distinct ways. Our studies show that a ubiquitin ligase-substrate pair can orchestrate the molecular program of HSC differentiation.
[show abstract][hide abstract] ABSTRACT: Tumor suppressor genes on the X chromosome may skew the gender distribution of specific types of cancer. T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with an increased incidence in males. In this study, we report the identification of inactivating mutations and deletions in the X-linked plant homeodomain finger 6 (PHF6) gene in 16% of pediatric and 38% of adult primary T-ALL samples. Notably, PHF6 mutations are almost exclusively found in T-ALL samples from male subjects. Mutational loss of PHF6 is importantly associated with leukemias driven by aberrant expression of the homeobox transcription factor oncogenes TLX1 and TLX3. Overall, these results identify PHF6 as a new X-linked tumor suppressor in T-ALL and point to a strong genetic interaction between PHF6 loss and aberrant expression of TLX transcription factors in the pathogenesis of this disease.
[show abstract][hide abstract] ABSTRACT: MicroRNAs (miRNAs) have emerged as novel cancer genes. In particular, the miR-17-92 cluster, containing six individual miRNAs, is highly expressed in haematopoietic cancers and promotes lymphomagenesis in vivo. Clinical use of these findings hinges on isolating the oncogenic activity within the 17-92 cluster and defining its relevant target genes. Here we show that miR-19 is sufficient to promote leukaemogenesis in Notch1-induced T-cell acute lymphoblastic leukaemia (T-ALL) in vivo. In concord with the pathogenic importance of this interaction in T-ALL, we report a novel translocation that targets the 17-92 cluster and coincides with a second rearrangement that activates Notch1. To identify the miR-19 targets responsible for its oncogenic action, we conducted a large-scale short hairpin RNA screen for genes whose knockdown can phenocopy miR-19. Strikingly, the results of this screen were enriched for miR-19 target genes, and include Bim (Bcl2L11), AMP-activated kinase (Prkaa1) and the phosphatases Pten and PP2A (Ppp2r5e). Hence, an unbiased, functional genomics approach reveals a coordinate clampdown on several regulators of phosphatidylinositol-3-OH kinase-related survival signals by the leukaemogenic miR-19.
[show abstract][hide abstract] ABSTRACT: Precursor T-cell lymphoblastic leukemias and lymphomas represent 15% of childhood acute lymphoblastic leukemias (ALLs) and
one third of pediatric non-Hodgkin lymphomas, respectively. T-cell ALLs are characterized by prominent (>30%) bone marrow
(BM) infiltration with or without mediastinal mass, while T-cell lymphoblastic lymphomas show mediastinal masses in the context
of limited or no BM involvement. These two clinical entities share a similar spectrum of molecular and cytogenetic abnormalities,
and most probably represent different manifestations of the same disease, commonly designated here as T-ALL.
[show abstract][hide abstract] ABSTRACT: The biology and outcome of adult T-cell acute lymphoblastic leukemia are poorly understood. We present here the clinical and biologic features of 356 patients treated uniformly on the prospective trial (UKALL XII/ECOG 2993) with the aim of describing the outcome and identifying prognostic factors. Complete remission was obtained in 94% of patients, and 48% survived 5 years. Positivity of blasts for CD1a and lack of expression of CD13 were associated with better survival (P = .01 and < .001, respectively). NOTCH1 and CDKN2A mutations were seen in 61% and 42% of those tested. Complex cytogenetic abnormalities were associated with poorer survival (19% vs 51% at 5 years, P = .006). Central nervous system involvement at diagnosis did not affect survival (47% vs 48%, P = not significant). For 99 patients randomized between autograft and chemotherapy, 5-year survival was 51% in each arm. Patients with a matched sibling donor had superior 5-year survival to those without donors (61% vs 46%, chi(2), P = .02); this was the result of less relapse (25% vs 51% at 5 years, P < .001). Only 8 of 123 relapsed patients survive. This study provides a baseline for trials of new drugs, such as nelarabine, and may allow risk-adapted therapy in patients with poor-prognosis T-cell ALL.
[show abstract][hide abstract] ABSTRACT: The molecular mechanisms involved in disease progression and relapse in T-cell acute lymphoblastic leukemia (T-ALL) are poorly understood. We used single nucleotide polymorphism array analysis to analyze paired diagnostic and relapsed T-ALL samples to identify recurrent genetic alterations in T-ALL. This analysis showed that diagnosis and relapsed cases have common genetic alterations, but also that relapsed samples frequently lose chromosomal markers present at diagnosis, suggesting that relapsed T-ALL emerges from an ancestral clone different from the major leukemic population at diagnosis. In addition, we identified deletions and associated mutations in the WT1 tumor suppressor gene in 2 of 9 samples. Subsequent analysis showed WT1 mutations in 28 of 211 (13.2%) of pediatric and 10 of 85 (11.7%) of adult T-ALL cases. WT1 mutations present in T-ALL are predominantly heterozygous frameshift mutations resulting in truncation of the C-terminal zinc finger domains of this transcription factor. WT1 mutations are most prominently found in T-ALL cases with aberrant rearrangements of the oncogenic TLX1, TLX3, and HOXA transcription factor oncogenes. Survival analysis demonstrated that WT1 mutations do not confer adverse prognosis in pediatric and adult T-ALL. Overall, these results identify the presence of WT1 mutations as a recurrent genetic alteration in T-ALL.
[show abstract][hide abstract] ABSTRACT: The recent identification of activating mutations in NOTCH1 in the majority of T-cell acute lymphoblastic leukemias (T-ALLs) has brought major interest toward targeting the NOTCH signaling pathway in this disease. Small-molecule gamma-secretase inhibitors (GSIs), which block a critical proteolytic step required for NOTCH1 activation, can effectively block the activity of NOTCH1 mutant alleles. However, the clinical development of GSIs has been hampered by their low cytotoxicity against human T-ALL and the development of significant gastrointestinal toxicity derived from the inhibition of NOTCH signaling in the gut. Improved understanding of the oncogenic mechanisms of NOTCH1 and the effects of NOTCH inhibition in leukemic cells and the intestinal epithelium are required for the design of effective anti-NOTCH1 therapies in T-ALL.
[show abstract][hide abstract] ABSTRACT: Gamma-secretase inhibitors (GSIs) block the activation of the oncogenic protein Notch homolog-1 (NOTCH1) in T cell acute lymphoblastic leukemia (T-ALL). However, limited antileukemic cytotoxicity and severe gastrointestinal toxicity have restricted the clinical application of these targeted drugs. Here we show that combination therapy with GSIs plus glucocorticoids can improve the antileukemic effects of GSIs and reduce their gut toxicity in vivo. Inhibition of NOTCH1 signaling in glucocorticoid-resistant T-ALL restored glucocorticoid receptor autoupregulation and induced apoptotic cell death through induction of the gene encoding BCL-2-like apoptosis initiator-11 (BCL2L11). GSI treatment resulted in cell cycle arrest and accumulation of goblet cells in the gut mediated by upregulation of the gene encoding the transcription factor Krüppel-like factor-4 (Klf4), a negative regulator of the cell cycle required for goblet cell differentiation. In contrast, glucocorticoid treatment induced transcriptional upregulation of cyclin D2 (Ccnd2) and protected mice from developing the intestinal goblet cell metaplasia typically induced by inhibition of NOTCH signaling with GSIs. These results support a role for glucocorticoids plus GSIs in the treatment of glucocorticoid-resistant T-ALL.
Nature medicine 01/2009; 15(1):50-8. · 27.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The identification of activating mutations in NOTCH1 in the majority of T-cell acute lymphoblastic leukemias and lymphomas (T-ALL) has brought much interest in inhibiting NOTCH1 signaling as therapeutic target in this disease. Small-molecule inhibitors of the gamma-secretase complex, which mediates a critical proteolytic cleavage required for NOTCH1 activation, hold the promise of becoming an effective molecular therapy against relapsed and refractory T-ALL. Recent progress in the elucidation of the transcriptional regulatory networks downstream of oncogenic NOTCH1 has uncovered a central role of NOTCH1 signaling in promoting leukemic cell growth and revealed an intricate circuitry that connects NOTCH1 signaling with MYC and the PI3K-AKT signaling pathway. The identification of the downstream effector pathways controlled by NOTCH1 should pave the way for the rational design of anti-NOTCH1 therapies for the treatment of T-ALL.
Clinical Cancer Research 10/2008; 14(17):5314-7. · 7.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Recent studies have shown that activating mutations of NOTCH1 are responsible for the majority of T cell acute lymphoblastic leukemia (T-ALL) cases. Most of these mutations truncate its C-terminal domain, a region that is important for the NOTCH1 proteasome-mediated degradation. We report that the E3 ligase FBW7 targets NOTCH1 for ubiquitination and degradation. Our studies map in detail the amino acid degron sequence required for NOTCH1-FBW7 interaction. Furthermore, we identify inactivating FBW7 mutations in a large fraction of human T-ALL lines and primary leukemias. These mutations abrogate the binding of FBW7 not only to NOTCH1 but also to the two other characterized targets, c-Myc and cyclin E. The majority of the FBW7 mutations were present during relapse, and they were associated with NOTCH1 HD mutations. Interestingly, most of the T-ALL lines harboring FBW7 mutations were resistant to gamma-secretase inhibitor treatment and this resistance appeared to be related to the stabilization of the c-Myc protein. Our data suggest that FBW7 is a novel tumor suppressor in T cell leukemia, and implicate the loss of FBW7 function as a potential mechanism of drug resistance in T-ALL.
Journal of Experimental Medicine 09/2007; 204(8):1825-35. · 13.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: Ikaros and Notch1 genes are critical to T-cell differentiation through transcriptional activation of target genes and interaction with chromatin remodeling complexes. An Ikaros (Plastic) point mutation inhibits activity of normal Ikaros and Ikaros family members, and leads to T-cell lymphoma in heterozygotes (Plstc/+). Analysis revealed Notch1 activating mutations in 12 of 17 Plstc/+ lymphomas (70%), analogous to those in human T-ALL. Mice acquired Notch1 mutations in lymph nodes as early as 7 weeks. Thus, combined Notch1 and Ikaros dysfunction can be a significant early event in T-cell proliferation and tumorigenesis.
Leukemia Research 04/2007; 31(3):321-7. · 2.76 Impact Factor