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.
"Inhibition of Notch signaling could lead to accelerated differentiation of HSCs in vitro and depletion of HSCs in vivo[59,60]. Furthermore, Notch1 drives cell fate decision (the choice between TCRγ/δ orα/β and between CD4+ or CD8+) by inductive interactions from thymic stromal cells [61,62], suggesting that Notch1 expression is finely regulated during T-cell lineage development . Notch1 is also reported to plays a role in rescuing T cells from apoptosis . "
[Show abstract][Hide abstract] ABSTRACT: The Notch signaling pathway plays a critical role in maintaining the balance between cell proliferation, differentiation and apoptosis, and is a highly conserved signaling pathway that regulates normal development in a context- and dose-dependent manner. Dysregulation of Notch signaling has been suggested to be key events in a variety of hematological malignancies. Notch1 signaling appears to be the central oncogenic trigger in T cell acute lymphoblastic leukemia (T-ALL), in which the majority of human malignancies have acquired mutations that lead to constitutive activation of Notch1 signaling. However, emerging evidence unexpectedly demonstrates that Notch signaling can function as a potent tumor suppressor in other forms of leukemia. This minireview will summarize recent advances related to the roles of activated Notch signaling in human lymphocytic leukemia, myeloid leukemia, stem cells and stromal microenvironment, and we will discuss the perspectives of Notch signaling as a potential therapeutic target as well.
"The role of NOTCH1 and NOTCH1 gain-of-function mutations in human T-ALL (including activating deletions) as well as its use as a target in the treatment of T-ALL has been well documented , , . There is also ample evidence for abnormal FLI-1 expression in human haematological malignancies including T cell malignancies (Figure S4, , ). "
[Show abstract][Hide abstract] ABSTRACT: The Ets transcription factor Fli-1 is preferentially expressed in hematopoietic tissues and cells, including immature T cells, but the role of Fli-1 in T cell development has not been closely examined. To address this we retrovirally overexpressed Fli-1 in various in vitro and in vivo settings and analysed its effect on T cell development. We found that Fli-1 overexpression perturbed the DN to DP transition and inhibited CD4 development whilst enhancing CD8 development both in vitro and in vivo. Surprisingly, Fli-1 overexpression in vivo eventuated in development of pre-T cell lymphoblastic leukaemia/lymphoma (pre-T LBL). Known Fli-1 target genes such as the pro-survival Bcl-2 family members were not found to be upregulated. In contrast, we found increased NOTCH1 expression in all Fli-1 T cells and detected Notch1 mutations in all tumours. These data show a novel function for Fli-1 in T cell development and leukaemogenesis and provide a new mouse model of pre-T LBL to identify treatment options that target the Fli-1 and Notch1 signalling pathways.
PLoS ONE 05/2013; 8(5):e62346. DOI:10.1371/journal.pone.0062346 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background:
In T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/LBL), activating mutations of NOTCH1 are observed in more than 50% of cases, whereas the t(7;9)(q34;q34) involving NOTCH1 at 9q34 and TRB@ at 7q34 is an extremely rare but recurrent translocation.
A 41-year-old male with a large mediastinal mass, pleural effusion, and lymphadenopathy was diagnosed as having T-LBL. Lymphoma cells were positive for CD4, CD8, CD2, CD3, CD5, CD7, CD10, and TdT.
G-banding and spectral karyotyping of pleural effusion cells showed 47,XY,dup(1)(q21q32),t(7;9)(q34;q34),+20. Genomic polymerase chain reaction (PCR) revealed that the 5' end of TRB@ J1-5 was connected with the middle of NOTCH1 exon 25 (434 bp downstream from its 5' end) in a 'head-to-head' configuration on the der(9)t(7;9), although nine extra bases were inserted between the two genes. Reverse transcription-PCR confirmed expression of the TRB@/NOTCH1 fusion transcripts. Similarly, the 5' end of J1-5 was fused to the shortened exon 25 with nine extra bases. The NOTCH1 breakpoint in exon 25 was very close to transcription start sites of deleted Notch1 in murine T-ALL.
The TRB@/NOTCH1 fusion gene with a NOTCH1 breakpoint in exon 25, which has not previously been detected in four other reported cases with t(7;9), could lead to aberrant expression of the truncated NOTCH1 by TRB@ enhancer elements. The resultant NOTCH1 receptor deleting most of the extracellular domain may be implicated in the pathogenesis of T-LBL by ligand-independent, constitutive activation of the NOTCH1 pathway, suggesting avenues for future therapy with γ-secretase inhibitors.
European Journal Of Haematology 10/2012; 90(1). DOI:10.1111/ejh.12019 · 2.07 Impact Factor
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