Distinct gene expression profiles of acute myeloid/T-lymphoid leukemia with silenced CEBPA and mutations in NOTCH1

Abstract

Gene expression profiling of acute myeloid leukemia (AML) allows the discovery of previously unrecognized molecular entities. Here, we identified a specific subgroup of AML, defined by an expression profile resembling that of AMLs with mutations in the myeloid transcription factor CCAAT/enhancer-binding protein alpha (C/EBP␣), while lacking such mutations. We found that in these leukemias, the CEBPA gene was silenced, which was associated with frequent promoter hypermethylation. The leukemias phenotypically showed aberrant expression of Tcell genes, of which CD7 was most consistent. We identified 2 mechanisms that may contribute to this phenotype. First, absence of Cebpa led to up-regulation of specific T-cell transcripts (ie, Cd7 and Lck) in hematopoietic stem cells isolated from conditional Cebpa knockout mice. Second, the enhanced expression of TRIB2, which we identify here as a direct target of the T-cell commitment factor NOTCH1, suggested aberrantly activated Notch signaling. Putatively activating NOTCH1 mutations were found in several specimens of the newly identified subgroup, while a large set of control AMLs was mutation negative. A gene expression prediction signature allowed the detection of similar cases of leukemia in independent series of AML. IntroductionAcute myeloid leukemia (AML) is a heterogeneous disease with respect to its underlying genetic abnormalities and clinical biology. 1 It has therefore been postulated that AML, although always characterized by a malignant accumulation of myeloid progenitor cells, in fact represents not a single disease, but a group of neoplasms. Cytogenetic and molecular analyses, studying specific chromosomal translocations and mutations, are used to identify subgroups of AML with distinct biologic and clinical behavior. Recent developments in microarray research have resulted in further improvements in the characterization of the molecular heterogeneity of AML, 2 and gene expression profiling (GEP) studies have demonstrated that specific chromosomal aberrations, such as the common translocations t(8;21), t(15;17), and inv(16), correlate with unique expression signatures. [3][4][5] In a GEP study of 285 cases of de novo AML, we found that specific expression profiles are associated with other recurrent genetic aberrations such as mutations in NPM1 and alterations involving MLL, and with overexpression of the proto-oncogene EVI1 as well. 4,6 Some AMLs lacking these particular abnormalities were found to express the same characteristic profiles, suggesting that deregulation of the same pathways had occurred through yet-unknown mechanisms. This study also showed that 2 distinct expression clusters (no. 4 and no. 15) consisted primarily of AML cases with mutations in CEBPA, the gene encoding the basic leucine zipper transcription factor CCAAT/enhancer-binding protein alpha (C/EBP␣). C/EBP␣ is a critical regulator of hematopoietic stem cell (HSC) homeostasis and myeloid differentiation, [7][8][9][10] and multiple studies have shown that C/EBP␣ function is frequently ...

The presence of C/EBPα and its degradation are both required for TRIB2-mediated leukaemia

“…This suggests that TRIB2 degrades C/EBPα p42 via ubiquitination of K313 and duplication of this residue as occurs in AML patients samples would lead to an increase in C/EBPα p42 degradation in the presence of TRIB2. Patients with K313dup had TCR rearrangements and CD7 expression (27), lymphoid features associated with unfavourable outcome and which we have previously linked with TRIB2 and C/EBPα perturbation (31). Previous investigation of the combination of a C-terminal mutation (K313 duplication) with C/EBPα p30 expression revealed co-operation and provides a possible explanation for the high prevalence of one N-term mutation and one C-term mutation in ~90% of biallelic C/EBPα mutant AMLs (23).…”

Cooperating gene mutations in acute myeloid leukemia: a review of the literature

“…[146][147][148][149] Three mechanisms of CEBPA inactivation have been reported: (1) downregulation of CEBPA expression consecutive to the AML1-ETO fusion transcript in t(8,21) leukemia cells, interestingly conditional expression of CEBPA in these cells is sufficient to trigger granulocytic differentiation; 150 recently, Wouters et al reported that the CEBPA gene could also be silenced by promoter hypermethylation in a specific subtype of AML that phenotypically showed aberrant expression of T-cell genes such as CD7 or enhanced expression of TRIB2, suggesting aberrantly activated NOTCH signaling. 151 (2) Suppression of CEBPA function through inhibition of the translation of CEBPA mRNA by interaction with hnRNPE2, which is induced by BCR-ABL; 152 this mechanism could explain transition of chronic phase to myeloid blast crisis in CML by blocking myeloid differentiation and (3) other genetic abnormalities affecting CEBPA gene, particularly mutations, which have been reported in hematological malignancies, mainly in AML. 153 Acquired point mutations of the CEBPA gene have been reported in 89 of 965 (9%) AML patients in 7 studies including 12 M0-AML, 159 M1-AML, 203 M2-AML, 44 M3-AML, 101 M4-AML, 98 M5-AML, 8 M6-AML, 4 M7-AML and 15 secondary AML and 321 AML for which FAB or WHO classification was not mentioned.…”

Mutant Wilms’ tumor 1 (WT1) mRNA with premature termination codons in acute myeloid leukemia (AML) is sensitive to nonsense-mediated RNA decay (NMD)

“…We have previously shown that SFKs can negatively regulate myeloid differentiation. 8 In this report, we sought to determine whether treatment of AML cell lines and primary cells with dasatinib might restore or enhance ATRA-induced differentiation.…”