Acute myeloid leukemia (AML) comprises a heterogeneous group of leukemias frequently defined by recurrent cytogenetic abnormalities, including rearrangements involving subunits of the core-binding factor (CBF) transcriptional complex. To better understand the genomic landscape of CBF-AMLs, we analyzed both pediatric (n=87) and adult (n=78) samples, including cases with RUNX1-RUNX1T1 (n=85) or CBFB-MYH11 (n=80) rearrangements, by whole-genome or whole-exome sequencing. In addition to previously reported somatic mutations in the Ras signaling pathway, we identified recurrent stabilizing mutations in CCND2, suggesting a recurrent and previously unappreciated cooperating pathway in CBF-AML. Outside of signaling alterations, RUNX1-RUNX1T1 and CBFB-MYH11 AMLs demonstrated a remarkably different spectrum of cooperating mutations as RUNX1-RUNX1T1 cases harbored recurrent somatic mutations in DHX15 and ZBTB7A, as well as an enrichment of somatic mutations in epigenetic regulators, including ASXL2, and in components of the cohesin complex. This detailed analysis provides insights into the pathogenesis and development of CBF-AML, while highlighting dramatic differences in the landscape of cooperating mutations between these related AML subtypes.

mcl-1, a bcl-2 family member, was originally identified as an early gene induced during differentiation of ML-1 myeloid leukemia cells. In the present study, we demonstrate that Mcl-1 is tightly regulated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway. Upon deprivation of survival factor from TF-1 myeloid progenitor cells, Mcl-1 levels quickly dropped prior to visible detection of apoptosis of these cells. Upon restimulation of these deprived cells with GM-CSF, the mcl-1 mRNA was immediately induced and its protein product was accordingly resynthesized. Analysis with Ba/F3 cells expressing various truncation mutants of the GM-CSF receptor revealed that the membrane distal region between amino acids 573 and 755 of the receptor ␤ chain was required for mcl-1 induction. Transient-transfection assays with luciferase reporter genes driven by various regions of the mcl-1 promoter demonstrated that the upstream sequence between ؊197 and ؊69 is responsible for cytokine activation of the mcl-1 gene. Overexpression of mcl-1 delayed but did not completely prevent apoptosis of cells triggered by cytokine withdrawal. Its down regulation by antisense constructs overcame, at least partially, the survival activity of GM-CSF and induced the apoptosis of TF-1 cells. Taken together, these results suggest that mcl-1 is an immediate-early gene activated by the cytokine receptor signaling pathway and is one component of the GM-CSF viability response.

Growth factors and cytokines play an important role in supporting cellular viability of various tissues during development due to their ability to suppress the default cell death program in each cell type. To date, neither the triggering molecule nor the transduction pathway of these default apoptosis programs is understood. In this study, we explored the possibility that cytokine receptors are involved in modulating cytokine withdrawal-induced apoptosis (CWIA) in hematopoietic cells. Expression of the exogenous cytokine receptor common beta chain (betac), but not the alpha chains, accelerated CWIA in multiple cytokine-dependent cell lines. Reduction of the expression level of endogenous betac by antisense transcripts resulted in prolonged survival during cytokine deprivation, suggesting a critical role of betac in modulating CWIA. Fine mapping of the betac subunit revealed that a membrane-proximal cytoplasmic sequence, designated the death enhancement region (DER), was critical to the death acceleration effect of betac. Furthermore, DER accelerated cell death either as a chimeric membrane protein or as a cytosolic protein, suggesting that DER functions independently of the cytokine receptor and membrane anchorage. Cross-linking of the chimeric membrane-bound DER molecules by antibody or of the FK506-binding protein-DER fusion protein by a synthetic dimerizing agent, AP1510, did not abrogate the death acceleration effect. Transient transfection assays further indicated that DER promoted cell death in the absence of serum in the nonhematopoietic 293 cell line. In summary, our data suggest that betac plays an important role in modulating CWIA via an anchorage-independent and aggregation-insensitive mechanism. These findings may facilitate further studies on the signaling pathways of CWIA.