[CANCERRESEARCH (SUPPL.) 59, 1789s-1793s, April 1, 1999] Core-Binding Factor: A Central Player in Hematopoiesis and Leukemia 1 Nancy A. Speck, z Terry Stacy, Qing Wang, Trista North, Ting-Lei Gu, Janelle Miller, Michael Binder, and Miguel Marin-Padilla Departments of Biochemistry [N. A. S., T. S., Q. W., T.N., T-L. G., J. M.] and Anatomy and Pathology [M. B., M. M-P.], Dartmouth Medical School, Hanover, New Hampshire 03755 Abstract The Involvement of CBFs in Human Disease Consistent chromosomal rearrangements are found in a large number CBFa2 and CBF/3 are members of a small family of transcription of hematopoietic tumors. In many cases, these rearrangements disrupt factors known as CBFs or polyomavirus enhancer binding protein 2 genes whose normal function is required for the proper development of (1). CBFs are heterodimeric transcription factors that contain one blood cells. Excellent examples are the chromosomal rearrangements subunit that binds DNA directly (CBFc0 and a second, non-DNA- t(8;21)(q22;q22), t(12;21)(p13;q22), and inv(16)(p13q22) that disrupt two binding CBF/3 subunit (Fig. 1; Refs. 2-4). Four genes encode sub- of the genes encoding a small family of heterodimeric transcription fac- units of CBF in humans: three encode CBFa subunits (CBFA1, tors, core-binding factors (CBFs). CBFs consist of a DNA-binding CBFa CBFA2, and CBFA3); and one gene encodes the common CBF/3 subunit and a non-DNA-binding CBF/3 subunit. The t(8;21), associated with de novo acute myeloid leukemias, disrupts the CBFA2 (AML1) gene, subunit, CBFB (2-7). which encodes a DNA-binding CBFa subunit. The t(12;21), the most CBFs play critical roles in both normal developmental processes common translocation in pediatric acute lymphocytic leukemias, also and disease. The CBFA1 gene, which encodes a DNA-binding disrupts CBFA2. The CBFB gene, which encodes the non-DNA-binding CBFa subunit, is required for bone development. Mice lacking subunit of the CBFs, is disrupted by the inv(16) in de novo acute myeloid both copies of the Cbfal gene are completely lacking in bone leukemias. All chromosomal rearrangements involving the CBFA2 and formation, due to a defect in osteoblast differentiation (8, 9). The CBFB genes create chimeric proteins, two of which have been unequivo- human homologue, CBFA1, is implicated in a human genetic cally demonstrated to function as transdominant negative inhibitors of disorder, cleidocranial dysplasia, an autosomal dominant trait char- CBF function. acterized by moderate skeletal malformations (10). The mutations Both the Cbfa2 and Cbfb genes are essential for normal hematopoiesis in cleidocranial dysplasia patients inactivate only one copy of the in mice, because homozygous disruption of either gene blocks definitive CBFA1 gene, indicating that the disorder is caused by haploinsuf- hematopoiesis. Recent data suggest that Cbfa2 and Cbfb are required for the emergence of definitive hematopoietic stem cells in the embryo from a ficiency of CBFA1. putative definitive hemangioblast precursor. The transdominant negative The Cbfa2 and Cbfb genes are required tor fetal liver hematopoiesis inhibitor of CBF created by the inv(16), when present from the beginning in mice and play major roles in the etiology of many human leuke- of embryogenesis, also blocks the emergence of definitive hematopoietic mias. The human homologue of Cbfa2 (CBFA2, more commonly cells in the embryo. On the other hand, chromosomal translocations known as AML1) is disrupted by the t(8;21)(q22;q22), t(12;21)(p13; involving the CBFA2 and CBFB genes in leukemias block hematopoiesis q22), and t(3;21)(q26;q22) in acute myeloid and lymphocytic leuke- at later steps. This may reflect a difference in the timing at which mias and in therapy-related leukemias and myelodysplasias (Fig. 1; translocations are acquired in the leukemias, which presumably is subse- Refs. 5 and 11-14). The CBFB gene, which encodes the non-DNA- quent to emergence of the definitive hematopoietic stem cell. The cumu- binding CBFI3 subunit, is disrupted in acute myeloid leukemias by lative data suggest that although the earliest requirement for Cbfa2 and inv(16)(p13;q22), t(16;16), and del(16)(q22) (15). Together, CBFA2 Cbfb is for emergence of definitive hematopoietic stem cells, both genes are also required at later stages in the differentiation of some hematopoietic and CBFB are disrupted in approximately a quarter of all de novo lineages. acute leukemias, making them the most frequently disrupted genes in acute human leukemias (16-20). Introduction The chromosomal translocations involving the CBFA2 and CBFB genes generate chimeric proteins that contain all or part of CBFoz2 Hematopoiesis is the process by which blood cell populations of all (AML1) or CBFI3 fused to a segment of a protein encoded on the lineages are continuously renewed through differentiation I?om a other chromosome involved in the translocation (Fig. 2). The t(8;21) common progenitor cell called the pluripotent HSC. 3 Many transcrip- fuses the NH2-terminus of CBFoz2, including its DNA-binding do- tion factors are required for blood cell development, and several, such main, to a protein called ETO (for eight twenty one), encoded on as Scl, Rbtn2, E2A, and the subjects of this review, CBFo~2 (AML1) chromosome 8. The t(3;21) fuses the NH2-terminus of CBFoz2 to one and CBFI3, also play key roles in the dysregulation of hematopoiesis of three different proteins encoded by genes closely linked on chro- manifested as leukemia. mosome 3: EAP, MDS1, or EVIl. The t(12;21) breaks the CBFA2 gene 5' to the first coding exon and fuses the NH2-terminus of a protein in the ets family called TEL to the full-length CBFoz2 protein. Received 2/5/99; accepted 2/8/99. All of these chimeric CBFol2 proteins contain the CBFoz2 (AML1) The costs of publication of this article were defrayed in part by the payment of page DNA-binding domain, and they are believed to deregulate the tran- charges. This article must therefore be hereby marked advertisement in accordance with scription of CBF target genes in a transdominant manner (21-27). 18 U.S.C. Section 1734 solely to indicate this fact. 1 Presented at the "General Motors Cancer Research Foundation Twentieth Annual The inv(16) that disrupts the CBFB gene results in a chimeric Scientific Conference: DevelopmentalBiology and Cancer," June 9-10, 1998, Bethesda, protein that contains most of the CBF~ protein fused to the COOH- MD. This work was supported by USPHS Grants CA58343 and CA75611. N. A. S. is a Leukemia Society of America Scholar. terminal c~-helical rod domain from a SMMHC (Fig. 2; Ref. 15). It is 2 To whom requests for reprints should be addressed. thought that the CBFI3-SMMHC protein blocks wild-type CBF func- 3 The abbreviations used are: HSC, hematopoietic stem cell; CBF, core-bindingfactor; SMMHC, smooth muscle myosin heavy chain; dpc, days post coitus; AGM, aorta/genital tion by assembling into multimers that sequester CBFc~ subunits into ridge/mesonephros. nonfunctional complexes (28-30). 1789s Downloaded from cancerres.aacrjournals.org on September 30, 2021. © 1999 American Association for Cancer Research. CBF IN HEMATOPOIESIS AND LEUKEMIA GENES DISEASE MUTATIONS CBFB AML M4Eo inv(16)(p13;q22) Fig. 1. The CBF complex and its association with leukemias. CBF binds the sequence CBFA 1 CCD Haploinsufficiency PyGPyGGT. The CBF/3 subunit forms a 1:1 com- plex with CBF~ and increases the binding affinity of CBFc~ for DNA (2, 4). Three genes encode CBFA2 ~ML1) AML M2 t(8;21)(q22;q22) CBFc~ subunits, and one of these genes, the CBFA2 gene, along with the CBFB gene, are the most frequently disrupted genes in acute human leuke- t-MDS t mias. t-AML t(3;21 )(q26.2;q22) CML-BC PyGPyGGT A L L t(12;21 )(p13 ;q22) CBFA3 Cbfa2 andCbfb Are Required for the Emergence of Definitive and are primarily primitive nucleated erythrocytes and small numbers Hematopoietic Stem Cells of granulocytes and macrophages (31). This first, transient wave of "primitive" yolk sac hematopoiesis is followed shortly thereafter by Gene disruption experiments in mice demonstrated that both Cbfa2 the appearance of "definitive" hematopoietic progenitor cells, which and Cbfb are required for the differentiation of all hematopoietic cells derived from the HSCs. Before describing the hematopoietic defect in are capable of differentiating into all adult blood cell lineages. De- Cbfa2- and Cbfb-deficient mice in more detail, it is worthwhile to finitive hematopoietic cells emerge from several sites in the embryo: briefly review the early steps of hematopoiesis in the developing from the extraembryonic yolk sac; the omphalomesenteric and um- embryo. bilical arteries; the embryonic splanchnopleure; and from the AGM Pluripotent HSCs are the source of all blood cells in the adult. region (32-37). The first-long term repopulating HSCs, which are However, paradoxically, they are not the first blood cells to develop cells capable of reconstituting an intact hematopoietic system when in the embryo. The first blood cells, which arise from mesoderm, transplanted into a lethally irradiated adult mouse, appear at 10.0 dpc appear in the extraembryonic yolk sac of mouse embryos at -8 dpc in the AGM region (36, 37). After their emergence, definitive hema- t(8;21) A t(12;21) t(3;21) CBF~2 (AML1) AML1-ETO ~....{:!...~:.~.:::~.:~.::::~...:~.:::~...::~.~:::.~::~.::~:..:2:~.~:.7:~:.~:..~:::~:.~:...~.:~.::.~::::~.:~:....~:.:~.::....:~.::.~.::~.:::~:~::~.] t(8;21) AML1-EAP t(3;21) AML1 -MDS1 / // / t(3;21) AML1 -EVIl t(3;21) TEL-AML1 I ~ ] t(12;21) inv(16) B CBF~ CBF~-SMMHC inv(16) Fig. 2. CBFot2 (AMLI) and CBF/3 fusion proteins. A, chimeric proteins resulting from chromosomal translocations involving the CBFA2 (AMLI) gene. Black rectangle, the DNA-binding domain. Sequences derived from fusion partners are indicated by the stippled, dashed, and lined rectangles.