The inv(16) encodes an acute myeloid leukemia 1 transcriptional corepressor

Abstract

The inv(16) is one of the most frequent chromosomal translocations associated with acute myeloid leukemia (AML). The inv(16) fusion protein acts by dominantly interfering with AML-1͞core binding factor ␤-dependent transcriptional regulation. Here we demonstrate that the inv(16) fusion protein cooperates with AML-1B to repress transcription. This cooperativity requires the ability of the translocation fusion protein to bind to AML-1B. Mutational analysis and cell fractionation experiments indicated that the inv(16) fusion protein acts in the nucleus and that repression occurs when the complex is bound to DNA. We also found that the inv(16) fusion protein binds to AML-1B when it is associated with the mSin3A corepressor. An AML-1B mutant that fails to bind mSin3A was impaired in cooperative repression, suggesting that the inv(16) fusion protein acts through mSin3 and possibly other corepressors. Finally, we demonstrate that the C-terminal portion of the inv(16) fusion protein contains a repression domain, suggesting a molecular mechanism for AML-1-mediated repression.T he inv (16) is one of the most frequent translocations in acute myeloid leukemia (AML) (1). It fuses most of core binding factor ␤ (CBF␤͞CBFB͞PEBP2B) to the C terminus of a smooth muscle myosin heavy chain (SMMHC), MYH11 (2). CBF␤ is a transcription factor that does not bind DNA directly but interacts with the AML-1 DNA-binding transcription factor to increase its ability to bind DNA and regulate transcription (3, 4). AML-1 is one of the most frequently mutated genes in human leukemia (5). It is disrupted by the t(8;21), t(3;21), and t(16;21) in AML and by the t(12;21) in childhood B cell acute lymphocytic leukemia (ALL). By disrupting CBF␤, the inv(16) also disrupts AML-1 functions (6). Together, these chromosomal translocations account for nearly one-quarter of all AML cases and one-fifth of all childhood B cell ALL-containing discernible chromosomal abnormalities (7,8).The largest form of AML1, termed AML-1B(9), activates transcription of numerous tissue-specific genes, including genes encoding cytokines and cytokine receptors, and differentiationspecific genes such as T cell receptors, neutrophil peptide-3, and myeloperoxidase (10). CBF␤ cooperates with AML-1 to activate transcription (11). Targeted deletion of the AML1 (Cbfa2͞ Pebp2aB2) or CBF␤ genes led to identical phenotypes: embryonic lethality at day 12.5-13.5 post coitus with a complete lack of fetal liver hematopoiesis (12-15). Thus, CBF␤ is required for AML-1 function.The targeting of AML-1 by multiple chromosomal translocations in acute leukemia suggests a convergent mechanism of leukemogenesis. The t(8;21) fusion protein creates a transcriptional repressor protein by fusing the AML-1 DNA-binding domain to ETO (MTG8), a corepressor that recruits histone deacetylases to inhibit transcription (5). Likewise, the t(16;21) fuses the AML-1 DNA-binding domain to an ETO family member (16). The t(3;21) fuses the AML-1 DNA-binding domain to the Evi I transcriptional repressor (17). Alternatively...

RUNX1 associates with histone deacetylases and SUV39H1 to repress transcription

“…RUNX1 residues 1-204 are also retained in the t(8;21) fusion protein, which again predicts that this fusion protein can recruit SUV39H1, although this association may negatively affect DNA binding (Chakraborty et al, 2003). Although the inv(16) contains no homology to RUNX1, it acts as a corepressor for RUNX1 (Lutterbach et al, 1999;Durst et al, 2003). Our initial analysis failed to detect an association between SUV39H1 and the inv(16) fusion protein.…”

“…To begin to dissect the function of the subdomains that contact HDACs and SUV39H1, we performed reporter assays using the p21 cyclin-dependent kinase inhibitor promoter linked to firefly luciferase, which contains multiple RUNX1-binding sites (Lutterbach et al, 1999;Durst et al, 2003). RUNX1 was able to repress this promoter up to five-fold in the absence of its co-factor CBFb, and the co-expression of CBFb stimulated RUNX1-mediated repression to nearly 10-fold (Figure 6d).…”

“…RUNX1 function is also impaired by the inv(16), which fuses the RUNX1 associating factor, core binding factor b (CBFb or polyoma enhancer binding protein 2 beta) to the smooth muscle myosin heavy-chain gene MYH11, in approximately 8% of acute myeloid leukemia (Liu et al, 1993). Like the t(8;21) and the t(12;21), the inv(16) also encodes a transcriptional repressor, but this factor must associate with RUNX1 to regulate transcription (Lutterbach et al, 1999;Durst et al, 2003).…”

PEBP2-β/CBF-β–dependent phosphorylation of RUNX1 and p300 by HIPK2: implications for leukemogenesis

“…35,47,48 Sitedirected mutation study elucidates Ser 249 , Thr 273 , and Ser 276 as the targets of phosphorylation. Computer software analysis of the signature motifs returned several candidate kinases that could be responsible for this phosphorylation, including MAPK, GSK3, and members of the CDK family.…”

Concepts of human leukemic development

“…Cloning of the breakpoint for this translocation identified the fusion protein CBFb-SMMHC (Liu et al, 1993). Similar to AML1-ETO, CBFb-SMMHC functions as a dominant-negative inhibitor of AML1 transcriptional activity (Lutterbach et al, 1999). To date, there have been more than 12 different translocations identified that target the CBF complex, accounting for 25% of all AML (Speck and Gilliland, 2002).…”