The synthetic peptide PFWT disrupts AF4–AF9 protein complexes and induces apoptosis in t(4;11) leukemia cells

Abstract

The MLL gene at chromosome band 11q23 is commonly involved in reciprocal translocations detected in acute leukemias. A number of experiments show that the resulting MLL fusion genes directly contribute to leukemogenesis. Among the many known MLL fusion partners, AF4 is relatively common, particularly in acute lymphoblastic leukemia in infants. The AF4 protein interacts with the product of another gene, AF9, which is also fused to MLL in acute leukemias. Based on mapping studies of the AF9-binding domain of AF4, we have developed a peptide, designated PFWT, which disrupts the AF4-AF9 interaction in vitro and in vivo. We provide evidence that this peptide is able to inhibit the proliferation of leukemia cells with t(4;11) chromosomal translocations expressing MLL-AF4 fusion genes. Further, we show that this inhibition is mediated through apoptosis. Importantly, the peptide does not affect the proliferative capacity of hematopoietic progenitor cells. Our findings indicate that the AF4-AF9 protein complex is a promising new target for leukemia therapy and that the PFWT peptide may serve as a lead compound for drug development.

The MLL recombinome of acute leukemias

“…Briefly, AF4 and AF9 colocalize at distinct nuclear foci, 17 and the disruption of the AF4/AF9 protein interaction induces apoptosis in t(4;11) cells. 18 By contrast, the AF4 protein seems to be required for growth and differentiation of lymphocytic progenitors. 19 ENL was shown to interact directly with the AF4 and AF10 proteins, 20 and in addition, AF10 binds to hDOT1L.…”

The eleven-nineteen-leukemia protein ENL connects nuclear MLL fusion partners with chromatin

“…This result is in line with the 'MLL-web' hypothesis postulated by Erfurth et al (2004) that showed that like ENL, also the related fusion partner AF9 binds to AF4. Interestingly, aptamere peptides that were able to disrupt the AF9/AF4 complex proved to be toxic for leukemic cells with MLL-AF4 translocations supporting a role for this molecular interaction in the transformation process (Srinivasan et al, 2004). With regard to the potential association of ENL with AF10, it is not yet clear if this is a two-hybrid artifact or if this result reflects a potential binding between these two proteins also inside the cell.…”

The heterogeneity of pediatric MLL-rearranged acute myeloid leukemia

“…50,51,53,58 Indeed, aptamere peptides that were able to disrupt the MLLT3/AFF1 complex proved to be toxic for leukemic cells with MLL-AFF1 translocations but not for blast cells of different etiology. 59 The MLL fusion with translocation partners that encode for cytosolic/membrane proteins (for example, MLLT11(AF1q) and MLLT4(AF6)) seems to have different pathways leading to the oncogenic activity of the MLL-fusion gene. However, it is thought that dimerization of these proteins is contributing to the activation of target genes.…”