An insertional mutagenesis screen identifies genes that cooperate with Mll-AF9 in a murine leukemogenesis model

Patients with a t(9;11) translocation (MLL-AF9) develop acute myeloid leukemia (AML), and while in mice the expression of this fusion oncogene also results in the development of myeloid leukemia, it is with long latency. To identify mutations that cooperate with Mll-AF9, we infected neonatal wild-type (WT) or Mll-AF9 mice with a murine leukemia virus (MuLV). MuLV-infected Mll-AF9 mice succumbed to disease significantly faster than controls presenting predominantly with myeloid leukemia while infected WT animals developed predominantly lymphoid leukemia. We identified 88 candidate cancer genes near common sites of proviral insertion. Analysis of transcript levels revealed significantly elevated expression of Mn1, and a trend toward increased expression of Bcl11a and Fosb in Mll-AF9 murine leukemia samples with proviral insertions proximal to these genes. Accordingly, FOSB and BCL11A were also overexpressed in human AML harboring MLL gene translocations. FOSB was revealed to be essential for growth in mouse and human myeloid leukemia cells using shRNA lentiviral vectors in vitro. Importantly, MN1 cooperated with Mll-AF9 in leukemogenesis in an in vivo BM viral transduction and transplantation assay. Together, our data identified genes that define transcription factor networks and important genetic pathways acting during progression of leukemia induced by MLL fusion oncogenes. (Blood. 2012; 119(19): 4512-4523

MLL-AF9-mediated immortalization of human hematopoietic cells along different lineages changes during ontogeny

<p>The MLL-AF9 fusion gene is associated with aggressive leukemias of both the myeloid and lymphoid lineage in infants, whereas in adults, this translocation is mainly associated with acute myeloid leukemia. These observations suggest that differences exist between fetal and adult tissues in terms of the 'cell of origin' from which the leukemia develops. Here we show that depending on extrinsic cues, human neonatal CD34(+) cells are readily immortalized along either the myeloid or lymphoid lineage upon MLL-AF9 expression and give rise to mainly lymphoid leukemia in immunocompromised mice. In contrast, immortalization of adult bone marrow CD34(+) cells is more difficult to achieve and is myeloid-biased, even when MLL-AF9 is expressed in purified hematopoietic stem cells (HSCs). Transcriptome analysis identified enrichment of HSC but not progenitor gene signatures in MLL-AF9-expressing cells. Although not observed in adult cells, neonatal cells expressing MLL-AF9 were enriched for gene signatures associated with poor prognosis, resistance to chemotherapeutic agents and MYC signaling. These results indicate that neonatal cells are inherently more prone to MLL-AF9-mediated immortalization than adult cells and suggest that intrinsic properties of the cell of origin, in addition to extrinsic cues, dictate lineage of the immortalized cell.</p>

Pontin is a critical regulator for AML1-ETO-induced leukemia.

International audienceThe oncogenic fusion protein AML1-ETO, also known as RUNX1-RUNX1T1 is generated by the t(8;21)(q22;q22) translocation, one of the most frequent chromosomal rearrangements in acute myeloid leukemia (AML). Identifying the genes that cooperate with or are required for the oncogenic activity of this chimeric transcription factor remains a major challenge. Our previous studies showed that Drosophila provides a genuine model to study how AML1-ETO promotes leukemia. Here, using an in vivo RNA interference screen for suppressors of AML1-ETO activity, we identified pontin/RUVBL1 as a gene required for AML1-ETO-induced lethality and blood cell proliferation in Drosophila. We further show that PONTIN inhibition strongly impaired the growth of human t(8;21)(+) or AML1-ETO-expressing leukemic blood cells. Interestingly, AML1-ETO promoted the transcription of PONTIN. Moreover, transcriptome analysis in Kasumi-1 cells revealed a strong correlation between PONTIN and AML1-ETO gene signatures and demonstrated that PONTIN chiefly regulated the expression of genes implicated in cell cycle progression. Concordantly, PONTIN depletion inhibited leukemic self-renewal and caused cell cycle arrest. All together our data suggest that the upregulation of PONTIN by AML1-ETO participate in the oncogenic growth of t(8;21) cells