%0 Thesis
%9 Doctoral
%A Walf-Voderwüelbecke, V.
%B UCL Molecular Haematology and Cancer Biology Unit
%D 2009
%F discovery:18608
%I UCL (University College London)
%P 265
%T A model to investigate the oncogenic activity of MLL-fusions in Acute Myeloid Leukaemia
%U https://discovery.ucl.ac.uk/id/eprint/18608/
%X The MLL gene, located on 11q23, is involved in a large number of chromosomal translocations, including t(9;11)(p22;q23) and t(11;19)(p22;q23).  These translocations encode the MLL-AF9 and MLL-ENL fusion transcription  factors and are prevalent in infant acute leukaemia and therapy-related leukaemia.  Leukaemias associated with these translocations have a particularly poor outcome. In  order to conditionally express the MLL-AF9 fusion oncogene in primary  haematopoietic progenitor cells, retroviral delivery of the Tet-off expression system  was used. Progenitors were purified from murine bone marrow and co-infected with  MSCV-TRE-fMLL-AF9 and MSCV-tTA retroviral supernatants. Using this  approach, eight independent cell lines with conditional expression of MLL-AF9 and  three independent cell lines with constitutive MLL-AF9 expression were generated.  Treatment of the conditional cells with Doxycycline caused a decrease in MLL-AF9  mRNA and protein expression, and resulted in terminal differentiation of the cells.  By analysing global changes in gene expression after treatment of cells with  Doxycycline, using Mouse genome Affymetrix Gene Chips (430 2.0), we have  identified a number of potential transcriptional target genes of the MLL-AF9 and  MLL-ENL fusion oncogenes. In order to examine the importance of target genes for  MLL-fusion mediated transformation, up-regulated target genes were knocked down  in vitro. Knock-down of a small proportion of the target genes analysed caused  MLL-ENL and MLL-AF9 immortalised cells to die. These data illustrate novel  approaches to interfering with MLL-fusion activity in leukaemia. In order to  establish the importance of MLL-fusion activity for leukaemia in vivo, and hence its  dependence on the transcriptional target genes identified, MLL-ENL immortalised  cell lines were chosen to be injected into primary recipients. Conditionally MLL-ENL immortalised cell lines were found to induced leukaemia in vivo. Leukaemic  cells isolated from primary recipient mice were shown to have acquired additional  genetic abnormalities and, when transplanted into secondary recipients, induced  leukaemia with shortened latencies. However, the leukaemic cells remained  dependent on MLL-ENL expression in vitro and in vivo, and its ablation resulted in  regression of established leukaemias.