Investigation of the role of MLL - ENL in leukaemogenesis

Acute leukaemia is the most common form of childhood cancer and is the primary cause of cancer-related mortality in children. The major initiating event in infant leukaemia is rearrangement of the Mil gene at 1 lq23, and such leukaemias have a poor survival rate. Chromosomal translocations occur commonly in leukaemia and an in-frame fusion gene is created with altered properties to the original genes involved. Translocations of chromosome 1 lq23 result in the fusion of Mil to a variety of partners genes. Mil-Aft results from t(9;l 1), Mll-A/4 from t(4; 11) and Mll-Enl from t( 11; 19) and are thought to cause aberrant transcriptional regulation. To identify candidate target genes of t( 11; 19), MLL-ENL has been over­ expressed in 32D cells, an immortalised myeloid progenitor cell line. The actions of MLL-ENL on cell survival following growth factor withdrawal, and on G-CSF mediated differentiation have been studied. Potential transcriptional targets of MLL-AF9 and MLL-ENL have been identified using microarray technology. Ten genes were identified as possible candidate target genes of the MLL-ENL protein that might be involved in leukaemogenesis. Of particular interest were Gatal and HTm4 which have a role in haematopoiesis and cell cycle regulation. shRNA constructs were generated to knock down MLL-ENL and allow validation of the potential target genes. The mechanism of leukaemic transformation by MLL-ENL has also been investigated. In leukaemia, fusion proteins may contribute to haematological malignancy in various ways, though the main routes are thought to be either a gain-of-function or dominant negative action. In order