3105 – IMPACT OF DACH1 DOWNREGULATION ON MLL-AF4 INFANT LEUKEMOGENESIS

Abstract

Leukaemia in infants, caused by a rearrangement of the MLL gene, has a very bad prognosis. The most common type of infant leukaemia is caused by the t(4;11) translocation that fuses the MLL and AF4 genes. Current lack of knowledge of its developmental origins and early stages of pathogenesis is one of the reasons for the slow progress in developing more targeted therapies. RNA-Seq studies have recently been completed in the lab to gain a more comprehensive insight into the molecular determinants that make foetal haematopoietic stem and progenitor cells more susceptible to transformation by MLL-AF4. A lack of expression of the DACH1 gene, which has been described as a tumour suppressor in a range of different cancers, was noted. The aim of this work is to assess the impact of DACH1 on the initiation of MLL-AF4+ infant leukaemia and on its maintenance. To determine the role of DACH1 on the initiation of leukaemia, we used our pre-leukaemia mouse model with Mll-AF4 expression in foetal cells and then transduced the cells with lentiviruses carrying a DACH1 overexpression construct. Using methylcellulose assays under B lymphoid or myeloid conditions, we observed that DACH1 reduces the size and numbers of B cell colonies and has a general negative effect on cell proliferation and differentiation. To establish whether DACH1 repression is required for leukaemia maintenance, we have overexpressed DACH1 in the SEM leukaemia cell line, which was derived from an MLL-AF4+ paediatric B-ALL. Our work shows that DACH1 affects negatively the proliferation and survival of the cells. To conclude, our data give new insights into the role of DACH1 in MLL-AF4 leukaemia. In the future, we will identify downstream targets of this protein to determine which genes are directly repressed by DACH1 to counteract the leukaemic phenotype.