Characterisation of the leukaemia-associated ETO homologues

Abstract: Acute myeloid leukemia (AML) is commonly associated with balanced chromosomal translocations. Characteristically, these translocations lead to the fusion of two unrelated genes, resulting in the expression of an aberrant fusion protein. t(8;21) is one of the most common translocations found in patients with AML. It results in the expression of the chimeric protein AML1-ETO. AML1 is a transcription factor of crucial importance during hematopoiesis. The function of the fusion partner eight-twenty-one (ETO) is much less understood. The aim of this thesis was to characterise ETO and its two homologues, myeloid translocation gene 16 (MTG16) and myeloid translocation gene related protein 1 (MTGR1), to elucidate their role in normal and disregulated hematopoiesis. We studied the interaction patterns of the ETO homologues as well as their expression pattern in hematopoietic cells. We also examined the consequences of upregulation or downregulation of the proteins. We found that all the ETO homologues as well as AML1-ETO can interact with each other as determined by IP-Western experiments. We also found that the ETO homologues, but not AML1-ETO can bind to the corepressor SIN3B. The proposed interactions of the ETO homologues might have implications for the onset of leukaemia, since it opens up for an AML1-ETO mediated disturbance of ETO homologue function as well as a regulation of AML1-ETO function by the ETO homologues.

Examination of the expression patterns of ETO homologues in hematopoetic cells show that the expression of ETO is restricted to erythroid cells, suggesting a role for ETO in erythropoiesis. MTG16 and MTGR1 are ubiquitously expressed in hematopoietic cells. However, the expression of MTG16 decresases during erythroid and granulocytic differentiation, suggesting a role for MTG16 in early hematopoiesis. Furthermore, the differential expression of the ETO homologues in hematopoetic cells implies a specific function for each protein in hematopoiesis. Attempts to knock-down MTG16 show a discrepancy between RNA levels and protein levels,which could propose a mechanism to keep the expression of MTG16 constant. Finally, overexpression experiments indicate a role for ETO in proliferation and apoptosis.