Functional studies of Wilms’ tumor gene 1 (WT1) in hematopoiesis and leukemia

Abstract: Wilms’ tumor gene 1 (WT1) is a zinc-finger transcription factor that is involved in the development of urogenital organs and mesothelial tissues. It was initially identified as a tumor suppressor gene, based on the observation that somatic inactivation of the gene predispose for development of the pediatric kidney cancer Wilms’ tumor. A role for WT1 in hematopoiesis was suggested based on the fact that WT1 is highly expressed in immature hematopoietic progenitor cells, followed by a rapid downregulation during differentiation. Also, overexpression of WT1 and presence of somatic mutations are frequently found in acute leukemia, indicating that WT1 may be involved in the pathogenesis of leukemia. The aim of this thesis was to bring further light on the role of WT1 in normal hematopoiesis and leukemia. To this end, I expressed different forms of WT1 in leukemic cell lines and normal CD34+ hematopoietic progenitor cells and studied their impact on proliferation, differentiation and viability. I show that a constitutive expression of WT1 in the monoblastic cell line U937 lead to impairment of differentiation, whereas a high expression of WT1 in erythroleukemic K562 cells is compatible with differentiation. I also demonstrate that a forced expression of WT1 in normal hematopietic progenitor cells conferred inhibition of both myeloid and erythroid clonogenic growth and enhancement of myeloid differentiation. Furthermore, my data indicate that WT1 affects proliferation and differentiation in erythroid and myeloid cells by distinct molecular mechanisms that are not exclusively based on direct transcriptional regulation by WT1.