Downregulation of Wilms' tumor gene (WT1) is not a prerequisite for erythroid or megakaryocytic differentiation of the leukemic cell line K562. 
The Wilms' tumor gene (WT1) encodes a transcription factor of the zinc finger type. A high expression of WT1 has been detected in a range of acute leukemias, and WT1 is downregulated during induced differentiation of some leukemic cell lines. Overexpression of WT1 in some myeloid cell lines confers resistance to differentiation induction. These observations suggest that a high WT1 expression in hematopoietic cells is incompatible with differentiation. In this study, each of the four different isoforms of WT1 was constitutively overexpressed in the leukemic cell line K562. K562 cells express endogenous WT1, which is downregulated as a response to induced differentiation along the erythroid and megakaryocytic pathways. We now demonstrate that a forced exogenous expression of the four different isoforms of WT1 in K562 does not affect the differentiation response, as judged by accumulation of hemoglobin in response to hemin or the expression of megakaryocytic cell surface markers in response to 12-O-tetradecanoylphorbol-13-acetate (TPA). We conclude that downregulation of WT1 during induced differentiation of K562 cells is not a prerequisite for erythroid or megakaryocytic differentiation of these cells.