SPI1 and acute myeloid leukemia: In the case of the PU.1ure/ure hypomorphic mutant, the level of PU.1 expression is low [3], although due to the demethylation action of AZA it can be effectively increased [15] by targeting the hypermethylated region of the PU.1 promoter in AML and also to some extent in control cells (Figure 2A).