Essential role of Jun family transcription factors in PU.1-induced leukemic stem cells

Knockdown of the transcription factor PU.1 (Spi1) leads to acute myeloid leukemia (AML) in mice. We examined the transcriptome of PU.1 knockdown hematopoietic stem cells (HSC) in the preleukemic phase by linear amplification and genome-wide array analysis to identify transcriptional changes preceding malignant transformation. Hierarchical cluster analysis and principal component analysis clearly distinguished PU.1 knockdown from wildtype HSC. Jun family transcription factors c-Jun and JunB were among the top downregulated targets. Retroviral restoration of c-Jun expression in bone marrow cells of preleukemic mice partially rescued the PU.1-initiated myelomonocytic differentiation block. Lentiviral restoration of JunB at the leukemic stage led to reduced clonogenic growth, loss of leukemic self-renewal capacity, and prevented leukemia in transplanted NOD-SCID mice. Examination of 305 AML patients confirmed the correlation between PU.1 and JunB downregulation and suggests its relevance in human disease. These results delineate a transcriptional pattern that precedes the leukemic transformation in PU.1 knockdown HSC and demonstrate that decreased levels of c-Jun and JunB contribute to the development of PU.1-induced AML by blocking differentiation (c-Jun) and increasing self-renewal (JunB). Therefore, examination of disturbed gene expression in HSC can identify genes whose dysregulation is essential for leukemic stem cell function and are targets for therapeutic interventions. Keywords: genetic modification Total RNA of HSC of PU.1 knockdown or wildtype animals (3 pools of 3 animals each) was amplified by two rounds of RT and T7 promoter-based in-vitro transcription and the resultant biotinylated cRNA was then hybridized to Affymetrix Mouse Genome 430 2.0 arrays.