The Steidl Lab

Albert Einstein College of Medicine

(PI:  Dr. Ulrich Steidl) 

Acute myeloid leukemias (AML) are malignant diseases that originate from a single transformed cell which has progressively acquired critical genetic changes that disrupt key growth-regulatory pathways. Despite the established use and optimization of regimens applying polychemotherapy and the development of multiple new agents that are effective at reducing the tumor burden in patients with leukemia, relapse continues to be the most common cause of death in AML. Newer experimental evidence demonstrates that AML arises from a small population of cancer stem cells / leukemia stem cells (LSC). Similar to normal hematopoietic stem cells (HSC), LSC are quiescent in terms of cell cycle and thus, conventional cytotoxic therapies are not effective against LSC in the majority of cases. However, therapeutic eradication of the LSC within the leukemia clone will be essential for a cure of disease. Therefore, an improved understanding of the molecular pathways that suppress the formation and maintenance of LSC is required for the development of therapies that target LSC rather than the bulk tumor cells (leukemic blasts). Recent findings from our own group and others demonstrate a critical role of transcriptional master regulators (e.g. PU.1) in the genesis and function of LSC in AML, and that transcription factors are already deregulated in the early stem cell compartment.  

The goal of our research is to identify critical mechanisms that drive leukemia stem cell (LSC) development and function, and to better understand the mechanisms of how transcriptional regulators (e.g. transcription factors and chromatin-remodeling factors) cause formation of LSC.

To identify implicated pathways we are utilizing rigorously defined stem and progenitor cell subsets isolated by means of multi-parameter high-speed fluorescence-activated cell sorting. Identified target genes are biochemically and functionally tested using lentiviral gene transfer and in vitro as well as in vivo assays for leukemia stem cell self-renewal and differentiation,
including colony-forming assays, serial replating assays, and
transplantation models that allow for assessing their function in LSC formation and maintenance. Our studies aim at providing the basis for development of targeted, LSC-directed therapies.

Recent publications in this field include:

Steidl et al., J Clin Invest 2007; 117:2611-20

Targeted disruption of a highly conserved distal enhancer reduces expression of the PU.1 transcription factor by 80% and leads to acute myeloid leukemia (AML) with frequent cytogenetic aberrations in mice. Here we identify a SNP within this element in humans that is more frequent in AML with a complex karyotype, leads to decreased enhancer activity, and reduces PU.1 expression in myeloid progenitors in a development-dependent manner. This SNP inhibits binding of the chromatin-remodeling transcriptional regulator special AT-rich sequence binding protein 1 (SATB1). Overexpression of SATB1 increased PU.1 expression, and siRNA inhibition of SATB1 downregulated PU.1 expression. Targeted disruption of the distal enhancer led to a loss of regulation of PU.1 by SATB1. Interestingly, disruption of SATB1 in mice led to a selective decrease of PU.1 RNA in specific progenitor types (granulocyte-macrophage and megakaryocyte-erythrocyte progenitors) and a similar effect was observed in AML samples harboring this SNP. Thus we have identified a SNP within a distal enhancer that is associated with a subtype of leukemia and exerts a deleterious effect through remote transcriptional dysregulation in specific progenitor subtypes.
[ PDF ]   [ Editorial ]

Steidl et al., Nat Genet 2006; 38:1269-77

Knockdown of the transcription factor PU.1 (encoded by Sfpi1) leads to acute myeloid leukemia (AML) in mice. We examined the transcriptome of preleukemic hematopoietic stem cells (HSCs) in which PU.1 was knocked down (referred to as 'PU.1-knockdown HSCs') to identify transcriptional changes preceding malignant transformation. Transcription factors c-Jun and JunB were among the top-downregulated targets. Restoration of c-Jun expression in preleukemic cells rescued the PU.1 knockdown-initiated myelomonocytic differentiation block. Lentiviral restoration of JunB at the leukemic stage led to loss of leukemic self-renewal capacity and prevented leukemia in NOD-SCID mice into which leukemic PU.1-knockdown cells were transplanted. Examination of human individuals with AML confirmed the correlation between PU.1 and JunB downregulation. These results delineate a transcriptional pattern that precedes leukemic transformation in PU.1-knockdown HSCs and demonstrate that decreased levels of c-Jun and JunB contribute to the development of PU.1 knockdown-induced AML by blocking differentiation and increasing self-renewal. Therefore, examination of disturbed gene expression in HSCs can identify genes whose dysregulation is essential for leukemic stem cell function and that are targets for therapeutic interventions.
[ PDF ]   [ Review_Cancer Cell 2006.pdf ]