Transcription factor-driven coordination of cell cycle exit and lineage-specification in vivo during granulocytic differentiation : In memoriam Professor Niels Borregaard.

Differentiation of multipotent stem cells into mature cells is fundamental for development and homeostasis of mammalian tissues, and requires the coordinated induction of lineage-specific transcriptional programs and cell cycle withdrawal. To understand the underlying regulatory mechanisms of this fundamental process, we investigated how the tissue-specific transcription factors, CEBPA and CEBPE, coordinate cell cycle exit and lineage-specification in vivo during granulocytic differentiation. We demonstrate that CEBPA promotes lineage-specification by launching an enhancer-primed differentiation program and direct activation of CEBPE expression.

ERG promotes the maintenance of hematopoietic stem cells by restricting their differentiation.

The balance between self-renewal and differentiation is crucial for the maintenance of hematopoietic stem cells (HSCs). Whereas numerous gene regulatory factors have been shown to control HSC self-renewal or drive their differentiation, we have relatively few insights into transcription factors that serve to restrict HSC differentiation. In the present work, we identify ETS (E-twenty-six)-related gene (ERG) as a critical factor protecting HSCs from differentiation.

Amplification of pico-scale DNA mediated by bacterial carrier DNA for small-cell-number transcription factor ChIP-seq.

Background: Chromatin-Immunoprecipitation coupled with deep sequencing (ChIP-seq) is used to map transcription factor occupancy and generate epigenetic profiles genome-wide. The requirement of nano-scale ChIP DNA for generation of sequencing libraries has impeded ChIP-seq on in vivo tissues of low cell numbers.

Results: We describe a robust, simple and scalable methodology for ChIP-seq of low-abundant cell populations, verified down to 10,000 cells.

Integrative analysis of histone ChIP-seq and transcription data using Bayesian mixture models.

Motivation: Histone modifications are a key epigenetic mechanism to activate or repress the transcription of genes. Datasets of matched transcription data and histone modification data obtained by ChIP-seq exist, but methods for integrative analysis of both data types are still rare. Here, we present a novel bioinformatics approach to detect genes that show different transcript abundances between two conditions putatively caused by alterations in histone modification.

C/EBPα is required for long-term self-renewal and lineage priming of hematopoietic stem cells and for the maintenance of epigenetic configurations in multipotent progenitors.

Transcription factors are key regulators of hematopoietic stem cells (HSCs) and act through their ability to bind DNA and impact on gene transcription. Their functions are interpreted in the complex landscape of chromatin, but current knowledge on how this is achieved is very limited. C/EBPα is an important transcriptional regulator of hematopoiesis, but its potential functions in HSCs have remained elusive.

C/EBPα is dispensable for the ontogeny of PD-1+ CD4+ memory T cells but restricts their expansion in an age-dependent manner.

Ageing and cancer is often associated with altered T cell distributions and this phenomenon has been suggested to be the main driver in the development of immunosenescence. Memory phenotype PD-1+ CD4+ T cells accumulate with age and during leukemic development, and they might account for the attenuated T cell response in elderly or diseased individuals. The transcription factor C/EBPα has been suggested to be responsible for the accumulation as well as for the senescent features of these cells including impaired TCR signaling and decreased proliferation.

Initiation of MLL-rearranged AML is dependent on C/EBPα.

MLL-fusion proteins are potent inducers of oncogenic transformation, and their expression is considered to be the main oncogenic driving force in ∼10% of human acute myeloid leukemia (AML) patients. These oncogenic fusion proteins are responsible for the initiation of a downstream transcriptional program leading to the expression of factors such as MEIS1 and HOXA9, which in turn can replace MLL-fusion proteins in overexpression experiments. To what extent MLL fusion proteins act on their own during tumor initiation, or if they collaborate with other transcriptional regulators, is unclear.

Phosphorylation of serine 248 of C/EBPα is dispensable for myelopoiesis but its disruption leads to a low penetrant myeloid disorder with long latency.

Background: Transcription factors play a key role in lineage commitment and differentiation of stem cells into distinct mature cells. In hematopoiesis, they regulate lineage-specific gene expression in a stage-specific manner through various physical and functional interactions with regulatory proteins that are simultanously recruited and activated to ensure timely gene expression. The transcription factor CCAAT/enhancer binding protein α (C/EBPα) is such a factor and is essential for the development of granulocytic/monocytic cells.

Mutation of C/EBPalpha predisposes to the development of myeloid leukemia in a retroviral insertional mutagenesis screen.

The CCAAT enhancer binding protein alpha (C/EBPalpha) is an important myeloid tumor suppressor that is frequently mutated in human acute myeloid leukemia (AML). We have previously shown that mice homozygous for the E2F repression-deficient Cebpa(BRM2) allele develop nonfatal AML with long latency and incomplete penetrance, suggesting that accumulation of secondary mutations is necessary for disease progression. Here, we use SRS19-6-driven retroviral insertional mutagenesis to compare the phenotypes of leukemias arising in Cebpa(+/+), Cebpa(+/BRM2), and Cebpa(BRM2/BRM2) mice, with respect to disease type, latency of tumor development, and identity of the retroviral insertion sites (RISs).

The proline-histidine-rich CDK2/CDK4 interaction region of C/EBPalpha is dispensable for C/EBPalpha-mediated growth regulation in vivo.

The C/EBPalpha transcription factor regulates growth and differentiation of several tissues during embryonic development. Several hypotheses as to how C/EBPalpha inhibits cellular growth in vivo have been derived, mainly from studies of tissue culture cells. In fetal liver it has been proposed that a short, centrally located, 15-amino-acid proline-histidine-rich region (PHR) of C/EBPalpha is responsible for the growth-inhibitory function of the protein through its ability to interact with CDK2 and CDK4, thereby inhibiting their activities.

Loss of C/EBP alpha cell cycle control increases myeloid progenitor proliferation and transforms the neutrophil granulocyte lineage.

CCAAT/enhancer binding protein (C/EBP)alpha is a myeloid-specific transcription factor that couples lineage commitment to terminal differentiation and cell cycle arrest, and is found mutated in 9% of patients who have acute myeloid leukemia (AML). We previously showed that mutations which dissociate the ability of C/EBP alpha to block cell cycle progression through E2F inhibition from its function as a transcriptional activator impair the in vivo development of the neutrophil granulocyte and adipose lineages. We now show that such mutations increase the capacity of bone marrow (BM) myeloid progenitors to proliferate, and predispose mice to a granulocytic myeloproliferative disorder and transformation of the myeloid compartment of the BM.