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. Subsequently, CEBPE confers promoter-driven cell cycle exit by sequential repression of MYC target gene expression at the G1/S transition and E2F-meditated G2/M gene expression, as well as by the up-regulation of Cdk1/2/4 inhibitors. Following cell cycle exit, CEBPE unleashes the CEBPA-primed differentiation program to generate mature granulocytes. These findings highlight how tissue-specific transcription factors coordinate cell cycle exit with differentiation through the use of distinct gene regulatory elements.

Here the authors show that differentiation of haematopoietic stem cells into mature blood cells is primed by cell type-specific transcription factors at the enhancer level during early differentiation, before they confere promoter-driven growth arrest, and activate post-mitotic terminal differentiation.

Inhibition of Oxidized Nucleotide Sanitation By TH1579 and Conventional Chemotherapy Cooperatively Enhance Oxidative DNA Damage and Survival in AML

Currently, the majority of patients with acute myeloid leukemia (AML) still die of their disease due to primary resistance or relapse toward conventional reactive oxygen species (ROS)- and DNA damage-inducing chemotherapy regimens. Herein, we explored the therapeutic potential to enhance chemotherapy response in AML, by targeting the ROS scavenger enzyme MutT homolog 1 (MTH1, NUDT1), which protects cellular integrity through prevention of fatal chemotherapy-induced oxidative DNA damage. We demonstrate that MTH1 is a potential druggable target expressed by the majority of patients with AML and the inv(16)/KITD816Y AML mouse model mimicking the genetics of patients with AML exhibiting poor response to standard chemotherapy (i.e., anthracycline & cytarabine). Strikingly, combinatorial treatment of inv(16)/KITD816Y AML cells with the MTH1 inhibitor TH1579 and ROS- and DNA damage-inducing standard chemotherapy induced growth arrest and incorporated oxidized nucleotides into DNA leading to significantly increased DNA damage. Consistently, TH1579 and chemotherapy synergistically inhibited growth of clonogenic inv(16)/KITD816Y AML cells without substantially inhibiting normal clonogenic bone marrow cells. In addition, combinatorial treatment of inv(16)/KITD816Y AML mice with TH1579 and chemotherapy significantly reduced AML burden and prolonged survival compared with untreated or single treated mice. In conclusion, our study provides a rationale for future clinical studies combining standard AML chemotherapy with TH1579 to boost standard chemotherapy response in patients with AML. Moreover, other cancer entities treated with ROS- and DNA damage-inducing chemo- or radiotherapies might benefit therapeutically from complementary treatment with TH1579.

Phosphorylation of SHP2 at Tyr62 enables acquired resistance to SHP2 allosteric inhibitors in FLT3-ITD-driven AML

The protein tyrosine phosphatase SHP2 is crucial for oncogenic transformation of acute myeloid leukemia (AML) cells expressing mutated receptor tyrosine kinases (RTK). SHP2 is required for full RAS-ERK activation to promote cell proliferation and survival programs. Allosteric SHP2 inhibitors act by stabilizing SHP2 in its auto-inhibited conformation and are currently being tested in clinical trials for tumors with overactivation of the RAS/ERK pathway, alone and in various drug combinations. In this study, we established cells with acquired resistance to the allosteric SHP2 inhibitor SHP099 from two FLT3-ITD-positive AML cell lines. Label-free and isobaric labeling quantitative mass spectrometry-based phosphoproteomics of these resistant models demonstrated that AML cells can restore phosphorylated ERK (pERK) in the presence of SHP099, thus developing adaptive resistance. Mechanistically, SHP2 inhibition induced tyrosine phosphorylation and feedback-driven activation of the FLT3 receptor, which in turn phosphorylated SHP2 on tyrosine 62. This phosphorylation stabilized SHP2 in its open conformation, preventing SHP099 binding and conferring resistance. Combinatorial inhibition of SHP2 and MEK or FLT3 prevented pERK rebound and resistant cell growth. The same mechanism was observed in a FLT3-mutated B-ALL cell line and in the inv(16)/KitD816Y AML mouse model, but allosteric inhibition of Shp2 did not impair the clonogenic ability of normal bone marrow progenitors. Together, these results support the future use of SHP2 inhibitor combinations for clinical applications.

Targeting of PI3K/AKT signaling and DNA damage response in acute myeloid leukemia: a novel therapeutic strategy to boost chemotherapy response and overcome resistance

Resistance of cancer patients to DNA damaging radiation therapy and chemotherapy remains a major problem in the clinic. The current review discusses the molecular mechanisms of therapy resistance in acute myeloid leukemia (AML) conferred by cooperative chemotherapy-induced DNA damage response (DDR) and mutational activation of PI3K/AKT signaling. In addition, strategies to overcome resistance are discussed, with particular focus on studies underpinning the vast potential of therapies combining standard chemotherapy AML regimens with small molecule inhibitors targeting key regulatory hubs at the interface of DDR and oncogenic signaling pathways.

Mutant CEBPA directly drives the expression of the targetable tumor-promoting factor CD73 in AML

The key myeloid transcription factor (TF), CEBPA, is frequently mutated in acute myeloid leukemia (AML), but the direct molecular effects of this leukemic driver mutation remain elusive. To investigate CEBPA mutant AML, we performed microscale, in vivo chromatin immunoprecipitation sequencing and identified a set of aberrantly activated enhancers, exclusively occupied by the leukemia-associated CEBPA-p30 isoform. Comparing gene expression changes in human CEBPA mutant AML and the corresponding Cebpa ^Lp30 mouse model, we identified Nt5e, encoding CD73, as a cross-species AML gene with an upstream leukemic enhancer physically and functionally linked to the gene. Increased expression of CD73, mediated by the CEBPA-p30 isoform, sustained leukemic growth via the CD73/A2AR axis. Notably, targeting of this pathway enhanced survival of AML-transplanted mice. Our data thus indicate a first-in-class link between a cancer driver mutation in a TF and a druggable, direct transcriptional target.

The collagen receptor uPARAP/Endo180 as a novel target for antibody-drug conjugate mediated treatment of mesenchymal and leukemic cancers

A key task in developing the field of personalized cancer therapy is the identification of novel molecular targets that enable treatment of cancers not susceptible to other means of specific therapy. The collagen receptor uPARAP/Endo180 is overexpressed by malignant cells in several non-epithelial cancers, notably including sarcomas, glioblastomas and subsets of acute myeloid leukemia. In contrast, in healthy adult individuals, expression is restricted to minor subsets of mesenchymal cells. Functionally, uPARAP/Endo180 is a rapidly recycling endocytic receptor that delivers its cargo directly into the endosomal-lysosomal system, thus opening a potential route of entry into receptor-positive cells. This combination of specific expression and endocytic function appears well suited for targeting of uPARAP/Endo180-positive cancers by antibody-drug conjugate (ADC) mediated drug delivery. Therefore, we utilized a specific monoclonal antibody against uPARAP/Endo180, raised through immunization of a uPARAP/Endo180 knock-out mouse, which reacts with both the human and the murine receptor, to construct a uPARAP-directed ADC. This antibody was coupled to the highly toxic dolastatin derivative, monomethyl auristatin E, via a cathepsin-labile valine-citrulline linker. With this ADC, we show strong and receptor-dependent cytotoxicity in vitro in uPARAP/Endo180-positive cancer cell lines of sarcoma, glioblastoma and leukemic origin. Furthermore, we demonstrate the potency of the ADC in vivo in a xenograft mouse model with human uPARAP/Endo180-positive leukemic cells, obtaining a complete cure of all tested mice following intravenous ADC treatment with no sign of adverse effects. Our study identifies uPARAP/Endo180 as a promising target for novel therapy against several highly malignant cancer types.

Low-molecular-weight carbohydrate Pentaisomaltose may replace dimethyl sulfoxide as a safer cryoprotectant for cryopreservation of peripheral blood stem cells

BACKGROUND

Cryopreserved hematopoietic stem cell products are widely used for certain hematologic malignancies. Dimethyl sulfoxide (DMSO) is the most widely used cryoprotective agent (CPA) today, but due to indications of cellular toxicity, changes of the cellular epigenetic state, and patient-related side effects, there is an increasing demand for DMSO-free alternatives. We therefore investigated whether Pentaisomaltose (PIM), a low-molecular-weight carbohydrate (1 kDa), can be used for cryopreservation of peripheral blood stem cells, more specifically hematopoietic progenitor cell apheresis (HPC(A)) product.

STUDY DESIGN AND METHODS

We cryopreserved patient or donor HPC(A) products using 10% DMSO or 16% PIM and quantified the recovery of CD34+ cells and CD34+ subpopulations by multicolor flow cytometry. In addition, we compared the frequency of HPCs after DMSO and PIM cryopreservation using the colony-forming cells (CFCs) assay.

RESULTS

The mean CD34+ cell recovery was 56.3 ± 23.7% (11.4%-97.3%) and 58.2 ± 10.0% (45.7%-76.9%) for 10% DMSO and 16% PIM, respectively. The distribution of CD34+ cell subpopulations was similar when comparing DMSO or PIM as CPA. CFC assay showed mean colony numbers of 70.7 ± 25.4 (range, 37.8-115.5) and 67.7 ± 15.7 (range, 48-86) for 10% DMSO and 16% PIM, respectively.

CONCLUSION

Our findings demonstrate that PIM cryopreservation of HPC(A) products provides recovery of CD34+ cells, CD34+ subpopulations, and CFCs similar to that of DMSO cryopreservation and therefore may have the potential to be used for cryopreservation of peripheral blood stem cells.

Molecular and cellular effects of oncogene cooperation in a genetically accurate AML mouse model

Biallelic CEBPA mutations and FMS-like tyrosine kinase receptor 3 (FLT3) length mutations are frequently identified in human acute myeloid leukemia (AML) with normal cytogenetics. However, the molecular and cellular mechanisms of oncogene cooperation remain unclear because of a lack of disease models. We have generated an AML mouse model using knockin mouse strains to study cooperation of an internal tandem duplication (ITD) mutation in the Flt3 gene with commonly observed CCAAT/enhancer binding protein alpha (C/EBPα) mutations. This study provides evidence that FLT3 ITD cooperates in leukemogenesis by enhancing the generation of leukemia-initiating granulocyte-monocyte progenitors (GMPs) otherwise prevented by a block in differentiation and skewed lineage priming induced by biallelic C/EBPα mutations. These cellular changes are accompanied by an upregulation of hematopoietic stem cell and STAT5 target genes. By gene expression analysis in premalignant populations, we further show a role of FLT3 ITD in activating genes involved in survival/transformation and chemoresistance. Both multipotent progenitors and GMP cells contain the potential to induce AML similar to corresponding cells in human AML samples showing that this model resembles human disease.

Molecular mechanisms underlying deregulation of C/EBPalpha in acute myeloid leukemia

The CEBPA gene encodes a transcription factor protein that is crucial for granulocytic differentiation, regulation of myeloid gene expression and growth arrest. Mutations in one or both alleles of CEBPA are observed in about 10% of patients with acute myeloid leukemia (AML). Moreover, other genetic events associated with AML have been identified to deregulate C/EBPalpha expression and function at various levels. Recently developed mouse models that accurately mimic the genetic C/EBPalpha alterations in human AML demonstrate C/EBPalpha's gatekeeper function in the control of self-renewal and lineage commitment of hematopoietic stem cells (HSCs). Moreover, these studies indicate that CEBPA mutations affect HSCs in early leukemia development by inducing proliferation and limiting their lineage potential. However, the exact relationship between 'pre-leukemic' HCSs and those cells that finally initiate leukemia (leukemia-initiating cells) with disturbed differentiation and aberrant proliferation remains elusive. More research is needed to identify and characterize these functionally distinct populations and the exact role of the different genetic alterations in the process of leukemia initiation and maintenance.

Copper related toxic effects on cellular protein metabolism in human astrocytes

INTRODUCTION

Copper overload due to a defect in the ATPase 7B mediated copper excretion within hepatocytes produces the phenotype of Wilson disease. The overload of hepatocytes with copper results in necrotic liver cells and is accompanied by a high concentration of blood copper levels. That occurs to be the reason for increasing neurological copper concentration. Although copper is linked to oxidation, there are no data on the direct copper related effects in human brain cells.

AIM

To test the copper induced changes in protein oxidation in human astrocyte like cells.

METHODS

We used U87 cells as model for human astrocytes. Cells were treated with increasing concentrations of copper(II)-chloride in Dulbeccos minimal essential medium. Subsequently, at different time points we investigated: cellular growth, cellular survival under copper treatment, the concentration of oxidized tryptophane in GADPH in vitro as well as the carbonyl concentration and the concentration of oxidized proteins in vivo in U87 glial cells.

RESULTS

The viability of cells decreased with both increasing copper concentration and duration of treatment. The concentration of oxidized proteins was directly correlated to the increase of copper concentration and duration of exposure.

CONCLUSION

These observations demonstrate the similarities between copper treatment and treatment with other commonly used oxidants, including hydrogen peroxide. Furthermore, the vulnerability of astrocytes towards copper exposure could be demonstrated. Therefore, these data give further insights into understanding of copper metabolism, which in turn is important to reveal the exact pathological mechanism in copper related diseases such as Wilson disease.