GATA2 regulates the erythropoietin receptor in t(12;21) ALL

Single-cell analysis of megakaryopoiesis in peripheral CD34+ cells: insights into ETV6-related thrombocytopenia

BACKGROUND

Germline mutations in the ETV6 transcription factor gene are responsible for familial thrombocytopenia and leukemia predisposition syndrome. Although previous studies have shown that ETV6 plays an important role in megakaryocyte (MK) maturation and platelet formation, the mechanisms by which ETV6 dysfunction promotes thrombocytopenia remain unclear.

OBJECTIVES

To decipher the transcriptional mechanisms and gene regulatory network linking ETV6 germline mutations and thrombocytopenia.

METHODS

Presuming that ETV6 mutations result in selective effects at a particular cell stage, we applied single-cell RNA sequencing to understand gene expression changes during megakaryopoiesis in peripheral CD34+ cells from healthy controls and patients with ETV6-related thrombocytopenia.

RESULTS

Analysis of gene expression and regulon activity revealed distinct clusters partitioned into 7 major cell stages: hematopoietic stem/progenitor cells, common-myeloid progenitors (CMPs), MK-primed CMPs, granulocyte-monocyte progenitors, MK-erythroid progenitors (MEPs), progenitor MKs/mature MKs, and platelet-like particles. We observed a differentiation trajectory in which MEPs developed directly from hematopoietic stem/progenitor cells and bypassed the CMP stage. ETV6 deficiency led to the development of aberrant cells as early as the MEP stage, which intensified at the progenitor MK/mature MK stage, with a highly deregulated core "ribosome biogenesis" pathway. Indeed, increased translation levels have been documented in patient CD34+-derived MKs with overexpression of ribosomal protein S6 and phosphorylated ribosomal protein S6 in both CD34+-derived MKs and platelets. Treatment of patient MKs with the ribosomal biogenesis inhibitor CX-5461 resulted in an increase in platelet-like particles.

CONCLUSION

These findings provide novel insight into both megakaryopoiesis and the link among ETV6, translation, and platelet production.

Functions and underlying mechanisms of miR-650 in human cancers

MicroRNAs (miRNAs) are one type of noncoding RNAs that interfere with mRNA translation to downregulate gene expression, which results in posttranscriptional gene silencing. Over the past two decades, miRNAs have been widely reported to impact the progression of malignant tumours by interfering with cancer initiation and progression; therefore, miRNAs represent potential new diagnostic and therapeutic tools. miR-650 is a newly identified miR, and increasing studies have demonstrated that miR-650 plays critical roles in cancer progression, such as mediating the Wnt signalling pathway/AXIN1 (axis inhibition protein 1) axis in hepatocellular carcinoma. Nevertheless, associations between the expression patterns and molecular mechanisms of miR-650 in cancer have not been comprehensively described. In this article, we review the existing evidence regarding the mechanisms by which miR-650 expression is altered and their relation to cancer. Moreover, the promising clinical application of miR-650 for diagnosis and treatment is highlighted.

Hematopoietic Stem Cells: Nature and Niche Nurture

Like all cells, hematopoietic stem cells (HSCs) and their offspring, the hematopoietic progenitor cells (HPCs), are highly sociable. Their capacity to interact with bone marrow niche cells and respond to environmental cytokines orchestrates the generation of the different types of blood and immune cells. The starting point for engineering hematopoiesis ex vivo is the nature of HSCs, and a longstanding premise is that they are a homogeneous population of cells. However, recent findings have shown that adult bone marrow HSCs are really a mixture of cells, with many having lineage affiliations. A second key consideration is: Do HSCs "choose" a lineage in a random and cell-intrinsic manner, or are they instructed by cytokines? Since their discovery, the hematopoietic cytokines have been viewed as survival and proliferation factors for lineage committed HPCs. Some are now known to also instruct cell lineage choice. These fundamental changes to our understanding of hematopoiesis are important for placing niche support in the right context and for fabricating an ex vivo environment to support HSC development.

Aberrant GATA2 Activation in Pediatric B-Cell Acute Lymphoblastic Leukemia

GATA2 is a transcription factor that is critical for the generation and survival of hematopoietic stem cells (HSCs). It also plays an important role in the regulation of myeloid differentiation. Accordingly, GATA2 expression is restricted to HSCs and hematopoietic progenitors as well as early erythroid cells and megakaryocytic cells. Here we identified aberrant GATA2 expression in B-cell acute lymphoblastic leukemia (B-ALL) by analyzing transcriptome sequencing data obtained from St. Jude Cloud. Differentially expressed genes upon GATA2 activation showed significantly myeloid-like transcription signature. Further analysis identified several tumor-associated genes as targets of GATA2 activation including BAG3 and EPOR. In addition, the correlation between KMT2A-USP2 fusion and GATA2 activation not only indicates a potential trans-activating mechanism of GATA2 but also suggests that GATA2 is a target of KMT2A-USP2. Furthermore, by integrating whole-genome and transcriptome sequencing data, we showed that GATA2 is also cis activated. A somatic focal deletion located in the GATA2 neighborhood that disrupts the boundaries of topologically associating domains was identified in one B-ALL patient with GATA2 activation. These evidences support the hypothesis that GATA2 could be involved in leukemogenesis of B-ALL and can be transcriptionally activated through multiple mechanisms. The findings of aberrant activation of GATA2 and its molecular function extend our understanding of transcriptional factor dysregulation in B-ALL.

Single cell characterization of B-lymphoid differentiation and leukemic cell states during chemotherapy in ETV6-RUNX1-positive pediatric leukemia identifies drug-targetable transcription factor activities

BACKGROUND

Tight regulatory loops orchestrate commitment to B cell fate within bone marrow. Genetic lesions in this gene regulatory network underlie the emergence of the most common childhood cancer, acute lymphoblastic leukemia (ALL). The initial genetic hits, including the common translocation that fuses ETV6 and RUNX1 genes, lead to arrested cell differentiation. Here, we aimed to characterize transcription factor activities along the B-lineage differentiation trajectory as a reference to characterize the aberrant cell states present in leukemic bone marrow, and to identify those transcription factors that maintain cancer-specific cell states for more precise therapeutic intervention.

METHODS

We compared normal B-lineage differentiation and in vivo leukemic cell states using single cell RNA-sequencing (scRNA-seq) and several complementary genomics profiles. Based on statistical tools for scRNA-seq, we benchmarked a workflow to resolve transcription factor activities and gene expression distribution changes in healthy bone marrow lymphoid cell states. We compared these to ALL bone marrow at diagnosis and in vivo during chemotherapy, focusing on leukemias carrying the ETV6-RUNX1 fusion.

RESULTS

We show that lymphoid cell transcription factor activities uncovered from bone marrow scRNA-seq have high correspondence with independent ATAC- and ChIP-seq data. Using this comprehensive reference for regulatory factors coordinating B-lineage differentiation, our analysis of ETV6-RUNX1-positive ALL cases revealed elevated activity of multiple ETS-transcription factors in leukemic cells states, including the leukemia genome-wide association study hit ELK3. The accompanying gene expression changes associated with natural killer cell inactivation and depletion in the leukemic immune microenvironment. Moreover, our results suggest that the abundance of G1 cell cycle state at diagnosis and lack of differentiation-associated regulatory network changes during induction chemotherapy represent features of chemoresistance. To target the leukemic regulatory program and thereby overcome treatment resistance, we show that inhibition of ETS-transcription factors reduced cell viability and resolved pathways contributing to this using scRNA-seq.

CONCLUSIONS

Our data provide a detailed picture of the transcription factor activities characterizing both normal B-lineage differentiation and those acquired in leukemic bone marrow and provide a rational basis for new treatment strategies targeting the immune microenvironment and the active regulatory network in leukemia.

Erythropoietin regulates metabolic response in mice via receptor expression in adipose tissue, brain, and bone

Erythropoietin (EPO) acts by binding to erythroid progenitor cells to regulate red blood cell production. While EPO receptor (Epor) expression is highest on erythroid tissue, animal models exhibit EPO activity in nonhematopoietic tissues, mediated, in part, by tissue-specific Epor expression. This review describes the metabolic response in mice to endogenous EPO and EPO treatment associated with glucose metabolism, fat mass accumulation, and inflammation in white adipose tissue and brain during diet-induced obesity and with bone marrow fat and bone remodeling. During high-fat diet-induced obesity, EPO treatment improves glucose tolerance, decreases fat mass accumulation, and shifts white adipose tissue from a pro-inflammatory to an anti-inflammatory state. Fat mass regulation by EPO is sex dimorphic, apparent in males and abrogated by estrogen in females. Cerebral EPO also regulates fat mass and hypothalamus inflammation associated with diet-induced obesity in males and ovariectomized female mice. In bone, EPO contributes to the balance between adipogenesis and osteogenesis in both male and female mice. EPO treatment promotes bone loss mediated via Epor in osteoblasts and reduces bone marrow adipocytes before and independent of change in white adipose tissue fat mass. EPO regulation of bone loss and fat mass is independent of EPO-stimulated erythropoiesis. EPO nonhematopoietic tissue response may relate to the long-term consequences of EPO treatment of anemia in chronic kidney disease and to the alternative treatment of oral hypoxia-inducible factor prolyl hydroxylase inhibitors that increase endogenous EPO production.