Histone demethylase KDM2B regulates lineage commitment in normal and malignant hematopoiesis

Analyses of publicly available genomics resources define FGF-2-expressing bladder carcinomas as EMT-prone, proliferative tumors with low mutation rates and high expression of CTLA-4, PD-1 and PD-L1

Fibroblast growth factor 2 (FGF-2) is overexpressed in a subset of invasive bladder carcinomas and its overexpression correlates with poor prognosis. Analyses of publicly available databases addressing the molecular mechanisms that may be responsible for the poor prognosis of these tumors, revealed that FGF-2 expression correlates positively with the expression of epithelial to mesenchymal transition (EMT)-promoting transcription factors and with changes in gene expression that are characteristic of EMT. The same analyses also revealed that FGF-2 correlates negatively with the expression, mutation and copy number variations of FGFR-3, all of which are associated with noninvasive bladder carcinomas. Finally, they showed that FGF-2 expression correlates with the expression of FGFR-1, the expression of the IIIc variant of FGFR-2 and with the expression of Akt3. The latter observation is significant because our earlier studies had shown that Akt3 regulates FGFR-2 alternative splicing, shifting the balance toward the IIIc relative to the IIIb FGFR-2 splice variant. As the IIIc variant is recognized by FGF-2, while the IIIb variant is not, we conclude that Akt3 may facilitate the FGF-2 response. FGF-2 is known to promote the expression of KDM2B, which functions in concert with EZH2 to repress the EZH2-targeting microRNA miR-101, activating a switch, which stably upregulates EZH2. The cancer genome atlas (TCGA) data showing a correlation between KDM2B and EZH2 expression and Oncomine data, showing a correlation between KDM2B and tumor progression, strongly support the role of the FGF-2/KDM2B/miR-101/EZH2 pathway in bladder cancer. These observations combined, suggest a model according to which FGF-2 induces EMT, cell proliferation and cancer stem cell self-renewal by coupling the Akt3 and KDM2B-controlled pathways outlined above, in bladder carcinomas. Further analyses of publicly available databases, revealed that FGF-2-expressing bladder carcinomas carry fewer genetic alterations and they tend to express high levels of CTLA-4, PD-1 and PD-L1, which suggests immune blockade by checkpoint activation. EMT, enhanced proliferation and immune checkpoint activation combined, may be responsible for the poor prognosis of FGF-2-expressing bladder carcinomas.

Fumarate hydratase is a critical metabolic regulator of hematopoietic stem cell functions

Strict regulation of stem cell metabolism is essential for tissue functions and tumor suppression. In this study, we investigated the role of fumarate hydratase (Fh1), a key component of the mitochondrial tricarboxylic acid (TCA) cycle and cytosolic fumarate metabolism, in normal and leukemic hematopoiesis. Hematopoiesis-specific Fh1 deletion (resulting in endogenous fumarate accumulation and a genetic TCA cycle block reflected by decreased maximal mitochondrial respiration) caused lethal fetal liver hematopoietic defects and hematopoietic stem cell (HSC) failure. Reexpression of extramitochondrial Fh1 (which normalized fumarate levels but not maximal mitochondrial respiration) rescued these phenotypes, indicating the causal role of cellular fumarate accumulation. However, HSCs lacking mitochondrial Fh1 (which had normal fumarate levels but defective maximal mitochondrial respiration) failed to self-renew and displayed lymphoid differentiation defects. In contrast, leukemia-initiating cells lacking mitochondrial Fh1 efficiently propagated Meis1/Hoxa9-driven leukemia. Thus, we identify novel roles for fumarate metabolism in HSC maintenance and hematopoietic differentiation and reveal a differential requirement for mitochondrial Fh1 in normal hematopoiesis and leukemia propagation.

Polycomb complexes PRC1 and their function in hematopoiesis

Hematopoiesis, the process by which blood cells are continuously produced, is one of the best studied differentiation pathways. Hematological diseases are associated with reiterated mutations in genes encoding important gene expression regulators, including chromatin regulators. Among them, the Polycomb group (PcG) of proteins is an essential system of gene silencing involved in the maintenance of cell identities during differentiation. PcG proteins assemble into two major types of Polycomb repressive complexes (PRCs) endowed with distinct histone-tail-modifying activities. PRC1 complexes are histone H2A E3 ubiquitin ligases and PRC2 trimethylates histone H3. Established conceptions about their activities, mostly derived from work in embryonic stem cells, are being modified by new findings in differentiated cells. Here, we focus on PRC1 complexes, reviewing recent evidence on their intricate architecture, the diverse mechanisms of their recruitment to targets, and the different ways in which they engage in transcriptional control. We also discuss hematopoietic PRC1 gain- and loss-of-function mouse strains, including those that model leukemic and lymphoma diseases, in the belief that these genetic analyses provide the ultimate test for molecular mechanisms driving normal hematopoiesis and hematological malignancies.

Long non-coding RNAs in the regulation of myeloid cells

Long non-coding RNAs (lncRNAs) have been attracting immense research interests. The relevance of lncRNAs in biological and physiological as well as in pathological processes has increased along with the understanding of their various regulatory mechanisms. Abundant studies have indicated that lncRNAs are involved in the differentiation, proliferation, activation, and initiation of apoptosis in different cell types. However, most studies about the regulating biology of lncRNAs are currently focused on cancer cells. This review is focused on the widely unexplored role of lncRNAs in the cell fate of myeloid cells. In this review, we summarize recent studies that have confirmed lncRNAs to be essential in the development of myeloid cells under normal and pathological conditions.

Epigenetic balance of gene expression by Polycomb and COMPASS families

Epigenetic regulation of gene expression in metazoans is central for establishing cellular diversity, and its deregulation can result in pathological conditions. Although transcription factors are essential for implementing gene expression programs, they do not function in isolation and require the recruitment of various chromatin-modifying and -remodeling machineries. A classic example of developmental chromatin regulation is the balanced activities of the Polycomb group (PcG) proteins within the PRC1 and PRC2 complexes, and the Trithorax group (TrxG) proteins within the COMPASS family, which are highly mutated in a large number of human diseases. In this review, we will discuss the latest findings regarding the properties of the PcG and COMPASS families and the insight they provide into the epigenetic control of transcription under physiological and pathological settings.

Polycomb complex PRC1 as gatekeeper of intestinal stem cell identity

Intestinal stem cells (ISCs) are adult multipotent cells essential for the maintenance of intestinal epithelial homeostasis. Wnt signaling activity ensures that the pool of ISCs at the basis of the intestinal crypts is preserved. Dysregulation of the Wnt pathway is often observed in cancer and supports malignant progression. Chiacchiera and colleagues recently demonstrated the implication of the polycomb complex PRC1 in the regulation of the Wnt pathway in adult ISCs. The authors show that PRC1 maintains intestinal homeostasis by repressing the expression of ZICs, a family of transcription factors inactivating the β-catenin/TCF complex. Importantly, interfering with PRC1 activity completely inhibits the formation of Wnt-dependent tumors. These findings reveal a new layer of epigenetic regulation of the Wnt pathway and open novel opportunities for cancer stem cell targeted therapy.

Lysine-specific histone demethylases in normal and malignant hematopoiesis

The epigenetic control of gene expression is central to the development of the hematopoietic system and the execution of lineage-specific transcriptional programs. During the last 10 years, mounting evidence has implicated the family of lysine-specific histone demethylases as critical regulators of normal hematopoiesis, whereas their deregulation is found in a broad spectrum of hematopoietic malignancies. Here, we review recent findings on the role of these enzymes in normal and malignant hematopoiesis and highlight how aberrant epigenetic regulation facilitates hematopoietic cell transformation through subversion of cell fate and lineage commitment programs.