The reprogramming factor KLF4 in normal and malignant blood cells

The Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger transcription factor that regulates cellular processes in stem cells, epithelial cells, and immune blood cells by controlling gene expression through genetic, epigenetic, and chromatin remodeling. The landmark 2006 publication identified KLF4 as one of the factors involved in reprogramming differentiated cells into pluripotent stem cells, sparking increased interest in KLF4 research a decade after its discovery, particularly in the fields of stem cell research, epithelial cell biology, endothelial cell function, and tumorigenesis. Over the years, KLF4 has emerged as a key transcription factor in modulating innate and adaptive immunity, especially in macrophage differentiation and function. This review summarizes the key findings regarding KLF4 in normal blood cells and leukemia

Protein Tyrosine Phosphatase PRL2 Mediates Notch and Kit Signals in Early T Cell Progenitors

The molecular pathways regulating lymphoid priming, fate, and development of multipotent bone marrow hematopoietic stem and progenitor cells (HSPCs) that continuously feed thymic progenitors remain largely unknown. While Notch signal is indispensable for T cell specification and differentiation, the downstream effectors are not well understood. PRL2, a protein tyrosine phosphatase that regulates hematopoietic stem cell proliferation and self-renewal, is highly expressed in murine thymocyte progenitors. Here we demonstrate that protein tyrosine phosphatase PRL2 and receptor tyrosine kinase c-Kit are critical downstream targets and effectors of the canonical Notch/RBPJ pathway in early T cell progenitors. While PRL2 deficiency resulted in moderate defects of thymopoiesis in the steady state, de novo generation of T cells from Prl2 null hematopoietic stem cells was significantly reduced following transplantation. Prl2 null HSPCs also showed impaired T cell differentiation in vitro. We found that Notch/RBPJ signaling upregulated PRL2 as well as c-Kit expression in T cell progenitors. Further, PRL2 sustains Notch-mediated c-Kit expression and enhances stem cell factor/c-Kit signaling in T cell progenitors, promoting effective DN1-DN2 transition. Thus, we have identified a critical role for PRL2 phosphatase in mediating Notch and c-Kit signals in early T cell progenitors

An ELF4 Hypomorphic Variant Results in NK Cell Deficiency

NK cell deficiencies (NKD) are a type of primary immune deficiency in which the major immunologic abnormality affects NK cell number, maturity, or function. Since NK cells contribute to immune defense against virally infected cells, patients with NKD experience higher susceptibility to chronic, recurrent, and fatal viral infections. An individual with recurrent viral infections and mild hypogammaglobulinemia was identified to have an X-linked damaging variant in the transcription factor gene ELF4. The variant does not decrease expression but disrupts ELF4 protein interactions and DNA binding, reducing transcriptional activation of target genes and selectively impairing ELF4 function. Corroborating previous murine models of ELF4 deficiency (Elf4-/-) and using a knockdown human NK cell line, we determined that ELF4 is necessary for normal NK cell development, terminal maturation, and function. Through characterization of the NK cells of the proband, expression of the proband\u27s variant in Elf4-/- mouse hematopoietic precursor cells, and a human in vitro NK cell maturation model, we established this ELF4 variant as a potentially novel cause of NKD

The Cytosolic Protein G0S2 Maintains Quiescence in Hematopoietic Stem Cells

Bone marrow hematopoietic stem cells (HSCs) balance proliferation and differentiation by integrating complex transcriptional and post-translational mechanisms regulated by cell intrinsic and extrinsic factors. We found that transcripts of G0/G1 switch gene 2 (G0S2) are enriched in lineage− Sca-1+ c-kit+ (LSK) CD150+ CD48− CD41− cells, a population highly enriched for quiescent HSCs, whereas G0S2 expression is suppressed in dividing LSK CD150+ CD48− cells. Gain-of-function analyses using retroviral expression vectors in bone marrow cells showed that G0S2 localizes to the mitochondria, endoplasmic reticulum, and early endosomes in hematopoietic cells. Co-transplantation of bone marrow cells transduced with the control or G0S2 retrovirus led to increased chimerism of G0S2-overexpressing cells in femurs, although their contribution to the blood was reduced. This finding was correlated with increased quiescence in G0S2-overexpressing HSCs (LSK CD150+ CD48−) and progenitor cells (LS−K). Conversely, silencing of endogenous G0S2 expression in bone marrow cells increased blood chimerism upon transplantation and promoted HSC cell division, supporting an inhibitory role for G0S2 in HSC proliferation. A proteomic study revealed that the hydrophobic domain of G0S2 interacts with a domain of nucleolin that is rich in arginine-glycine-glycine repeats, which results in the retention of nucleolin in the cytosol. We showed that this cytosolic retention of nucleolin occurs in resting, but not proliferating, wild-type LSK CD150+ CD48− cells. Collectively, we propose a novel model of HSC quiescence in which elevated G0S2 expression can sequester nucleolin in the cytosol, precluding its pro-proliferation functions in the nucleolus

Pharmacological inhibition of the MAP2K7 kinase in human disease

The MAP2K7 signaling pathway activates the c-Jun NH2-terminal protein kinase (JNK) in response to stress signals, such as inflammatory cytokines, osmotic stress, or genomic damage. While there has been interest in inhibiting JNK due to its involvement in inflammatory processes and cancer, there is increasing focus on developing MAP2K7 inhibitors to enhance specificity when MAP2K7 activation is associated with disease progression. Despite some progress, further research is needed to fully comprehend the role of MAP2K7 in cancer and assess the potential use of kinase inhibitors in cancer therapy. This review examines the role of MAP2K7 in cancer and the development of small-molecule inhibitors

DYRK2 controls a key regulatory network in chronic myeloid leukemia stem cells

AbstractChronic myeloid leukemia is a hematological cancer driven by the oncoprotein BCR-ABL1, and lifelong treatment with tyrosine kinase inhibitors extends patient survival to nearly the life expectancy of the general population. Despite advances in the development of more potent tyrosine kinase inhibitors to induce a durable deep molecular response, more than half of patients relapse upon treatment discontinuation. This clinical finding supports the paradigm that leukemia stem cells feed the neoplasm, resist tyrosine kinase inhibition, and reactivate upon drug withdrawal depending on the fitness of the patient’s immune surveillance. This concept lends support to the idea that treatment-free remission is not achieved solely with tyrosine kinase inhibitors and that new molecular targets independent of BCR-ABL1 signaling are needed in order to develop adjuvant therapy to more efficiently eradicate the leukemia stem cell population responsible for chemoresistance and relapse. Future efforts must focus on the identification of new targets to support the discovery of potent and safe small molecules able to specifically eradicate the leukemic stem cell population. In this review, we briefly discuss molecular maintenance in leukemia stem cells in chronic myeloid leukemia and provide a more in-depth discussion of the dual-specificity kinase DYRK2, which has been identified as a novel actionable checkpoint in a critical leukemic network. DYRK2 controls the activation of p53 and proteasomal degradation of c-MYC, leading to impaired survival and self-renewal of leukemia stem cells; thus, pharmacological activation of DYRK2 as an adjuvant to standard therapy has the potential to induce treatment-free remission.</jats:p

The emerging role of the myeloid Elf-1 like transcription factor in hematopoiesis

MEF (myeloid Elf-1 like factor) is a member of the ETS family of transcription factors (TF) with transcriptional activating properties. ETS proteins have been implicated in widely divergent physiological and pathological processes (such as development and oncogenesis). MEF is expressed in non-hematopoietic and hematopoietic (lymphoid and myeloid) tissues, and after generating MEF-deficient mice by homologous recombination, we have studied its role in lymphopoiesis (Immunity 17 (2002), 437). MEF plays a critical role in NK and NK-T cell development and the constitutive expression of perforin by NK cells. MEF interacts with other TFs such as AML1 (Runx1) and with the cyclin A/cdk2 kinase complex. In this review, we discuss the biology of MEF in the context of the other members of this family of transcriptional regulators