Epigenetic regulation by ASXL1 in myeloid malignancies

Can O-GIcNAc Transferase (OGT) Complex Be Used as a Target for the Treatment of Hematological Malignancies?

The circulatory system is a closed conduit system throughout the body and consists of two parts as follows: the cardiovascular system and the lymphatic system. Hematological malignancies usually grow and multiply in the circulatory system, directly or indirectly affecting its function. These malignancies include multiple myeloma, leukemia, and lymphoma. O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) regulates the function and stability of substrate proteins through O-GlcNAc modification. Abnormally expressed OGT is strongly associated with tumorigenesis, including hematological malignancies, colorectal cancer, liver cancer, breast cancer, and prostate cancer. In cells, OGT can assemble with a variety of proteins to form complexes to exercise related biological functions, such as OGT/HCF-1, OGT/TET, NSL, and then regulate glucose metabolism, gene transcription, cell proliferation, and other biological processes, thus affecting the development of hematological malignancies. This review summarizes the complexes involved in the assembly of OGT in cells and the role of related OGT complexes in hematological malignancies. Unraveling the complex network regulated by the OGT complex will facilitate a better understanding of hematologic malignancy development and progression.

Additional Sex Combs-like Family Associated with Epigenetic Regulation

The additional sex combs-like (ASXL) family, a mammalian homolog of the additional sex combs (Asx) of Drosophila, has been implicated in transcriptional regulation via chromatin modifications. Abnormal expression of ASXL family genes leads to myelodysplastic syndromes and various types of leukemia. De novo mutation of these genes also causes developmental disorders. Genes in this family and their neighbor genes are evolutionary conserved in humans and mice. This review provides a comprehensive summary of epigenetic regulations associated with ASXL family genes. Their expression is commonly regulated by DNA methylation at CpG islands preceding transcription starting sites. Their proteins primarily engage in histone tail modifications through interactions with chromatin regulators (PRC2, TrxG, PR-DUB, SRC1, HP1α, and BET proteins) and with transcription factors, including nuclear hormone receptors (RAR, PPAR, ER, and LXR). Histone modifications associated with these factors include histone H3K9 acetylation and methylation, H3K4 methylation, H3K27 methylation, and H2AK119 deubiquitination. Recently, non-coding RNAs have been identified following mutations in the ASXL1 or ASXL3 gene, along with circular ASXLs and microRNAs that regulate ASXL1 expression. The diverse epigenetic regulations linked to ASXL family genes collectively contribute to tumor suppression and developmental processes. Our understanding of ASXL-regulated epigenetics may provide insights into the development of therapeutic epigenetic drugs.

Deciphering signaling pathways in hematopoietic stem cells: the molecular complexity of Myelodysplastic Syndromes (MDS) and leukemic progression

Myelodysplastic Syndromes, a heterogeneous group of hematological disorders, are characterized by abnormalities in phosphoinositide-dependent signaling, epigenetic regulators, apoptosis, and cytokine interactions within the bone marrow microenvironment, contributing to disease pathogenesis and neoplastic growth. Comprehensive knowledge of these pathways is crucial for the development of innovative therapies that aim to restore normal apoptosis and improve patient outcomes.

Ring Chromosomes in Hematological Malignancies Are Associated with TP53 Gene Mutations and Characteristic Copy Number Variants

Ring chromosomes (RC) are present in <10% of patients with hematological malignancies and are associated with poor prognosis. Until now, only small cohorts of patients with hematological neoplasms and concomitant RCs have been cytogenetically characterized. Here, we performed a conventional chromosome analysis on metaphase spreads from >13,000 patients diagnosed with hematological malignancies at the Johns Hopkins University Hospital and identified 98 patients with RCs-90 with myeloid malignancies and 8 with lymphoid malignancies. We also performed a targeted Next-Generation Sequencing (NGS) assay, using a panel of 642 cancer genes, to identify whether these patients harbor relevant pathogenic variants. Cytogenetic analyses revealed that RCs and marker chromosomes of unknown origin are concurrently present in most patients by karyotyping, and 93% of patients with NGS data have complex karyotypes. A total of 72% of these individuals have pathogenic mutations in TP53, most of whom also possess cytogenetic abnormalities resulting in the loss of 17p, including the loss of TP53. All patients with a detected RC and without complex karyotypes also lack TP53 mutations but have pathogenic mutations in TET2. Further, 70% of RCs that map to a known chromosome are detected in individuals without TP53 mutations. Our data suggest that RCs in hematological malignancies may arise through different mechanisms, but ultimately promote widespread chromosomal instability.

Stem cell regulation and dynamics in myeloid malignancies

In this issue of PIH, we asked four researchers to write about basic research on the molecular mechanisms of the development of myeloid malignancies, in particular two epigenetic regulation and two space- and time-dependent factors. Regarding epigenomic regulation, Dr. Yang reviewed ASXL1, a polycomb modifier gene that is often mutated in myeloid malignancies, but also in clonal hematopoiesis in healthy elderly people, and Dr. Vu reviewed RNA modifications, which are critical for development and tissue homeostasis, and are now recognized as an important driver for cancer development. Regarding spatiotemporal factors, Dr. Inoue reviewed the role of extracellular vesicles in leukemic stem cell niches. As some cancers develop preferentially in infancy or old age, Dr. Osato discussed the time-specific development of leukemia involving the RUNX1-ETO mutation, which is often found in leukemia in adolescents and young adults. Recent studies on hematopoietic development have shown that hematopoietic stem cells do not generate multipotent progenitor cells, but that these cells develop in parallel. We hope that reconsideration of the definition of leukemic stem cells and their origin will help us understand the regulatory mechanisms of these cells, but also enable us to develop future therapies by targeting factors that regulate the leukemic stem cell and the niche.