The role of the PZP domain of AF10 in acute leukemia driven by AF10 translocations

Histone H4K16ac Binding Function of the Triple PHD Finger Cassette of MLL4

The human methyltransferase MLL4 plays a critical role in embryogenesis and development, and aberrant activity of MLL4 is linked to neurodegenerative and developmental disorders and cancer. MLL4 contains the catalytic SET domain that catalyzes mono methylation of lysine 4 of histone H3 (H3K4me1) and seven plant homeodomain (PHD) fingers, six of which have not been structurally and functionally characterized. Here, we demonstrate that the triple PHD finger cassette of MLL4, harboring its fourth, fifth and sixth PHD fingers (MLL4PHD456) forms an integrated module, maintains the binding selectivity of the PHD6 finger toward acetylated lysine 16 of histone H4 (H4K16ac), and is capable of binding to DNA. Our findings highlight functional correlation between H4K16ac and H3K4me1, two major histone modifications that are recognized and written, respectively, by MLL4.

Guiding the HBO1 complex function through the JADE subunit

JADE is a core subunit of the HBO1 acetyltransferase complex that regulates developmental and epigenetic programs and promotes gene transcription. Here we describe the mechanism by which JADE facilitates recruitment of the HBO1 complex to chromatin and mediates its enzymatic activity. Structural, genomic and complex assembly in vivo studies show that the PZP (PHD1-zinc-knuckle-PHD2) domain of JADE engages the nucleosome through binding to histone H3 and DNA and is necessary for the association with chromatin targets. Recognition of unmethylated H3K4 by PZP directs enzymatic activity of the complex toward histone H4 acetylation, whereas H3K4 hypermethylation alters histone substrate selectivity. We demonstrate that PZP contributes to leukemogenesis, augmenting transforming activity of the NUP98-JADE2 fusion. Our findings highlight biological consequences and the impact of the intact JADE subunit on genomic recruitment, enzymatic function and pathological activity of the HBO1 complex.

Signature construction and molecular subtype identification based on liver-specific genes for prediction of prognosis, immune activity, and anti-cancer drug sensitivity in hepatocellular carcinoma

BACKGROUND

Liver specific genes (LSGs) are crucial for hepatocyte differentiation and maintaining normal liver function. A deep understanding of LSGs and their heterogeneity in hepatocellular carcinoma (HCC) is necessary to provide clues for HCC diagnosis, prognosis, and treatment.

METHODS

The bulk and single-cell RNA-seq data of HCC were downloaded from TCGA, ICGC, and GEO databases. Through unsupervised cluster analysis, LSGs-based HCC subtypes were identified in TCGA-HCC samples. The prognostic effects of the subtypes were investigated with survival analyses. With GSVA and Wilcoxon test, the LSGs score, stemness score, aging score, immune score and stromal score of the samples were estimated and compared. The HCC subtype-specific genes were identified. The subtypes and their differences were validated in ICGC-HCC samples. LASSO regression analysis was used for key gene selection and risk model construction for HCC overall survival. The model performance was estimated and validated. The key genes were validated for their heterogeneities in HCC cell lines with quantitative real-time PCR and at single-cell level. Their dysregulations were investigated at protein level. Their correlations with HCC response to anti-cancer drugs were estimated in HCC cell lines.

RESULTS

We identified three LSGs-based HCC subtypes with different prognosis, tumor stemness, and aging level. The C1 subtype with low LSGs score and high immune score presented a poor survival, while the C2 subtype with high LSGs score and immune score indicated an enduring survival. Although no significant survival difference between C2 and C3 HCCs was shown, the C2 HCCs presented higher immune score and stroma score. The HCC subtypes and their differences were confirmed in ICGC-HCC dataset. A five-gene prognostic signature for HCC survival was constructed. Its good performance was shown in both the training and validation datasets. The five genes presented significant heterogeneities in different HCC cell lines and hepatocyte subclusters. Their dysregulations were confirmed at protein level. Furthermore, their significant associations with HCC sensitivities to anti-cancer drugs were shown.

CONCLUSIONS

LSGs-based HCC subtype classification and the five-gene risk model might provide useful clues not only for HCC stratification and risk prediction, but also for the development of more personalized therapies for effective HCC treatment.

Genetic Characterization of Pediatric Mixed Phenotype Acute Leukemia (MPAL)

BACKGROUND/AIM

Mixed phenotype acute leukemia (MPAL) is a rare hematologic malignancy in which the leukemic cells cannot be assigned to any specific lineage. The lack of well-defined, pathogenetically relevant diagnostic criteria makes the clinical handling of MPAL patients challenging. We herein report the genetic findings in bone marrow cells from two pediatric MPAL patients.

PATIENTS AND METHODS

Bone marrow cells were examined using G-banding, array comparative genomic hybridization, RNA sequencing, reverse transcription polymerase chain reaction, Sanger sequencing, and fluorescence in situ hybridization.

RESULTS

In the first patient, the genetic analyses revealed structural aberrations of chromosomal bands 8p11, 10p11, 11q21, and 17p11, the chimeras MLLT10::PICALM and PICALM::MLLT10, and imbalances (gains/losses) on chromosomes 2, 4, 8, 13, and 21. A submicroscopic deletion in 21q was also found including the RUNX1 locus. In the second patient, there were structural aberrations of chromosome bands 1p32, 8p11, 12p13, 20p13, and 20q11, the chimeras ETV6::LEXM and NCOA6::ETV6, and imbalances on chromosomes 2, 8, 11, 12, 16, 19, X, and Y.

CONCLUSION

The leukemic cells from both MPAL patients carried chromosome aberrations resulting in fusion genes as well as genomic imbalances resulting in gain and losses of many gene loci. The detected fusion genes probably represent the main leukemogenic events, although the gains and losses are also likely to play a role in leukemogenesis.

Non-histone binding functions of PHD fingers

Plant homeodomain (PHD) fingers comprise a large and well-established family of epigenetic readers that recognize histone H3. A typical PHD finger binds to the unmodified or methylated amino-terminal tail of H3. This interaction is highly specific and can be regulated by post-translational modifications (PTMs) in H3 and other domains present in the protein. However, a set of PHD fingers has recently been shown to bind non-histone proteins, H3 mimetics, and DNA. In this review, we highlight the molecular mechanisms by which PHD fingers interact with ligands other than the amino terminus of H3 and discuss similarities and differences in engagement with histone and non-histone binding partners.

Atypical histone targets of PHD fingers

Plant homeodomain (PHD) fingers are structurally conserved zinc fingers that selectively bind unmodified or methylated at lysine 4 histone H3 tails. This binding stabilizes transcription factors and chromatin-modifying proteins at specific genomic sites, which is required for vital cellular processes, including gene expression and DNA repair. Several PHD fingers have recently been shown to recognize other regions of H3 or histone H4. In this review, we detail molecular mechanisms and structural features of the non-canonical histone recognition, discuss biological implications of the atypical interactions, highlight therapeutic potential of PHD fingers, and compare inhibition strategies.

Histone Readers and Their Roles in Cancer

Histone proteins in eukaryotic cells are subjected to a wide variety of post-translational modifications, which are known to play an important role in the partitioning of the genome into distinctive compartments and domains. One of the major functions of histone modifications is to recruit reader proteins, which recognize the epigenetic marks and transduce the molecular signals in chromatin to downstream effects. Histone readers are defined protein domains with well-organized three-dimensional structures. In this Chapter, we will outline major histone readers, delineate their biochemical and structural features in histone recognition, and describe how dysregulation of histone readout leads to human cancer.

KDM4 Demethylases: Structure, Function, and Inhibitors

KDM4 histone demethylases mainly catalyze the removal of methyl marks from H3K9 and H3K36 to epigenetically regulate chromatin structure and gene expression. KDM4 expression is strictly regulated to ensure proper function in a myriad of biological processes, including transcription, cellular proliferation and differentiation, DNA damage repair, immune response, and stem cell self-renewal. Aberrant expression of KDM4 demethylase has been documented in many types of blood and solid tumors, and thus, KDM4s represent promising therapeutic targets. In this chapter, we summarize the current knowledge of the structures and regulatory mechanisms of KDM4 proteins and our understanding of their alterations in human pathological processes with a focus on development and cancer. We also review the reported KDM4 inhibitors and discuss their potential as therapeutic agents.

CXCR4 Mediates Enhanced Cell Migration in CALM-AF10 Leukemia

Leukemia transformed by the CALM-AF10 chromosomal translocation is characterized by a high incidence of extramedullary disease, central nervous system (CNS) relapse, and a poor prognosis. Invasion of the extramedullary compartment and CNS requires leukemia cell migration out of the marrow and adherence to the cells of the local tissue. Cell adhesion and migration are increasingly recognized as contributors to leukemia development and therapeutic response. These processes are mediated by a variety of cytokines, chemokines, and their receptors, forming networks of both secreted and cell surface factors. The cytokines and cytokine receptors that play key roles in CALM-AF10 driven leukemia are unknown. We find high cell surface expression of the cytokine receptor CXCR4 on leukemia cells expressing the CALM-AF10 oncogenic protein, contributing to the migratory nature of this leukemia. Our discovery of altered cytokine receptor expression and function provides valuable insight into the propagation and persistence of CALM-AF10 driven leukemia.