Dynamic regulation of diverse nuclear processes is intimately linked to covalent modifications of chromatin. Much attention has focused on methylation at lysine 4 of histone H3 (H3K4), owing to its association with euchromatic genomic regions. H3K4 can be mono-, di- or tri-methylated. Trimethylated H3K4 (H3K4me3) is preferentially detected at active genes, and is proposed to promote gene expression through recognition by transcription-activating effector molecules. Here we identify a novel class of methylated H3K4 effector domains--the PHD domains of the ING (for inhibitor of growth) family of tumour suppressor proteins. The ING PHD domains are specific and highly robust binding modules for H3K4me3 and H3K4me2. ING2, a native subunit of a repressive mSin3a-HDAC1 histone deacetylase complex, binds with high affinity to the trimethylated species. In response to DNA damage, recognition of H3K4me3 by the ING2 PHD domain stabilizes the mSin3a-HDAC1 complex at the promoters of proliferation genes. This pathway constitutes a new mechanism by which H3K4me3 functions in active gene repression. Furthermore, ING2 modulates cellular responses to genotoxic insults, and these functions are critically dependent on ING2 interaction with H3K4me3. Together, our findings establish a pivotal role for trimethylation of H3K4 in gene repression and, potentially, tumour suppressor mechanisms.

The RAG1 and RAG2 proteins catalyze V(D)J recombination and are essential for generation of the diverse repertoire of antigen receptor genes and effective immune responses. RAG2 is composed of a "core" domain that is required for the recombination reaction and a C-terminal nonessential or "non-core" region. Recent evidence has emerged arguing that the non-core region plays a critical regulatory role in the recombination reaction, and mutations in this region have been identified in patients with immunodeficiencies. Here we present the first structural data for the RAG2 protein, using NMR spectroscopy to demonstrate that the C terminus of RAG2 contains a noncanonical PHD finger. All of the non-core mutations of RAG2 that are implicated in the development of immunodeficiencies are located within the PHD finger, at either zinc-coordinating residues or residues adjacent to an ␣-helix on the surface of the domain that participates in binding to the signaling molecules, phosphoinositides. Functional analysis of disease and phosphoinositide-binding mutations reveals novel intramolecular interactions within the noncore region and suggests that the PHD finger adopts two distinct states. We propose a model in which the equilibrium between these states modulates recombination activity. Together, these data identify the PHD finger as a novel and functionally important domain of RAG2.During immune system development, immunoglobulin and T cell receptor genes are assembled from their component gene segments. This process, called V(D)J recombination, is initiated by the lymphoid-specific recombination activating genes 1 and 2 (RAG1 and RAG2) (1, 2). The RAG proteins recognize and bind recombination signal sequences flanking each coding segment and introduce double-strand DNA breaks, which are subsequently resolved into coding joints and signal joints. Processing and joining of the ends require the activity of the ubiquitously expressed proteins from the nonhomologous end joining pathway of DNA repair (reviewed in Ref.3). V(D)J recombination is critical for proper immune system function; accordingly, mutations in the RAG or nonhomologous end joining proteins result in immunodeficiencies, and inappropriate RAG activity can lead to genomic instability and cancer (4, 5).RAG2 can be divided into two functionally defined regions, an N-terminal "core" domain (amino acids 1-383) and a Cterminal "non-core" domain (amino acids 384 -527) (see Fig. 1A). The core domain is necessary and sufficient for carrying out V(D)J recombination in vivo on exogenous plasmid substrates (6, 7), as well as V(D)J cleavage in vitro (8). The noncore domain is dispensable for activity in both of these assays; however, its high conservation throughout evolution suggests it serves critical functions. Indeed, replacement of the endogenous RAG2 gene with only the core domain results in impaired development of B and T cells in mice (9, 10). Moreover, recent studies have implicated the C terminus of RAG2 in the restriction of RAG1/2-mediated transposition (11-13) ...

Key Points Responses and survival with venetoclax for “real-world” AML patients were promising but inferior to those treated in a clinical trial. Compared with induction, response rates are as high as would be predicted and venetoclax patients had a lower than expected early death rate.

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Myeloproliferative neoplasms arise from hematopoietic stem cells with somatically altered tyrosine kinase signaling. Classification of myeloproliferative neoplasms is based on hematologic, histopathologic and molecular characteristics including the presence of the BCR-ABL1 and JAK2 V617F. Although thought to be mutually exclusive, a number of cases with co-occurring BCR-ABL1 and JAK2 V617F have been identified. To characterize the clinicopathologic features of myeloproliferative neoplasms with concomitant BCR-ABL1 and JAK2 V617F, and define the frequency of co-occurrence, we conducted a retrospective multi-institutional study. Cases were identified using a search of electronic databases over a decade at six major institutions. Of 1570 patients who were tested for both BCR-ABL1 and JAK2 V617F, six were positive for both. An additional five patients were identified via clinical records providing a total of 11 cases for detailed evaluation. For each case, clinical variables, hematologic and genetic data, and bone marrow histomorphologic features were analyzed. The sequence of identification of the genetic abnormalities varied: five patients were initially diagnosed with a JAK2 V617F+ myeloproliferative neoplasm, one patient initially had BCR-ABL1+ chronic myeloid leukemia, while both alterations were identified simultaneously in five patients. Classification of the BCR-ABL1-negative myeloproliferative neoplasms varied, and in some cases, features only became apparent following tyrosine kinase inhibitor therapy. Seven of the 11 patients showed myelofibrosis, in some cases before identification of the second genetic alteration. Our data, reflecting the largest reported study comprehensively detailing clinicopathologic features and response to therapy, show that the co-occurrence of BCR-ABL1 and JAK2 V617F is rare, with an estimated frequency of 0.4%, and most often reflects two distinct ('composite') myeloproliferative neoplasms. Although uncommon, it is important to be aware of this potentially confounding genetic combination, lest these features be misinterpreted to reflect resistance to therapy or disease progression, considerations that could lead to inappropriate management.

Background The use of next‐generation sequencing for fusion identification is being increasingly applied and aids our understanding of tumor biology. Some fusions are responsive to approved targeted agents, while others have future potential for therapeutic targeting. Although some pediatric central nervous system tumors may be cured with surgery alone, many require adjuvant therapy associated with acute and long‐term toxicities. Identification of targetable fusions can shift the treatment paradigm toward earlier integration of molecularly targeted agents. Methods Patients diagnosed with glial, glioneuronal, and ependymal tumors between 2002 and 2019 were retrospectively reviewed for fusion testing. Testing was done primarily using the ArcherDx FusionPlex Solid Tumor panel, which assesses fusions in 53 genes. In contrast to many previously published series chronicling fusions in pediatric patients, we compared histological features and the tumor classification subtype with the specific fusion identified. Results We report 24 cases of glial, glioneuronal, or ependymal tumors from pediatric patients with identified fusions. With the exception of BRAF:KIAA1549 and pilocytic/pilomyxoid astrocytoma morphology, and possibly QKI‐MYB and angiocentric glioma, there was not a strong correlation between histological features/tumor subtype and the specific fusion. We report the unusual fusions of PPP1CB‐ALK, CIC‐LEUTX, FGFR2‐KIAA159, and MN1‐CXXC5 and detail their morphological features. Conclusions Fusion testing proved to be informative in a high percentage of cases. A large majority of fusion events in pediatric glial, glioneuronal, and ependymal tumors can be identified by relatively small gene panels.

To address the clinical relevance of small DNA variants in chronic myeloid neoplasms (CMNs), an Association for Molecular Pathology Working Group comprehensively reviewed published literature, summarized key findings that support clinical utility, and defined critical gene inclusions for high-throughput sequencing testing panels. This review highlights the biological complexity of CMNs [including myelodysplastic syndromes, myeloproliferative neoplasms, entities with overlapping features (myelodysplastic syndromes/myeloproliferative neoplasms), and systemic mastocytosis], the genetic heterogeneity within diagnostic categories, and similarities between apparently disparate diagnostic entities. The founding variant's hematopoietic differentiation compartment, specific genes and variants present, order of variant appearance, individual subclone dynamics, and therapeutic intervention all contribute to the clinicopathologic features of CMNs. Selection and efficacy of targeted therapies are increasingly based on DNA variant profiles present at various time points; therefore, high-throughput sequencing remains critical for patient management. The following genes are a minimum recommended list to provide relevant clinical information for the management of most CMNs: ASXL1, BCOR, BCORL1, CALR, CBL, CEBPA, CSF3R, DNMT3A, ETV6, EZH2, FLT3, IDH1, IDH2, JAK2, KIT, KRAS, MPL, NF1, NPM1, NRAS, PHF6, PPM1D, PTPN11, RAD21, RUNX1, SETBP1, SF3B1, SMC3, SRSF2, STAG2, TET2, TP53, U2AF1, and ZRSR2. This list is not comprehensive for all myeloid neoplasms and will evolve as insights into effects of combinations of relevant biomarkers on specific clinicopathologic characteristics of CMNs accumulate.