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Cardiac fibrosis is mediated by the persistent activity of myofibroblasts, which differentiates from resident cardiac fibroblasts in response to tissue damage and stress signals. The signaling pathways and transcription factors regulating fibrotic transformation have been thoroughly studied. In contrast, the roles of chromastin factors in myofibroblast differentiation and their contribution to pathogenic cardiac fibrosis remain poorly understood. Here, we combined bulk and single-cell CRISPR screens to characterize the roles of chromatin factors in the fibrotic transformation of primary cardiac fibroblasts. We uncover strong regulators of fibrotic states including Srcap and Kat5 chromatin remodelers. We confirm that these factors are required for functional processes underlying fibrosis including collagen synthesis and cell contractility. Using chromatin profiling in perturbed cardiac fibroblasts, we demonstrate that pro-fibrotic chromatin complexes facilitate the activity of well-characterized pro-fibrotic transcription factors. Finally, we show that KAT5 inhibition alleviates fibrotic responses in patient-derived human fibroblasts. Cardiac fibrosis arises from persistent myofibroblast activity. This study reveals how chromatin factors control scar-forming cells in the heart and shows that inhibiting KAT5 can reduce harmful cardiac fibrosis.

B-cell acute lymphoblastic leukemia (B-ALL) is a leading cause of death in childhood and outcomes in adults remain dismal. There is therefore an urgent clinical need for therapies that target the highest risk cases. Mutations in the histone acetyltransferase CREBBP confer high-risk and increased chemoresistance in ALL. Performing a targeted drug-screen in isogenic human cell lines, we identify a number of small molecules that specifically target CREBBP -mutated B-ALL, the most potent being the BCL2-inhibitor Venetoclax. Of note, this acts through a non-canonical mechanism resulting in ferroptotic rather than apoptotic cell death. CREBBP -mutated cell lines show differences in cell-cycle, metabolism, lipid composition and response to oxidative stress, predisposing them to ferroptosis, which are further dysregulated upon acquisition of Venetoclax resistance. Lastly, small-molecule inhibition of CREBBP pharmacocopies CREBBP -mutation, sensitizing B-ALL cells, regardless of genotype, to Venetoclax-induced ferroptosis in-vitro and in-vivo, providing a promising drug combination for broader clinical translation in B-ALL. CREBBP mutations in B-cell acute lymphoblastic leukemia (B-ALL) are linked to poor prognosis and chemoresistance. Here, the authors show that genetic or pharmacological inactivation of CREBBP sensitizes B-ALL cells to the BCL2 inhibitor Venetoclax, inducing ferroptotic cell death and extending survival in B-ALL preclinical mouse models.

Deletion of long arm of chromosome 20 [del(20q)] is the second most frequent recurrent chromosomal abnormality in hematological malignancies. It is detected in 10% of myeloproliferative neoplasms, 4–5% of myelodysplastic syndromes, and 1–2% of acute myeloid leukaemia. Recurrent, non-random occurrence of del(20q) indicates that it is a pathogenic driver in myeloid malignancies. Genetic mapping of patient samples has identified two regions of interest on 20q – the “Common Deleted Region” (CDR) and “Common Retained Region” (CRR), which was often amplified. We proposed that the CDR contained tumor suppressor gene(s) (TSG) and the CRR harbored oncogene(s); loss of a TSG together with over-expression of an oncogene favored development of myeloid malignancies. Protein Tyrosine Phosphatase Receptor T (PTPRT) and Hemopoietic cell kinase (HCK) were identified to be the likely candidate TSG and oncogene respectively. Retroviral transduction of HCK into PTPRT-null murine LKS+ stem and progenitor cells resulted in hyperproliferation in colony forming assays and hyperphosphorylation of intracellular STAT3. Furthermore, over half of the murine recipients of these transduced cells developed erythroid hyperplasia, polycythemia and splenomegaly at 12 months, although no leukemic phenotype was observed. The findings suggested that HCK amplification coupled with PTPRT loss in del(20q) leads to development of a myeloproliferative phenotype.

Cellular differentiation requires extensive alterations in chromatin structure and function, which is elicited by the coordinated action of chromatin and transcription factors. By contrast with transcription factors, the roles of chromatin factors in differentiation have not been systematically characterized. Here, we combine bulk ex vivo and single-cell in vivo CRISPR screens to characterize the role of chromatin factor families in hematopoiesis. We uncover marked lineage specificities for 142 chromatin factors, revealing functional diversity among related chromatin factors (i.e. barrier-to-autointegration factor subcomplexes) as well as shared roles for unrelated repressive complexes that restrain excessive myeloid differentiation. Using epigenetic profiling, we identify functional interactions between lineage-determining transcription factors and several chromatin factors that explain their lineage dependencies. Studying chromatin factor functions in leukemia, we show that leukemia cells engage homeostatic chromatin factor functions to block differentiation, generating specific chromatin factor–transcription factor interactions that might be therapeutically targeted. Together, our work elucidates the lineage-determining properties of chromatin factors across normal and malignant hematopoiesis. Bulk ex vivo and single-cell in vivo CRISPR knockout screens are used to characterize 680 chromatin factors during mouse hematopoiesis, highlighting lineage-specific and normal and leukemia-specific functions.

Altered transcription is a cardinal feature of acute myeloid leukemia (AML); however, exactly how mutations synergize to remodel the epigenetic landscape and rewire three-dimensional DNA topology is unknown. Here, we apply an integrated genomic approach to a murine allelic series that models the two most common mutations in AML: Flt3 - ITD and Npm1c . We then deconvolute the contribution of each mutation to alterations of the epigenetic landscape and genome organization, and infer how mutations synergize in the induction of AML. Our studies demonstrate that Flt3-ITD signals to chromatin to alter the epigenetic environment and synergizes with mutations in Npm1c to alter gene expression and drive leukemia induction. These analyses also allow the identification of long-range cis -regulatory circuits, including a previously unknown superenhancer of Hoxa locus, as well as larger and more detailed gene-regulatory networks, driven by transcription factors including PU.1 and IRF8, whose importance we demonstrate through perturbation of network members. Mice bearing mutations in Flt3-ITD and Npm1c , which are commonly found in acute myeloid leukemia, are used to characterize the cooperative effects of these cancer drivers on the cellular epigenome and three-dimensional genome conformation during tumor development.

Although initially viewed as unregulated, increasing evidence suggests that cellular necrosis often proceeds through a specific molecular program. In particular, death ligands such as tumour necrosis factor (TNF)-α activate necrosis by stimulating the formation of a complex containing receptor-interacting protein 1 (RIP1) and receptor-interacting protein 3 (RIP3). Relatively little is known regarding how this complex formation is regulated. Here, we show that the NAD-dependent deacetylase SIRT2 binds constitutively to RIP3 and that deletion or knockdown of SIRT2 prevents formation of the RIP1–RIP3 complex in mice. Furthermore, genetic or pharmacological inhibition of SIRT2 blocks cellular necrosis induced by TNF-α. We further demonstrate that RIP1 is a critical target of SIRT2-dependent deacetylation. Using gain- and loss-of-function mutants, we demonstrate that acetylation of RIP1 lysine 530 modulates RIP1–RIP3 complex formation and TNF-α-stimulated necrosis. In the setting of ischaemia-reperfusion injury, RIP1 is deacetylated in a SIRT2-dependent fashion. Furthermore, the hearts of Sirt2 −/− mice, or wild-type mice treated with a specific pharmacological inhibitor of SIRT2, show marked protection from ischaemic injury. Taken together, these results implicate SIRT2 as an important regulator of programmed necrosis and indicate that inhibitors of this deacetylase may constitute a novel approach to protect against necrotic injuries, including ischaemic stroke and myocardial infarction. Here it is shown that the NAD-dependent deacetylase SIRT2 is an essential component of necrosis, and that mouse hearts that do not contain SIRT2 or that are treated with a pharmacological inhibitor of SIRT2 are largely protected from ischaemic injury. SIRT2 a cell death regulator The death ligand TNF-α activates necrosis by stimulating the formation of a complex containing receptor-interacting protein 1 (RIP1) and receptor-interacting protein 3 (RIP3). Here, working in mice, Toren Finkel and colleagues show that the NAD-dependent deacetylase SIRT2 binds constitutively to RIP3. Without SIRT2, the RIP1–RIP3 complex does not form following TNF-α stimulation, and necrosis is prevented. RIP1 is the target of SIRT2-dependent deacetylation, and its acetylation regulates RIP1–RIP3 complex formation and TNF-α-stimulated necrosis. During ischaemia-reperfusion injury, in which necrosis is prevalent, RIP1 is deacetylated in a SIRT2-dependent fashion. The authors further show that hearts lacking the Sirt2 gene, or those treated with a pharmacological inhibitor of SIRT2, are largely protected from ischaemic injury. Thus, SIRT2 is an important regulator of programmed necrosis and a promising pharmacological target in the prevention of necrotic injuries.

Altered transcription is a cardinal feature of acute myeloid leukemia (AML), however, exactly how mutations synergize to remodel the epigenetic landscape and rewire 3-Dimensional (3D) DNA topology is unknown. Here we apply an integrated genomic approach to a murine allelic series that models the two most common mutations in AML, Flt3-ITD and Npm1c. We then deconvolute the contribution of each mutation to alterations of the epigenetic landscape and genome organization, and infer how mutations synergize in the induction of AML. Our studies demonstrate that Flt3-ITD signals to chromatin to alter the epigenetic environment and synergizes with Npm1c mutation to alter gene expression and drive leukemia induction. These analyses also allow the identification of long-range cis-regulatory circuits, including a novel super-enhancer of Hoxa locus, as well as larger and more detailed gene-regulatory networks, driven by transcription factors including PU.1 and IRF8, whose importance we demonstrate through perturbation of network members.