Danis, E. | Search bioRxiv

bioRxiv2020

Suppression of canonical TGF-β signaling enables GATA4 to interact with H3K27me3 demethylase JMJD3 to promote cardiomyogenesis

Direct reprogramming of fibroblasts into cardiomyocytes (CMs) represents a promising strategy to regenerate CMs lost after ischemic heart injury. Overexpression of GATA4, HAND2, MEF2C, TBX5, miR-1, and miR-133 (GHMT2m) along with transforming growth factor beta (TGF-{beta}) inhibition efficiently promotes reprogramming. However, the mechanisms by which TGF-{beta} blockade promotes cardiac reprogramming remain unknown. Here, we identify interactions between the histone H3 lysine 27 trimethylation (H3K27me3) - demethylase JMJD3, the SWI/SNF remodeling complex subunit BRG1, and cardiac transcription factors. Furthermore, canonical TGF-{beta} signaling regulates the interaction between GATA4 and JMJD3. TGF-{beta} activation impairs the ability of GATA4 to bind target genes and prevents demethylation of H3K27 at cardiac gene promoters during cardiac reprogramming. Finally, a mutation in GATA4 (V267M) exhibits reduced binding to JMJD3 and impaired cardiomyogenesis. Thus, we have identified an epigenetic mechanism wherein canonical TGF-{beta} pathway activation impairs cardiac gene programming by interfering with GATA4-JMJD3 interactions.

cell biology↗

bioRxiv2020

Super elongation complex as a targetable dependency in diffuse midline glioma

Mutations in the histone 3 gene (H3K27M) are the eponymous drivers in diffuse intrinsic pontine gliomas (DIPGs) and other diffuse midline gliomas (DMGs), aggressive pediatric brain cancers for which no curative therapy currently exists. The salient molecular consequence of these recurrent oncohistones is a global loss of repressive H3K27me3 residues and broad epigenetic dysregulation. In order to identify specific, therapeutically targetable epigenetic dependencies within this disease context, we performed an shRNA screen targeting 408 genes classified as epigenetic/chromatin-associated molecules in patient-derived DMG cultures. This approach identified AFF4, the scaffold protein of the super elongation complex (SEC), as a previously-undescribed dependency in DMG. Interrogation of SEC function demonstrated a key role for maintaining DMG cell viability and clonogenic potential while promoting self-renewal of DMG tumor stem cells. Small-molecule inhibition of the SEC with the highly-specific, clinically relevant CDK9 inhibitors atuveciclib and AZD4573 restores regulatory RNA polymerase II pausing, promotes cellular differentiation, and leads to potent anti-tumor effect both in vitro and in patient-derived xenograft models. These studies present a biologic rationale for translational exploration of CDK9 inhibition as a promising therapeutic approach in a disease which currently has no effective medical therapies.

cancer biology↗