RAP1 regulates TIP60 function during fate transition between 2 cell-like and pluripotent states

In mammals, the conserved telomere binding protein RAP1 serves a diverse set of non-telomeric functions including activation of the NF-kB signaling pathway, maintenance of metabolic function in vivo, and transcriptional regulation. Here, we uncover the mechanism by which RAP1 modulates gene expression. Using a separation-of-function allele, we show that RAP1 transcriptional regulation is independent of TRF2-mediated binding to telomeres and does not involve direct binding to genomic loci. Instead, RAP1 interacts with the TIP60/p400 complex and modulates its histone acetyltransferase activity. Notably, we show that deletion of RAP1 in mouse embryonic stem cells increases the fraction of 2-cell-like cells. Specifically, RAP1 enhances the repressive activity of Tip60/p400 across a subset of 2-cell-stage genes, including Zscan4 and the endogenous retrovirus MERVL. Preferential upregulation of genes proximal to MERVL elements in Rap1 deficient settings implicate these endogenous retroviral elements in the de-repression of proximal genes. Altogether, our study reveals an unprecedented link between RAP1 and TIP60/p400 complex in the regulation of totipotency.

TAMI-30. THERAPY INDUCED REPROGRAMMING DRIVES GLIOMA VASCULAR TRANSDIFFERENTIATION AND TUMOR RECURRENCE

Therapy-resistant glioma cells elicit phenotypic plasticity leading to aggressive tumor recurrence. Here, we employed single-cell and whole transcriptomic analyses to uncover that a standard glioma treatment, radiation induces a dynamic shift in functional states of glioma cells allowing for acquisition of mesenchymal-like and vascular-like phenotypes. The predominant phenotype switch induced by radiation in surviving tumor cells is transdifferentiation to endothelial-like and pericyte-like cells. The transdifferentiated cells in turn promote proliferation of radiated tumor cells, and their selective depletion results in reduced tumor growth and recurrence post-treatment. The acquisition of vascular-like phenotype is driven by increased chromatin accessibility in vascular genes, and blocking P300-mediated histone acetyltransferase activity prior to radiation treatment inhibits vascular transdifferentiation and tumor growth. Our findings indicate that radiation therapy reprograms tumor cells driving vascular transdifferentiation, and highlights HAT inhibitors as potential therapeutic target for preventing GBM relapse

Aptamer-mediated rolling circle amplification for label-free and sensitive detection of histone acetyltransferase activity

An aptamer-mediated histone modification site-specific rolling circle amplification is developed for label-free detection of histone-modifying enzyme at the femtomolar level.

SVA insertion in X-linked Dystonia Parkinsonism alters histone H3 acetylation associated with TAF1 gene

X-linked Dystonia-Parkinsonism (XDP) is a neurodegenerative disease linked to an insertion of a SINE-VNTR-Alu (SVA)-type retrotransposon within an intron of TAF1. This SVA insertion induces aberrant TAF1 splicing and partial intron retention, thereby decreasing levels of the full-length transcript. Here we sought to determine if these altered transcriptional dynamics caused by the SVA are also accompanied by local changes in histone acetylation, given that these modifications influence gene expression. Because TAF1 protein may itself exhibit histone acetyltransferase activity, we also examined whether decreased TAF1 expression in XDP cell lines and post-mortem brain affects global levels of acetylated histone H3 (AcH3). The results demonstrate that total AcH3 are not altered in XDP post-mortem prefrontal cortex or cell lines. We also did not detect local differences in AcH3 associated with TAF1 exons or intronic sites flanking the SVA insertion. There was, however, a decrease in AcH3 association with the exon immediately proximal to the intronic SVA, and this decrease was normalized by CRISPR/Cas-excision of the SVA. Collectively, these data suggest that the SVA insertion alters histone status in this region, which may contribute to the dysregulation of TAF1 expression.