Biology subjects

Saldana-Meyer, R.

Publications and source records attributed to Saldana-Meyer, R..

4 recordsLinked to original sources

bioRxiv2021

The H3K36me2 writer-reader dependency in H3K27M-DIPG

The lysine-to-methionine mutation at residue 27 of histone H3 (H3K27M) is a driving mutation in Diffuse Intrinsic Pontine Glioma (DIPG), a highly aggressive form of pediatric brain tumor with no effective treatment and little chance of survival. H3K27M reshapes the epigenome through a global inhibition of PRC2 catalytic activity, the placement of methylation at lysine 27 of histone H3 (H3K27me2/3), promoting oncogenesis of DIPG. As a consequence, a histone modification H3K36me2, antagonistic to H3K27me2/3, is aberrantly elevated. Here, we investigate the role of H3K36me2 in H3K27M-DIPG by tackling its upstream catalyzing enzymes (writers) and downstream binding factors (readers). We determine that NSD1 and NSD2 are the key writers for H3K36me2. Loss of NSD1/2 in H3K27M-DIPG impedes cellular proliferation in vitro and tumorigenesis in vivo, and disrupts tumor-promoting gene expression programs. Further, we demonstrate that LEDGF and HDGF2 are the main readers that mediate the pro-tumorigenic effects downstream of NSD1/2-H3K36me2. Treatment with a chemically modified peptide mimicking endogenous H3K36me2 dislodges LEDGF/HDGF2 from chromatin and specifically inhibits the proliferation of H3K27M-DIPG. Together, our results indicate a functional pathway of NSD1/2-H3K36me2-LEDGF/HDGF2 as an acquired dependency in H3K27M-DIPG and suggest a possibility to target this pathway for therapeutic interventions.

cancer biology↗

bioRxiv2019

RNA interactions with CTCF are essential for its proper function

The function of the CCCTC-binding factor (CTCF) in the organization of the genome has become an important area of investigation, but the mechanisms of how CTCF dynamically contributes to genome organization is not clear. We previously discovered that CTCF binds to large numbers of endogenous RNAs; promoting its oligomerization. Here we found that inhibition of transcription or interfering with CTCF ability to bind RNA through mutations of two of its 11 zinc fingers that are not involved with CTCF binding to its cognate site in vitro, zinc finger-1 (ZF1) or -10 (ZF10), disrupt CTCF association to chromatin. These mutations alter gene expression profiles as CTCF mutants lose their ability to promote local insulation. Our results highlight the importance of RNA as a structural component of the genome, in part by affecting the association of CTCF with chromatin and likely its interaction with other factors. O_LITranscriptional inhibition disrupts CTCF binding to chromatin C_LIO_LIRNA-binding regions (RBR) in CTCF are found within ZF1 and ZF10 C_LIO_LILocal insulation is markedly decreased in ZF1{triangleup} and ZF10{triangleup} mutant rescues C_LIO_LIGene expression and chromatin organization are disrupted by RBR mutants C_LI

molecular biology↗

bioRxiv2018

Multiple modes of PRC2 inhibition elicit global chromatin alterations in H3K27M pediatric glioma

A methionine substitution at lysine 27 on histone H3 variants (H3K27M) characterizes ~80% of diffuse intrinsic pontine gliomas (DIPG) and inhibits PRC2 in a dominant negative fashion. Yet, the mechanisms for this inhibition and abnormal epigenomic landscape have not been resolved. Using quantitative proteomics, we discovered that robust PRC2 inhibition requires levels of H3K27M greatly exceeding those of PRC2, seen in DIPG. While PRC2 inhibition requires interaction with H3K27M, we found this interaction on chromatin is transient with PRC2 largely being released from H3K27M. Unexpectedly, inhibition persisted even after PRC2 dissociated from H3K27M-chromatin suggesting a lasting impact on PRC2. Furthermore, allosterically activated PRC2 is particularly sensitive to K27M leading to a failure to spread H3K27me3 at distinct foci. In turn, levels of Polycomb antagonists such as H3K36me2 are elevated suggesting a more global, downstream effect on the epigenome. Together, these findings reveal the conditions required for H3K27M-mediated PRC2 inhibition and reconcile seemingly paradoxical effects of H3K27M on PRC2 recruitment and activity.

molecular biology↗

bioRxiv2017

Distinct stimulatory mechanisms regulate the catalytic activity of Polycomb Repressive Complex 2 (PRC2)

The maintenance of gene expression patterns during metazoan development is carried out, in part, by the actions of the Polycomb Repressive Complex 2 (PRC2). PRC2 catalyzes mono-, di-and trimethylation of histone H3 at lysine 27 (H3K27), with H3K27me2/3 being strongly associated with silenced genes. We demonstrate that EZH1 and EZH2, the two mutually exclusive catalytic subunits of PRC2, are differentially activated by various mechanisms. While both PRC2-EZH1 and PRC2-EZH2 are able to catalyze monomethylation, only PRC2-EZH2 is strongly activated by allosteric modulators and specific chromatin substrates to catalyze di-and trimethylation of H3K27. However, we also show that a PRC2 associated protein, AEBP2, can stimulate the activity of both complexes through a mechanism independent of and additive to allosteric activation. These results have strong implications regarding the cellular requirements for and accompanying adjustments in PRC2 activity, given the difference in the expression of EZH1 and EZH2 upon cellular differentiation.

biochemistry↗