Biology subjects

Hunold, P.

Publications and source records attributed to Hunold, P..

3 recordsLinked to original sources

bioRxiv2023

Activation of automethylated PRC2 by dimerization on chromatin

Polycomb Repressive Complex 2 (PRC2) is an epigenetic regulator that trimethylates lysine 27 of histone 3 (H3K27me3) and is essential for embryonic development and cellular differentiation. H3K27me3 is associated with transcriptionally repressed chromatin and is established when PRC2 is allosterically activated upon methyl-lysine binding by the regulatory subunit EED. Automethylation of the catalytic subunit EZH2 stimulates its activity by an unknown mechanism. Here, we show that PRC2 forms a dimer on chromatin in which an inactive, automethylated PRC2 protomer is the allosteric activator of a second PRC2 that is poised to methylate H3 of a substrate nucleosome. Functional assays support our model of allosteric trans-autoactivation via EED, suggesting a novel mechanism mediating context- dependent activation of PRC2. Our work showcases the molecular mechanism of auto- modification coupled dimerization in the regulation of chromatin modifying complexes.

biochemistry↗

bioRxiv2023

Functional diversity of the TP53 mutome revealed by saturating CRISPR mutagenesis

The tumor suppressor gene TP53 is the most frequently mutated gene in various cancers. Unlike other tumor suppressors, TP53 is mostly hit by missense mutations, of which more than 2,000 have been described in cancer patients. To take advantage of TP53 mutation status for personalized therapy, a deeper knowledge of the functional ramifications of specific mutations is required as evidence of the functional heterogeneity of mutant p53 proteins mounts. Here, we report on a CRISPR-based saturation mutagenesis screen of 9,225 variants expressed from the endogenous TP53 gene locus of a cancer cell. By tracking changes in the abundance of individual variants in response to specific p53-pathway stimulation, we were able to construct high-resolution functional activity maps of the TP53 mutome, covering [~]94.5% of all cancer-associated missense mutations. The results demonstrate the impact of individual mutations on tumor cell fitness with unprecedented precision and coverage, even revealing underlying mechanisms such as apoptosis. The high discriminatory power also resolves subtle loss-of-function phenotypes and highlights a subset of mutants as particularly promising targets for pharmacological reactivation. Moreover, the data offer intriguing insight into the role of aberrant splicing and nonsense-mediated mRNA decay in clearing truncated proteins due to not only nonsense, frameshift, and splice-site mutations but also missense and synonymous mutations. Surprisingly, no missense mutation provided an immediate proliferative advantage over a null mutation. Nonetheless, cells with a missense, but not null mutations, acquired pro-metastatic properties after prolonged growth in mice, emphasizing the significance of mutant p53-directed clonal evolution in the progression of tumors towards metastasis.

cancer biology↗

bioRxiv2023

G-quadruplex DNA structures mediate non-autonomous instruction of breast tumour microenvironments

Breast cancer is characterised by genetic and epigenetic alterations, such as G-quadruplex (G4) DNA secondary structures. Here, we uncover differentially enriched G4 structure-forming regions ({triangleup}G4Rs) and interlinked transcriptomes in the tumour microenvironment (TME) of breast cancer PDX models in vivo. We show that well-defined breast cancer cell models non-autonomously instruct {triangleup}G4Rs and transcriptomes in the epigenomes of primary macrophages in vitro. Mechanistically, we uncover that TNBC secretes, amongst other factors, glucocorticoids to promote G4-linked activation of octamer-binding transcription factor 1 (OCT-1) and thereby reprogramme macrophages into an immunosuppressed and immunosuppressive state. This epigenetic mechanism is of clinical importance since instructed macrophages selectively associate with the triple-negative breast cancer (TNBC) basal-like 2 (BL2) subtype and with the distinct TNBC molecular signature derived from 2,000 primary breast cancer samples. Altogether, our data suggest that G4 formation is not only prevalent in breast cancer genomes but relevant in their TMEs as well, which is of clinical importance for cancer stratification and the discovery of novel actionable drivers.

cancer biology↗