HP1β carries an acidic linker domain and requires H3K9me3 for phase separation

Qin, Weihua; Stengl, Andreas; Ugur, Enes; Leidescher, Susanne; Ryan, Joël; Cardoso, M. Cristina; Leonhardt, Heinrich

doi:10.1080/19491034.2021.1889858

Cited by 25 publications

(36 citation statements)

References 46 publications

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“…Recently we found that HP1β shows phase separation properties in the presence of H3K9me3 histones in vitro ( 11 ). We next investigated its function in heterochromatin organization in cells.…”

Section: Resultsmentioning

confidence: 99%

“…For generation of HP1β −/− mESCs, the MINtag strategy was used as described previously ( 11 , 22 ). After generation of the MIN-tagged line, the attB-RFP-Stop-PolyA was inserted into the N-terminus of the endogenous HP1β attP/attP locus by Bxb1 mediated recombination.…”

Section: Methodsmentioning

confidence: 99%

“…HP1 cDNA was cloned into a pET28 expression vector, mutants were made using overlap extension PCR and proteins were subsequently expressed in Escherichia coli . Purifications of HP1β proteins were described previously ( 11 ).…”

Section: Methodsmentioning

confidence: 99%

“…This phase separation correlates with the formation of heterochromatin compartments (chromocenters) in the nucleus. Recently, we found that the charge of the hinge IDR (IDR-H) is a distinctive feature of HP1 homologues and plays a decisive role in liquid-liquid phase separation (LLPS) ( 10 , 11 ) and that HP1β also undergoes phase separation in a histone H3K9me3 dependent manner ( 11 ). HP1α/β together with other chromatin binding proteins, such as SUV39H1 and KAP1, coalesce around the solid chromatin scaffold ( 12–15 ).…”

Section: Introductionmentioning

confidence: 99%

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Phosphorylation of the HP1β hinge region sequesters KAP1 in heterochromatin and promotes the exit from naïve pluripotency

Qin

Ugur

Mulholland

et al. 2021

Nucleic Acids Research

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Heterochromatin binding protein HP1β plays an important role in chromatin organization and cell differentiation, however the underlying mechanisms remain unclear. Here, we generated HP1β−/− embryonic stem cells and observed reduced heterochromatin clustering and impaired differentiation. We found that during stem cell differentiation, HP1β is phosphorylated at serine 89 by CK2, which creates a binding site for the pluripotency regulator KAP1. This phosphorylation dependent sequestration of KAP1 in heterochromatin compartments causes a downregulation of pluripotency factors and triggers pluripotency exit. Accordingly, HP1β−/− and phospho-mutant cells exhibited impaired differentiation, while ubiquitination-deficient KAP1−/− cells had the opposite phenotype with enhanced differentiation. These results suggest that KAP1 regulates pluripotency via its ubiquitination activity. We propose that the formation of subnuclear membraneless heterochromatin compartments may serve as a dynamic reservoir to trap or release cellular factors. The sequestration of essential regulators defines a novel and active role of heterochromatin in gene regulation and represents a dynamic mode of remote control to regulate cellular processes like cell fate decisions.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Phosphorylation of the HP1β hinge region sequesters KAP1 in heterochromatin and promotes the exit from naïve pluripotency

Qin

Ugur

Mulholland

et al. 2021

Nucleic Acids Research

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“…The recent experimental studies have provided a fresh new perspective on the mechanistic roles of HP1a by showing that solutions of HP1a can undergo spontaneous liquid–liquid phase separation [ 15 , 16 , 17 ]. Phase separation of HP1a has a distinct electrostatic origin confirmed by the fact of HP1a condensing in vitro by the change of ionic conditions [ 15 ], the addition of phosphate groups [ 16 ] or sequence mutations [ 18 , 19 ] in the disordered hinge regions.…”

Section: Introductionmentioning

confidence: 99%

Solvent Exposure and Ionic Condensation Drive Fuzzy Dimerization of Disordered Heterochromatin Protein Sequence

Mueterthies

Potoyan

2021

Biomolecules

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Proteins with low complexity, disordered sequences are receiving increasing attention due to their central roles in the biogenesis and regulation of membraneless organelles. In eukaryotic organisms, a substantial fraction of disordered proteins reside in the nucleus, thereby facilitating the formation of nuclear bodies, nucleolus, and chromatin compartmentalization. The heterochromatin family of proteins (HP1) is an important player in driving the formation of gene silenced mesoscopic heterochromatin B compartments and pericentric regions. Recent experiments have shown that the HP1a sequence of Drosophila melanogaster can undergo liquid-liquid phase separation under both in vitro and in vivo conditions, induced by changes of the monovalent salt concentration. While the phase separation of HP1a is thought to be the mechanism underlying chromatin compartmentalization, the molecular level mechanistic picture of salt-driven phase separation of HP1a has remained poorly understood. The disordered hinge region of HP1a is seen as the driver of salt-induced condensation because of its charge enriched sequence and post-translational modifications. Here, we set out to decipher the mechanisms of salt-induced condensation of HP1a through a systematic study of salt-dependent conformations of single chains and fuzzy dimers of disordered HP1a hinge sequences. Using multiple independent all-atom simulations with and without enhanced sampling, we carry out detailed characterization of conformational ensembles of disordered HP1a chains under different ionic conditions using various polymeric and structural measures. We show that the mobile ion release, enhancement of local transient secondary structural elements, and side-chain exposure to solvent are robust trends that accompany fuzzy dimer formation. Furthermore, we find that salt-induced changes in the ensemble of conformations of HP1a disordered hinge sequence fine-tune the inter-chain vs. self-chain interactions in ways that favor fuzzy dimer formation under low salt conditions in the agreement with condensation trends seen in experiments.

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Liquid–liquid phase separation in diseases

Zhang,

Yuan,

Zhang

et al. 2024

MedComm

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Liquid–liquid phase separation (LLPS), an emerging biophysical phenomenon, can sequester molecules to implement physiological and pathological functions. LLPS implements the assembly of numerous membraneless chambers, including stress granules and P‐bodies, containing RNA and protein. RNA–RNA and RNA–protein interactions play a critical role in LLPS. Scaffolding proteins, through multivalent interactions and external factors, support protein–RNA interaction networks to form condensates involved in a variety of diseases, particularly neurodegenerative diseases and cancer. Modulating LLPS phenomenon in multiple pathogenic proteins for the treatment of neurodegenerative diseases and cancer could present a promising direction, though recent advances in this area are limited. Here, we summarize in detail the complexity of LLPS in constructing signaling pathways and highlight the role of LLPS in neurodegenerative diseases and cancers. We also explore RNA modifications on LLPS to alter diseases progression because these modifications can influence LLPS of certain proteins or the formation of stress granules, and discuss the possibility of proper manipulation of LLPS process to restore cellular homeostasis or develop therapeutic drugs for the eradication of diseases. This review attempts to discuss potential therapeutic opportunities by elaborating on the connection between LLPS, RNA modification, and their roles in diseases.

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HP1β carries an acidic linker domain and requires H3K9me3 for phase separation

Cited by 25 publications

References 46 publications

Phosphorylation of the HP1β hinge region sequesters KAP1 in heterochromatin and promotes the exit from naïve pluripotency

Phosphorylation of the HP1β hinge region sequesters KAP1 in heterochromatin and promotes the exit from naïve pluripotency

Solvent Exposure and Ionic Condensation Drive Fuzzy Dimerization of Disordered Heterochromatin Protein Sequence

Liquid–liquid phase separation in diseases

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