Biology subjects

Boulon, S.

Publications and source records attributed to Boulon, S..

4 recordsLinked to original sources

bioRxiv2026

A large-scale analysis of the R2TP chaperone network reveals its contribution to the assembly of INO80, SRCAP and TIP60

HSP90/R2TP is an essential quaternary chaperone composed of RPAP3, PIH1D1 and the RUVBL1/RUVBL2 AAA+ ATPases. These enzymes are also part of the INO80, SRCAP and TIP60 complexes, but the relationship between these chromatin remodelers and R2TP remains unclear. Here, we performed systematic analyses of the R2TP-specific subunits RPAP3 and PIH1D1. We validated 115 interaction partners and found that many were sensitive to HSP90 or R2TP inhibition. In yeast, epistatic screens revealed functional interactions with Ino80, Swr1 (SRCAP) and NuA4 (TIP60). Consistently, human RPAP3 physically interacted with subunits of INO80, SRCAP and TIP60 and was required for the formation of these complexes. More specifically, RPAP3 enabled the co-translational association of RUVBL1/RUVBL2 with the motor subunit of these chromatin remodelers. In vitro, the client-binding domain of RUVBL1/RUVBL2 modulated their interaction with RPAP3, suggesting that client subunits displace RPAP3 from nascent complexes. Thus, R2TP is an early chaperone of TIP60, SRCAP and INO80, which leaves RUVBL1/RUVBL2 as resident scaffolding subunits.

molecular biology↗

bioRxiv2025

Co-translational determination of quaternary structures in chaperone factories

The HSP90/R2TP quaternary chaperone assembles key cellular machines, including the three nuclear RNA polymerases and many non-coding RNPs. Here, we characterized the RNA associated to R2TP and found that it binds many partners co-translationally. Its co-translational interactome further reveals many novel potential clients and identifies clients bound only co-translationally, only post-translationally, or both. For pairs of subunits assembling together and bound co-translationally by R2TP, only a marginal proportion of their mRNAs is co-localized and co-translated. Instead, the HSP90 and R2TP chaperones induce the formation of condensates accumulating client mRNAs and thus favoring co-translational interactions between chaperones and clients. The R2TP then cycles between co- and post-translational steps and this is regulated by ATP: it binds co-translationally in absence of ATP and becomes released from post-translational assembly intermediates by ATP hydrolysis. Assembly of protein complexes is thus initiated early by chaperones and this mechanism, dubbed co-translational chaperone channeling (cha-cha), substitutes for the rarity of co-localized/co-translated mRNAs.

cell biology↗

bioRxiv2019

The 20S proteasome activator PA28γ controls the compaction of HP1β-linked heterochromatin

PA28{gamma}, a nuclear activator of the 20S proteasome, is involved in the degradation of several proteins regulating cell growth and proliferation and in the dynamics of various nuclear bodies, but its precise cellular functions remain unclear. Here, using a quantitative FLIM-FRET based microscopy assay monitoring close proximity between nucleosomes in living human cells, we show that PA28{gamma} controls chromatin compaction. We find that its depletion induces a decompaction of pericentromeric heterochromatin, similarly to that observed upon the knockdown of HP1{beta}, a key factor in heterochromatin structure. We show that PA28{gamma} is present at HP1{beta}-containing repetitive-DNA sequences abundant in heterochromatin and importantly, that HP1{beta} on its own is unable to drive chromatin compaction without the presence of PA28{gamma}. At the molecular level, we show that this novel function of PA28{gamma} is independent of its stable interaction with the 20S proteasome, and most likely depends on its ability to maintain appropriate levels of H3K9me3 and H4K20me3, histone modifications that are both involved in heterochromatin formation. Overall, our results implicate PA28{gamma} as a key factor involved in the higher order structuration of chromatin.

cell biology↗

bioRxiv2017

FAM192A/PIP30 regulates Cajal body dynamics by antagonizing PA28γ/coilin interaction

PA28{gamma} is a nuclear activator of the 20S proteasome involved in the regulation of several essential cellular processes, such as cell proliferation, apoptosis, nuclear dynamics and cellular stress response. Unlike the 19S regulator of the proteasome, which specifically recognizes ubiquitylated proteins, PA28{gamma} promotes the degradation of several substrates by the proteasome in an ATP- and ubiquitin-independent manner. However its exact mechanisms of action are unclear and likely to involve additional partners that remain to be identified. Here we report the identification of the first cofactor of PA28{gamma}, PIP30/FAM192A. PIP30 binds directly and specifically via its C-terminal end and in an interaction stabilized by casein kinase 2 phosphorylation to both free and 20S proteasome-associated PA28{gamma}. Its recruitment to proteasome-containing complexes depends on PA28{gamma} and its expression increases the association of PA28{gamma} with the 20S proteasome in cells. Further dissection of its possible roles shows that PIP30 alters PA28{gamma}-dependent activation of peptide degradation by the 20S proteasome in vitro and negatively controls in cells the presence of PA28{gamma} in Cajal Bodies by inhibition of its association with the key Cajal body component coilin. Altogether, our data show that PIP30 deeply affects PA28{gamma} interactions with cellular proteins, including 20S proteasome, demonstrating that it is an important regulator of PA28{gamma} in cells and thus a new player in the control of the multiple functions of the proteasome within the nucleus.\n\nSignificance StatementThe 20S proteasome is a key actor of the control of protein levels and integrity in cells. To perform its multiple functions, it works with a series of regulators, among which a nuclear complex called PA28{gamma}. In particular, PA28{gamma} participates in the regulation of cell proliferation and nuclear dynamics. We describe here the characterization of a novel protein, PIP30/FAM192A, which binds tightly to PA28{gamma} and favors its interaction with the 20S proteasome while inhibiting its association with coilin, a central component of nuclear Cajal bodies. Thus PIP30/FAM192A critically controls the interactome and consequently the functions of PA28{gamma}, and appears to be a new player in the fine regulation of intracellular proteostasis in the cell nucleus.

cell biology↗