Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2023.12.28.573526

Interplay between Two Paralogous Human Silencing Hub (HuSH) Complexes in Regulating LINE-1 Element Silencing

Jensvold, Z. D.·Christenson, A. E.·Flood, J. R.·Lewis, P. W.
View original source ↗Export metadata ↓

Abstract

The Human Silencing Hub (HuSH) complex is composed of TASOR, MPP8, and PPHLN1 subunits and serves as a conserved protein complex responsible for silencing transposable elements in vertebrate animals. Despite its importance, the regulatory mechanisms and recruitment dynamics governing this complex remain poorly understood. In this study, we have identified a second HuSH complex, termed HuSH2, centered around TASOR2, a paralog of the core TASOR protein in HuSH. Our findings indicate that every subunit in both HuSH and HuSH2 has an important role in achieving precise genomic localization to distinct, non-overlapping genomic loci. We utilized in silico protein structure prediction to simulate the interactions between MPP8 and both TASOR paralogs. Drawing on the insights gained from these predictions, we implemented amino acid substitutions that interfered with the binding of MPP8 to each HuSH complex. Leveraging these MPP8 transgenes and other constructs, we identified an important role played by the relative quantities of HuSH complexes in controlling the activity of LINE-1 elements. Furthermore, our results suggest that dynamic changes in TASOR and TASOR2 expression enable cells to finely tune the extent of HuSH-mediated silencing. Our study provides insights into the intricate interplay between HuSH complexes, illuminating their important role in the regulation of retrotransposon silencing. Key PointsO_LIThe identification of a previously unknown HuSH2 complex, with TASOR2 as its central component. C_LIO_LIHuSH and HuSH2 complexes exhibit unique genomic localization patterns within the human genome. C_LIO_LIDisruption of the delicate balance between the two HuSH complexes results in the desilencing of LINE-1. C_LIO_LITASOR and TASOR2 engage in a competitive interaction for the HuSH subunit MPP8. C_LIO_LIThe localization of MPP8 to either HuSH or HuSH2 sites is intricately regulated by its interaction with TASOR and TASOR2. C_LI

Source connections

Explore related subjects

molecular biologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Jensvold, Z. D., Christenson, A. E., Flood, J. R., Lewis, P. W.. 2023-12-28. Interplay between Two Paralogous Human Silencing Hub (HuSH) Complexes in Regulating LINE-1 Element Silencing. https://doi.org/10.1101/2023.12.28.573526

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

An ssRNA Phage Single-gene Lysis Protein Targeting MraY Reveals Convergent Evolution Across the RNA-DNA Phage Boundary

Small lytic phages of the ssRNA Leviviricetes and ssDNA Microviricetes achieve host lysis by expression of a single protein, designated as an Sgl protein. Four ssRNA Sgls have been shown to inhibit steps in peptidoglycan biosynthesis: three target MurJ, the Lipid II flippase, and one targets MurA, the committed step of the pathway. A fifth Sgl, the E protein of the canonical ssDNA microvirus {varphi}X174, inhibits MraY, which catalyzes the synthesis of the first lipid-linked intermediate. This inhibition requires SlyD, a cytoplasmic FKBP-type peptidyl-prolyl cis-trans isomerase. The Sgl of the Caulobacter ssRNA phage {varphi}Cb5 (Cebevirus halophobicum) has not been characterized. Here, we present physiological evidence that Sgl{varphi}Cb5 targets MraY. Moreover, we show that, despite the absence of detectable sequence similarity, Sgl{varphi}Cb5 shares several features with the {varphi}X174 E protein, including the distribution of hydrophobic and charged residues, a proposed N-out, C-in membrane topology, and retention of lytic activity in an Sgl{varphi}Cb5 -LacZ fusion. Furthermore, expression of the Caulobacter cytoplasmic FKBP-type peptidyl-prolyl cis-trans isomerase CC2799 enhances Sgl{varphi}Cb5 -mediated lysis in E. coli. These parallels between Sgl function in a DNA phage and an RNA phage either represent remarkably consonant convergent evolution or some evolutionary cross-over event for which there is currently no precedent.

molecular biology↗
bioRxiv2026

HERC1-mediated orphan subunit quality control maintains proteasome homeostasis and is disrupted in HERC1-associated neurodevelopmental disease

Biallelic hypomorphic variants in the E3 ubiquitin ligase HERC1 cause a neurological disorder clinically characterized by macrocephaly, dysmorphic facies, and psychomotor delay. Identifying the substrates of HERC1 is essential for understanding its biological functions and the mechanisms underlying disease-associated variants. To address this, we performed a quantitative proteomic analysis using biotinylated ubiquitin to identify HERC1 targets and examine their regulation in cells expressing HERC1 with or without ubiquitin ligase activity. This approach revealed a broad set of HERC1-dependent ubiquitylation substrates, including proteins from major multiprotein complexes such as the proteasome, the translation initiation machinery, and pathways involved in cell metabolism. Focusing on the proteasome, the most prominently represented complex, we identified several regulatory particle subunits, including PSMC6, PSME1, and PSME2. Specifically, within the 19S regulatory particle, we demonstrated that ubiquitylation of the PSMC6 subunit involves the formation of K48-linked polyubiquitin chains and depends on HERC1 activity. Other 19S subunits, such as PSMC2, PSMC4, and PSMC5, undergo a similar modification. Mechanistically, we show that HERC1 selectively recognizes unassembled subunits, promotes their ubiquitylation, and targets them for proteasomal degradation. Notably, in HERC1-deficient cells, disruption of this mechanism impaired proteasomal activity. At the disease level, quantitative proteomic analysis of the pathogenic HERC1 variant c.1448G>A (p.Gly483Glu) likewise identified altered ubiquitylation of proteasome subunits and components of the translation initiation machinery. Biochemical analyses further revealed impaired ubiquitylation of PSMC6 by the mutant HERC1 protein, associated with a loss of interaction between HERC1 and PSMC6. Together, these findings establish a link between HERC1-associated neurological disorders and defective ubiquitylation pathways. They elucidate the molecular mechanisms by which HERC1 regulates proteostasis and demonstrate how disruption of these processes contributes to disease pathogenesis, thereby highlighting potential avenues for therapeutic intervention.

molecular biology↗
bioRxiv2026

PKR inhibition prevents maladaptive responses to endoplasmic reticulum (ER) stress in early-onset dystonia DYT-PRKRA.

DYT-PRKRA is a rare, childhood-onset dystonia caused by mutations in the PRKRA gene, which encodes the protein PACT. PACT activates protein kinase R (PKR) in response to endoplasmic reticulum (ER) stress. In DYT-PRKRA patient cells, the PACT-PKR interaction is enhanced, increasing sensitivity to ER stress-induced apoptosis. The canonical protein kinase activated by ER stress is PKR-like endoplasmic reticulum kinase (PERK), which phosphorylates the subunit of eukaryotic translation initiation factor 2 (eIF2) to initiate the integrated stress response (ISR) and restore cellular homeostasis via the transcription factor ATF4. However, under persistent stress, ATF4 induces CHOP, shifting the adaptive response toward apoptosis. PKR, also activated by ER stress, phosphorylates eIF2, but its contribution to cellular homeostasis remains understudied. This work shows, for the first time, that PKR activation is essential for CHOP induction during ISR, directly linking enhanced apoptosis in DYT-PRKRA cells to prolonged PKR activation and heightened CHOP induction. Strikingly, a small-molecule PKR inhibitor effectively blocks CHOP expression and significantly decreases apoptosis in DYT-PRKRA cells, suggesting PKR inhibition as an effective therapeutic strategy for DYT-PRKRA.

molecular biology↗