Biology subjects

See, S. K.

Publications and source records attributed to See, S. K..

5 recordsLinked to original sources

bioRxiv2022

Orphan quality control shapes network dynamics and gene expression

All eukaryotes require intricate protein networks to translate developmental signals into accurate cell fate decisions. Mutations that disturb crucial interactions between network components often result in disease, but how the composition and dynamics of complex networks are established is unknown. Here, we identify the tumor suppressor E3 ligase UBR5 as a quality control enzyme that helps degrade unpaired subunits of multiple transcription factors that operate within a single network. By constantly turning over orphan subunits, UBR5 forces cells to continuously replenish network components through new protein synthesis. The resulting cycles of transcription factor synthesis and degradation allow cells to effectively execute the gene expression program, while remaining susceptible to environmental signals. We conclude that orphan quality control plays an essential role in establishing the dynamics of protein networks, which may explain the conserved need for protein degradation in transcription and offers unique opportunities to modulate gene expression in disease.

biochemistry↗

bioRxiv2022

An E3 ligase network engages GCN1 to promote elongation factor-1α degradation on stalled ribosomes

How cells monitor the status of translating ribosomes is a major question in gene regulation. Elongating ribosomes frequently stall during mRNA translation, resulting in context- dependent activation of quality control pathways. However, surveillance mechanisms that specifically respond to stalled ribosomes with an elongation factor occupying the GTPase center have not been identified. By employing ternatin-4, an allosteric elongation factor-1 (eEF1A) inhibitor, we unveil an E3 ligase network that triggers ubiquitination and degradation of eEF1A on stalled ribosomes. A CRISPRi screen revealed two E3 ligases of unknown function, RNF14 and RNF25, which are both essential for ternatin-induced eEF1A degradation. Based on quantitative proteomics analysis, we find that RNF14 and RNF25 promote ubiquitination of eEF1A and a discrete set of ribosomal proteins. By forming a complex with RNF14, the ribosome collision sensor GCN1 plays an essential role in eEF1A degradation. Our findings illuminate a translation elongation checkpoint that monitors the ribosomal GTPase center.

cell biology↗

bioRxiv2021

PIKfyve inhibition blocks endolysosomal escape of α-synuclein fibrils and spread of α-synuclein aggregation

The inter-cellular prion-like propagation of -synuclein aggregation is emerging as an important mechanism driving the progression of neurodegenerative diseases including Parkinsons disease and multiple system atrophy (MSA). To discover therapeutic strategies reducing the spread of -synuclein aggregation, we performed a genome-wide CRISPR interference screen in a human cell-based model. We discovered that inhibiting PIKfyve dramatically reduced -synuclein aggregation induced with both recombinant -synuclein fibrils and fibrils isolated from MSA patient brain. While PIKfyve inhibition did not affect fibril uptake or -synuclein clearance or secretion, it reduced -synuclein trafficking from the early endosome to the lysosome, thereby limiting fibril escape from the lysosome and reducing the amount of fibrils that reach cytosolic -synuclein to induce aggregation. These findings point to the endolysosomal transport of fibrils as a critical step in the propagation of -synuclein aggregation and a potential therapeutic target.

cell biology↗

bioRxiv2019

Compromised function of an ESCRT complex promotes endolysosomal escape of tau seeds and propagation of tau aggregation

Intercellular propagation of protein aggregation is emerging as a key mechanism in the progression of several neurodegenerative diseases, including Alzheimers Disease and frontotemporal dementia. However, we lack a systematic understanding of the cellular path-ways controlling prion-like propagation. To uncover such pathways, we performed CRISPR interference (CRISPRi) screens in a human cell-based model of propagation of tau aggregation. Our screens uncovered that knockdown of several components of the ESCRT machinery, including CHMP6, or CHMP2A in combination with CHMP2B (a gene linked to familial fronto-temporal dementia), promote propagation of tau aggregation. We found that knockdown of these genes caused damage to endolysosomal membranes, consistent with a role for the ESCRT pathway in endolysosomal membrane repair. Leakiness of the endolysosomal compartment significantly enhanced prion-like propagation of tau aggregation, likely by making tau seeds more available to pools of cytoplasmic tau. Together, these findings suggest that endolysosomal escape is a critical step in tau propagation.

cell biology↗

bioRxiv2017

Tau Internalization is Regulated by 6-O Sulfation on Heparan Sulfate Proteoglycans (HSPGs)

The misfolding and accumulation of tau protein into intracellular aggregates known as neurofibrillary tangles is a pathological hallmark of neurodegenerative diseases such as Alzheimers disease. However, while tau propagation is a known marker for disease progression, exactly how tau propagates from one cell to another and what mechanisms govern this spread are still unclear. Here, we report that cellular internalization of tau is regulated by quaternary structure and have developed a cellular assay to screen for genetic modulators of tau uptake. Using CRISPRi technology we have tested 3200 genes for their ability to regulate tau entry and identified enzymes in the heparan sulfate proteoglycan biosynthetic pathway as key regulators. We show that 6-O-sulfation is critical for tauheparan sulfate interactions and that this modification regulates uptake in human central nervous system cell lines, iPS-derived neurons, and mouse organotypic brain slice culture. Together, these results suggest novel strategies to halt tau transmission.

neuroscience↗