Biology subjects

Chung, C.-I.

Publications and source records attributed to Chung, C.-I..

5 recordsLinked to original sources

bioRxiv2026

A genetically encoded ionic-stress sensor reveals protons as a sleep driver

Dynamic ionic changes are hallmarks of physiological and behavioral state transitions, including sleep in animals. Although biosensors for specific cellular ions are widely available, real-time monitoring of overall ionic strength in living organisms remains challenging. Here, we present a genetically encoded nuclear translocation ionic sensor (GENTIS) that enables direct visualization of ionic stress in vivo. Using GENTIS in C. elegans, we uncover rhythmic elevations in ionic strength during larval molting transitions that coincide with the lethargus sleep. Cytosolic proton ionic increase through inhibition of v-ATPase is sufficient to induce GENTIS nuclear translocation and evoke behavioral quiescence, characterized by reduced feeding and activation of sleep-active neurons. Apical membrane v-ATPases undergo disassembly during lethargus and under sleep-inducing stress conditions, leading to proton accumulation. Notably, this proton-mediated sleep is suppressed by proton buffering with ammonium. Together, these findings establish GENTIS as a powerful tool for tracking ionic strength dynamics in living organisms and support protons as a physiological driver of sleep.

animal behavior and cognition↗

bioRxiv2025

Design of an ultrabright biosensor for dynamic imaging of kinase activity in cells

Protein kinases regulate almost every major signaling pathway. Visualizing spatiotemporal dynamics of kinase activity is thus essential to understand cell signaling. Here we report a de novo-designed activity reporter of kinase, dubbed NOVARK, which contains a single polypeptide chain with multiple modular motifs that act as specific kinase substrates and reporters. NOVARK undergoes phosphorylation-induced higher order-assembly, which are detectable as ultrabright GFP droplets with a greater dynamic range than existing Forster resonance energy transfer-based kinase reporters. We designed versions of NOVARK that rapidly and reversibly report intracellular activity of protein kinase A, C, and ERK following stimulation/inhibition by upstream GPCR agonists. Our work provides a generalizable platform that enables the design of ultrabright biosensors for illuminating dynamic architecture of kinase signaling.

bioengineering↗

bioRxiv2024

YAP charge patterning mediates signal integration through transcriptional co-condensates

Transcription factor dynamics are used to selectively engage gene regulatory programs. Biomolecular condensates have emerged as an attractive signaling substrate in this process, but the underlying mechanisms are not well-understood. Here, we probed the molecular basis of YAP signal integration through transcriptional condensates. Leveraging light-sheet single-molecule imaging and synthetic condensates, we demonstrate charge-mediated co-condensation of the transcriptional regulators YAP and Mediator into transcriptionally active condensates in stem cells. IDR sequence analysis and YAP protein engineering demonstrate that instead of the net charge, YAP signaling specificity is established through its negative charge patterning that interacts with Mediators positive charge blocks. The mutual enhancement of YAP/Mediator co-condensation is counteracted by negative feedback from transcription, driving an adaptive transcriptional response that is well-suited for decoding dynamic inputs. Our work reveals a molecular framework for YAP condensate formation and sheds new light on the function of YAP condensates for emergent gene regulatory behavior.

cell biology↗

bioRxiv2022

Phase separation of Myc differentially regulates gene transcription

Dysregulation and enhanced expression of MYC transcription factors (TFs) including MYC and MYCN contribute to the majority of human cancers. For example, MYCN is amplified up to several hundred-fold in high-risk neuroblastoma. The resulting overexpression of N-myc aberrantly activates genes that are not activated at low N-myc levels and drives proliferation and cell survival. Whether increasing N-myc levels simply mediate binding to lower-affinity binding sites in the genome or fundamentally changes the activation process remains unclear. One such activation mechanism that could become important above threshold levels of N-myc is the formation of aberrant transcriptional condensates through phase separation. Phase separation has recently been linked to transcriptional regulation, but how strongly it contributes to gene activation remains unclear. Here we characterized the phase behavior of N-myc and showed that it can form dynamic condensates that bear the hallmarks of transcriptional activity. We tested the contribution of phase separation to N-myc-mediated gene expression by using a chemogenetic tool that allowed us to compare non-phase-separated and phase-separated conditions at identical N-myc levels, which both showed a strong impact on gene expression compared to no N-myc expression. However, we found that only a small fraction of <3% of N-myc-regulated genes is further affected by phase separation, but that these events include the activation of key oncogenes and the repression of tumor suppressors. Indeed, phase separation increases cell survival by [~]15% corroborating the biological effects of the transcriptional changes. However, our results also show that >97% of N-myc-regulated genes are not affected by N-myc phase separation, highlighting that transcription can be activated effectively by diffuse complexes of TFs with the transcriptional machinery.

cell biology↗

bioRxiv2019

Enhancing Intracellular Concentration and Target Engagement of PROTACs with Reversible Covalent Chemistry

Current efforts in the proteolysis targeting chimera (PROTAC) field mostly focus on choosing an appropriate E3 ligase for the target protein, improving the binding affinities towards the target protein and the E3 ligase, and optimizing the PROTAC linker. However, due to the large molecular weights of PROTACs, their cellular uptake remains an issue. Through comparing how different warhead chemistry, reversible noncovalent (RNC), reversible covalent (RC), and irreversible covalent (IRC) binders, affects the degradation of Brutons Tyrosine Kinase (BTK), we serendipitously discover that cyano-acrylamide-based reversible covalent chemistry can significantly enhance the intracellular accumulation and target engagement of PROTACs and develop RC-1 as a reversible covalent BTK PROTAC with a high target occupancy as its corresponding kinase inhibitor and effectiveness as a dual functional inhibitor and degrader, a different mechanism-of-action for PROTACs. Importantly, this reversible covalent strategy is generalizable to improve other PROTACs, opening a path to enhance PROTAC efficacy.

pharmacology and toxicology↗