Biology subjects

Kang, S.-U.

Publications and source records attributed to Kang, S.-U..

7 recordsLinked to original sources

bioRxiv2026

Non-Covalent Poly(ADP-ribose) Signaling Organizes a Circadian E3 Ligase Network in the Brain

Although PAR biology has traditionally been studied through covalent PARylation, non-covalent PAR-binding proteins provide an additional mechanism for interpreting transient PAR signals and converting them into downstream regulatory programs. Among these effectors, E3 ubiquitin ligases are uniquely positioned to couple PAR sensing to selective ubiquitination, thereby integrating stress signaling with proteostatic control. Because circadian systems depend heavily on temporally coordinated protein turnover, we hypothesized that PAR-binding E3 ligases may form a circadian-structured regulatory layer within the brain. To test this, we integrated GTEx v10 brain transcriptomics, GWAS Catalog gene-mapped associations, CIRCA circadian phase annotations, and Human Protein Atlas single-cell transcriptomic resources to characterize the organization of PAR-binding E3 ubiquitin ligases across neural tissues. Across the brain, the E3 ligase repertoire was broadly deployed yet regionally structured, with cerebellar and cortical enrichment patterns preserved within the PAR-binding subset. Representative ligases spanning circadian regulation, DNA repair, and neurodegeneration-relevant pathways displayed distinct abundance and regional-variability archetypes across GTEx brain regions. Human genetic analyses demonstrated that E3 ligases associated with cognition-, neurodegeneration-, and sleep/circadian-related phenotypes were disproportionately PAR-binding, supporting convergence between PAR-responsive ubiquitin regulation and disease-relevant biology. Circadian phase analyses further revealed that PAR-binding ligases occupy structured, non-random circadian windows within the broader E3 background, including distinct co-phasing relationships with BMAL1 and CRY1. Finally, cell-type enrichment analyses identified microglia as the dominant compartment for circadian-linked and PAR-binding circadian E3 weighting within the brain E3 program. Together, these findings support a systems-level framework in which non-covalent PAR-binding E3 ubiquitin ligases constitute a brain-deployed, circadian-organized regulatory layer that couples PAR signaling to time-dependent ubiquitin control in neural systems.

bioinformatics↗

bioRxiv2026

Microglial Lag3 Drives α-Synuclein--induced Neurotoxic Activated (A1) Astrocytes and Neurodegeneration

BackgroundNeuroinflammation and pathologic -synuclein (-syn) aggregation cooperate to drive dopaminergic neurodegeneration in Parkinsons disease, but the glial receptors that couple extracellular -syn to inflammatory cascades remain incompletely defined. Microglia express higher levels of lymphocyte activation gene 3 (Lag3) than neurons, yet the contribution of microglial Lag3 to -syn recognition, glial crosstalk, and neurodegeneration is unknown. MethodsBiochemical binding assays, live-cell imaging, cytokine profiling, and neuron-microglia-astrocyte co-culture paradigms were used to define Lag3-dependent -syn preformed fibril (PFF) binding, uptake, and microglial activation. To interrogate in vivo function, microglia-specific Lag3 conditional knockout mice (Lag3L/L-Cx3cr1CreER) and littermate controls received unilateral intrastriatal -syn PFF injections, followed by histological, biochemical, and behavioral assessments of -syn pathology, gliosis, nigrostriatal integrity, and motor performance. Results-syn PFFs bound microglial Lag3 with high specificity and nanomolar affinity and required Lag3 for efficient fibril internalization and induction of proinflammatory cytokines. Microglial Lag3 deficiency markedly blunted -syn PFF-evoked microglial activation, prevented cytokine-driven conversion of astrocytes into neurotoxic reactive A1 astrocytes, and abolished astrocyte-dependent neuronal death in vitro. In vivo, microglia-specific Lag3 deletion reduced cortical, striatal, and substantia nigra pS129 -syn pathology, suppressed microgliosis and A1 astrocyte induction, preserved substantia nigra dopaminergic neurons and striatal dopamine transporter/tyrosine hydroxylase expression, and ameliorated -syn PFF-induced motor deficits. ConclusionsThis study identifies microglial Lag3 as a key receptor linking extracellular -syn PFF recognition to inflammatory amplification, neurotoxic reactive A1 astrocyte conversion, and dopaminergic neurodegeneration. Together with prior work on neuronal Lag3, these findings support a cell-type-specific dual-axis model in which neuronal Lag3 mediates -syn propagation while microglial Lag3 drives glia-dependent neurotoxicity, positioning Lag3 as a promising precision therapeutic target in -synucleinopathies.

neuroscience↗

bioRxiv2025

Neuronal PARIS-STAT3 axis drives tau pathology and glial activation in Alzheimers disease

PARIS, a substrate of Parkin, accumulates in Parkinsons disease and promotes disease progression. Here, we demonstrate that PARIS also contributes to Alzheimers disease by elevating STAT3 transcriptional activity, thereby inducing tau pathology, hippocampal atrophy, and glial activation. Genetic depletion of Paris reduced tau phosphorylation and cognitive decline in tauopathy mice, whereas neuron-specific PARIS overexpression caused tau accumulation, gliosis, and memory impairment. In contrast, astrocyte-specific overexpression did not induce pathology, indicating that PARIS acts in neurons to drive tau phosphorylation and glial activation. The pathological features induced by neuronal PARIS overexpression were rescued by STAT3 inhibition, demonstrating that PARIS-STAT3 signaling underlies these effects. Moreover, Paris knockout did not alter pathology in the amyloid-driven mouse model, highlighting specificity for tau pathology. Together, these findings reveal PARIS as a neuronal regulator of STAT3 signaling that exacerbates tau-mediated neurodegeneration and identify the PARIS-STAT3 pathway as a potential therapeutic target in Alzheimers disease.

neuroscience↗

bioRxiv2023

Mature microRNA-binding protein QKI promotes microRNA-mediated gene silencing

Although Argonaute (AGO) proteins have been the focus of microRNA (miRNA) studies, we observed AGO-free mature miRNAs directly interacting with RNA-binding proteins, implying the sophisticated nature of fine-tuning gene regulation by miRNAs. To investigate microRNA-binding proteins (miRBPs) globally, we analyzed PAR-CLIP data sets to identify RBP quaking (QKI) as a novel miRBP for let-7b. Potential existence of AGO-free miRNAs were further verified in genetically engineered AGO-depleted human and mouse cells. We have shown that QKI serves as an auxiliary factor empowering AGO2/let-7b-mediated gene silencing. Depletion of QKI decreases interaction of AGO2 with let-7b and target mRNA, consequently controlling target mRNA decay. QKI, however, also suppresses the dissociation of let-7b from AGO2, and slows assembly of AGO2/miRNA/target mRNA complexes at the single-molecule level. We also revealed that QKI suppresses cMYC expression at post-transcriptional level, and decreases proliferation and migration of HeLa cells, demonstrating that QKI is a tumor suppressor gene by in part augmenting let-7b activity. Our data show that QKI is a new type of RBP implicated in the versatile regulation of miRNA-mediated gene silencing.

biochemistry↗

bioRxiv2022

A TMT-based quantitative proteomics approach toward α-syn PFF associated Lewy Body Dementia (LBD) using α-syn PFF-injected mouse brain tissues

The aggregation of -synuclein in the nervous system leads to a class of neurodegenerative disorders termed -synucleinopathies. A form of primary degenerative dementia called Lewy body dementia (LBD) often develops in the case these aggregations develop into intracellular inclusions called Lewy bodies (LB) and Lewy neurites (LN). Despite the high frequency of LBD, being the leading cause of dementia following Alzheimers disease (AD), there is relatively little information discovered about its pathological pathway or diagnostic criteria. In this report, we attempt to address such shortcomings via utilizing a proteomic approach to identify the proteomic changes following intrastriatal injection of -synuclein preformed fibril (-syn PFF). Through mass spectrometry, we have identified a total of 179 proteins that were either up- or down-regulated at different time points, with the four proteins - TPP3, RAB10, CAMK2A, and DYNLL1 - displaying the most significant changes throughout the timeframe. Further examining the modulated proteins with network-based enrichment analyses, we have found that 1) the most significantly associated neurodegenerative pathways were Parkinsons (pV = 3.0e-16) and Huntingtons (pV = 1.9e-15) disease, and 2) the majority of molecular functions specific to the pathology only appeared at later time points. While these results do not expose a conclusive biomarker for LBD, they suggest a potential framework that may be utilized to diagnose and differentiate LBD pathology from other forms of dementia by focusing on the cortical proteomic changes which occur in a later time span.

cell biology↗

bioRxiv2022

Proteome-wide microarray-based screening of PAR-binding proteins

Poly(ADP-ribose) (PAR) plays a crucial role in intracellular signaling and scaffolding through covalent modification or non-covalent binding to target proteins. The non- covalent binding PARylome has not been extensively characterized. Here we performed a PAR-binding screen using a human protein microarray that covers most of the human proteome to characterize the non-covalent binding PARylome. A total of 356 PAR- binding proteins were identified. The PAR-binding PARylome suggests that PAR- binding regulates a variety of biological processes beyond well-characterized DNA damage signaling and DNA repair. Proteins that may be reprogrammed by PAR-binding include signaling molecules, transcription factors, nucleic acid binding proteins, calcium binding proteins, ligases, oxidoreductases, enzymes, transferases, hydrolases, and receptors. The global database of PAR-binding proteins that we established will be a valuable tool for further in-depth analysis of the role of PARylation in a wide range of biological contexts.

biochemistry↗

bioRxiv2019

Metastatic function of METTL18 in breast cancer via actin methylation and Src

Recently, a SET domain containing 3 (SETD3) was identified as an actin histidine methyltransferase, functioning to control replication and pathogenesis in multiple mouse models for enterovirus infection as well as the regulation of smooth muscle contractility linked to primary dystocia. Here, in this study, we report another type of actin histidine methyltransferase, METTL18, that regulates the metastatic potential of breast cancer in human. Among methyltransferases, METTL18 was highly amplified in human breast cancer. In particular, poor prognosis was associated with high expression of METTL18 in HER2-negative breast cancer patients. This gene product was also found to be a critical component of metastatic responses. Loss of METTL18 expression significantly reduced metastatic responses of breast tumor cells both in vitro and in vivo. Mechanistically, it was observed that METTL18 increased actin polymerization, upregulated complex formation with HSP90AA1 and Src, enhanced the activity of an intermediate form of Src with tyrosine phosphorylation at both Y416 and Y527, and induced cellular metastatic responses, including morphological change, migration, and invasion of MDA-MB-231 cells in vitro and in mice. Methylated actin at His73 served as a critical site for interaction with HSP90AA1 and Src to activate p85/PI3K and STAT3. Our findings suggest that METTL18 plays critical roles in metastatic responses of HER2-negative breast cancer cells via actin polymerization and the generation of an intermediate form of Src.

cancer biology↗