Biology subjects

Hsu, T. Y.-T.

Publications and source records attributed to Hsu, T. Y.-T..

3 recordsLinked to original sources

bioRxiv2026

A dynamic molecular glue targets a plastic MDA5 filament interface to stimulate innate immunity

Innate immune signaling is a double-edged sword: uncontrolled activation drives autoinflammatory diseases, while controlled activation enhances antiviral and antitumor immunity. MDA5, a cytosolic dsRNA sensor that activates type I interferon signaling, mediates both immunopathology and protective immunity, yet small-molecule modulators have remained elusive. Here we report MA2, a first-in-class selective MDA5 agonist that acts as a molecular glue. MA2 binds a cryptic inter-protomer pocket within MDA5 filaments that undergoes ATPase-associated conformational remodeling. Rather than rigidly locking the interface, MA2 remains bound while accommodating and reshaping these structural transitions, strengthening MDA5-dsRNA and inter-protomer interactions and attenuating ATP hydrolysis. MA2 does not induce new filament assembly but potentiates pre-existing filaments, enabling context-dependent activation in dsRNA-enriched cells. MA2 enhances antiviral activity and synergizes with chemotherapeutic agents and natural killer cells to promote tumor cell killing. These findings establish dynamic molecular glues as a strategy for targeting conformationally plastic interfaces previously considered undruggable.

immunology↗

bioRxiv2026

Identification of highly immunogenic endogenous dsRNAs from cellular MDA5 filaments

ADAR1 converts adenosine to inosine in endogenous double-stranded RNAs (dsRNAs) to prevent excessive MDA5-driven interferon-stimulated gene expression. The source of endogenous immunogenic dsRNAs remains enigmatic because only a small fraction of ADAR1 substrates activate MDA5, and cellular MDA5 filaments have not been isolated. Here, we couple affinity purification of cellular MDA5 filaments with RNA sequencing to define immunogenic endogenous dsRNAs. Greater than 84% of dsRNAs suppressed by combined DDX3X RNA helicase and ADAR1 base-editing activities were present in MDA5 filaments, compared to less than 1% of dsRNA substrates acted on by ADAR1 alone. Dual substrate dsRNAs consisted of inverted repeats embedded in 3-UTRs with high base-pair complementarity and longer intervening sequences between repeats, with a minor contribution coming from intermolecular dsRNAs formed by sense and antisense transcripts. Moreover, the majority of dual substrate immunogenic dsRNAs were hyperedited in DDX3X mutant cancers. This reveals the identity of endogenous immunogenic dsRNAs and quality control mechanisms underlying their suppression.

cell biology↗

bioRxiv2026

MDA5 multimerization on LINE RNA drives pathogenic extracellular immune complexes in autoimmunity

Autoantibodies are hallmarks of many autoimmune diseases, but their potential pathogenic roles, particularly for those targeting intracellular proteins, remain unclear. Anti-MDA5-positive dermatomyositis (anti-MDA5 DM) is characterized by autoantibodies against the intracellular protein MDA51,2, a conserved innate immune receptor that recognizes viral dsRNA by forming filaments3. Here, using four patient-derived monoclonal autoantibodies (mAbs), we reconstitute and define the molecular architecture, biogenesis, and immunological activity of pathogenic MDA5 immune complexes. Our cryo-EM analysis revealed that these mAbs bind dsRNA-scaffolded MDA5 filaments in at least two distinct binding modes, each exhibiting striking epitope convergence using germline-encoded residues. Extracellular immune complexes formed between mAbs and filamentous, but not monomeric, MDA5 potently activate multiple innate immune pathways, with the magnitude of activation determined by antibody binding mode and immune complex stoichiometry. Antibody bivalency further crosslinks MDA5 filaments into higher-order aggregates with heightened immunostimulatory activity, demonstrating an active role of autoantibodies in shaping immune complex architecture. Analysis of patient plasma reveals elevated levels of extracellular MDA5 filaments and identifies LINE retroelement-derived dsRNA as a structural scaffold. Notably, MDA5 immune complexes induce endogenous LINE dsRNA expression, likely promoting additional MDA5 filament formation and extracellular release through inflammatory cell death. These data thus support a self-amplifying inflammatory cycle as a pathogenic mechanism for anti-MDA5 DM. Collectively, our study defines a broadly applicable architectural principle, in which higher-order organization and binding modes of autoantibodies--beyond antibody affinity or nucleic acid presence alone--govern innate immune activation.

biochemistry↗