Heling, L. W. H. J. | bioRxiv Science

bioRxiv2025

Modulation of Nur77-DNA Interactions by the Glucocorticoid Receptor

Nuclear receptors (NRs) comprise a superfamily of (ligand-)regulated transcription factors that are pivotal in orchestrating gene networks essential for development, metabolism, and cellular homeostasis. Their activity is critical for normal physiology, and consequently, dysregulation of NR signaling is implicated in a wide array of human diseases. Within this superfamily, the orphan nuclear receptor Nur77 and the glucocorticoid receptor (GR) are key regulators that exhibit significant crosstalk, primarily antagonistic, which is crucial for modulating inflammatory and stress responses. Despite the recognized importance of their interplay, the precise molecular mechanisms by which GR modulates Nur77s engagement with DNA remain incompletely defined. This study elucidates the direct impact of GR and its ligand, dexamethasone (Dex), on the DNA binding dynamics of Nur77. Single-molecule DNA tightrope assays revealed that Nur77 employs a three-dimensional diffusion-based search mechanism on non-specific DNA, characterized by transient interactions with two distinct dissociation kinetic profiles. GR significantly stabilizes Nur77-DNA interactions, evidenced by a shift towards longer residence times, primarily achieved by slowing the dissociation of the more transiently interacting Nur77 population. Conversely, single-molecule analysis and biochemical assays demonstrated that Dex alone markedly reduces Nur77s overall DNA binding affinity kinetics and frequency in a sequence-dependent manner, to such an extent that accurate quantification was unfeasible. These findings delineate distinct modulatory effects of the GR protein and its ligand on Nur77-DNA interactions, providing crucial biophysical insights into their complex regulatory interplay and revealing a direct, GR-independent impact of dexamethasone on Nur77s DNA engagement. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/685035v1_ufig1.gif" ALT="Figure 1"> View larger version (14K): org.highwire.dtl.DTLVardef@1207cdorg.highwire.dtl.DTLVardef@1be29eborg.highwire.dtl.DTLVardef@1b23eaaorg.highwire.dtl.DTLVardef@13030b2_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2024

Polyglutamine expansion induced dynamic misfolding of Androgen Receptor

Spinal bulbar muscular atrophy (SBMA) is caused by a polyglutamine expansion (pQe) in the N-terminal transactivation domain of human androgen receptor (AR-NTD), resulting in a combination of toxic gain- and loss-of-function mechanisms. The structural basis of these processes has not been resolved due to the disordered nature of the NTD, which hinders experimental analyses of its detailed conformations. Here, using extensive computational modelling, we show that AR-NTD forms dynamic compact regions, which upon pQe re-organize dynamically, mediated partly by direct pQ interaction with the Androgen N-Terminal Signature (ANTS) motif. The altered dynamics of the NTD result in a perturbation of interdomain interactions, with potential implications for binding of the receptor protein to its response element. Oligomeric aggregation of the dynamic misfolded NTD exposes pQe, but blocks tau-5 and the FQNLF motif, which could lead to aberrant receptor transcriptional activity. These observations suggest a structural mechanism for AR dysfunction in SBMA.

pathology↗