8644 Dynamic Insights into Glucocorticoid Receptor Dysfunction: Novel patient-derived T437I Mutation and Its Impact on Glucocorticoid Receptor Function

Abstract Disclosure: T. Tettey: None. S. Kim: None. K. Wagh: None. Q. Lao: None. L.R. Schiltz: None. D.A. Stavreva: None. D.M. Presman: None. D.P. Merke: None. G.L. Hager: None. The glucocorticoid receptor (GR) is a hormone regulated transcription factor which binds chromatin to regulate many genes, including stress-response and inflammatory genes. Dexamethasone, a GR agonist, is widely used in the treatment of severe inflammation, including COVID-19. GR is vital for life and several GR mutations have been linked to severe pathophysiological conditions. Here we report a novel mutation in the DNA binding domain (DBD) of GR (T437I) in a patient with partial glucocorticoid resistance, a rare genetic disorder characterized by generalized insensitivity to glucocorticoids and a consequent hyperactivation of the hypothalamic pituitary adrenal axis. While the clinical manifestations of this hT437I GR mutation are apparent, its molecular mechanisms remain unexplored. Employing a comprehensive approach that integrates biophysical methods, molecular biology, and genomics, we investigate the molecular underpinnings of this genetic anomaly. Using CRISPR/Cas9 gene editing, we introduce GFP or Halo-tagged hT437I GR mutant into GR null mouse cells. Our findings indicate that the T437I GR variant exhibits normal hormone binding and nuclear translocation. Live-cell imaging using number and brightness analysis reveals that the mutant receptor maintains a wildtype-like oligomeric state but adopts a heterodimeric conformation in the presence of endogenous GR. Global transcriptomics analyses of the mouse hT437I mutant show that most dexamethasone-regulated genes are unresponsive following hormone treatment. We hypothesize that this mutation within the DBD compromises the binding of GR to regulatory sites of target genes. Leveraging fluorescence high-resolution microscopy, we employ single molecule tracking to study the dynamic behavior of Halo-tagged hT437I GR in mouse cells. Our results indicate that the GR mutant has a higher dwell-time on chromatin compared to the wild-type receptor. This suggests that the hT437I mutation impairs the receptor's binding to genomic sites, potentially leading to a failure in regulating GR target genes. This ongoing exploration of the molecular intricacies aims to deepen our understanding of the clinical phenotype observed in the patient. Presentation: 6/2/2024