616:
STAT1 and Glucocorticoid Receptor Interaction: Mechanism for Steroid Insensitivity in Type 1 High Severe Asthma
Sunday, March 4, 2018: 4:30 PM
South Hall A2 (Convention Center)
Marc Gauthier, MD, Krishnendu Chakraborty, PhD, Timothy B. Oriss, PhD, Prabir Ray, PhD, Sally E. Wenzel, MD FAAAAI, Anuradha Ray, PhD
RATIONALE: We recently described a phenotype of severe asthma with elevated airway levels of the IFN-γ target gene CXCL10. This pathway is refractory to corticosteroid (CS) therapy, but the mechanism of resistance is not well understood. We investigated interactions between STAT1, a downstream IFN-γ messenger, and the glucocorticoid receptor (GR) on target CXCL10 promoter sequences.

METHODS: THP-1 cells were cultured with dexamethasone overnight prior to IFN-γ exposure. RNA was isolated for quantitative RT-PCR (qPCR) and chromatin-immunoprecipitation (CHIP) assay was performed for binding of STAT1 and GR to CXCL10 gene regulatory sequences. Similarly treated human PBMCs underwent imaging cytometry (AMNIS Imagestream) for GR nuclear translocation.

RESULTS: In THP-1 cells, dexamethasone induction of the GR transactivation target Dual Specificity Phosphatase-1 (DUSP1) was not impaired by IFN-γ. ChIP analysis revealed association of both STAT1 and GR with the key CXCL10 promoter regulatory sequence ISRE in the presence of IFN-γ alone; this association was further increased with dexamethasone pretreatment. Imaging cytometry showed marked nuclear GR translocation with dexamethasone. However, IFN-γ alone also induced nuclear GR translocation.

CONCLUSIONS: We have shown that IFN-γ causes un-liganded GR nuclear translocation without inducing GR-mediated transactivation but promotes binding to a key regulatory sequence, ISRE, in the CXCL10 promoter. Combined exposure of cells to IFN-γ and dexamethasone induces increased association of STAT1 and GR with the ISRE. This suggests that GR may stabilize IFN-γ-activated STAT1 on target CXCL10 promoter sequences. Ultimately, IFN-γ and CS cooperation could foster a feed forward loop, as CXCL10 recruits IFN-γ producing Th1 cells to sites of inflammation.