Presenter of 1 Presentation
PATHOGENESIS OF STAT1 GAIN-OF-FUNCTION PRIMARY IMMUNODEFICIENCY
Abstract
Background and Aims
Germline, monoallelic, gain-of-function (GOF) mutations in STAT1 cause an ultra-rare form of primary immunodeficiency (PID) through overactivation of the Janus-associated kinase STAT1 signalling pathway. Heightened basal levels of STAT1 protein have previously been shown to be a key driver of disease1 2 but the exact mechanism of STAT1 GOF still remains unclear.
Methods
A nanoBRET system was developed to investigate the conformations adopted by STAT1 dimers pre- and post-IFNγ stimulation in STAT1 (-/-) cell lines lentivirally transduced with wild-type or GOF STAT1. Nuclear localisation and transcriptomics were assessed in the same cell lines pre- and post-IFN stimulation, and in response to Ruxolitinib.
Results
We show that the majority of GOF mutations destabilise the inactive dimeric conformations of STAT1 and promote the adoption of an active-like conformation at baseline. In contrast, some mutations stabilise the active conformation and induce stronger DNA binding, suggesting that discreet GOF mutations function through different mechanisms. We show that the nuclear localisation sequence is exposed in the active orientation, and that consequently, GOF mutants had greater nuclear presence at baseline. Transcriptomic analysis detailed that STAT1-mediated gene expression was induced under inactive status for GOF mutants and that each mode of pathogenesis has unique gene expression signatures. We compared the clinical phenotypes described for different for STAT1 GOF mutations and identified that patients with mutations that stabilise the active conformation are more likely to experience autoimmune complications.
Conclusions
This work has identified alternative modes of pathogenesis for STAT1 GOF which may explain clinical heterogeneity.