Autosomal dominant (AD) signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations result in a primary immunodeficiency (PID) characterized by chronic mucocutaneous candidiasis (CMC), recidivating respiratory infections, autoimmunity, and vascular anomalies. While CMC is the most common symptom, additional phenotypes such as JC virus induced progressive multifocal leukoencephalopathy, IPEX-like syndromes with CMC, and a combined immunodeficiency (CID) without CMC have been associated with STAT1 GOF mutations, but remain unexplained from a pathophysiological point-of-view. We hypothesize that differences in phenotypes could be linked to varying molecular mechanisms associated with different STAT1 GOF mutation. Therefore, we studied the molecular dynamics of four STAT1 GOF mutations (R274W, R321S, N574I and T419R) situated in three distinct domains of the protein.
We evaluated phosphorylation level, efficiency in activating the transcription of interferon stimulated genes (ISGs) and nuclear accumulation rate of the different GOF mutants in different cell lines. Next, we used Raster Imaging Correlation Spectroscopy (RICS) to study the cellular dynamic behavior of the different mutants.
We observed distinct routes towards a STAT1 GOF phenotype: an increased nuclear accumulation rate (R274W), increased affinity for DNA (T419R), and a reduced nuclear diffusion speed (R321S and N574I) upon stimulation with IFN gamma.
Our results suggest that STAT1 GOF is the resultant of various molecular mechanisms. We speculate that this might contribute to the spectrum of clinical phenotypes and/or responsiveness for targeted therapy.