Live Cell Imaging Demonstrates Multiple Routes Toward a STAT1 Gain-of-Function Phenotype.

Simone Giovannozzi,Veerle Lemmens,Rik Schrijvers,Jelle Hendrix,Rik Gijsbers

doi:10.3389/fimmu.2020.01114

Abstract

Signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF) mutations result in a primary immunodeficiency (PID) characterized typically by chronic mucocutaneous candidiasis (CMC), but a wider phenotypic range is reported and remains unexplained from a pathophysiological point-of-view. We hypothesized that different STAT1 GOF mutations may result in distinct molecular mechanisms, possibly explaining the variable phenotypes observed in patients. We selected STAT1 GOF mutants (R274W, R321S, T419R, and N574I) that are spread over the protein and studied their dynamic behavior in vitro in U3A and HeLa cell lines. All GOF mutants showed increased STAT1 phosphorylation compared to STAT1 WT. Real-time imaging demonstrated three underlying mechanisms for STAT1 GOF: (i) R274W showed a faster nuclear accumulation, (ii) both R321S and N574I showed a reduced nuclear mobility and slower dephosphorylation, whereas (iii) T419R was near-immobile in the nucleus, potentially due to enhanced binding to chromatin.

Highlights

Autosomal dominant (AD) signal transducer and activator of transcription 1 (STAT1) gainof-function (GOF) mutations result in a primary immunodeficiency (PID) characterized by chronic mucocutaneous candidiasis (CMC), recidivating respiratory infections, autoimmunity, and vascular anomalies
We selected Signal transducer and activator of transcription 1 (STAT1) GOF mutants (R274W, R321S, T419R, and N574I) that are spread over the protein and associate with diverse GOF phenotypes in patients
To STAT1 WT, we generated cell lines for a selection of STAT1 GOF mutants that are spread over the protein and associate with diverse GOF phenotypes in patients

Summary

Introduction

Autosomal dominant (AD) signal transducer and activator of transcription 1 (STAT1) gainof-function (GOF) mutations result in a primary immunodeficiency (PID) characterized by chronic mucocutaneous candidiasis (CMC), recidivating respiratory infections, autoimmunity, and vascular anomalies. Additional phenotypes including John Cunningham (JC)-virus induced progressive multifocal leukoencephalopathy [11], Orf infection [6], Immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX)-like syndromes with CMC [4, 15], and a combined immunodeficiency (CID) without CMC [16] have been associated with STAT1 GOF mutations, but remain unexplained from a pathophysiological point-of-view and require further investigation. We hypothesized that different STAT1 GOF mutations may result in distinct molecular mechanisms, possibly explaining the variable phenotypes observed in patients.

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Conclusion