Splitting STAT Dimers to Understand Interferon Balance: A Strategy to Dissociate Beneficial and Detrimental Interferon Effects in Infection?

Interferons (IFNs) are naturally occurring signalling proteins that were discovered almost 60 years ago due to their potent anti-viral properties. It is now generally appreciated that interferons constitute the vital first line of defence against harmful microbes, and moreover function as key immune modulators that control the survival of normal and tumour cells. Accordingly, IFNs are used for treating various serious conditions including cancers, multiple sclerosis and viral hepatitis, and current clinical trials assess if IFNs also protect from serious illness in SARS infections. The mechanism of action of IFNs is intricate, involves several transcription complexes that function in two distinct signalling pathways, and is still not well understood. There are particular hurdles in the study of dynamic processes such as IFN signalling that involve transient protein interactions and the rapid translocation of large protein complexes from the cell membrane to the nucleus. Advances in protein production and new assays developed in our lab that visualize crucial signalling events have opened the door to new ways to study these multifaceted processes, and we now have the necessary tools we need to examine the molecular underpinnings of IFN signalling in detail. By molecularly dissecting STAT transcription factor complexes we can for the first time lay bare key determinants for balancing the type I and type II IFN pathways. Our preliminary results raise the prospect that the splitting of STAT dimers constitutes a novel strategy for rebalancing IFN responses in a controlled manner. This, in turn, is of particular interest regarding a number of important microbial infections, where antagonistic type I and type II IFN responses damage host protection. The proposed research will lead to a step change in the fundamental knowledge of a central aspect of our immune system, and thus also considerably advance the unmet quest for interferon-modulating precision medicines.

Interferons (IFNs) provide resistance to infections, cancer immunosurveillance, and the suppression of autoimmunity in animals and humans; they have served as a paradigm for cytokine signalling for about three decades. Our proposal focuses on an understudied yet intriguing step in interferon signalling, namely the assembly of preformed STAT1 and STAT2 homo- and heterodimers. We have discovered that preformed STAT dimers are crucial determinants for the outcome of interferon signalling, in particular the balancing between type I and type II IFN pathways. Given their distinct target gene repertoires and often antagonistic effects on viral and bacterial pathogens, the proposed work will achieve a step change in molecular understanding of IFN signalling and the consequences of perturbations. We have developed new STAT protein expression, imaging and assay strategies for the human IFN pathways. To assess the biological role of preformed STAT dimers we will use genome editing to generate immune cell lines devoid of preformed STAT1 dimers, and apply a range of techniques including fluorescence cell imaging, systemic genome-wide RNA-sequencing, analytical ultracentrifugation and infection experiments, and corroborate the findings with patient-derived cell lines expressing dimerization-deficient STAT1 gain-of-function mutations. This work is at the cutting edge of molecular studies of complex cellular processes, and will fill substantial gaps in the molecular and functional understanding at the heart of cytokine biology. Given the ubiquity of STATs and interferons in immunity and protection against infections, the work will have a major impact on a very broad field. The project supports the BBSRC's long-term aims to deliver discovery-led frontier bioscience research that will underpin strategies for innovation in tackling infections and improving health.