Disentangling molecular mechanisms regulating sensitization of interferon alpha signal transduction

Abstract

Tightly interlinked feedback regulators control the dynamics of intracellular responses elicited by the activation of signal transduction pathways. Interferon alpha (IFNa) orchestrates antiviral responses in hepatocytes, yet mechanisms that define pathway sensitization in response to prestimulation with different IFNa doses remained unresolved. We establish, based on quantitative measurements obtained for the hepatoma cell line Huh7.5, an ordinary differential equation model for IFNa signal transduction that comprises the feedback regulators STAT1, STAT2, IRF9, USP18, SOCS1, SOCS3, and IRF2. The model-based analysis shows that, mediated by the signaling proteins STAT2 and IRF9, prestimulation with a low IFNa dose hypersensitizes the pathway. In contrast, prestimulation with a high dose of IFNa leads to a dose-dependent desensitization, mediated by the negative regulators USP18 and SOCS1 that act at the receptor. The analysis of basal protein abundance in primary human hepatocytes reveals high heterogeneity in patient-specific amounts of STAT1, STAT2, IRF9, and USP18. The mathematical modeling approach shows that the basal amount of USP18 determines patient-specific pathway desensitization, while the abundance of STAT2 predicts the patient-specific IFNa signal response.

Human Ubiquitin-Specific Peptidase 18 Is Regulated by microRNAs via the 3'Untranslated Region, A Sequence Duplicated in Long Intergenic Non-coding RNA Genes Residing in chr22q11.21

“…To exert its function as a negative regulator, USP18 binds to the IFN receptor/JAK complex and attenuates the magnitude of the response ( Francois-Newton et al, 2011 ; Wilmes et al, 2015 ; Arimoto et al, 2017 ). The abundance of other IFN-stimulated components (i.e., STAT2/1, IRF9, and SOCS1) will also impact cell context-specific ISG activation, but in distinct and less specific manners ( Kok et al, 2020 ). Given the critical non-redundant role of USP18, we conceived this study to assess whether USP18 can be post-transcriptionally regulated by miRNAs directed to the 3’UTR.…”

AFM-Based Correlative Microscopy Illuminates Human Pathogens

“…Certain pathogen processes, such as adhesion to host cells, lead to biochemical and physical changes at the molecular surface of both the host and pathogen, which are eventually transmitted intracellularly through signal-transduction to determine cell physiology (Kok et al, 2020). Since AFM is restricted to surface measurements, its physical integration with other microscopes allows insight into intracellular events that accompany or are impacted by surface alterations.…”

Determinants of Ligand Specificity and Functional Plasticity in Type I Interferon Signaling

“…Our results thus far suggest that functional plasticity in Type I IFN signaling does not arise from absolute discrimination of the initial pSTAT response within the first 60 minutes. However, differential refractoriness in the pSTAT response mediated by the protein USP18 offers another potential mechanism to achieve absolute discrimination (52,81). It has been established that the upregulation of USP18 in response to Type I IFN stimulation over the course of 24-48 hours leads to somewhere between a 15and 60-fold increase in the in-membrane dissociation rate of IFNAR1 from the ternary complex, with the magnitude of this effect varying between cell types (10,81).…”

“…However, differential refractoriness in the pSTAT response mediated by the protein USP18 offers another potential mechanism to achieve absolute discrimination (52,81). It has been established that the upregulation of USP18 in response to Type I IFN stimulation over the course of 24-48 hours leads to somewhere between a 15and 60-fold increase in the in-membrane dissociation rate of IFNAR1 from the ternary complex, with the magnitude of this effect varying between cell types (10,81). Inhibition by USP18 leads to significantly reduced response to further IFN stimulation, which is relevant for clinical uses of Type I IFN (10,42,81).…”

“…It has been established that the upregulation of USP18 in response to Type I IFN stimulation over the course of 24-48 hours leads to somewhere between a 15and 60-fold increase in the in-membrane dissociation rate of IFNAR1 from the ternary complex, with the magnitude of this effect varying between cell types (10,81). Inhibition by USP18 leads to significantly reduced response to further IFN stimulation, which is relevant for clinical uses of Type I IFN (10,42,81). Importantly, IFNa2 typically exhibits much greater refractoriness than IFNb at equivalent doses, although the degree of deactivation can be partially compensated by increasing the stimulation dose (42,46).…”