Temporal regulation of interferon signalling in human EndoC-beta H1 cells

During the development of type 1 diabetes, interferons (IFN) are elaborated from islet-infiltrating immune cells and/or from virally infected beta-cells. They act via specific receptors to increase, acutely, the phosphorylation of the transcription factors STAT1 and 2. However, the longer-term impacts of chronic IFN stimulation are poorly understood and were investigated in the current study. Human EndoC-beta H1 cells were treated with IFN alpha, IFN gamma or IFN lambda either acutely (<2 h) or chronically (>= 24 h) and STAT phosphorylation, expression and activity were assessed by Western blotting and transcriptional reporter assays. Exposure of beta-cells to IFN alpha or IFN lambda induced a swift increase in the phosphorylation of both STAT1 and STAT2, whereas IFN gamma increased only pSTAT1. Over more extended periods (>= 24 h), STAT phosphorylation declined but STAT1 and STAT2 expression were enhanced in a sustained manner. All IFNs stimulated ISRE transcriptional activity (but with different time courses), whereas GAS activity was responsive only to IFN gamma. The re-addition of a second bolus of IFN alpha, 24 h after an initial dose, failed to cause renewed STAT1/2 phosphorylation. By contrast, when IFN gamma was added 24 h after exposure to IFN alpha, rapid STAT1 phosphorylation was re-initiated. Exposure of beta-cells to IFNs leads to rapid, transient, STAT phosphorylation and to slower and more sustained increases in total STAT1/2 levels. The initial phosphorylation response is accompanied by marked desensitisation to the cognate agonist. Together, the results reveal that the response of beta-cells to IFNs is regulated both temporally and quantitatively to achieve effective signal integration.