STAT1 Is a Master Regulator of Pancreatic β-Cell Apoptosis and Islet Inflammation

Fabrice Moore,Najib Naamane,Maikel L Colli,Thomas Bouckenooghe,Fernanda Ortis,Esteban N Gurzov,Mariana Igoillo-Esteve,Chantal Mathieu,Gianluca Bontempi,Thomas Thykjaer,Torben F Ørntoft,Decio L Eizirik

doi:10.1074/jbc.m110.162131

Fabrice Moore, Najib Naamane + Show 10 more

Open Access

https://doi.org/10.1074/jbc.m110.162131

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Abstract

Cytokines produced by islet-infiltrating immune cells induce β-cell apoptosis in type 1 diabetes. The IFN-γ-regulated transcription factors STAT1/IRF-1 have apparently divergent effects on β-cells. Thus, STAT1 promotes apoptosis and inflammation, whereas IRF-1 down-regulates inflammatory mediators. To understand the molecular basis for these differential outcomes within a single signal transduction pathway, we presently characterized the gene networks regulated by STAT1 and IRF-1 in β-cells. This was done by using siRNA approaches coupled to microarray analysis of insulin-producing cells exposed or not to IL-1β and IFN-γ. Relevant microarray findings were further studied in INS-1E cells and primary rat β-cells. STAT1, but not IRF-1, mediates the cytokine-induced loss of the differentiated β-cell phenotype, as indicated by decreased insulin, Pdx1, MafA, and Glut2. Furthermore, STAT1 regulates cytokine-induced apoptosis via up-regulation of the proapoptotic protein DP5. STAT1 and IRF-1 have opposite effects on cytokine-induced chemokine production, with IRF-1 exerting negative feedback inhibition on STAT1 and downstream chemokine expression. The present study elucidates the transcriptional networks through which the IFN-γ/STAT1/IRF-1 axis controls β-cell function/differentiation, demise, and islet inflammation.

Highlights

The stress signals internally by modulating the expression, activation, and localization of transcription factors, and second, these transcription factors trigger the expression of key downstream genes that mediate diverse cellular responses to the stress [1, 2]
Cytokine-induced STAT1 activation in ␤-cells is associated with the induction of apoptosis and diabetes progression in murine models of type 1 diabetes (T1D) [14, 15, 30], whereas the STAT1 downstream transcription factor IRF-1 may decrease islet inflammation without directly regulating ␤-cell death [16, 31]
The nonspecific siRNA used as control did not affect ␤-cell viability or function [32] and had only minimal effect (Ͻ0.5%) on gene expression, as evaluated by array analysis. Using this well controlled approach, we observed that cytokine-induced STAT1 and IRF-1 expression regulate gene networks associated with cell cycle, signal transduction, apoptosis, endoplasmic reticulum stress, and inflammation in ␤-cells

Summary

The abbreviations used are

T1D, type 1 diabetes; ANOVA, analysis of variance; Ad, adenovirus; si, small interfering; F, forward; R, reverse; RT, realtime (PCR); Std, standard. To characterize the broad network of genes regulated by STAT1 and IRF-1, we first validated siRNAs targeting each of these transcription factors and coupled RNA interference to global evaluation of gene expression. This was done by the use of microarray analysis of insulin-producing INS-1E cells exposed or not to proinflammatory cytokines. Our data highlighted a novel role for IRF-1 in providing a negative feedback on STAT1-driven chemokine production through the induction of the regulatory protein SOCS-1 As a whole, these findings allow us to propose a unifying hypothesis explaining the effects of the transcription factors STAT1 and IRF-1 on ␤-cells

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION