Genome-Wide Polysome Profiling Reveals an Inflammation-Responsive Posttranscriptional Operon in Gamma Interferon-Activated Monocytes

Abstract

ABSTRACT We previously showed that ribosomal protein L13a is required for translational silencing of gamma interferon (IFN-γ)-induced ceruloplasmin (Cp) synthesis in monocytes. This silencing also requires the presence of the GAIT (IFN- g amma a ctivated i nhibitor of t ranslation) element in the 3′ untranslated region (UTR) of Cp mRNA. Considering that Cp is an inflammatory protein, we hypothesized that this mechanism may have evolved to silence a family of proinflammatory proteins, of which Cp is just one member. To identify the other mRNAs that are targets for this silencing, we performed a genome-wide analysis of the polysome-profiled mRNAs by using an Affymetrix GeneChip and an inflammation-responsive gene array. A cluster of mRNAs encoding different chemokines and their receptors was identified as common hits in the two approaches and validated by real-time PCR. In silico predicted GAIT hairpins in the 3′ UTRs of the target mRNAs were confirmed as functional cis -acting elements for translational silencing by luciferase reporter assays. Consistent with Cp, the newly identified target mRNAs also required L13a for silencing. Our studies have identified a new inflammation-responsive posttranscriptional operon that can be regulated directly at the level of translation in IFN-γ-activated monocytes. This regulation of a cohort of mRNAs encoding inflammatory proteins may be important to resolve inflammation.