Tumor necrosis factor-α mRNA remains unstable and hypoadenylated upon stimulation of macrophages by lipopolysaccharides

Abstract

TNF-α gene expression is regulated at transcriptional and post-transcriptional levels in mouse macrophages. The post-transcriptional regulation is mediated by the AU-rich element (ARE) located in the TNF-α mRNA 3' untranslated region (UTR), which controls its translation and stability. In resting macrophages, the ARE represses TNF-α mRNA translation. Activation of macrophages with various agents [for example lipopolysaccharide (LPS), viruses] results in translational derepression, leading to the production of high levels of TNF-α. TNF-α ARE has also been shown to confer mRNA instability as its deletion from the mouse genome leads to an increase in the TNF-α mRNA half-life [Kontoyiannis, D., Pasparakis, M., Pizzaro, T., Cominelli, F. and Kollias, G. (1999) Immunity 10, 387-398]. In this study, we measured the half-life as well as the poly(A) tail length of TNF-α mRNA in the course of macrophage activation by LPS. We report that TNF-α mRNA is short lived even in conditions of maximal TNF-α synthesis. Moreover, TNF-α mRNA is hypoadenylated in a constitutive manner. These results reveal that TNF-α mRNA rapid turnover does not constitute a regulatory step of TNF-α biosynthesis in macrophages and that TNF-α mRNA translational activation upon LPS stimulation is not accompanied by a change of poly(A) tail length.