Post-transcriptional regulation of RNase-L expression is mediated by the 3′-untranslated region of its mRNA

Abstract

RNase-L mediates critical cellular functions including antiviral, pro-apoptotic, and tumor suppressive activities; accordingly, its expression must be tightly regulated. Little is known about the control of RNASEL expression; therefore, we examined the potential regulatory role of a conserved 3′-untranslated region (3′-UTR) in its mRNA. The 3′-UTR mediated a potent decrease in the stability of RNase-L mRNA, and of a chimeric β-globin-3′-UTR reporter mRNA. AU-rich elements (AREs) are cis-acting regulatory regions that modulate mRNA stability. Eight AREs were identified in the RNase-L 3′-UTR, and deletion analysis identified positive and negative regulatory regions associated with distinct AREs. In particular, AREs 7 and 8 served a strong positive regulatory function.HuRis an ARE-binding protein that stabilizes ARE-containing mRNAs, and a predicted HuRbinding site was identified in the region comprising AREs 7 and 8. Co-transfection of HuR and RNase-L enhanced RNase-L expression and mRNA stability in a manner that was dependent on this 3′-UTR region. Immunoprecipitation demonstrated that RNase-L mRNA associates with a HuR containing complex in intact cells. Activation of endogenous HuR by cell stress, or during myoblast differentiation, increased RNase-L expression, suggesting that RNase-L mRNA is a physiologic target for HuR. HuR-dependent regulation of RNase-L enhanced its antiviral activity demonstrating the functional significance of this regulation. These findings identify a novel mechanism of RNase-L regulation mediated by its 3′-UTR. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.