Ubiquitin-dependent mechanism regulates rapid turnover of AU-rich cytokine mRNAs

Abstract

An AU rich element (ARE) in the 3 noncoding region promotes the rapid degradation of mammalian cytokine and proto-oncogene mRNAs, such as tumor necrosis factor-␣, granulocyte-macrophage colony-stimulating factor (GM-CSF) and c-fos. Destabilization of ARE-mRNAs involves the association of ARE-binding proteins tristetraprolin or AUF1 and proteasome activity, of which the latter has not been characterized. Here, we show that the stability of a model short-lived mRNA containing the GM-CSF ARE was regulated by the level of ubiquitin-conjugating activity in the cell, which links ARE-mRNA decay to proteasome activity. Increased expression of a cytokine-inducible deubiquitinating protein (DUB) that impairs addition of ubiquitin to proteins fully blocked ARE-mRNA decay, whereas increased expression of a DUB that promotes ubiquitin addition to proteins strongly accelerated ARE-mRNA decay. AREmRNA turnover was found to be activated by the ubiquitinaddition reaction and blocked by the ubiquitin-removal reaction. Saturation of the ARE-mRNA decay machinery by high levels of ARE-mRNA, which is well established but not understood, was found to be relieved by increased expression of a DUB that promotes ubiquitin addition to proteins. Finally, inhibition of proteasome activity also blocked accelerated ARE-mRNA decay that is mediated by increased ubiquitin recycling. These results demonstrate that both ubiquitinating activity and proteasome activity are essential for rapid turnover of a model cytokine ARE-mRNA containing the GM-CSF ARE.

Lipopolysaccharide (LPS)-stimulated iNOS Induction Is Increased by Glucosamine under Normal Glucose Conditions but Is Inhibited by Glucosamine under High Glucose Conditions in Macrophage Cells

“…The expression of iNOS must be tightly regulated by both transcriptional and post-transcriptional mechanisms. Post-transcriptional regulation of gene expression is often dependent on sequences located in the 3Ј-untranslated region (3Ј-UTR) of mRNAs (47,48). The zinc-finger protein TTP, KH-type splicing regulatory protein, and HuR all bind the iNOS mRNA 3Ј-UTR and recruits the exosome to the mRNA (49).…”

Post‐transcriptional regulation of gene expression by degradation of messenger RNAs

“…In stress, Hsp70 might chaperone the AUF1 protein to a number of AREs, thus accelerating their degradation. At the end of the stimuli, AUF1 would leave the degradation complex or would be eliminated by ubiquitination (Laroia et al, 2002), which induces the stabilized RNA to reset the steady-state concentration of the proteins in the cells.…”

The role of the ubiquitin/proteasome system in cellular responses to radiation

“…The reason is that many cytokine, growth factor, and protooncogene mRNAs have AU-rich elements (ARE) in their 3 0 noncoding region. Association of this region with factors such as tristetraprolin or AUF1 promotes their rapid degradation through Ub/proteasome pathways (Laroia et al, 2002). Radiation-induced impairment of proteasome activity could also be involved in hypersensitivity, adaptive responses, and bystander effects that have been observed following low-dose irradiation, and about which there is currently little mechanistic information (Joiner et al, 1999(Joiner et al, , 2001Mothersill and Seymour, 2001).…”