Rapid Proteasomal Degradation of Posttranscriptional Regulators of the TIS11/Tristetraprolin Family Is Induced by an Intrinsically Unstructured Region Independently of Ubiquitination

Abstract

The TIS11/tristetraprolin (TTP) CCCH tandem zinc finger proteins are major effectors in the destabilization of mRNAs bearing AU-rich elements (ARE) in their 3′ untranslated regions. In this report, we demonstrate that the Drosophila melanogaster dTIS11 protein is short-lived due to its rapid ubiquitin-independent degradation by the proteasome. Our data indicate that this mechanism is tightly associated with the intrinsically unstructured, disordered N- and C-terminal domains of the protein. Furthermore, we show that TTP, the mammalian TIS11/TTP protein prototype, shares the same three-dimensional characteristics and is degraded by the same proteolytic pathway as dTIS11, thereby indicating that this mechanism has been conserved across evolution. Finally, we observed a phosphorylation-dependent inhibition of dTIS11 and TTP degradation by the proteasome in vitro, raising the possibility that such modifications directly affect proteasomal recognition for these proteins. As a group, RNA-binding proteins (RNA-BPs) have been described as enriched in intrinsically disordered regions, thus raising the possibility that the mechanism that we uncovered for TIS11/TTP turnover is widespread among other RNA-BPs.

ACKNOWLEDGMENTS

We thank Vincent Raussens for helpful discussions and William Rigby for providing CARP-3 anti-TTP antibody.

Work in our laboratory is supported by the Fund for Medical Scientific Research (Belgium; grant 2.4556.08), the Fonds Brachet, the Fonds Van Buuren, the Actions de Recherches Concertées (grants AV.06/11-345 and AV.12/17), and the FEDER Hainaut Biomed program. L. V. Ngoc is supported by a doctoral grant of the Fonds pour la Recherche en Industrie et Agriculture (Belgium).