Yeast Cth2 protein represses the translation of ARE-containing mRNAs in response to iron deficiency

摘要

In response to iron deficiency, the budding yeast Saccharomyces cerevisiae undergoes a metabolic remodeling in order to optimize iron utilization. The tandem zinc finger (TZF)-containing protein Cth2 plays a critical role in this adaptation by binding and promoting the degradation of multiple mRNAs that contain AU-rich elements (AREs). Here, we demonstrate that Cth2 also functions as a translational repressor of its target mRNAs. By complementary approaches, we demonstrate that Cth2 protein inhibits the translation of SDH4 , which encodes a subunit of succinate dehydrogenase, and CTH2 mRNAs in response to iron depletion. Both the AREs within SDH4 and CTH2 transcripts, and the Cth2 TZF are essential for translational repression. We show that the role played by Cth2 as a negative translational regulator extends to other mRNA targets such as WTM1 , CCP1 and HEM15 . A structure-function analysis of Cth2 protein suggests that the Cth2 amino-terminal domain (NTD) is important for both mRNA turnover and translation inhibition, while its carboxy-terminal domain (CTD) only participates in the regulation of translation, but is dispensable for mRNA degradation. Finally, we demonstrate that the Cth2 CTD is physiologically relevant for adaptation to iron deficiency. Author summary Iron is essential for eukaryotes because it is required for many fundamental processes such as DNA replication, protein translation or respiration, but it is very insoluble and can, therefore, easily go scarce. For this reason, eukaryotic cells have developed adaptive responses to iron deficiency. Under iron limitation conditions, the yeast Saccharomyces cerevisiae induces the expression of Cth2, a protein with tandem zinc fingers that binds to adenine and uracil-rich sequences in the 3’-UTR of specific mRNAs related to iron metabolism, promoting their degradation. Here we show that Cth2 inhibits the translation of ARE-containing mRNAs, including SDH4 , WTM1 , HEM15 and CCP1 , which encode proteins that contain iron or participate in iron-dependent pathways, and CTH2 itself, which is subjected to an autoregulatory loop that controls its expression. We also dissected different domains of Cth2 that are differentially involved in mRNA decay and translational inhibition. The involvement of Cth2 in translational control reinforces the importance of this ARE-binding protein as a post-transcriptional regulator of the iron response in yeast. By acting at different steps in the life of specific mRNA targets, Cth2 action ensures yeast cells a proper distribution of iron by optimizing its utilization in essential processes.