The zinc-finger protein tristetraprolin (TTP) binds to AU-rich elements present in the 3' untranslated regions of transcripts that mainly encode proteins of the inflammatory response. TTP-bound mRNAs are targeted for destruction via recruitment of the eight-subunit deadenylase complex "carbon catabolite repressor protein 4 (CCR4)-negative on TATA-less (NOT)，" which catalyzes the removal of mRNA poly-(A) tails， the first obligatory step in mRNA decay. Here we show that a novel interaction between TTP and the CCR4-NOT subunit， CNOT9， is required for recruitment of the deadenylase complex. In addition to CNOT1， CNOT9 is now included in the identified CCR4-NOT subunits shown to interact with TTP. We find ... More
The zinc-finger protein tristetraprolin (TTP) binds to AU-rich elements present in the 3' untranslated regions of transcripts that mainly encode proteins of the inflammatory response. TTP-bound mRNAs are targeted for destruction via recruitment of the eight-subunit deadenylase complex "carbon catabolite repressor protein 4 (CCR4)-negative on TATA-less (NOT)，" which catalyzes the removal of mRNA poly-(A) tails， the first obligatory step in mRNA decay. Here we show that a novel interaction between TTP and the CCR4-NOT subunit， CNOT9， is required for recruitment of the deadenylase complex. In addition to CNOT1， CNOT9 is now included in the identified CCR4-NOT subunits shown to interact with TTP. We find that both the N- and C-terminal domains of TTP are involved in an interaction with CNOT9. Through a combination of SPOT peptide array， site-directed mutagenesis， and bio-layer interferometry， we identified several conserved tryptophan residues in TTP that serve as major sites of interaction with two tryptophan-binding pockets of CNOT9， previously found to interact with another modulator GW182. We further demonstrate that these interactions are also required for recruitment of the CCR4-NOT complex and TTP-directed decay of an mRNA containing an AU-rich element in its 3'-untranslated region. Together the results reveal new molecular details for the TTP-CNOT interaction that shape an emerging mechanism whereby TTP targets inflammatory mRNAs for deadenylation and decay.
