Pervasive TTP binding but selective target mRNA destabilization in the macrophage transcriptome [RNA-Seq_2]

Precise control of mRNA decay is fundamental for robust yet not exaggerated inflammatory responses to pathogens. Parameters determining the specificity and extent of mRNA degradation within the entire inflammation-associated transcriptome remain incompletely understood. Using transcriptome-wide high resolution occupancy assessment of the mRNA-destabilizing protein TTP, a major inflammation-limiting factor, we qualitatively and quantitatively characterize TTP binding positions and functionally relate them to TTP-dependent mRNA decay in immunostimulated macrophages. We identify pervasive TTP binding with incompletely penetrant linkage to mRNA destabilization. A necessary but not sufficient feature of TTP-mediated mRNA destabilization is binding to 3’ untranslated regions (UTRs). Mapping of binding positions of the mRNA-stabilizing protein HuR in activated macrophages revealed that TTP and HuR binding sites in 3’ UTRs occur mostly in different transcripts implicating only a limited co-regulation of inflammatory mRNAs by these proteins. Remarkably, we identify robust and widespread TTP binding to introns of stable transcripts. Nuclear TTP is associated with spliced-out introns and maintained in the nucleus throughout the inflammatory response. Our study establishes a functional annotation of binding positions dictating TTP-dependent mRNA decay in immunostimulated macrophages. The findings allow navigating the transcriptome-wide landscape of RNA elements controlling inflammation. Overall design: Experiment comparing RNA decay rates in WT and TTP-/- macrophages at LPS 3 h and 6 h. Transcription was blocked with actinomycin D for 0, 45 or 90 min. Decay rates was calculated using linear model.

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Sedlyarov V, Fallmann J, Ebner F, Huemer J, Sneezum L, Ivin M, Kreiner K, Tanzer A, Vogl C, Hofacker I, Kovarik P