Characterization of the RNA binding proteins forming complexes with a novel putative regulatory region in the 3′-UTR of TNF-α mRNA

Tumor necrosis factor-alpha (TNF-(alpha)) is a key cytokine regulator of an early immune response and the central mediator of deleterious effects of systemic inflammatory response syndrome. High production of TNF-alpha by macrophages requires two signals: the first signal induces transcription, while the second signal releases the translational repression of TNF-alpha mRNA. The translational control of TNF-alpha expression is conferred by sequences in the 3'-untranslated region (3'-UTR) of its mRNA. Previously, we have characterized protein complexes binding to the main AU-rich region in the 3'-UTR of murine TNF-alpha mRNA. Here we describe a second protein binding region which is located 147 bases downstream of the first region and interacts with at least seven distinct protein species present in murine macrophages. The second protein binding motif contains a single AUAUUUAU sequence motif; a mutation of this sequence to AUAGGUAU abrogates the binding of proteins. Some of the macrophage proteins mutually compete for the binding to both regions, while others seem to be region specific. The existence of the two protein binding domains explains the previously published data addressing the translatibility of a reporter gene linked to various deletion mutants of the TNF-alpha 3'-UTR. Both the sequence and position of the two putative protein binding regions are highly conserved across species, indicating their important role in the regulation of translational repression and inducibility of TNF-alpha synthesis.