Evidence that tristetraprolin binds to AU-rich elements and promotes the deadenylation and destabilization of tumor necrosis factor alpha mRNA

Mice deficient in tristetraprolin (TTP), the prototype of a family of CCCH zinc finger proteins, develop an inflammatory syndrome mediated by excess t umor necrosis factor alpha (TNF-alpha). Macrophages derived from these mice oversecrete TNF-alpha, by a mechanism that involves stabilization of TNF-a lpha mRNA, and TTP can bind directly to the AU-rich element (ARE) in TNF-al pha mRNA (E. Carballo, W. S. Lai, and P. J. Blackshear, Science 281:1001-10 05, 1998), We show here that TTP binding to the TNF-alpha ARE is dependent upon the integrity of both zinc fingers, since mutation of a single cystein e residue in either zinc finger to arginine severely attenuated the binding of TTP to the TNF-alpha ARE. In intact cells, TTP at low expression levels promoted a decrease in size of the TNF-alpha mRNA as well as a decrease in its amount; at higher expression levels, the shift to a smaller TNF-alpha mRNA size persisted, while the accumulation of this smaller species increas ed. RNase H experiments indicated that the shift to a smaller size was due to TTP-promoted deadenylation of TNF-alpha mRNA. This CCCH protein is likel y to be important in the deadenylation and degradation of TNF-alpha mRNA an d perhaps other ARE-containing mRNAs, both in normal physiology and in cert ain pathological conditions.