Regulation of human tissue factor expression by mRNA turnover

Abstract

Tissue factor serves as the cellular receptor for circulating blood coagulation factor VII and is the principal physiological initiator of blood coagulation. Tissue factor is not normally expressed in cells that contact blood, such as endothelial cells and monocytes, but can be induced in these cells by tumor necrosis factor or tumor-promoting phorbol esters. Following induction, the human tissue factor mRNA is degraded with a half-life of ∼0.75-1.5 h. The cellular mechanisms responsible for this rapid mRNA turnover were investigated with chimeric tissue factor·β-globin constructs expressed in stably transfected mouse NIH/3T3 cells. These constructs were expressed with the transiently inducible c-fos promoter which eliminated the need to use transcriptional inhibitors to determine mRNA half-lives. Sequences capable of conferring rapid turnover to the normally stable β-globin transcript were localized to the last 600 nucleotides of the tissue factor mRNA. The 3′ end of this fragment is similar to previously described AU-rich mRNA destabilizing elements. Activity of the tissue factor element was dependent on its specific sequence and not simply a high AU nucleotide content. The degradation of unstable chimeric tissue factor·β-globin mRNAs was prevented by inhibition of transcription with actinomycin D. Chimeric tissue factor·β-globin mRNAs were superinduced by the protein synthesis inhibitor cycloheximide, and this superinduction may be due in part to stabilization of the mRNA.