Plasminogen activator inhibitor type 2 gene induction by tumor necrosis factor and phorbol ester involves transcriptional and post-transcriptional events. Identification of a functional nonameric AU-rich motif in the 3'- untranslated region

Plasminogen activator inhibitor type 2 (PAI-2) mRNA and antigen levels are synergistically induced in HT-1080 fibrosarcoma cells when treated with a combination of tumor necrosis factor (TNF) and phorbol 12-myristate 13- acetate (PMA). Here we demonstrate that this effect is not fully reflected at the level of gene transcription, suggesting a contribution of post- transcriptional events in this induction. Insertion of the 3'-untranslated region (3'-UTR) of PAI-2 mRNA into the 3'-UTR of a rabbit β-globin reporter gene reduces β-globin-PAI-2 chimeric mRNA expression in stably transfected cells. The region within the PAI-2 3'-UTR responsible for this effect is located within the 368-nucleotide sequence preceding the poly(A) tail, a segment that includes a nonameric UUAUUUAUU motif. Mutagenesis of this element abolishes the PAI-2 3'-UTR destabilizing effect, revealing a functional role for this motif. TNF and PMA co-treatment of transfected cells increases β-globin-PAI-2 chimeric mRNA expression 3-4-fold, indicating that the inherently unstable 3'-UTR of PAI-2 mRNA can become stabilized in response to TNF and PMA. Our results indicate that induction of PAI-2 gene expression by TNF and PMA involves both direct transcription as well as mRNA stabilization, the latter involving an AU-rich nonameric motif in the 3'- UTR.