Plasminogen activator inhibitor type 2 contains mRNA instability elements within exon 4 of the coding region - Sequence homology to coding region instability determinants in other mRNAs

Plasminogen activator inhibitor type 2 (PAI-2) is a serine protease inhibit or that inhibits urokinase. Constitutive and regulated PAI-2 gene expressio n involves post-transcriptional events, and an AU-rich mRNA instability mot if within the 3'-untranslated region of PAI-2 mRNA is required for this pro cess (Maurer, F., Tierney, M., and Medcalf, R. L. (1999) Nucleic Acids Res. 27, 1664-1673). Here we show that instability determinants are present wit hin various exons of the PAI-2 coding region, most notably within exon 4. D eletion of exon 4 from the full-length PAI-2 cDNA results in a doubling in the half-life of PAI-2 mRNA, whereas a 28-nucleotide region within exon 4 c ontains binding sites for cytoplasmic proteins. Inducible stabilization of PAI-2 mRNA in HT-1080 cells treated with phorbol ester and tumor necrosis f actor does not alter the binding of proteins to the exon 4 instability dete rminant, but resulted in a transient increase in the binding of factors to the AU-rich RNA instability element. Hence, PAI-2 mRNA stability is influen ced by elements located within both the coding region and the S'-untranslat ed region and that cytoplasmic mRNA binding factors may influence steady st ate and inducible PAI-2 mRNA expression. Finally a 10-nucleotide region fla nking the exon 4 protein-binding site is homologous to instability elements within five other transcripts, suggesting that a common coding region dete rminant may exist.