CLONING OF THE MINK PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 MESSENGER-RNA - AN MESSENGER-RNA WITH A SHORT HALF-LIFE

In mink lung CCL64 epithelial cells the rate of synthesis of plasminog en activator inhibitor type I (PAI-1) increases 10-100-fold within 3h in response to 12-O-tetradecanoyl phorbol-13-acetate (PMA). The PAI-1 gene is regulated transcriptionally. Parallel studies of the time-cour ses of PAI-1 synthesis and secretion and of mRNA accumulation indicate that the amount of secreted PAI-1 produced by the cells is tightly co upled to the level of its transcript. The half-life of the PAI-1 mRNA was found to be 25 min which is much shorter than previously reported for PAI-1 in other cells. Actinomycin D, which is commonly used to det ermine mRNA half-life, stabilized the PAI-1 mRNA. Cycloheximide also s tabilized the mRNA. The short half-life and the superinducibility of P AI mRNA are properties shared with rapidly degraded mRNAs encoding pro tooncoproteins. A 2.97-kb cDNA clone containing the entire coding sequ ence of PAI-1 was isolated from a cDNA library made from mink lung CCL 64 epithelial cells stimulated with PMA. The PAI-1 cDNA contains a lon g 3'-untranslated region (UTR) of 1720 bp whose sequence is highly con served among PAI-1 mRNAs from different species. The PAI-1 mRNA also c ontains several AUUUA pentamer sequences which are the features of an A + U-rich regulatory element such as is found on the fos protooncogen e mRNA. Upstream of one of these AUUUA pentamers are several highly co nserved sequences that are also found in the 3' UTR of the fos and int egrin receptor alpha-subunit mRNAs. These are mRNAs that encode protei ns which are involved in the cellular response to tissue wounds. Thus, it is possible that these conserved 3' sequences may be important for regulating the production of Fos, the integrin alpha-subunit and PAI- 1 during wound healing.