Transcriptional antagonism of phorbol ester-mediated induction of plasminogen activator inhibitor types 1 and 2 by cyclic adenosine 3',5'-monophosphate.

Gene expression of plasminogen activator inhibitor (PAI) types 1 and 2 is modulated by the protein kinase-C (PKC) and cAMP-dependent protein kinase-A (PKA) signal transduction pathways. To determine whether the PKC and PKA pathways functionally interact during modulation of PAI gene expression, we assessed changes in gene transcription rates, mRNA, and antigen levels of PAI-1 and PAI-2 in HT-1080 fibrosarcoma cells treated with the PKC activator phorbol 12-myristate 13-acetate (PMA), alone or in combination with cAMP agonists and analogs. PMA produced a transient increase in PAI-1 and a sustained increase in PAI-2, which was evident at the level of gene transcription and mRNA. Treatment with the cAMP agonist forskolin or the cAMP analog 8-bromo-cAMP decreased constitutive and PMA-mediated expression of PAI-1 mRNA. PAI-2 mRNA was below detection limits in nontreated and cAMP-treated cells. However, elevated levels of cAMP reduced the stimulatory effect of PMA on PAI-2 mRNA. The antagonism of the PMA effect by cAMP was evident at the level of gene transcription, suggesting that the end point of the functional interplay between the PKC and PKA pathways requires modulation of a nuclear transcription factor(s). Our results suggest that the PKC- and PKA-dependent signaling pathways have counteractive effects on transcriptional expression of the PAI-1 and PAI-2 genes in HT-1080 cells.