| Popis: |
Type-1 plasminogen activator-inhibitor (PAI-1) is a major physiologic inhibitor of plasminogen activation. Incubation of HTC rat hepatoma cells with the cyclic nucleotide analogue, 8-bromo-cAMP, causes a dramatic increase in tissue-type plasminogen activator activity secondary to a 90% decrease in PAI-1 mRNA. Although 8-bromo-cAMP causes a modest decrease in PAI-1 transcription, regulation is primarily the result of a 3-fold increase in the rate of PAI-1 mRNA degradation. To determine the cis-acting sequences required for cyclic nucleotide regulation, we have stably transfected HTC cells with chimeric genes containing sequences from the rat PAI-1 cDNA and the mouse β-globin gene and examined the effect of cyclic nucleotides on the decay rate of these transcripts. The mRNA transcribed from the β-globin gene is stable and not cyclic nucleotide-regulated, whereas the transcript from a construct containing the β-globin coding region and the PAI-1 3′-untranslated region (UTR) is destabilized in the presence of 8-bromo-cAMP, suggesting that this response is mediated by sequences in the PAI-1 3′-UTR. Analyses by deletion of sequences from this chimeric construct indicate that, whereas more than one region of the PAI-1 3′-UTR can confer cyclic nucleotide responsiveness, the 3′-most 134-nucleotide sequence alone is sufficient to do so. Insertion of PAI-1 sequences within the β-globin 3′-UTR confirms that the 3′-most 134 nucleotides of PAI-1 mRNA can confer cyclic nucleotide regulation of stability on a heterologous transcript, suggesting that this sequence may play a major role in hormonal regulation of PAI-1 mRNA stability. |
