Post-transcriptional regulation of endothelial cell plasminogen activator inhibitor-1 expression during R-rickettsii infection

Intracellular infection of endothelial cells with Rickettsia rickettsii res ults in increased steady-state levels of plasminogen activator inhibitor-1 (PAI-1) mRNA. Control mechanisms governing such increased expression in res ponse to this novel stimulus have not been defined. In this study, we compa red the stability of PAI-1 mRNA in infected and uninfected endothelial cell s (EC) and explored the requirement for de novo host cell protein synthesis in the infection-induced increase of steady-state levels. The half-life of PAI-1 mRNA, which is constitutively expressed in cultured EC, increased fr om 18 h in uninfected EG to greater than 30 h in EC infected for 24 h, a ti me point at which increases in steady-state PAI-1 mRNA levels are noted. Th ere was no change in stability of gamma-actin due to infection. Nuclear run -on studies revealed no apparent increase in transcription rate at 4, 18 an d 24 h. R. rickettsii-induced increase in PAI-1 mRNA was blocked by the euk aryotic protein synthesis inhibitor, cycloheximide, which suggests that thi s response requires de novo host cell protein synthesis. These results prov ide evidence that post-transcriptional control mechanisms are operative in the regulation of PAI-1 during R. rickettsii infection. (C) 2000 Academic P ress.