Secretion of plasminogen activator inhibitor type-1 (PAI-1) by cultured cells is increased after exposure to specific cytokines and growth factors. We have shown previously that incubation of Hep G2 cells with epidermal growth factor (EGF) results in a marked increase in steady state levels of PAI-1 mRNA (Lucore, C.L., et al. (1988) J. Biol. Chem. 263, 15845-15848). The present study was undertaken to determine whether the regulation of expression of PAI-1 mRNA by EGF is mediated at the level of transcription and/or by post-transcriptional mechanisms. The rate of transcription of the PAI-1 gene measured by nuclear run-on assays was found to be increased within 2 h after stimulation of the cells with EGF (5 ng/ml) (3.2 fold increase relative to control, n = 2, range 3.0-3.4). It reached a maximum in 3 h, (9.2 fold increase relative to control, n = 2, range 8.8-9.6) and returned to baseline in 5 h. Exposure of the cells to EGF did not increase the rate of transcription of the glyceraldehyde-3-phosphate dehydrogenase gene. The half life of PAI-1 mRNA in Hep G2 cells was 120 min as determined by RNA blot analysis after exposure of the cells to actinomycin D to inhibit transcription. Stimulation of the cells with EGF did not result in significant change in the half life of PAI-1 mRNA. The results demonstrate that exposure of Hep G2 cells to EGF increases PAI-1 gene transcription.