Transit of serumstimulated normal rat kidney (NRK) epthelial cells through the first division cycle after release from quiescence (G 0 ) provided a model system to assess the kinetics and mechanisms underlying PAI-1 expression in a growth "activated" phenotype. PAI-1 mRNA transcripts increased by more than 20-fold during the G 0 3 G 1 transition; induced expression had immediate-early response characteristics and abruptly declined prior to the onset of DNA synthesis. Transcriptional activity of the PAI-1 gene paralleled the steady-state mRNA abundance profile during this first synchronized growth cycle after release from quiescence. Although PAI-1 mRNA levels were up-regulated (approximately threefold) upon exposure to several different growth factors, neutralizing antibodies to transforming growth factor-1 (TGF-1) effectively attenuated the more than ninefold serum-associated PAI-1 inductive response by more than 70% (at both the mRNA transcript and protein levels). Similar to the metabolic requirements for serum-mediated PAI-1 transcription, PAI-1 induction upon addition of TGF-1 to quiescent NRK cell cultures was actinomycin D sensitive and resistant to cyclohexamide and puromycin, suggesting a primary mode of transcript control. The response to protein synthesis inhibitors, however, was complex. While cyclohexamide appeared to stabilize, or at least maintain, fetal bovine serum (FBS)-or TGF-1-stimulated PAI-1 mRNA levels, puromycin had no such affect. The amplitude and duration of induced PAI-1 expression were the same in either the presence or absence of puromycin. Cyclohexamide when used alone (i.e., in non-FBS-or TGF-1-treated cultures), moreover, effectively stimulated PAI-1 induction whereas puromycin was ineffective. Although TGF-1 was not a complete mitogen in the NRK cell system, incubation of quiescent renal cell cultures with TGF-1, prior to serum stimulation, resulted in a 10-to 12-fold increase in PAI-1 expression coincident with exit out of G 0 . These data support a model in which PAI-1 gene expression is closely associated with creation of the growth-activated state and that cell cycle controls appear to be superimposed on the time course of the serum-induced expression of the PAI-1 gene.