H1299 lung carcinoma cells lacking p53 (p53-/-) express minimal amounts of plasminogen activator inhibitor-1 (PAI-1) protein as well as mRNA. p53-/- cells express highly unstable PAI-1 mRNA. Transfection of p53 in p53-/- cells enhanced PAI-1 expression and stabilized PAI-1 mRNA. On the contrary, inhibition of p53 expression by RNA silencing (SiRNA) in non-malignant human lung epithelial (Beas2B) cells decreased basal as well as uPA-induced PAI-1 expression due to accelerated degradation of PAI-1 mRNA. Purified p53 protein specifically binds to the PAI-1 mRNA 3’UTR and endogenous PAI-1 mRNA forms an immune-complex with p53. Treatment of purified p53 protein with anti-p53 antibody abolished p53 binding to the 3’UTR of PAI-1 mRNA. The p53 binding region maps to a 70 nt PAI-1 mRNA 3’UTR sequence and insertion of the p53 binding sequence into beta-globin mRNA destabilized the chimeric transcript. Deletion experiments indicate that the C-terminal region (amino acid residues 296-393) of p53 protein interacts with PAI-1 mRNA. These observations demonstrate a novel role for p53 as an mRNA binding protein that regulates increased PAI-1 expression and stabilization of PAI-1 mRNA in human lung epithelial and carcinoma cells.