Regulation of urokinase receptor expression by p53: Novel role in stabilization of uPAR mRNA

We found that p53-deficient (p53^-/-) lung carcinoma (H1299) cells express robust levels of cell surface uPAR and uPAR mRNA. Expression of p53 protein in p53^-/- cells suppressed basal and urokinase (uPA)-induced cell surface uPAR protein and increased uPAR mRNA degradation. Inhibition of p53 by RNA silencing in Beas2B human airway epithelial cells conversely increased basal as well as uPA-mediated uPAR expression and stabilized uPAR mRNA. Purified p53 protein specifically binds to the uPAR mRNA 3′ untranslated region (3′UTR), and endogenous uPAR mRNA associates with p53. The p53 binding region involves a 37-nucleotide uPAR 3′UTR sequence, and insertion of the p53 binding sequence into β-globin mRNA destabilized β-globin mRNA. Inhibition of p53 expression in these cells reverses decay of chimeric β-globin-uPAR mRNA. These observations demonstrate a novel regulatory role for p53 as a uPAR mRNA binding protein that downregulates uPAR expression, destabilizes uPAR mRNA, and thereby contributes to the viability of human airway epithelial or lung carcinoma cells.