mRNA stabilization by TPA and transcriptional activation by U0126 of p21WAF1 expression.(A). RD cells were transfected with plasmid expressing β-galactosidase (β-gal) gene and a plasmid carrying p21 promoter (DM-Luc). Luciferase activity was normalized for the expression levels of transfected β-gal protein. Data show mean values ± s.e.m. of triplicates of a representative experiment. (B) Northern blots from RD cells left untreated (C) or treated with TPA (upper panel) or U0126 (U) (lower panel) for 5 hours, pre-treated with 0.05 μg/ml of actinomycin D for 1 hour and then left untreated (ActD) or treated with TPA (ActD+TPA) or U0126 (ActD+U) for 5 hours. The levels of GAPDH mRNA are shown. Similar results were obtained in three independent experiments for A and two for B.