FIG. 2.
Turnover of tropoelastin pre-mRNA and mRNA. (A) Second-passage neonatal (NN) and adult (Ad) rat lung fibroblasts were grown to confluence and were treated with 50 μM DRB for 0 to 60 min or 24 h. At the indicated times, total RNA was isolated, and levels of tropoelastin pre-mRNA were determined by RT-PCR. As seen in intact tissue (Fig. 1), equivalent levels of pre-mRNA were detected in control (0- and 24-h-DRB) neonatal and adult fibroblasts. In the presence of DRB, tropoelastin pre-mRNA levels decayed at about the same rate (t1/2 = ∼15 min) in both neonatal and adult fibroblasts. (B) Neonatal and adult rat lung fibroblasts were treated with DRB for 1 or 24 h, and total RNA was isolated and analyzed by Northern hybridization. Tropoelastin mRNA in neonatal fibroblasts did not decay over the 24-h treatment. In contrast, tropoelastin mRNA in adult fibroblasts decayed rapidly to undetectable levels by 1 h post-DRB. In another experiment, fibroblasts were treated with 10 μg of actinomycin D (Act-D) per ml for 0.5 or 1 h. As with DRB, tropoelastin mRNA was stable in neonatal fibroblasts but decayed rapidly in adult cells.