Synthesis and degradation of type I procollagen mRNAs in cultured human skin fibroblasts and the effect of cortisol.

The metabolism of type I procollagen mRNAs was studied in confluent cultures of human skin fibroblasts using the recombinant plasmids Hf677 and Hf32, which contain DNA sequences complementary to human pro-alpha 1(I) and pro-alpha 2(I) mRNAs, respectively. The ratio for the amount of pro-alpha 1(I) mRNAs to pro-alpha 2(I) mRNAs was 2.06:1. These mRNAs were labeled during in vitro transcription of isolated nuclei in the ratio 2.16:1 and during a pulse in cellulo in the ratio 1.96:1, suggesting that the two species are synthesized in the ratio 2:1. No significant differences were found in the rates of degradation, the half-lives of the pro-alpha 1(I) and pro-alpha 2(I) mRNAs being 9.2 and 8.4 h, respectively. Addition of 10 microM cortisol to the growth medium reduced the amounts of the type I procollagen mRNAs by half in 6 h, leaving their ratio unaltered. Incubation of the cells with cortisol had only minor effects on the subsequent synthesis of the mRNAs in isolated nuclei in vitro, whereas the degradation rates in cellulo were distinctly accelerated.