Ribosomal RNA Synthesis Throughout Epidermal Hyperplastic Growth Induced by Abrasion or Treatment with 12-0-Tetradecanoyl-phorbol-13-acetate

During the production of an epidermal hyperplasia following abrasion, or the application of 17 nmoles of 12-0-tetradecanoyl-phorbol-13-acetate (TPA) on the back skin of female CD-1 mice there is a marked increase in ribosomes. During the period of regression, when the epidermis returns to its normal size, the ribosome content also returns to normal.To determine the contribution of ribosome synthesis to the accumulation of ribosomes, mice at varying intervals after abrasion or treatment with 17 nmoles of TPA were injected with (5–3H) uridine (100 μCi, I.P.), 3hr later the mice were sacrificed, the cytoplasmic ribosomes isolated, and the incorporation of (5–3H) uridine into the cytoplasmic ribosomes was determined. During the production of epidermal hyperplasia, following either abrasion or TPA treatment, there is a significant increase in the incorporation of (5–3H) uridine into the rRNA of the cytoplasmic ribosomes, suggesting that there is an increase in ribosome synthesis. During the period of epidermal regression, ribosome synthesis returns toward normal levels. There is a rough correlation between the amount of hyperplastic growth and the degree of ribosome synthesis. Abrasion induces about a 2-fold greater increase in epidermal mass, compared to TPA treatment. Accordingly, at its peak ribosome synthesis is about 2 times greater after abrasion than after TPA treatment