Epidermal ribosome accumulation during two-stage skin tumorigenesis

The increase in interfollicular epidermal ribosomes on the backs of mice initiated with 7,12-dimethylbenz(a)-anthracene and promoted with 12-0-tetradecanoyl-phorbol-13-acetate was disproportionate to the increase in epidermal wet weight, protein, and DNA. Whereas ribosome numbers increased five- to sixfold 48 hr after the first, fourth, or eight application of 12-3-tetradecanoyl-phorbol-13-acetate, epidermal tissue increased only two- to threefold at these times. This disproportionate increase was due to the fact that, concurrent with the increased amount of interfollicular epidermal tissue and cells, ribosomes per g epidermis and per mg DNA increased two to three times normal. The tissue concentration and cellular content of ribosomes were also increased in the epidermal component of induced squamous papillomas. The work of others has demonstrated that, during growth of other tissues and organs, ribosome accumulation is proportionate to accumulation of tissue and/or cells. The results of our study indicate that the epidermis may have unique kinetics of ribosome accumulation during induced growth. Furthermore, these findings suggest the interesting possibility that other tumor-prone surface epithelia, such as the linings of the respiratory and gastrointestinal tracts, have similar kinetics of ribosome accumulation during induced growth.