PRomotion of smooth surface tumorigenicity by phorbol myristate acetate in Balb/3T3 cells and Balb/3T3 T proadipocytes.

In vitro exposure of Balb/3T3 cells to phorbol and phorbol myristate acetate significantly increased their tumorigenic potential when implanted sc on smooth surface plates into syngeneic mice. This finding supports the hypothesis that many so-called normal cell lines may actually represent initiated cells that can be induced to become tumorigenic following exposure to promoting agents. Since the tumorigenic potential of many tissues in vivo is inversely proportional to the state of differentiation of the stem cell populations undergoing transformation, we assayed the relative tumorigenicity of Balb/3T3 T proadipocytes, which can differentiate in culture, and Balb/3T3 cells, which cannot differentiate in culture. The effects of tumor-promoting agents on these cells were also tested. Plate-implanted Balb/3T3 T proadipocytes were markedly less tumorigenic than Balb/3T3 cells, and Balb/3T3 T proadipocytes were not sensitive to the promotional effects of phorbol myristate acetate.