Effects of a tumor-promoting agent on chondrogenesis.

Chondroblasts exposed to the phorbol ester, PMA, rapidly lose their polygonal morphology, and rapidly cease to synthesize or accumulate the chondroblast-specific Type IV sulfated proteoglycan. This striking effect is reversible if the cells are kept in PMA for up to 72 hours. A longer exposure induces irreversible effects and results in a population of cells, the vast majority of which lack the phenotypic properties of terminal chondroblasts.