VACO-330, a nontransformed cell line established from a human colon adenoma, undergoes spontaneous apoptosis and shedding of cells into the culture medium. Shed cells were shown to be apoptotic, both by nuclear morphology and by generation of a typical "laddered" pattern of degraded DNA. Quantitation of DNA released into the medium, compared with the amount retained on the plate, demonstrated that 6.2 +/- 1.1% of the total cell mass underwent apoptotic death daily. The addition of transforming growth factor beta (20 ng/ml) accelerated this spontaneous apoptotic rate 3.2-fold. Moreover, apoptosis could be rapidly induced in up to 45% of the VACO-330 cells by using brief exposure to a calcium chelating medium to release the cells from the substratum. We suggest that transforming growth factor beta is a likely physiological regulator of apoptosis during maturation of the colonic epithelial cells. We additionally suggest the existence of an alternate pathway, which at the time of shedding from the crypt induces apoptosis in colonic epithelial cells that have escaped earlier apoptotic signals.