Spontaneous nucleosomal DNA fragmentation in murine leukemic L1210 cells

Spontaneous nucleosomal DNA fragmentation (SNDF), characteristic of apoptotic cell death was observed in a murine leukemic cell line grown to high density. This effect was eliminated by permitting free diffusional exchange with a large amount of complete medium. Cells seeded at low density did not show SNDF in a conditioned medium that had been used to culture cells with severe SNDF. Cells seeded at high density in the same conditioned medium showed pronounced SNDF, but addition of 10% fetal bovine serum to such a medium significantly reduced SNDF. These observations indicate that neither physical contact among cells in high density culture per se nor secretion of a death factor by the high density culture could account for the induction of SNDF. The results support a model in which the gradual depletion of a serum factor(s) leads to the activation of a cell death program that is manifested as SNDF.