Partially purified bacteriocin kills malignant cells by apoptosis: programmed cell death

Bacterial proteins, partially purified bacteriocin (PPB), were investigated for their selective killing of malignant cells. It is shown here that upon PPB-cell interaction DNA fragmentation starts within one hour and peaks at 6 hrs. This process requires an on-going cellular metabolism. It is prevented by both actinomycin D, a DNA dependent RNA synthesis inhibitor, and cycloheximide, a protein synthesis inhibitor. We show here that the DNA fragmentation is triggered by PPB-cell membrane-receptor interaction which signals the activation of endogenous cellular endonucleases rather than actually penetrating the cell and interacting directly with the DNA, or serving as a nuclease itself. Thus, it is suggested that the cell death initiated by the lethal bacterial proteins, PPB, is a programmed, step-wise cell death involving apoptosis.