Reactive oxygen species act at both TGF-beta-dependent and -independent steps during induction of apoptosis of transformed cells by normal cells.

We have recently shown that TGF-beta-treated normal fibroblasts can induce apoptosis of transformed cells. The overall process was inhibited by antioxidants and radical scavengers, pointing to a role of reactive oxygen species (ROS). To define the ROS-dependent steps precisely, our experimental system was dissected into three phases. During phase I, TGF-beta 1 induced production and release of apoptosis-inducing signal molecules by normal cells. In phase II, these signal molecules were transferred between normal and transformed cells. During phase III, transformed cells went into apoptosis. The use of antibody directed against TGF-beta revealed that TGF-beta was required only during phase I. Application of radical scavengers and antioxidants at defined phases revealed that reactive oxygen species are involved specifically with biochemical processes induced by TGF-beta in normal cells and early in signal transfer between normal cells and transformed cells. These data therefore point to a functional role of reactive oxygen species both for the TGF-beta 1-induced signal pathway in normal cells and for the induction of apoptosis in transformed cells.