Intercellular HOCl-mediated Apoptosis Induction in Malignant Cells: Interplay Between NOX1-Dependent Superoxide Anion...

Intercellular apoptosis-inducing HOCl signaling is discussed as a control step during oncogenesis. It is defined as a sophisticated interplay between transformed target cells and non-transformed or transformed effector cells. In this study, transformed target cells were seeded as clumps of high local cell density, but low total cell number. They were surrounded by large numbers of effector cells, seeded at low local density. This spatially defined experimental arrangement allowed study of the impact of siRNA-mediated knockdown of NADPH oxidase 1 (NOX1) or dual oxidase 1 (DUOX1) on intercellular HOCl signaling. Our data show that the target function of transformed cells is defined as expression of NOX1 and subsequent extracellular superoxide anion generation. The NOX domain of DUOX1 does not contribute to the target function. The peroxidase domain of DUOX1 is released from transforming growth factor β1-treated non-transformed and transformed cells and acts in trans as HOCl-synthesizing peroxidase. These findings clarify the biochemical source of HOCl during HOCl-mediated signaling.