Proapoptotic and redox state-related signaling of reactive oxygen species generated by transformed fibroblasts

Area of Science:

• Biochemistry
• Cell Biology
• Oncology

Background:

• Oncogenic transformed fibroblasts produce extracellular superoxide via NADPH oxidase.
• Glutathione depletion enhances the apoptosis-inducing potential of extracellular reactive oxygen species (ROS).

Purpose of the Study:

• To elucidate the mechanism of apoptosis induction by extracellular ROS in glutathione-depleted transformed fibroblasts.
• To investigate the role of intracellular ROS and catalase in this process.
• To differentiate ROS signaling in transformed versus nontransformed fibroblasts.

Main Methods:

• Measurement of extracellular and intracellular ROS generation.
• Assessment of apoptosis induction under conditions of glutathione depletion.
• Inhibition studies using catalase, apocynin, superoxide dismutase, terephthalate, and deferoxamine.
• Evaluation of endogenous catalase levels and response to exogenous catalase.

Main Results:

• Extracellular ROS from transformed fibroblasts induce apoptosis through the metal-catalyzed Haber-Weiss reaction, as evidenced by inhibition with specific scavengers and chelators.
• Intracellular ROS are initially not involved in apoptosis of transformed cells due to high catalase activity, which is induced by extracellular hydrogen peroxide.
• Nontransformed fibroblasts induce apoptosis via intracellular ROS when glutathione-depleted, unlike transformed cells.

Conclusions:

• Extracellular ROS in transformed fibroblasts act as both redox signaling molecules and apoptosis inducers via the Haber-Weiss reaction under glutathione depletion.
• Intracellular catalase plays a crucial role in protecting transformed cells from hydrogen peroxide-induced apoptosis, but this protection can be modulated.
• Distinct ROS-mediated apoptosis pathways exist in transformed versus nontransformed fibroblasts depending on glutathione status and ROS localization.