Cell cycle modulation through subcellular spatially resolved production of singlet oxygen via direct 765 nm irradiation: manipulating the onset of mitosis.

Reactive oxygen species, ROS, are acknowledged signaling molecules in cellular processes. Singlet molecular oxygen, O2(a1Δg), is one ROS that can initiate cell responses that range from death to proliferation. To better understand the mechanisms involved, it is necessary to further investigate cell response to the "dose" of O2(a1Δg) that has been selectively produced at the expense of other ROS. In this context, dose refers not just to the amount of O2(a1Δg) produced, but also to the subcellular spatial domain in which it is produced. In this study, we selectively produced small and non-toxic amounts of O2(a1Δg) in sensitizer-free experiments by irradiating oxygen at 765 nm using a laser focused either into the nucleus or cytoplasm of HeLa cells. We find that O2(a1Δg)-mediated cell proliferation depends appreciably on the site of O2(a1Δg) production. At the same incident laser power, irradiation into the cytoplasm elicits moderate enhancement of proliferation, whereas irradiation into the nucleus leads to an appreciable delay in the onset and completion of mitosis. We discuss these results in light of what is known about the intracellular photophysics of O2(a1Δg) and the redox state of different cell domains.