Induction of cancer stem cell sphere explosion by UV irradiation/cold shock or therapeutic chemicals: detection of autofluorescence using visible wavelength

Abstract

We have recently identified a new type of cell death, called “bubbling cell death”. When cells are exposed to UV irradiation followed by incubation at 37°C, they undergo typical apoptosis. However, when the UV‐irradiated cells are incubated at room temperature or down to 4°C, they generate bubbles – one bubble per cell – from the nucleus. The bubbles contain nitric oxide. There is occurrence of no caspase activation, flip‐over of phosphatidylserine, and DNA fragmentation, indicating that bubbling death is a novel type of cell death (Oncotarget 2015;6:8007–18). Here, by time‐lapse microscopy, we demonstrated that when breast cancer 4T1 stem cell spheres were subjected to UV and a brief cold shock (5 min at 4°C), followed by imaging at room temperature. The spheres initially shrank, then slowly expanded and finally exploded, and the cells died. Similar results were observed when the spheres were exposed to an aliquot of cocktail of protease inhibitors and an ERK inhibitor U0126, or an anti‐lung cancer drug ceritinib. Notably, prior to sphere explosion, there was an emission of luminescent light under bright light stimulation. We developed a novel approach to measure visible wavelength‐induced autofluorescence up to energy for DAPI imaging. In addition, a time‐dependent initial increase and then reduction in redox activity and formation of stress fibers occurred. Loss of cellular lipids and nuclear uptake of DAPI first and then propidium iodide prior to death were also observed. The entire course lasts 24–48 hr at room temperature. However, sphere explosion is accelerated dramatically by blebbistatin, an inhibitor of myosin II, suggesting the participation of cytoskeletal proteins in the sphere explosion.Support or Funding InformationMOST, TaiwanThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.