Ca(2+)-dependent and caspase-3-independent apoptosis caused by damage in Golgi apparatus due to 2,4,5,7-tetrabromorhodamine 123 bromide-induced photodynamic effects

To clarify the role of the Golgi apparatus in photodynamic therapy-induced Apoptosis, its signaling pathway was studied after photodynamic treatment of human cervix carcinoma cell line HeLa, in which a photosensitizer, 2,4,5,7-tetrabromorhodamine 123 bromide (TBR), was incorporated into the Golgi apparatus. Laser scanning microscopic analysis of TBR-loaded HeLa cells confirmed that TBR was exclusively located in the Golgi apparatus. HeLa cells incubated with TBR for 1 h were then exposed to visible LIGHT using an Xe lamp. LIGHT of wavelength below 670 nm was eliminated with a filter. Morphological observation of nuclei stained with Hoechst 33342 revealed that Apoptosis of cells was induced by exposure to LIGHT. Electron spin resonance spectrometry showed that light-exposed TBR produced both singlet oxygen (1O2) and superoxide anion (O2-). Apoptosis induction by TBR was inhibited by pyrrolidine dithiocarbamate, an O2- scavenger, but not by NaN3, a quencher of 1O2. Furthermore, TBR-induced Apoptosis was inhibited by aurintricarboxylic acid and ZnCl2, which are known as inhibitors of deoxyribonuclease (DNase) gamma, and (acetoxymethyl)-1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, a chelator of Ca2+, but not by acetyl Asp-Glu-Val-Asp-aldehyde, an inhibitor of Caspase-3. These results suggested that O2- was responsible for TBR-induced Apoptosis, and Ca(2+)-dependent and caspase-3-independent nuclease such as DNase gamma played an important role in apoptotic signaling triggered by Golgi dysfunction.