Dynamin-related protein Drp1 is required for Bax translocation to mitochondria in response to irradiation-induced apoptosis

// Ping Wang 1 , Peiguo Wang 1 , Becky Liu 2 , Jing Zhao 1 , Qingsong Pang 1 , Samir G. Agrawal 3 , Li Jia 4 , Feng-Ting Liu 1 1 Department of Radiobiology, Key Laboratory of Cancer Prevention and Therapy, National Clinical Research Centre of Cancer, Tianjin Medical University Cancer Institute and Hospital, Tianjin, China 2 East Surrey Hospital, Surrey and Sussex Healthcare NHS Trust, Redhill, Surrey, United Kingdom 3 Pathology Group, Blizard Institute, Queen Mary University of London, London, United Kingdom 4 Centre for Haemato-Oncology, Barts Cancer Institute, Queen Mary University of London, London, United Kingdom Correspondence to: Ping Wang, e-mail: wangping@tjmuch.com Feng-Ting Liu, e-mail: liufengting@tjmuch.com Keywords: Bax, DRP1, mitochondrial fragmentation, apoptosis, UV irradiation Received: March 09, 2015      Accepted: May 21, 2015      Published: June 04, 2015 ABSTRACT Translocation of the pro-apoptotic protein Bax from the cytosol to the mitochondria is a crucial step in DNA damage-mediated apoptosis, and is also found to be involved in mitochondrial fragmentation. Irradiation-induced cytochrome c release and apoptosis was associated with Bax activation, but not mitochondrial fragmentation. Both Bax and Drp1 translocated from the cytosol to the mitochondria in response to irradiation. However, Drp1 mitochondrial translocation and oligomerization did not require Bax, and failed to induce apoptosis in Bax deficient diffuse large B-cell lymphoma (DLBCL) cells. Using fluorescent microscopy and the intensity correlation analysis, we demonstrated that Bax and Drp1 were colocalized and the levels of colocalization were increased by UV irradiation. Using co-immuno-precipitation, we confirmed that Bax and Drp1 were binding partners. Irradiation induced a time-associated increase in the interaction between active Bax and Drp1. Knocking down Drp1 using siRNA blocked UV irradiation-mediated Bax mitochondrial translocation. In conclusion, our findings demonstrate for the first time, that Drp1 is required for Bax mitochondrial translocation, but Drp1-induced mitochondrial fragmentation alone is not sufficient to induce apoptosis in DLBCL cells.