Phytosphingosine in combination with ionizing radiation enhances apoptotic cell death in radiation-resistant cancer cells through ROS-dependent and -independent AIF release.
The use of chemical modifiers as radiosensitizers in combination with low-dose irradiation may increase the therapeutic effect on cancer by overcoming a high apoptotic threshold. Here, we showed that phytosphingosine treatment in combination with gamma-radiation enhanced apoptotic cell death of radiation-resistant human T-cell lymphoma in a caspase-independent manner. Combination treatment induced an increase in intracellular reactive oxygen species (ROS) level, mitochondrial relocalization of B-cell lymphoma-2(Bcl-2)-associated X protein (Bax), poly-adenosine diphosphate (ADP)-ribose polymerase 1 (PARP-1) activation, and nuclear translocation of apoptosis-inducing factor (AIF). siRNA targeting of AIF effectively protected cells from the combination treatment-induced cell death. An antioxidant, N-acetyl-L-cysteine (NAC), inhibited Bax relocalization and AIF translocation but not PARP-1 activation. Moreover, transfection of Bax-siRNA significantly inhibited AIF translocation. Pretreatment of PARP-1 inhibitor, DPQ (3,4-dihydro-5-[4-(1-piperidinyl)-butoxy]-1(2H)-isoquinolinone), or PARP-1-siRNA also partially attenuated AIF translocation, whereas the same treatment did not affect intracellular ROS level and Bax redistribution. Taken together, these results demonstrate that enhancement of cell death of radiation-resistant cancer cells by phytosphingosine treatment in combination with gamma-radiation is mediated by nuclear translocation of AIF, which is in turn mediated both by ROS-dependent Bax relocalization and ROS-independent PARP-1 activation. The molecular signaling pathways that we elucidated in this study may provide potential drug targets for radiation sensitization of cancers refractive to radiation therapy.
Laboratory of Radiation Effect, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
Moon-Taek
MT
Park
Min-Jung
MJ
Kim
Young-Hee
YH
Kang
Soon-Young
SY
Choi
Jae-Hoon
JH
Lee
Jung-A
JA
Choi
Chang-Mo
CM
Kang
Chul-Koo
CK
Cho
Seongman
S
Kang
Sangwoo
S
Bae
Yun-Sil
YS
Lee
Hee Yong
HY
Chung
Su-Jae
SJ
Lee
D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000528:radiation effects; D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D051033:Apoptosis Inducing Factor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D002999:Clone Cells; D003131:Combined Modality Therapy; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D005420:Flavoproteins / Q000378:metabolism*; D005720:Gamma Rays; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D019169:Jurkat Cells; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011836:Radiation Tolerance; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
C494829:AIFM1 protein, human; D051033:Apoptosis Inducing Factor; C494826:BAX protein, human; D005420:Flavoproteins; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D011065:Poly(ADP-ribose) Polymerases; C012491:phytosphingosine; D013110:Sphingosine