Carbon-Ion Irradiation Suppresses Migration and Invasiveness of Human Pancreatic Carcinoma Cells MIAPaCa-2 via Rac1 and RhoA Degradation.
OBJECTIVE
To investigate the mechanisms underlying the inhibition of cancer cell migration and invasion by carbon (C)-ion irradiation.


METHODS
Human pancreatic cancer cells MIAPaCa-2, AsPC-1, and BxPC-3 were treated by x-ray (4 Gy) or C-ion (0.5, 1, 2, or 4 Gy) irradiation, and their migration and invasion were assessed 2 days later. The levels of guanosine triphosphate (GTP)-bound Rac1 and RhoA were determined by the active GTPase pull-down assay with or without a proteasome inhibitor, and the binding of E3 ubiquitin ligase to GTP-bound Rac1 was examined by immunoprecipitation.


RESULTS
Carbon-ion irradiation reduced the levels of GTP-bound Rac1 and RhoA, 2 major regulators of cell motility, in MIAPaCa-2 cells and GTP-bound Rac1 in AsPC-1 and BxPC-3 cells. Proteasome inhibition reversed the effect, indicating that C-ion irradiation induced Rac1 and RhoA degradation via the ubiquitin (Ub)-proteasome pathway. E3 Ub ligase X-linked inhibitor of apoptosis protein (XIAP), which directly targets Rac1, was selectively induced in C-ion--irradiated MIAPaCa-2 cells and coprecipitated with GTP-bound Rac1 in C-ion--irradiated cells, which was associated with Rac1 ubiquitination. Cell migration and invasion reduced by C-ion radiation were restored by short interfering RNA--mediated XIAP knockdown, indicating that XIAP is involved in C-ion--induced inhibition of cell motility.


CONCLUSIONS
In contrast to x-ray irradiation, C-ion treatment inhibited the activity of Rac1 and RhoA in MIAPaCa-2 cells and Rac1 in AsPC-1 and BxPC-3 cells via Ub-mediated proteasomal degradation, thereby blocking the motility of these pancreatic cancer cells.
Advanced Radiation Biology Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Mayumi
M
Fujita
Advanced Radiation Biology Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Kaori
K
Imadome
Advanced Radiation Biology Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Yoshimi
Y
Shoji
Research Center Hospital for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Tetsurou
T
Isozaki
Research Center Hospital for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Satoshi
S
Endo
Research Center Hospital for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Shigeru
S
Yamada
Advanced Radiation Biology Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan. Electronic address: imait@nirs.go.jp.
Takashi
T
Imai
D002465:Cell Movement / Q000528:radiation effects*; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D009361:Neoplasm Invasiveness; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism / Q000528:radiation effects*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism / Q000528:radiation effects*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism / Q000528:radiation effects*
D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein