Opposite effects of Ha-Ras and Ki-Ras on radiation-induced apoptosis via differential activation of PI3K/Akt and Rac/p38 mitogen-activated protein kinase signaling pathways.
It has been well known that Ras signaling is involved in various cellular processes, including proliferation, differentiation, and apoptosis. However, distinct cellular functions of Ras isozymes are not fully understood. Here we show the opposing roles of Ha-Ras and Ki-Ras genes in the modulation of cell sensitivity to ionizing radiation. Overexpression of active isoform of Ha-Ras (12V-Ha-Ras) in Rat2 cells increases resistance to the ionizing radiation. Constitutive activation of phosphoinositide-3-kinase (PI3K) and Akt is detected specifically in 12V-Ha-Ras-overexpressing cells. The specific PI3K inhibitor LY294002 inhibits PI3K/Akt signaling and potentiates the radiation-induced apoptosis, suggesting that activation of the PI3K/Akt signaling pathway is involved in the increased radio-resistance in cells overexpressing 12V-Ha-Ras. Overexpression of activated Ki-Ras (12V-Ki-Ras), on the other hand, markedly increases radiation sensitivity. The p38 mitogen-activated protein kinase (MAPK) activity is selectively enhanced by ionizing radiation in cells overexpressing 12V-Ki-Ras. The specific p38 MAPK inhibitor, PD169316, or dominant-negative p38 MAPK decreases radiation-induced cell death. We further show that the mechanism that underlies potentiation of cell death in cells overexpressing 12V-Ki-Ras involves Bax translocation to the mitochondrial membrane. Elevated Bax translocation following ionizing irradiation in 12V-Ki-Ras-overexpressing cells is completely inhibited by PD169316 or dominant-negative p38 MAPK. In addition, introduction of cells with RacN17, a dominant-negative mutant of Rac, resulted in a marked inhibition of radiation-induced Bax translocation and apoptotic cell death as well as p38 MAPK activation. Taken together, these findings explain the opposite effects of Ha-Ras and Ki-Ras on modulation of radiosensitivity, and suggest that differential activation of PI3K/Akt and Rac/p38 MAPK signaling by Ha-Ras and Ki-Ras may account for the opposing response to the ionizing radiation. These data provide an explanation for the diverse biological functions of Ras isozymes, and partly accounts for the differential response of transformed cells to anticancer treatments.
Choi
Jung-A
JA
Laboratory of Radiation Effect, Korea Institute of Radiological & Medical Sciences, Seoul 139-706, Korea.
Park
Moon-Taek
MT
Kang
Chang-Mo
CM
Um
Hong-Duck
HD
Bae
Sangwoo
S
Lee
Kee-Ho
KH
Kim
Tae-Hwan
TH
Kim
Jae-Hong
JH
Cho
Chul-Koo
CK
Lee
Yun-Sil
YS
Chung
Hee Yong
HY
Lee
Su-Jae
SJ
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D011836:Radiation Tolerance; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D051028:bcl-2-Associated X Protein; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins / Q000502:physiology*
D053148:Caspase 3; D020169:Caspases; D045304:Cytochromes c; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D016283:Proto-Oncogene Proteins p21(ras); D051028:bcl-2-Associated X Protein; D048051:p38 Mitogen-Activated Protein Kinases; D020744:rac GTP-Binding Proteins; C494827:Bax protein, mouse; C494828:Bax protein, rat; C494920:Akt1 protein, rat; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat