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Increased radiation‐induced apoptosis of Saos2 cells via inhibition of NFκB: A role for c‐Jun N‐terminal kinase
Author(s) -
Eliseev Roman A.,
Zuscik Michael J.,
Schwarz Edward M.,
O'Keefe Regis J.,
Drissi Hicham,
Rosier Randy N.
Publication year - 2005
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.20607
Subject(s) - apoptosis , radioresistance , transfection , c jun , downregulation and upregulation , microbiology and biotechnology , kinase , cancer research , cell culture , chemistry , biology , biochemistry , transcription factor , gene , genetics
To elucidate the possible effect of NFκB on radioresistance, we used the osteosarcoma cell line Saos2, stably expressing the NFκB constitutive inhibitor, mIκB (Saos2‐mIκB) or stably transfected with the empty vector (Saos2‐EV). Ionizing radiation induced “intrinsic” apoptosis in Saos2‐mIκB cells but not in Saos2‐EV control cells, with intact NFκB activity. We find as expected, that this NFκB activity was enhanced following irradiation in the Saos2‐EV control cells. On the other hand, inhibition of NFκB signaling in Saos2‐mIκB cells led to the upregulation of the pro‐apoptotic systems, such as Bax protein and c‐Jun N‐terminal Kinase (JNK)/c‐Jun/AP1 signaling. Inhibition of NFκB resulted in decreased expression of the DNA damage protein GADD45β, a known inhibitor of JNK. Subsequently, JNK activation of c‐Jun/AP‐1 proteins increased radiation‐induced apoptosis in these mutants. Radiation‐induced apoptosis in Saos2‐mIκB cells was inhibited by the JNK specific inhibitor SP600125 as well as by Bcl‐2 over‐expression. Furthermore, release of cytochrome‐ c from mitochondria was increased and caspase‐9 and ‐3 were activated following irradiation in Saos2‐mIκB cells. Antisense inhibition of GADD45β in Saos2‐EV cells significantly enhanced apoptosis following irradiation. Our results demonstrate that radioresistance of Saos2 osteosarcoma cells is due to NFκB‐mediated inhibition of JNK. Our study brings new insight into the mechanisms underlying radiation‐induced apoptosis of osteosarcoma, and may lead to development of new therapeutic strategies against osteosarcoma. J. Cell. Biochem. © 2005 Wiley‐Liss, Inc.