Response of cyclin B1 to ionizing radiation: regulation by NF-kappaB and mitochondrial antioxidant enzyme MnSOD.
BACKGROUND
To understand the molecular response of tumor cells to therapeutic ionizing radiation (IR), we previously reported that human breast cancer cells derived following chronic exposure to fractionated ionizing radiation (MCF+FIR) showed a transient radioresistance. MCF+FIR cells also demonstrated increased activity of NF-kappaB, increased expression of the mitochondrial antioxidant enzyme (MnSOD), and increased expression of a cell cycle regulatory protein (Cyclin B1). The present studies were designed to determine the relationship of NF-kappaB, MnSOD and Cyclin B1 expression in cellular adaptive responses to ionizing radiation.


METHODS
The first intron of the cyclin B1 gene with a putative NF-kappaB element was cloned into the pGL3 luciferase reporter (pGL3CB1EI1). PGL3CB1EI1 and control NF-kappaB luciferase activities were determined in MCF-7 and MCF+FIR cells treated with a single dose of radiation, over expression of the dominant negative mutant IkB (mIkB) or over expression of the SOD2 gene.


RESULTS
MCF+FIR cells derived from fractionated IR demonstrated increased transactivation of the pGL3CB1EI1 and NF-kappaB controlled reporter activities, relative to the parental cell line. Transfection of dominant negative mutant IkB that inhibits NF-kappaB nuclear translocation, inhibited pGL3CB1EI1 and NF-kappaB activity, indicating the NF-kappaB dependence of pGL3CB1EI1 mediated transcription. In addition, over expression of the human SOD2 gene (MnSOD) inhibited NF-kappaB and pGL3CB1EI1 activity, indicating that superoxide or some species derived from superoxide may have participated in the up-regulation of reporter activity in response to chronic exposure to fractionated ionizing radiation. These results provide evidence suggesting that a signaling pathway involving NF-kappaB and Cyclin B1 may contribute to adaptive radioresistance induced by chronic exposure to fractionated IR and support the conclusion that MnSOD appears to be a negative regulator of this pathway.
Ozeki
Munetaka
M
Radiation Biology, Division of Radiation Oncology, Beckman Research Institute, City of Hope National Medical Center, Duarte, California 91010, USA.
Tamae
Daniel
D
Hou
De-Xing
DX
Wang
Tieli
T
Lebon
Thomas
T
Spitz
Douglas R
DR
Li
Jian Jian
JJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics / Q000532:radiotherapy; D045744:Cell Line, Tumor; D019926:Cyclin B / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics* / Q000528:radiation effects*; D056744:Cyclin B1; D004789:Enzyme Activation / Q000528:radiation effects; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology / Q000528:radiation effects*; D006801:Humans; D007438:Introns / Q000235:genetics / Q000528:radiation effects*; D008928:Mitochondria / Q000201:enzymology* / Q000528:radiation effects; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D011836:Radiation Tolerance / Q000235:genetics / Q000502:physiology; D013482:Superoxide Dismutase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation / Q000528:radiation effects; D014162:Transfection
C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; D016328:NF-kappa B; D013482:Superoxide Dismutase