Modulation of ionizing radiation-induced G2 arrest by cyclooxygenase-2 and its inhibitor celecoxib.
OBJECTIVE
Prolongation or attenuation of ionizing radiation (IR)-induced G(2)-M arrest in cyclooxygenase-2 (COX-2) overexpressing or celecoxib-treated cells, respectively, has been previously observed. To better understand the molecular mechanisms involved, we investigated the molecules involved in G(2) checkpoint pathways after treatment with IR +/- celecoxib.


METHODS
Various molecules in the G(2) checkpoint pathways were investigated in HCT-116-Mock and -COX-2 cells. Western blot, reverse transcriptase polymerase chain reaction, confocal microscopy, and fluorescence activated cell sorter (FACS) analyses were performed to investigate whether expression and activity of the ataxia telangiectasia and rad3-related (ATR) could be modulated by COX-2 and its selective inhibitors.


RESULTS
COX-2 overexpression increased expression and activity of ATR after IR exposure. Celecoxib downregulated ATR in all tested cell lines independent of COX-2 expression, but downregulation was greater in COX-2 overexpressing cells after cells were irradiated. Celecoxib pretreatment before radiation caused strongly inhibited G(2) arrest.


CONCLUSIONS
COX-2 appears to prolong IR-induced G(2) arrest by upregulating ATR. Celecoxib downregulated ATR preferentially in irradiated COX-2 overexpressing cells. Celecoxib may radiosensitize cancer cells by inhibiting G(2) arrest through ATR downregulation.
Jun
Hyun Jung
HJ
Research Institute and Hospital, National Cancer Center, Goyang, Gyeonggi, Republic of Korea.
Kim
Young Mee
YM
Park
Soo Yeon
SY
Park
Ji Sun
JS
Lee
Eun Jung
EJ
Choi
Shin Ae
SA
Pyo
Hongryull
H
D064007:Ataxia Telangiectasia Mutated Proteins; D000068579:Celecoxib; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000378:metabolism / Q000502:physiology*; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology*; D004260:DNA Repair / Q000187:drug effects; D015536:Down-Regulation; D005434:Flow Cytometry / Q000379:methods; D016195:G2 Phase / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D045325:HCT116 Cells; D006801:Humans; D008938:Mitosis / Q000528:radiation effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology; D013449:Sulfonamides / Q000494:pharmacology*; D013997:Time Factors; D015854:Up-Regulation
D018797:Cell Cycle Proteins; D052246:Cyclooxygenase 2 Inhibitors; D011720:Pyrazoles; D012333:RNA, Messenger; D013449:Sulfonamides; D051546:Cyclooxygenase 2; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D000068579:Celecoxib