CUGBP2 downregulation by prostaglandin E2 protects colon cancer cells from radiation-induced mitotic catastrophe.
Prostaglandin E(2) (PGE(2)) is a potent inhibitor of ionizing radiation (IR)-induced cell death. Exposure of colon cancer cells to IR leads to increased CUGBP2 expression. Therefore, we tested the hypothesis that PGE(2) radioprotects colon cancer cells by inhibiting CUGBP2 expression. Exposure of HCT-116 cells to gamma-IR (0-12 Gy) resulted in a dose-dependent reduction in cell growth and an increase in the G(2)-M phase of the cell cycle. Western blot analyses demonstrated increased levels of activated caspase 9 and caspase 3. In addition, whereas Bax expression is increased, that of Bcl-2 and Bcl-x(L) was reduced. Further analyses demonstrated increased activation of Chk1 and Chk2 kinases, coupled with higher levels of nuclear cyclin B1 and Cdc2. Pretreatment with PGE(2) suppressed the activation of caspase 3 and caspase 7 and inhibited Bax expression. In addition, PGE(2) treatment restored growth and colony formation to control levels. IR significantly upregulated the expression of CUGBP2 in the cells, which was suppressed when cells were pretreated with PGE(2). Ectopic overexpression of CUGBP2 also induced apoptosis. Furthermore, it reversed the PGE(2)-mediated protection from IR-induced mitotic catastrophe. Furthermore, there was an increase in nuclear localization of cyclin B1 and Cdc2 coupled with increased phosphorylation of p53, Chk1, Chk2, and Cdc25c proteins. Cell cycle analysis also demonstrated increased G(2)-M transition. In contrast, siRNA-mediated suppression of CUGBP2 expression restored normal cell cycle progression and decreased IR-induced apoptosis. Taken together, these data demonstrate that PGE(2) protects colon cancer cells from IR-induced mitotic catastrophe in part through suppression of CUGBP2 expression.
Natarajan
Gopalan
G
Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
Ramalingam
Satish
S
Ramachandran
Ilangovan
I
May
Randal
R
Queimado
Lurdes
L
Houchen
Courtney W
CW
Anant
Shrikant
S
D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D000067878:CELF Proteins; D053179:Caspase 7 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D019926:Cyclin B / Q000378:metabolism; D015232:Dinoprostone / Q000494:pharmacology*; D015536:Down-Regulation; D005720:Gamma Rays; D045325:HCT116 Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D008938:Mitosis / Q000187:drug effects* / Q000528:radiation effects*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism; D020687:cdc25 Phosphatases / Q000378:metabolism
C494811:BCL2L1 protein, human; D000067878:CELF Proteins; C117363:CELF2 protein, human; D019926:Cyclin B; D006657:Histones; D009419:Nerve Tissue Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D011837:Radiation-Protective Agents; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C000605867:CHEK1 protein, human; C578634:CHEK2 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D020687:cdc25 Phosphatases; D053179:Caspase 7; D053453:Caspase 9; D015232:Dinoprostone