Inhibition of phosphorylation of a forkhead transcription factor sensitizes human ovarian cancer cells to cisplatin.
The Forkhead family transcription factor FKHRL1 is an inducer of apoptosis in its unphosphorylated form and was recently reported to be a substrate of Akt kinase. We studied the roles of FKHRL1 in both cisplatin-resistant Caov-3 (a papillary adenocarcinoma cell line) and cisplatin-sensitive A2780 human ovarian cancer cell lines. Treatment of Caov-3 cells but not A2780 cells with cisplatin transiently stimulated the phosphorylation of FKHRL1. Transfection experiments revealed that a kinase inactive-mutant of Akt or a triple mutant (TM) of FKHRL1, in which all three of the putative Akt phosphorylation sites were converted to alanine, was unable to phosphorylate the FKHRL1 protein in cells treated with cisplatin. Because the phosphorylated form of FKHRL1 is known to be localized in the cytoplasm, we examined whether cisplatin-induced phosphorylation of FKHRL1 might have an effect on the subcellular distribution of FKHRL1. Cisplatin induced the localization of FKHRL1 in the cytoplasm in Caov-3 cells but not in A2790 cells. Moreover, cisplatin induced the association of 14-3-3 protein with phosphorylated-FKHRL1 in Caov-3 cells but not in A2790 cells. Because the unphosphorylated form of FKHRL1 binds the Fas ligand promoter, thereby inducing apoptosis, we further examined the effect of the phosphorylation status of FKHRL1 on the activity of the Fas ligand promoter in the presence of cisplatin. Transfection with the kinase-inactive mutant of Akt or TM of FKHRL1 induced the activity of the Fas ligand promoter in Caov-3 cells. Moreover, exogenous expression of TM of FKHRL1 in Caov-3 cells decreased the cell viability after treatment with cisplatin. Our findings suggest that cisplatin causes the phosphorylation of FKHRL1 via a phosphatidylinositol 3-kinase/Akt cascade, and inhibition of this cascade sensitizes ovarian cancer cells to cisplatin.
Arimoto-Ishida
Emi
E
Department of Obstetrics and Gynecology, Osaka University Medical School, Suita, Japan.
Ohmichi
Masahide
M
Mabuchi
Seiji
S
Takahashi
Toshifumi
T
Ohshima
Chika
C
Hayakawa
Jun
J
Kimura
Akiko
A
Takahashi
Kazuhiro
K
Nishio
Yukihiro
Y
Sakata
Masahiro
M
Kurachi
Hirohisa
H
Tasaka
Keiichi
K
Murata
Yuji
Y
D048948:14-3-3 Proteins; D000231:Adenocarcinoma, Papillary / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D053222:Fas Ligand Protein; D005260:Female; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics; D009154:Mutation; D010051:Ovarian Neoplasms / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D014018:Tissue Distribution / Q000187:drug effects; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D048948:14-3-3 Proteins; D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; C505661:FASLG protein, human; C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; D053222:Fas Ligand Protein; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D008562:Membrane Glycoproteins; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D014446:Tyrosine 3-Monooxygenase; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D002945:Cisplatin