Constitutively nuclear FOXO3a localization predicts poor survival and promotes Akt phosphorylation in breast cancer.
BACKGROUND
The PI3K-Akt signal pathway plays a key role in tumorigenesis and the development of drug-resistance. Cytotoxic chemotherapy resistance is linked to limited therapeutic options and poor prognosis.


RESULTS
Examination of FOXO3a and phosphorylated-Akt (P-Akt) expression in breast cancer tissue microarrays showed nuclear FOXO3a was associated with lymph node positivity (p = 0.052), poor prognosis (p = 0.014), and P-Akt expression in invasive ductal carcinoma. Using tamoxifen and doxorubicin-sensitive and -resistant breast cancer cell lines as models, we found that doxorubicin- but not tamoxifen-resistance is associated with nuclear accumulation of FOXO3a, consistent with the finding that sustained nuclear FOXO3a is associated with poor prognosis. We also established that doxorubicin treatment induces proliferation arrest and FOXO3a nuclear relocation in sensitive breast cancer cells. Induction of FOXO3a activity in doxorubicin-sensitive MCF-7 cells was sufficient to promote Akt phosphorylation and arrest cell proliferation. Conversely, knockdown of endogenous FOXO3a expression reduced PI3K/Akt activity. Using MDA-MB-231 cells, in which FOXO3a activity can be induced by 4-hydroxytamoxifen, we showed that FOXO3a induction up-regulates PI3K-Akt activity and enhanced doxorubicin resistance. However FOXO3a induction has little effect on cell proliferation, indicating that FOXO3a or its downstream activity is deregulated in the cytotoxic drug resistant breast cancer cells. Thus, our results suggest that sustained FOXO3a activation can enhance hyperactivation of the PI3K/Akt pathway.


CONCLUSIONS
Together these data suggest that lymph node metastasis and poor survival in invasive ductal breast carcinoma are linked to an uncoupling of the Akt-FOXO3a signaling axis. In these breast cancers activated Akt fails to inactivate and re-localize FOXO3a to the cytoplasm, and nuclear-targeted FOXO3a does not induce cell death or cell cycle arrest. As such, sustained nuclear FOXO3a expression in breast cancer may culminate in cancer progression and the development of an aggressive phenotype similar to that observed in cytotoxic chemotherapy resistant breast cancer cell models.
Chen
Jie
J
Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
Gomes
Ana R
AR
Monteiro
Lara J
LJ
Wong
San Yu
SY
Wu
Lai Han
LH
Ng
Ting-Ting
TT
Karadedou
Christina T
CT
Millour
Julie
J
Ip
Ying-Chi
YC
Cheung
Yuen Nei
YN
Sunters
Andrew
A
Chan
Kelvin Y K
KY
Lam
Eric W-F
EW
Khoo
Ui-Soon
US
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D044584:Carcinoma, Ductal / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008207:Lymphatic Metastasis; D009361:Neoplasm Invasiveness; D010766:Phosphorylation / Q000187:drug effects; D011379:Prognosis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016019:Survival Analysis; D013629:Tamoxifen / Q000494:pharmacology
C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D013629:Tamoxifen; D004317:Doxorubicin; D051057:Proto-Oncogene Proteins c-akt
Cell. 2004 Apr 16;117(2):225-37
15084260
Ann Oncol. 2003 Jul;14(7):1051-6
12853346
J Steroid Biochem Mol Biol. 2001 Jan-Mar;76(1-5):71-84
11384865
Mol Cell Biol. 2009 Sep;29(18):4906-17
19564415
J Biol Chem. 2003 Dec 12;278(50):49795-805
14527951
Blood. 2009 Mar 5;113(10):2302-11
19064725
Vitam Horm. 2005;71:201-37
16112269
Mol Cancer Ther. 2008 Jul;7(7):2022-32
18645012
Mol Cell Biol. 2008 Oct;28(19):5886-98
18644865
Nat Rev Cancer. 2002 Feb;2(2):101-12
12635173
Mol Cancer Ther. 2008 Mar;7(3):670-8
18347152
Acta Med Okayama. 2004 Aug;58(4):197-205
15551757
Mol Cancer Ther. 2005 Jan;4(1):33-41
15657351
Cancer Cells. 1989 Nov;1(3):81-6
2701652
Mol Cancer Ther. 2009 Mar;8(3):582-91
19276163
Cell. 1999 Mar 19;96(6):857-68
10102273
Endocr Relat Cancer. 2005 Sep;12(3):599-614
16172194
Pharmacol Rev. 2001 Mar;53(1):25-71
11171938
Mol Cancer Ther. 2007 Dec;6(12 Pt 1):3169-79
18089711
Curr Med Res Opin. 2001;17(4):282-9
11922402
Anticancer Drugs. 1997 Nov;8(10):911-30
9436634
Clin Chem. 2005 Mar;51(3):494-503
15637130
Clin Cancer Res. 2003 Aug 1;9(8):2933-9
12912939
Mol Cancer Ther. 2002 Jul;1(9):707-17
12479367
ACS Chem Biol. 2006 Dec 15;1(12):780-90
17240976
Nat Rev Cancer. 2007 Nov;7(11):847-59
17943136
Cancer Treat Rev. 2005 Feb;31(1):1-17
15707700
Clin Breast Cancer. 2008 Oct;8(5):411-7
18952554
Int J Clin Oncol. 2008 Oct;13(5):380-3
18946747
J Biol Chem. 2001 Mar 30;276(13):9817-24
11139588
Cancer Res. 2006 Jan 1;66(1):212-20
16397234
Clin Cancer Res. 2009 Feb 1;15(3):752-7
19188143
Mol Cancer Ther. 2008 Oct;7(10):3237-46
18852127