Downregulation of FOXO3a promotes tumor metastasis and is associated with metastasis-free survival of patients with clear cell renal cell carcinoma.
OBJECTIVE
To explore the mechanisms underlying clear-cell renal cell carcinoma (ccRCC) metastasis using transcriptional profiling and bioinformatics analysis of ccRCC samples, and to elucidate the role of FOXO3a in ccRCC metastasis.


METHODS
Gene expression profiling was performed using four primary metastatic and five primary nonmetastatic ccRCC samples. The mRNA and protein levels of FOXO3a in ccRCC samples were investigated by real-time reverse transcription PCR and immunohistochemistry, respectively. The association between metastasis-free survival of patients with ccRCC and FOXO3a mRNA levels was analyzed. Biologic functions of FOXO3a in renal cancer cell lines were investigated. The influence of FOXO3a on tumor metastasis was also studied in vivo orthotopic xenograft tumor model. Finally, the mechanism by which FOXO3a attenuation could increase invasion and migration of tumor cells was explored.


RESULTS
Bioinformatics analysis of the profiling data identified FOXO3a as a key factor in ccRCC metastasis. FOXO3a expression was decreased in primary metastatic ccRCC samples. Patients with low FOXO3a mRNA levels had poor metastasis-free survival (P = 0.003). Knocking down FOXO3a induced tumor cell invasion and migration in the nonmetastatic ccRCC cells. Induced FOXO3a overexpression in SN12-PM6 cells could inhibit tumor metastasis in vivo. Downregulation of FOXO3a increased SNAIL1 expression, thereby activating the epithelial-mesenchymal transition (EMT) of RCC cell lines.


CONCLUSIONS
The loss of FOXO3a induced EMT of tumor cells by upregulating SNAIL1, which promoted tumor cells metastasis in vitro and in vivo. Thus, FOXO3a could be considered as an independent prognostic factor in ccRCC metastasis and could be a marker of occult metastases.
Authors' Affiliations: State Key Laboratory of Kidney Diseases, Department of Urology, Military Postgraduate Medical College, Chinese People's Liberation Army General Hospital, Beijing; and Department of Urology, Zhongnan Hospital, Wuhan University, Wuhan, People's Republic of China.
Dong
D
Ni
Xin
X
Ma
Hong-Zhao
HZ
Li
Yu
Y
Gao
Xin-Tao
XT
Li
Yu
Y
Zhang
Qing
Q
Ai
Peng
P
Zhang
Er-Lin
EL
Song
Qing-Bo
QB
Huang
Yang
Y
Fan
Xu
X
Zhang
D000368:Aged; D002292:Carcinoma, Renal Cell / Q000235:genetics* / Q000473:pathology; D002460:Cell Line; D018572:Disease-Free Survival; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics; D005260:Female; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D053208:Kaplan-Meier Estimate; D007680:Kidney Neoplasms / Q000235:genetics* / Q000473:pathology; D008297:Male; D046228:Microarray Analysis; D008875:Middle Aged; D009362:Neoplasm Metastasis / Q000235:genetics; D011379:Prognosis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics
C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D012333:RNA, Messenger