Overexpression of FOXG1 contributes to TGF-beta resistance through inhibition of p21WAF1/CIP1 expression in ovarian cancer.
BACKGROUND
Loss of growth inhibitory response to transforming growth factor-beta (TGF-beta) is a common feature of epithelial cancers. Recent studies have reported that genetic lesions and overexpression of oncoproteins in TGF-beta/Smads signalling cascade contribute to the TGF-beta resistance. Here, we showed that the overexpressed FOXG1 was involved in attenuating the anti-proliferative control of TGF-beta/Smads signalling in ovarian cancer.


METHODS
FOXG1 and p21(WAF1/CIP1) expressions were evaluated by real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR), western blot and immunohistochemical analyses. The effect of FOXG1 on p21(WAF1/CIP1) transcriptional activity was examined by luciferase reporter assays. Cell lines stably expressing or short hairpin RNA interference-mediated knockdown FOXG1 were established for studying the gain-or-loss functional effects of FOXG1. XTT cell proliferation assay was used to measure cell growth of ovarian cancer cells.


RESULTS
Quantitative RT-PCR and western blot analyses showed that FOXG1 was upregulated and inversely associated with the expression levels of p21(WAF1/CIP1) in ovarian cancer. The overexpression of FOXG1 was significantly correlated with high-grade ovarian cancer (P=0.025). Immunohistochemical analysis on ovarian cancer tissue array was further evidenced that FOXG1 was highly expressed and significantly correlated with high-grade ovarian cancer (P=0.048). Functionally, enforced expression of FOXG1 selectively blocked the TGF-beta-induced p21(WAF1/CIP1) expressions and increased cell proliferation in ovarian cancer cells. Conversely, FOXG1 knockdown resulted in a 20-26% decrease in cell proliferation together with 16-33% increase in p21(WAF1/CIP1) expression. Notably, FOXG1 was able to inhibit the p21(WAF1/CIP1) promoter activity in a p53-independent manner by transient reporter assays.


CONCLUSIONS
Our results suggest that FOXG1 acts as an oncoprotein inhibiting TGF-beta-mediated anti-proliferative responses in ovarian cancer cells through suppressing p21(WAF1/CIP1) transcription.
Chan
D W
DW
Department of Obstetrics and Gynaecology, LKS Faculty of Medicine, University of Hong Kong, Hong Kong SAR, PR China.
Liu
V W S
VW
To
R M Y
RM
Chiu
P M
PM
Lee
W Y W
WY
Yao
K M
KM
Cheung
A N Y
AN
Ngan
H Y S
HY
D021581:Active Transport, Cell Nucleus; D000328:Adult; D000368:Aged; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000037:antagonists & inhibitors* / Q000235:genetics; D019008:Drug Resistance, Neoplasm; D005260:Female; D051858:Forkhead Transcription Factors / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000473:pathology; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C090173:FOXG1 protein, human; D051858:Forkhead Transcription Factors; D009419:Nerve Tissue Proteins; D016212:Transforming Growth Factor beta