Hypoxia-induced up-regulation of angiogenin, besides VEGF, is related to progression of oral cancer.
OBJECTIVE
Angiogenin (ANG) is a prominent angiogenic factor that has been shown to have a dual effect on tumor progression by inducing both angiogenesis and cancer cell proliferation through stimulating ribosomal RNA transcription in both endothelial cells and cancer cells. In the present study, we investigated the expression profiles of ANG and vascular endothelial growth factor (VEGF) in oral cancer and their correlation with hypoxia and evaluated the possible value of ANG as a therapeutic target for oral cancer.


METHODS
Immunohistochemistry (IHC), ELISA, real-time RT-PCR and Western blotting were used to examine the expression of ANG, VEGF, and hypoxia-inducible factor 1α (HIF-1α) in oral squamous cell carcinoma (OSCC) specimens and human OSCC cell lines. In order to examine the role of ANG, we knocked down ANG expression in HSC-2 cells by means of plasmid-mediated RNA interference.


RESULTS
IHC showed that the expression of ANG was significantly correlated with that of HIF-1α in 50 OSCC specimens (P = 0.031). However, no significant correlation between VEGF and HIF-1α expression was found (P = 0.243). Consistently, ANG secretion increased under hypoxia in all of the 10 OSCC cell lines tested; and a significant increase was observed in 6 of them. In contrast, there was no noticeable increase in VEGF secretion under hypoxia in any of these cell lines. In HSC-2 and SAS OSCC cells, the increase in ANG mRNA expression correlated very well with that of HIF-1α protein expression after hypoxia onset. However, no noticeable increase in VEGF mRNA expression was observed even after 12 h of hypoxia. Down-regulation of ANG expression in HSC-2 cells highly expressing and secreting VEGF inhibited ribosome biogenesis, cell proliferation, tumor angiogenesis, and xenograft growth in athymic mice.


CONCLUSIONS
These results suggest that ANG is up-regulated in the hypoxic environment of oral cancers and that its inhibition can have a therapeutic implication.
Department of Oral and Maxillofacial Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8525, Japan. koujik@md.okayama-u.ac.jp
Koji
K
Kishimoto
Shoko
S
Yoshida
Soichiro
S
Ibaragi
Norie
N
Yoshioka
Tatsuo
T
Okui
Guo-fu
GF
Hu
Akira
A
Sasaki
D000818:Animals; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000378:metabolism*; D015687:Cell Hypoxia; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009062:Mouth Neoplasms / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D012259:Ribonuclease, Pancreatic / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D042461:Vascular Endothelial Growth Factor A; C046366:angiogenin; D012259:Ribonuclease, Pancreatic