Increased NBS1 expression is a marker of aggressive head and neck cancer and overexpression of NBS1 contributes to transformation.
OBJECTIVE
Head and neck squamous cell carcinoma (HNSCC) represents the sixth most frequent type of cancer worldwide. However, the molecular genetic alterations underlying its malignant behavior and progression are little known. We showed previously that c-MYC directly activates the expression of the DNA double-strand break repair gene NBS1, and NBS1 overexpression contributes to transformation. Here, we investigate the role of NBS1 overexpression in HNSCC.


METHODS
Immunohistochemistry analysis of NBS1 expression was done in 81 locally advanced HNSCC patients. Real-time PCR and Western blot analysis were used to confirm immunohistochemistry results. Human hypopharyngeal cancer cell lines (FADU) with overexpressing NBS1 (FADUNBS) or inducible short interference RNA to repress endogenous NBS1 (FADUNBSi) were generated by stable transfection. Soft agar clonogenicity assay was used to determine the transformation activity. Western blot analysis and phosphatidylinositol 3-kinase (PI3K) assay were done to evaluate the signaling pathways that were involved.


RESULTS
NBS1 overexpression was identified in 45% of advanced HNSCC patients. It was an independent marker of poor prognosis. NBS1 expression levels correlated with the transformation activity of FADU clones and also correlated with the phosphorylation levels of Akt and its downstream target mammalian target of rapamycin (mTOR). PI3K activity was increased in NBS1-overexpressing FADU clones. NBS1 overexpression also correlated with increased Akt phosphorylation levels in tumor samples.


CONCLUSIONS
Increased NBS1 expression is a significant prognostic marker of advanced HNSCC, and the underlying mechanism may involve the activation of the PI3K/Akt pathway.
Yang
Muh-Hwa
MH
Institute of Clinical Medicine, National Yang-Ming University, No. 155 Li-Nong Street Sec. 2, Peitou, Taipei 112, Taiwan.
Chiang
Wei-Chung
WC
Chou
Teh-Ying
TY
Chang
Shyue-Yih
SY
Chen
Po-Min
PM
Teng
Shu-Chun
SC
Wu
Kou-Juey
KJ
D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D058534:Class I Phosphatidylinositol 3-Kinases; D005260:Female; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D014408:Biomarkers, Tumor; D018797:Cell Cycle Proteins; C112156:NBN protein, human; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D019869:Phosphatidylinositol 3-Kinases; D058534:Class I Phosphatidylinositol 3-Kinases; C484760:PIK3CA protein, human; D051057:Proto-Oncogene Proteins c-akt