Putative tumour-suppressor gene DAB2 is frequently down regulated by promoter hypermethylation in nasopharyngeal carcinoma.
BACKGROUND
Human disabled-2 (DAB2), is a multi-function signalling molecule that it is frequently down-regulated in human cancers. We aimed to investigate the possible tumour suppressor effect of DAB2 in nasopharyngeal carcinoma (NPC).


METHODS
We studied the expression of DAB2 in NPC cell lines, xenografts and primary tumour samples. The status of promoter methylation was assessed by methylation specific PCR and bisulfite sequencing. The functional role of DAB2 in NPC was investigated by re-introducing DAB2 expression into NPC cell line C666-1.


RESULTS
Decrease or absent of DAB2 transcript was observed in NPC cell lines and xenografts. Loss of DAB2 protein expression was seen in 72% (33/46) of primary NPC as demonstrated by immunohistochemistry. Aberrant DAB2 promoter methylation was detected in 65.2% (30/46) of primary NPC samples by methylation specific PCR. Treatment of the DAB2 negative NPC cell line C666-1 with 5-aza-2'-deoxycytidine resulted in restoration of DAB2 expression in a dose-dependent manner. Overexpression of DAB2 in NPC cell line C666-1 resulted in reduced growth rate and 35% reduction in anchorage-dependent colony formation, and inhibition of serum-induced c-Fos expression compared to vector-transfected controls. Over expression of DAB2 resulted in alterations of multiple pathways as demonstrated by expression profiling and functional network analysis, which confirmed the role of DAB2 as an adaptor molecule involved in multiple receptor-mediated signalling pathways.


CONCLUSIONS
We report the frequent down regulation of DAB2 in NPC and the promoter hypermethylation contributes to the loss of expression of DAB2. This is the first study demonstrating frequent DAB2 promoter hypermethylation in human cancer. Our functional studies support the putative tumour suppressor effect of DAB2 in NPC cells.
Tong
Joanna H
JH
Department of Anatomical and Cellular Pathology, The Chinese University of Hong Kong, Hong Kong, PR China.
Ng
David C
DC
Chau
Shuk L
SL
So
Ken K
KK
Leung
Patrick P
PP
Lee
Tin L
TL
Lung
Raymond W
RW
Chan
Michael W
MW
Chan
Anthony W
AW
Lo
Kwok W
KW
To
Ka F
KF
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics* / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002277:Carcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019175:DNA Methylation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000077209:Decitabine; D015536:Down-Regulation; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D053263:Gene Regulatory Networks; D016147:Genes, Tumor Suppressor; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009368:Neoplasm Transplantation; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins; D055815:Young Adult
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C102885:DAB2 protein, human; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; C012589:trichostatin A; D000077209:Decitabine; D015254:DNA Modification Methylases; D001374:Azacitidine