Frequent promoter hypermethylation of RASSF1A and p16INK4a and infrequent allelic loss other than 9p21 in betel-associated oral carcinoma in a Vietnamese non-smoking/non-drinking female population.
BACKGROUND
Betel-chewing, a risk factor for oral carcinoma, is a common habit of elderly Vietnamese females, but concomitant habits of tobacco and alcohol are uncommon.


METHODS
In the present study, 36 paraffin-embedded betel-associated oral carcinoma samples including 27 squamous cell carcinoma (SCC) and nine verrucous carcinomas (VC) were analyzed for the hypermethylation of tumor suppressor genes (TSGs) and loss of heterozygosity (LOH) of important TSG loci. Methylation-specific polymerase chain reaction (MSP) was used to identify promoter hypermethylation of p16INK4a and RASSF1A. For LOH analysis, 39 microsatellite markers at 12 chromosomal arms were examined by p olymerase chain reaction (PCR)-based microsatellite assay.


RESULTS
Hypermethylation of p16IKN4a was detected in 63% of SCC and 67% of VC. In addition, LOH at 9p21 (locus for p16INK4a) was 58% for SCC and 22% for VC, and hypermethylation of RASSF1A was 93% for SCC and 100% for VC. LOH at 3p21.3-3p22.1 (where RASSF1A is located) was detected in only 12% of SCC and 0% of VC. LOH of other chromosomal arms were infrequent.


CONCLUSIONS
As LOH for chromosomes other than 9p was uncommon, epigenetic silencing of RASSF1A and p16INK4a gene expression by promoter hypermethylation may play a critical role in betel-associated oral carcinogenesis.
Tran
Tu Ngoc
TN
Molecular Pathology, Department of Oral Restitution, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
Liu
Yenchun
Y
Takagi
Minoru
M
Yamaguchi
Akira
A
Fujii
Hiroaki
H
D000368:Aged; D000369:Aged, 80 and over; D001114:Areca / Q000009:adverse effects*; D002277:Carcinoma / Q000235:genetics*; D002294:Carcinoma, Squamous Cell / Q000235:genetics; D018289:Carcinoma, Verrucous / Q000235:genetics; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics*; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D020868:Gene Silencing; D006801:Humans; D019656:Loss of Heterozygosity; D018895:Microsatellite Repeats / Q000235:genetics; D009062:Mouth Neoplasms / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D013785:Thailand; D025521:Tumor Suppressor Proteins / Q000235:genetics*
D019941:Cyclin-Dependent Kinase Inhibitor p16; D004273:DNA, Neoplasm; C411762:RASSF1 protein, human; D025521:Tumor Suppressor Proteins