title: Aberrant promoter hypermethylation and silencing of the critical 3p21 tumour suppressor gene, RASSF1A, in Chinese oesophageal squamous cell carcinoma.
abstract: 3p21 is an important locus harbouring critical tumour suppressor genes (TSG), which are implicated in the pathogenesis of multiple tumours, including oesophageal carcinoma. RASSF1A is a 3p21.3 candidate TSG frequently inactivated by promoter methylation in multiple tumours. We investigated RASSF1A promoter methylation and gene expression in Chinese oesophageal squamous cell carcinoma (ESCC) to compare it to data from Japanese patients. Methylation-specific PCR (MSP) showed that RASSF1A was partially methylated in 3/7 (43%) cell lines; 22/64 (34%) primary tumours and 3/64 (5%) corresponding non-tumour samples; and was not methylated in 2 immortalized normal oesophageal epithelial cell lines and 6 normal oesophageal epithelium samples. Bisulfite genome sequencing confirmed the MSP results. Promoter hypermethylation correlated well with RASSF1A mRNA down-regulation. Treatment of cell lines with 5-aza-2'-deoxycytidine activated RASSF1A mRNA expression along with promoter demethylation. RASSF1A hypermethylation in the Chinese cohort was much lower than in a published report of Japanese ESCC patients (52%) and cell lines (74%). Our own analysis of Japanese ESCC cell lines for direct comparison also detected a high frequency of RASSF1A hypermethylation (8/10; 80%) and high levels of hypermethylation at each CpG site. No significant association between RASSF1A hypermethylation and histological differentiation (p=0.953), tumour staging (p=0.117), or survival (p=0.7571) was found in Chinese ESCC, unlike the results of Japanese patients. The incidence of oesophageal cancer shows marked variation by geographic area and ethnic group; it is almost three times higher in China than in Japan, indicating possible different pathogenetic mechanisms. Our results show that RASSF1A hypermethylation in ESCC has epidemiological/ethnic differences, and suggest that Chinese ESCC may result from different pathogenetic mechanisms.
authors.affiliation: Department of Pathology, The University of Hong Kong, Hong Kong, PR China.
authors.forename: Michelle Ly
authors.initials: ML
authors.lastname: Wong
authors.forename: Qian
authors.initials: Q
authors.lastname: Tao
authors.forename: Li
authors.initials: L
authors.lastname: Fu
authors.forename: Kai-Yau
authors.initials: KY
authors.lastname: Wong
authors.forename: Guo-Hua
authors.initials: GH
authors.lastname: Qiu
authors.forename: Fian B F
authors.initials: FB
authors.lastname: Law
authors.forename: Pui-Chi
authors.initials: PC
authors.lastname: Tin
authors.forename: Wai-Ling
authors.initials: WL
authors.lastname: Cheung
authors.forename: Ping-Yin
authors.initials: PY
authors.lastname: Lee
authors.forename: Johnny Cheuk-On
authors.initials: JC
authors.lastname: Tang
authors.forename: George S W
authors.initials: GS
authors.lastname: Tsao
authors.forename: King-Yin
authors.initials: KY
authors.lastname: Lam
authors.forename: Simon
authors.initials: S
authors.lastname: Law
authors.forename: John
authors.initials: J
authors.lastname: Wong
authors.forename: Gopesh
authors.initials: G
authors.lastname: Srivastava
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000453:epidemiology / Q000235:genetics / Q000473:pathology*; D045744:Cell Line, Tumor; D002681:China / Q000453:epidemiology; D002893:Chromosomes, Human, Pair 3 / Q000235:genetics; D019175:DNA Methylation; D004938:Esophageal Neoplasms / Q000453:epidemiology / Q000235:genetics / Q000473:pathology*; D016147:Genes, Tumor Suppressor; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D009367:Neoplasm Staging; D011401:Promoter Regions, Genetic / Q000235:genetics*; D016019:Survival Analysis; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: C411762:RASSF1 protein, human; D025521:Tumor Suppressor Proteins