Genetic characterization of fas-associated phosphatase-1 as a putative tumor suppressor gene on chromosome 4q21.3 in hepatocellular carcinoma.
OBJECTIVE
Allelic loss at chromosome 4q21-23 occurs frequently in human hepatocellular carcinoma, and the putative tumor suppressor gene (TSG) has not yet been identified. We studied the Fas-associated phosphatase-1 (FAP-1) gene as a potential candidate TSG in this region.


METHODS
The expression level of FAP-1 RNA in hepatocellular carcinomas was evaluated by RNase protection and quantitative PCR. Sodium bisulfite modification and subsequent single-strand conformational polymorphism and sequence analyses were used to assay the methylation of CpGs at FAP-1 promoter. Direct sequencing of the FAP-1 coding region was conducted for detecting the genetic mutations. Two common single nucleotide polymorphisms of FAP-1 were selected for evaluating their association with the hepatocellular carcinoma trait in sporadic and familial hepatocellular carcinomas. Moreover, the functional effect of FAP-1 on cellular proliferation has been evaluated by small interfering RNA approach.


RESULTS
Around 50% of hepatocellular carcinomas showed significantly decreased expression of FAP-1 compared with the corresponding nontumorous liver tissues. In most cases, the RNA level was well correlated with the methylation status of promoter CpGs, suggesting that the promoter methylation may contribute to the down-regulation. Several genetic mutations of FAP-1 have been identified in hepatocellular carcinomas. The G/G genotype of FAP-1 cSNP6304 was significantly associated with the increased risk of multiplex familial hepatocellular carcinomas (odds ratio, 2.44; 95% confidence interval, 1.19-5.01). Finally, knockdown expression of FAP-1 was shown to enhance the cellular proliferation in PLC5 cells.


CONCLUSIONS
FAP-1 could be inactivated during hepatocarcinogenesis, mainly attributed by allelic loss and promoter methylation. The genetic mutations and polymorphisms may also confront with the higher hepatocellular carcinoma risk. These results first suggested FAP-1 as a putative TSG in hepatocarcinogenesis.
Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan.
Shiou-Hwei
SH
Yeh
Dai-Chen
DC
Wu
Ching-Yi
CY
Tsai
Ti-Jung
TJ
Kuo
Wei-Che
WC
Yu
Yuan-Shau
YS
Chang
Chi-Ling
CL
Chen
Ching-Fang
CF
Chang
Ding-Shinn
DS
Chen
Pei-Jer
PJ
Chen
D000483:Alleles; D015152:Blotting, Northern; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D002894:Chromosomes, Human, Pair 4 / Q000235:genetics*; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D004252:DNA Mutational Analysis; D015536:Down-Regulation / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D005787:Gene Frequency; D016147:Genes, Tumor Suppressor; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D018807:Polymorphism, Single-Stranded Conformational; D011401:Promoter Regions, Genetic / Q000235:genetics; D054645:Protein Phosphatase 1; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D017027:Protein Tyrosine Phosphatases / Q000235:genetics* / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism
D012334:RNA, Neoplasm; D054645:Protein Phosphatase 1; C516742:PTPN13 protein, human; D054595:Protein Tyrosine Phosphatase, Non-Receptor Type 13; D017027:Protein Tyrosine Phosphatases