Genetic and epigenetic alterations of DLC-1 gene in hepatocellular carcinoma.
Hepatocellular carcinoma (HCC) is one of the most common fatal cancers in the world. However, the underlying molecular mechanisms contributing to hepatocarcinogenesis are still unclear. A putative tumor suppressor gene, namely DLC-1 (frequently deleted in liver cancer) was identified and mapped at chromosome 8p21.3-22, a recurrently deleted region in human cancers. The gene exerts inhibitory effects on the cell proliferation of HCC cells. In this study, we investigated the biological function, and genetic and epigenetic status of this gene in human HCC. With in vitro GTPase activating proteins activity assay, we established that DLC-1 protein was a GTPase-activating protein specific for RhoA and Cdc42. Deletion of the DLC-1 gene was frequent in human HCC, as revealed by loss of heterozygosity analysis performed on 100 human HCC cases with markers mapped at the DLC-1 locus, and allelic losses ranging from 44% to 50% of the informative cases. However, somatic mutations of the DLC-1 gene were rare. Moreover, with real-time quantitative PCR, we found that DLC-1 mRNA was significantly underexpressed in HCCs when compared with the corresponding nontumorous livers (P < 0.0001). In addition, the CpG island 5' to the DLC-1 gene was methylated in 3 of 7 HCC cell lines and in 6 (24%) of 25 primary HCCs. These data suggest that transcriptional silencing by hypermethylation may contribute to the inactivation of the DLC-1 gene. Taken together, the results of our study suggest that both genetic and epigenetic alterations play an important role in inactivation of the DLC-1 gene in hepatocarcinogenesis.
Wong
Chun-Ming
CM
Department of Pathology, the University of Hong Kong, Queen Mary Hospital, Pokfulam, Hong Kong, People's Republic of China.
Lee
Joyce Man-Fong
JM
Ching
Yick-Pang
YP
Jin
Dong-Yan
DY
Ng
Irene Oi-lin
IO
D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D000077209:Decitabine; D020690:GTPase-Activating Proteins / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics* / Q000378:metabolism; D019656:Loss of Heterozygosity; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
C112352:DLC1 protein, human; D020690:GTPase-Activating Proteins; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; C085379:rho GTPase-activating protein; D000077209:Decitabine; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein; D001374:Azacitidine