title: The major 8p22 tumor suppressor DLC1 is frequently silenced by methylation in both endemic and sporadic nasopharyngeal, esophageal, and cervical carcinomas, and inhibits tumor cell colony formation.
abstract: Identification of tumor suppressor genes (TSG) silenced by methylation uncovers mechanisms of tumorigenesis and identifies new epigenetic tumor markers for early cancer detection. Both nasopharyngeal carcinoma (NPC) and esophageal carcinoma are major tumors in Southern China and Southeast Asia. Through expression subtraction of NPC, we identified Deleted in Liver Cancer 1 (DLC1)/ARHGAP7 (NM_006094)--an 8p22 TSG as a major downregulated gene. Although expressed in all normal tissues, DLC1 was silenced or downregulated in 11/12 (91%) NPC, 6/15 (40%) esophageal, 5/8 (63%) cervical and 3/9 (33%) breast carcinoma cell lines. No genetic deletion of DLC1 was detected in NPC although a hemizygous deletion at 8p22-11 was found by 1-Mb array-CGH in some cell lines. We then located the functional DLC1 promoter by 5'-RACE and promoter activity assays. This promoter was frequently methylated in all downregulated cell lines and in a large collection of primary tumors including 89% (64/72) NPC (endemic and sporadic types), 51% (48/94) esophageal, 87% (7/8) cervical and 36% (5/14) breast carcinomas, but seldom in paired surgical marginal tissues and not in any normal epithelial tissue. The transcriptional silencing of DLC1 could be reversed by 5-aza-2'-deoxycytidine or genetic double knock-out of DNMT1 and DNMT3B. Furthermore, ectopic expression of DLC1 in NPC and esophageal carcinoma cells strongly inhibited their colony formation. We thus found frequent epigenetic silencing of DLC1 in NPC, esophageal and cervical carcinomas, and a high correlation of methylation with its downregulation, suggesting a predominant role of epigenetic inactivation. DLC1 appears to be a major TSG implicated in the pathogenesis of these tumors, and should be further tested as a molecular biomarker in patients with these cancers.
authors.affiliation: Johns Hopkins Singapore, Biopolis, Singapore.
authors.forename: T J
authors.initials: TJ
authors.lastname: Seng
authors.forename: J S W
authors.initials: JS
authors.lastname: Low
authors.forename: H
authors.initials: H
authors.lastname: Li
authors.forename: Y
authors.initials: Y
authors.lastname: Cui
authors.forename: H K
authors.initials: HK
authors.lastname: Goh
authors.forename: M L Y
authors.initials: ML
authors.lastname: Wong
authors.forename: G
authors.initials: G
authors.lastname: Srivastava
authors.forename: D
authors.initials: D
authors.lastname: Sidransky
authors.forename: J
authors.initials: J
authors.lastname: Califano
authors.forename: R D M
authors.initials: RD
authors.lastname: Steenbergen
authors.forename: S Y
authors.initials: SY
authors.lastname: Rha
authors.forename: J
authors.initials: J
authors.lastname: Tan
authors.forename: W-S
authors.initials: WS
authors.lastname: Hsieh
authors.forename: R F
authors.initials: RF
authors.lastname: Ambinder
authors.forename: X
authors.initials: X
authors.lastname: Lin
authors.forename: A T C
authors.initials: AT
authors.lastname: Chan
authors.forename: Q
authors.initials: Q
authors.lastname: Tao
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002898:Chromosomes, Human, Pair 8 / Q000235:genetics; D019175:DNA Methylation; D004938:Esophageal Neoplasms / Q000235:genetics* / Q000378:metabolism; D005260:Female; D020690:GTPase-Activating Proteins; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008969:Molecular Sequence Data; D009303:Nasopharyngeal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism; D002583:Uterine Cervical Neoplasms / Q000235:genetics* / Q000378:metabolism
chemical_list: C112352:DLC1 protein, human; D020690:GTPase-Activating Proteins; D025521:Tumor Suppressor Proteins