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

• Published in: Oncogene Vol. 26; no. 6; pp. 934 - 944
• Main Authors: SENG, T. J, LOW, J. S. W, RHA, S. Y, TAN, J, HSIEH, W.-S, AMBINDER, R. F, LIN, X, CHAN, A. T. C, TAOL, Q, LIL, H, CUI, Y, GOH, H. K, WONG, M. L. Y, SRIVASTAVA, G, SIDRANSKY, D, CALIFANO, J, STEENBERGEN, R. D. M
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing 08-02-2007; Nature Publishing Group
• Subjects: Base Sequence; Biological and medical sciences; Breast cancer; Breast carcinoma; Cancer; Cell Line; Cell Line, Tumor; Cell physiology; Cell Proliferation; Cell transformation and carcinogenesis. Action of oncogenes and antioncogenes; Cervical cancer; Cervical carcinoma; Cervix; Chromosomes, Human, Pair 8 - genetics; Clonal deletion; Colonies; Demographic aspects; Development and progression; Distribution; DNA Methylation; DNMT1 protein; Ectopic expression; Epigenetics; Esophageal cancer; Esophageal carcinoma; Esophageal Neoplasms - genetics; Esophageal Neoplasms - metabolism; Esophagus; Evaluation; Female; Female genital diseases; Fundamental and applied biological sciences. Psychology; Gastroenterology. Liver. Pancreas. Abdomen; Gene deletion; Gene expression; Gene Expression Regulation, Neoplastic; Gene Silencing; Genes; Genetic aspects; Genetic transcription; GTPase-Activating Proteins; Gynecology. Andrology. Obstetrics; Health aspects; Humans; Identification and classification; Liver cancer; Medical sciences; Methylation; Molecular and cellular biology; Molecular biology; Molecular Sequence Data; Nasopharyngeal cancer; Nasopharyngeal carcinoma; Nasopharyngeal Neoplasms - genetics; Nasopharyngeal Neoplasms - metabolism; Nasopharyngeal Neoplasms - pathology; Oncology; Promoter Regions, Genetic - genetics; Properties; Risk factors; Throat cancer; Tumor cell lines; Tumor markers; Tumor suppressor genes; Tumor Suppressor Proteins - genetics; Tumor Suppressor Proteins - metabolism; Tumorigenesis; Tumors; Uterine Cervical Neoplasms - genetics; Uterine Cervical Neoplasms - metabolism; Hong Kong; nasopharyngeal carcinoma; 8p22; Sporadic; Esophageal disease; cervical carcinoma; Esophagus carcinoma; Malignant tumor; Nasopharynx carcinoma; Carcinogenesis; Female genital diseases; DLC1; Digestive diseases; ENT disease; Pharynx disease; Cervix carcinoma; Methylation; esophageal carcinoma; Uterine cervix diseases; Tumor cell; Tumor suppressor gene
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/sj.onc.1209839

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.