title: Epigenetic silencing of MAL, a putative tumor suppressor gene, can contribute to human epithelium cell carcinoma.
abstract: BACKGROUND
  To identify new and useful candidate biomarkers in head and neck squamous cell carcinoma (HNSCC), we performed a genome-wide survey and found that Myelin and lymphocyte-associated protein (MAL) was a gene that was markedly down-regulated in HNSCC. Hence, we investigated the mechanism of MAL silencing and the effects of MAL on the proliferation, invasion, and apoptotic potential in HNSCC.
  
  
  RESULTS
  MAL was significantly down-regulated in 91.7% of HNSCC specimens at the mRNA level as compared with adjacent normal tissues (P = 0.0004). Moreover, the relative transcript levels of the MAL gene were remarkably decreased by five-fold in nine HNSCC cell lines as compared with normal head and neck epithelium cells. MAL gene expression was restored in 44%, 67%, and 89% in HNSCC cell lines treated with TSA, 5-Aza-dC, and TSA plus 5-Aza-dC, respectively. Furthermore, bisulfate-treated DNA sequencing demonstrated that the two CpG islands (that is, M1 and M2) located in MAL promoter region were completely methylated in the HNSCC cell lines (CpG methylated ratio was more than 90%), and only one CpG island (that is, M1) was partially methylated in HNSCC tissues (CpG methylated ratio between 20% and 90%). A significant reduction in cell proliferation and a change in the cell cycle profile were also observed in MAL transfectants. Matrigel assay demonstrated that the invasiveness of HNSCC cells significantly decreased. A significant increase in the population of apoptotic cells was observed in MAL transfected cells. The exogenous expression of the MAL gene suppressed malignant phenotypes, while the cell death induced by MAL gene transfer was a result of apoptosis as demonstrated by the induction of cleavage of the poly (that is, ADP-ribose) polymerase. Additionally, tumor growth was suppressed in cells expressing MAL as compared with cells not expressing MAL.
  
  
  CONCLUSIONS
  Our data suggest that the epigenetic inactivation of MAL, as a candidate tumor suppressor gene, can contribute to human epithelial cell carcinoma and may be served as a biomarker in HNSCC.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Cao
authors.forename: Zhi-Yuan
authors.initials: ZY
authors.lastname: Zhang
authors.forename: Qin
authors.initials: Q
authors.lastname: Xu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Sun
authors.forename: Ming
authors.initials: M
authors.lastname: Yan
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Ping
authors.initials: P
authors.lastname: Zhang
authors.forename: Ze-Guang
authors.initials: ZG
authors.lastname: Han
authors.forename: Wan-Tao
authors.initials: WT
authors.lastname: Chen
mesh_terms: D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D015153:Blotting, Western; D002277:Carcinoma / Q000235:genetics / Q000378:metabolism; D002294:Carcinoma, Squamous Cell; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019175:DNA Methylation / Q000235:genetics; D044127:Epigenesis, Genetic / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics / Q000502:physiology; D006258:Head and Neck Neoplasms / Q000235:genetics / Q000378:metabolism; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D018613:Microscopy, Confocal; D009185:Myelin Proteins / Q000235:genetics* / Q000378:metabolism*; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D018307:Neoplasms, Squamous Cell / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics; D011510:Proteolipids / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D000077195:Squamous Cell Carcinoma of Head and Neck
chemical_list: C569026:MAL protein, human; D026901:Membrane Transport Proteins; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D011510:Proteolipids; D012333:RNA, Messenger