title: LDOC1 silenced by cigarette exposure and involved in oral neoplastic transformation.
abstract: Previously, we identified global epigenetic aberrations in smoking-associated oral squamous cell carcinoma (OSCC). We hypothesized that cigarette exposure triggers OSCC through alteration of the methylome of oral cells. Here we report that cigarette smoke condensate (CSC) significantly changes the genomic 5-methyldeoxycytidine content and nuclear accumulation of DNA methyltransferase 1 (DNMT1) and DNMT3A in human untransformed oral cells. By using integrated analysis of cDNA and methylation arrays of the smoking-associated dysplastic oral cell line and OSCC tumors, respectively, we identified four epigenetic targets--UCHL1, GPX3, LXN, and LDOC1--which may be silenced by cigarette. Results of quantitative methylation-specific PCR showed that among these four genes, LDOC1 promoter was the most sensitive to CSC. LDOC1 promoter hypermethylation and gene silencing followed 3 weeks of CSC treatment. LDOC1 knockdown led to a proliferative response and acquired clonogenicity of untransformed oral cells. Immunohistochemistry showed that LDOC1 was downregulated in 53.3% (8/15) and 57.1% (20/35) of premalignant oral tissues and early stage OSCCs, respectively, whereas 76.5% (13/17) of normal oral tissues showed high LDOC1 expression. Furthermore, the microarray data showed that LDOC1 expression had decreased in the lung tissues of current smokers compared with that in those of never smokers and had significantly decreased in the lung tumors of smokers compared with that in normal lung tissues. Our data suggest that CSC-induced promoter methylation may contribute to LDOC1 downregulation, thereby conferring oncogenic features to oral cells. These findings also imply a tumor suppressor role of LDOC1 in smoking-related malignancies such as OSCC and lung cancer.
authors: National Institute of Cancer Research, National Health Research Institutes, Taipei, Taiwan.
authors: Chia-Huei
authors: CH
authors: Lee
authors: National Institute of Environmental Health Sciences, National Health Research Institutes, Taipei, Taiwan.
authors: Kao-Lu
authors: KL
authors: Pan
authors: National Institute of Cancer Research, National Health Research Institutes, Taipei, Taiwan.
authors: Ya-Chu
authors: YC
authors: Tang
authors: National Institute of Environmental Health Sciences, National Health Research Institutes, Taipei, Taiwan.
authors: Ming-Hsien
authors: MH
authors: Tsai
authors: Department of Medical Biotechnology and Laboratory Science, Chang Gung University, Taoyuan City, Taiwan.
authors: Ann-Joy
authors: AJ
authors: Cheng
authors: National Institute of Environmental Health Sciences, National Health Research Institutes, Taipei, Taiwan.
authors: Mei-Ya
authors: MY
authors: Shen
authors: National Institute of Cancer Research, National Health Research Institutes, Taipei, Taiwan.
authors: Ying-Min
authors: YM
authors: Cheng
authors: Department of Oral Medicine, National Cheng Kung University, Tainan City, Taiwan.
authors: Tze-Ta
authors: TT
authors: Huang
authors: National Institute of Environmental Health Sciences, National Health Research Institutes, Taipei, Taiwan.
authors: Pinpin
authors: P
authors: Lin
mesh_terms: D014408:Biomarkers, Tumor / Q000235:genetics* / Q000378:metabolism; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D020869:Gene Expression Profiling / Q000379:methods; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D006965:Hyperplasia; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009062:Mouth Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012906:Smoke / Q000009:adverse effects*; D012907:Smoking / Q000009:adverse effects* / Q000235:genetics* / Q000473:pathology; D000077195:Squamous Cell Carcinoma of Head and Neck; D013997:Time Factors; D046888:Tissue Array Analysis; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; C000717967:DNMT3A protein, human; C120625:LDOC1 protein, human; D009687:Nuclear Proteins; D012906:Smoke; D025521:Tumor Suppressor Proteins; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; C000619380:DNMT1 protein, human
keywords: DNA methylation; cigarette smoke condensate (CSC); leucine-zipper downregulated in cancer 1 (LDOC1); malignant transformation; oral squamous cell carcinoma (OSCC)