title: Latexin expression is downregulated in human gastric carcinomas and exhibits tumor suppressor potential.
abstract: BACKGROUND
  Latexin, also known as endogenous carboxypeptidase inhibitor (CPI), has been found to inhibit mouse stem cell populations and lymphoma cell proliferation, demonstrating its potential role as a tumor suppressor. Our previous study also suggested a correlation between latexin expression and malignant transformation of immortalized human gastric epithelial cells. Here, we examined latexin expression in human gastric carcinomas and investigated the effect of differential latexin expression on proliferation of gastric cancer cells in vitro and in vivo.
  
  
  METHODS
  Monoclonal antibody against human latexin was prepared and immunohistochemical analysis was performed to detect latexin expression in 41 paired gastric carcinomas and adjacent normal control tissues. Human gastric cancer cells MGC803 (latexin negative) stably transfected with LXN gene and BGC823 cells (latexin positive) stably transfected with antisense LXN gene were established for anchorage-dependent colony formation assay and tumorigenesis assay in nude mice. Differentially expressed genes in response to exogeneous latexin expression were screened using microarray analysis and identified by RT-PCR. Bisulfite sequencing was performed to analyze the correlation of the methylation status of LXN promoter with latexin expression in cell lines.
  
  
  RESULTS
  Immunohistochemical analysis showed significantly reduced latexin expression in gastric carcinomas (6/41, 14.6%) compared to control tissues (31/41, 75.6%) (P < 0.05). Overexpression of LXN gene in MGC803 cells inhibited colony formation and tumor growth in nude mice. Conversely, BGC823 cells transfected with antisense LXN gene exhibited enhanced tumor growth and colony formation. Additionally, several tumor related genes, including Maspin, WFDC1, SLPI, S100P, and PDGFRB, were shown to be differentially expressed in MGC803 cells in response to latexin expression. Differential expression of Maspin and S100P was also identified in BGC823 cells while latexin expression was downregulated. Further bisulfite sequencing of the LXN gene promoter indicated CpG hypermethylation was correlated with silencing of latexin expression in human cells.
  
  
  CONCLUSIONS
  Latexin expression was reduced in human gastric cancers compared with their normal control tissues. The cellular and molecular evidences demonstrated the inhibitory effect of latexin in human gastric cancer cell growth and tumorigenicity. These results strongly suggest the possible involvement of latexin expression in tumor suppression.
authors.affiliation: Key Laboratory of Carcinogenesis and Translational Research, Ministry of Education, Department of Genetics, Peking University School of Oncology, Beijing Cancer Hospital & Institute, Hai Dian District, Beijing 100142, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Li
authors.forename: Zhuoma
authors.initials: Z
authors.lastname: Basang
authors.forename: Huirong
authors.initials: H
authors.lastname: Ding
authors.forename: Zheming
authors.initials: Z
authors.lastname: Lu
authors.forename: Tao
authors.initials: T
authors.lastname: Ning
authors.forename: Haoran
authors.initials: H
authors.lastname: Wei
authors.forename: Hong
authors.initials: H
authors.lastname: Cai
authors.forename: Yang
authors.initials: Y
authors.lastname: Ke
mesh_terms: D000818:Animals; D000941:Antigens / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002277:Carcinoma / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D019175:DNA Methylation / Q000235:genetics; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008819:Mice, Nude; D046228:Microarray Analysis; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015843:Serpins / Q000235:genetics / Q000378:metabolism; D013274:Stomach Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D019076:Transgenes / Q000235:genetics; D014410:Tumor Stem Cell Assay; D023041:Xenograft Model Antitumor Assays
chemical_list: D000941:Antigens; D002135:Calcium-Binding Proteins; C086812:Lxn protein, rat; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; C103003:S100P protein, human; C085344:SERPIN-B5; D015843:Serpins