title: Expression of a LINE-1 endonuclease variant in gastric cancer: its association with clinicopathological parameters.
abstract: BACKGROUND
  Long interspersed nuclear element-1 (LINE-1 or L1), the most abundant and only autonomously active family of non-LTR retrotransposons in the human genome, expressed not only in the germ lines but also in somatic tissues. It contributes to genetic instability, aging, and age-related diseases, such as cancer. Our previous study identified in human gastric adenocarcinoma an upregulated transcript GCRG213, which shared 88% homology with human L1 sequence and contained a putative conserved apurinic/apyrimidinic endonucleas1 domain.
  
  
  METHODS
  Immunohistochemistry was carried out by using a monoclonal mouse anti-human GCRG213 protein (GCRG213p) antibody produced in our laboratory, on tissue microarray constructed with specimens from 175 gastric adenocarcinoma patients. The correlation between GCRG213p expression and patient clinicopathological parameters was evaluated. GCRG213p expression in gastric cancer cell lines were studied using Western blotting analysis. L1 promoter methylation status of gastric cancer cells was tested using methylation-specific PCR. BLASTP was used at the NCBI Blast server to identify GCRG213p sequence to any alignments in the Protein Data Bank databases.
  
  
  RESULTS
  Most primary gastric cancer, lymph node metastases and gastric intestinal metaplasia glands showed positive GCRG213p immunoreactivity. High GCRG213p immunostaining score in the primary gastric cancer was positively correlated with tumor differentiation (well differentiated, p = 0.001), Lauren's classification (intestinal type, p < 0.05) and a late age onset of gastric adenocarcinoma (≥65 yrs; p < 0.05). GCRG213p expression has no association with other clinicopathological parameters, including survival. Western blotting analysis of GCRG213p expression in gastric cancer cells indicated that GCRG213p level was higher in gastric cancer cell lines than in human normal gastric epithelium immortalized cell line GES-1. Partial methylation of L1 in gastric cancer cells was confirmed by methylation-specific PCR. BLASTP program analysis revealed that GCRG213p peptide shared 83.0% alignment with the C-terminal region of L1 endonuclease (L1-EN). GCRG213p sequence possesses the important residues that compose the conserved features of L1-EN.
  
  
  CONCLUSIONS
  GCRG213p could be a variant of L1-EN, a functional member of L1-EN family. Overexpression of GCRG213p is common in both primary gastric cancer and lymph node metastasis. These findings provide evidence of somatic L1 expression in gastric cancer, and its potential consequences in the form of tumor.
authors.forename: Gangshi
authors.initials: G
authors.lastname: Wang
authors.forename: Jie
authors.initials: J
authors.lastname: Gao
authors.forename: Haili
authors.initials: H
authors.lastname: Huang
authors.forename: Yu
authors.initials: Y
authors.lastname: Tian
authors.forename: Liyan
authors.initials: L
authors.lastname: Xue
authors.forename: Weihua
authors.initials: W
authors.lastname: Wang
authors.forename: Weidi
authors.initials: W
authors.lastname: You
authors.forename: Hongwei
authors.initials: H
authors.lastname: Lian
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Duan
authors.forename: Benyan
authors.initials: B
authors.lastname: Wu
authors.forename: Mengwei
authors.initials: M
authors.lastname: Wang
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism* / Q000401:mortality / Q000556:secondary; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000595:Amino Acid Sequence; D015153:Blotting, Western; D019175:DNA Methylation; D003850:Deoxyribonuclease I / Q000235:genetics*; D005260:Female; D005500:Follow-Up Studies; D005753:Gastric Mucosa / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007124:Immunoenzyme Techniques; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D060787:Neoplasm Grading; D009367:Neoplasm Staging; D036361:Peptide Hormones / Q000378:metabolism*; D011379:Prognosis; D060888:Real-Time Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013274:Stomach Neoplasms / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D015996:Survival Rate; D046888:Tissue Array Analysis; D014407:Tumor Cells, Cultured
chemical_list: C477000:GKN1 protein, human; D036361:Peptide Hormones; D003850:Deoxyribonuclease I; C538849:LINE-1 endonuclease, human