title: A novel splice variant of XIAP-associated factor 1 (XAF1) is expressed in peripheral blood containing gastric cancer-derived circulating tumor cells.
abstract: BACKGROUND
  XIAP-associated factor 1 (XAF1) is ubiquitously expressed in normal tissues, but its suppression in cancer cells is strongly associated with tumor progression. Although downregulation of XAF1 is observed in tumors, its expression profile in the peripheral blood of cancer patients has not yet been investigated. Here, we identified a novel XAF1 splice variant in cancer cells and then investigated the expression level of this variant in peripheral blood containing gastric cancer-derived circulating tumor cells (CTCs).
  
  
  METHODS
  To identify splice variants, RT-PCR and DNA sequencing were performed in mRNAs extracted from many cancer cells. We then carried out quantitative RT-PCR to investigate expression in peripheral blood from all 96 gastric cancer patients and 22 healthy volunteers.
  
  
  RESULTS
  The XAF1 variant harbored a premature termination codon (PTC) and was differentially expressed in highly metastatic cancer cells versus the parental cells, and that nonsense-mediated mRNA decay (NMD) was suppressed in the variant-expressing cells. Furthermore, splice variants of XAF1 were upregulated in peripheral blood containing CTCs. In XAF1 variant-expressing patients, the expression levels of other NMD-targeted genes also increased, suggesting that the NMD pathway was suppressed in CTCs.
  
  
  CONCLUSIONS
  Our study identified a novel splice variant of XAF1 in cancer cells. This variant was regulated through the NMD pathway and accumulated in NMD-suppressed metastatic cancer cells and peripheral blood containing CTCs. The presence of XAF1 transcripts harboring the PTC in the peripheral blood may be useful as an indicator of NMD inhibition in CTCs.
authors.affiliation: Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Hatakeyama
authors.affiliation: Division of Gastric Surgery, Shizuoka Cancer Center Hospital, 1077 Shimonagakubo, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan.|Division of Colon and Rectal Surgery, Shizuoka Cancer Center Hospital, Shizuoka, Japan.
authors.forename: Yushi
authors.initials: Y
authors.lastname: Yamakawa
authors.affiliation: Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan.|G&G Science, Fukushima, Japan.
authors.forename: Yorikane
authors.initials: Y
authors.lastname: Fukuda
authors.affiliation: Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Ohshima
authors.affiliation: Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan.
authors.forename: Kanako
authors.initials: K
authors.lastname: Wakabayashi-Nakao
authors.affiliation: Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Sakura
authors.affiliation: Division of Gastric Surgery, Shizuoka Cancer Center Hospital, 1077 Shimonagakubo, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Tanizawa
authors.affiliation: Division of Colon and Rectal Surgery, Shizuoka Cancer Center Hospital, Shizuoka, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kinugasa
authors.affiliation: Shizuoka Cancer Center Hospital and Research Institute, Shizuoka, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Yamaguchi
authors.affiliation: Division of Gastric Surgery, Shizuoka Cancer Center Hospital, 1077 Shimonagakubo, Nagaizumi-cho, Sunto-gun, Shizuoka, 411-8777, Japan. m.terashima@scchr.jp.
authors.forename: Masanori
authors.initials: M
authors.lastname: Terashima
authors.affiliation: Medical Genetics Division, Shizuoka Cancer Center Research Institute, Shizuoka, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Mochizuki
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D051017:Apoptosis Regulatory Proteins; D005260:Female; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000235:genetics*; D009360:Neoplastic Cells, Circulating / Q000473:pathology*; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D013274:Stomach Neoplasms / Q000097:blood / Q000235:genetics* / Q000473:pathology*; D059467:Transcriptome
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C417551:XAF1 protein, human
keywords: Alternative splicing; Circulating tumor cells; Gastric cancer; Nonsense-mediated mRNA decay; Quantitative real-time polymerase chain reaction (qRT-PCR)