title: TCEB3C a putative tumor suppressor gene of small intestinal neuroendocrine tumors.
abstract: Small intestinal neuroendocrine tumors (SI-NETs), formerly known as midgut carcinoids, are rare and slow-growing neoplasms. Frequent loss of one copy of chromosome 18 in primary tumors and metastases has been observed. The aim of the study was to investigate a possible role of TCEB3C (Elongin A3), currently the only imprinted gene on chromosome 18, as a tumor suppressor gene in SI-NETs, and whether its expression is epigenetically regulated. Primary tumors, metastases, the human SI-NET cell line CNDT2.5, and two other cell lines were included. Immunohistochemistry, gene copy number determination by PCR, colony formation assay, western blotting, real-time quantitative RT-PCR, RNA interference, and quantitative CpG methylation analysis by pyrosequencing were performed. A large majority of tumors (33/43) showed very low to undetectable Elongin A3 expression and as expected 89% (40/45) displayed one gene copy of TCEB3C. The DNA hypomethylating agent 5-aza-2'-deoxycytidine induced TCEB3C expression in CNDT2.5 cells, in primary SI-NET cells prepared directly after surgery, but not in two other cell lines. Also siRNA to DNMT1 and treatment with the general histone methyltransferase inhibitor 3-deazaneplanocin A induced TCEB3C expression in a cell type-specific way. CpG methylation at the TCEB3C promoter was observed in all analyzed tissues and thus not related to expression. Overexpression of TCEB3C resulted in a 50% decrease in clonogenic survival of CNDT2.5 cells, but not of control cells. The results support a putative role of TCEB3C as a tumor suppressor gene in SI-NETs. Epigenetic repression of TCEB3C seems to be tumor cell type-specific and involves both DNA and histone methylation.
authors.affiliation: Departments of Surgical Sciences Medical Sciences, Uppsala University Hospital, Uppsala University, Entrance 70, 3 tr, SE-75185 Uppsala, Sweden.
authors.forename: Katarina
authors.initials: K
authors.lastname: Edfeldt
authors.forename: Tanveer
authors.initials: T
authors.lastname: Ahmad
authors.forename: Göran
authors.initials: G
authors.lastname: Åkerström
authors.forename: Eva Tiensuu
authors.initials: ET
authors.lastname: Janson
authors.forename: Per
authors.initials: P
authors.lastname: Hellman
authors.forename: Peter
authors.initials: P
authors.lastname: Stålberg
authors.forename: Peyman
authors.initials: P
authors.lastname: Björklund
authors.forename: Gunnar
authors.initials: G
authors.lastname: Westin
mesh_terms: D045744:Cell Line, Tumor; D018899:CpG Islands; D000075065:Elongin; D016147:Genes, Tumor Suppressor; D006657:Histones / Q000378:metabolism; D006801:Humans; D007414:Intestinal Neoplasms / Q000235:genetics* / Q000378:metabolism; D007421:Intestine, Small; D008745:Methylation; D018358:Neuroendocrine Tumors / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics*
chemical_list: C000616399:ELOA3P pseudogene, human; D000075065:Elongin; D006657:Histones; D014157:Transcription Factors
keywords: LOH; carcinoid; elongation; epigenetic; imprinting