TCEB3C a putative tumor suppressor gene of small intestinal neuroendocrine tumors

• Published in: Endocrine-related cancer Vol. 21; no. 2; pp. 275 - 284
• Main Authors: Edfeldt, Katarina, Ahmad, Tanveer, Åkerström, Göran, Janson, Eva Tiensuu, Hellman, Per, Stålberg, Peter, Björklund, Peyman, Westin, Gunnar
• Format: Journal Article
• Language: English
• Published: England Bioscientifica Ltd 01.04.2014
• Subjects: Cell Line, Tumor; CpG Islands; Elongin; Genes, Tumor Suppressor; Histones - metabolism; Humans; Intestinal Neoplasms - genetics; Intestinal Neoplasms - metabolism; Intestine, Small; Methylation; Neuroendocrine Tumors - genetics; Neuroendocrine Tumors - metabolism; Promoter Regions, Genetic; Transcription Factors - genetics; imprinting; LOH; carcinoid; elongation; epigenetic
• ISSN: 1351-0088; 1479-6821
• DOI: 10.1530/ERC-13-0419

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.