Epigenetic alterations in neuroendocrine tumors: methylation of RAS-association domain family 1, isoform A and p16 genes are associated with metastasis

Abstract

Well-differentiated neuroendocrine tumors including pancreatic endocrine tumors and carcinoid tumors are uncommon neoplasms that have site-specific differences in clinicopathological features, clinical course and genetic alterations. The epigenetic alterations in these tumors are not well characterized. We therefore compared methylation of the RAS-association domain family 1, isoform A (RASSF1A), p14, p16 and O 6 -methylguanine methyltransferase genes in neuroendocrine tumors from 47 patients including 16 pancreatic, 15 nonileal and 16 ileal neuroendocrine tumors. Methylation of the RASSF1A gene was present in 57% of tumors, p14 in 49%, p16 in 26% and O 6 -methyl-guanine methyltransferase in 13% of tumors. Ileal neuroendocrine tumors lacked methylation of O 6 -methyl-guanine methyltransferase gene (P ¼ 0.04). RASSF1A methylation was associated with histopathologic type of tumors (P ¼ 0.03) and lymph node metastasis (P ¼ 0.004), and p16 methylation with older patient age (P ¼ 0.002) and liver metastasis (P ¼ 0.04). Two or more genes were methylated in 53% of tumors, one gene was methylated in 30% of tumors, and all four genes were unmethylated in 17% of tumors. Methylation of one or more gene was associated with older age of patients (P ¼ 0.01), and methylation of two or more genes was associated with liver metastasis (P ¼ 0.044). Our study shows that in neuroendocrine tumors epigenetic alterations vary by tumor subsite and clinicopathologic features, including age of onset, histopatholoic type and metastasis status.

Hypomethylation of LINE-1 and Alu in well-differentiated neuroendocrine tumors (pancreatic endocrine tumors and carcinoid tumors)

“…10 However, no association was present among RASSF1A gene methylation, lymph node metastasis and LINE-1 RASSF1A gene methylation, lymph node metastasis and 410% LINE tumor hypomethylation (RASSF1A unmethylated, no metastasis three of 10; unmethylated, metastasis present three of six; methylated, no metastasis one of two; and methylated, metastasis present 13 of 17, not significant).…”

“…9,10 Chromosome 11q loss was present in seven (20%), chromosome 16q loss in six (17%) and chromosome 18 loss in 11 (31%) tumors; methylation of p14 gene was present in 20 tumors (57%), p16 gene in nine (26%), O 6 -methyl-guanine methyltransferase (MGMT) gene in three (9%) and RAS-association domain family 1, isoform A (RASSF1A) gene in 19 (54%) tumors.…”

“…9,10 Eleven patients had a pancreatic endocrine tumor and 24 had a carcinoid tumor. The primary site of carcinoid tumors was lung for four patients, stomach for two patients, duodenum for one patient, ileum for 15 patients and colon (cecum) for two patients.…”

“…1,2 The molecular mechanisms of neuroendocrine tumors are poorly understood but have been the focus of many recent reports. [3][4][5][6][7][8][9][10] The methylation of cytosine in CpG dinucleotides is an important epigenetic modification of DNA in the vertebrate genome. 11 Methylation of cytosines and other associated epigenetic modifications is associated with transcriptional silencing of about one-half of the human genes with abundant CpG dinucleotides (CpG islands) in the promoter region, and is important in development and aging.…”

“…Some tumors produce endocrine activity causing a clinical syndrome, variable growth patterns and behavior and involvement of multiple endocrine neoplasia type 1 gene, but have site-specific differences in other genetic and epigenetic alterations. [3][4][5][6][7][8][9][10] We studied methylation of LINE-1 and Alu in low-grade neuroendocrine tumors and corresponding normal tissue from the same patients, and compared methylation densities of tumor, normal tissue and relative tumor hypomethylation (difference in methylation between normal and tumor) with clinicopathologic features.…”