title: Silencing of RASSF3 by DNA hypermethylation is associated with tumorigenesis in somatotroph adenomas.
abstract: The pathogenic mechanisms underlying pituitary somatotroph adenoma formation, progression are poorly understood. To identify candidate tumor suppressor genes involved in pituitary somatotroph adenoma tumorigenesis, we used HG18 CpG plus Promoter Microarray in 27 human somatotroph adenomas and 4 normal human adenohypophyses. RASSF3 was found with frequent methylation of CpG island in its promoter region in somatotroph adenomas but rarely in adenohypophyses. This result was confirmed by pyrosequencing analysis. We also found that RASSF3 mRNA level correlated negatively to its gene promoter methylation level. RASSF3 hypermethylation and downregulation was also observed in rat GH3 and mouse GT1.1 somatotroph adenoma cell lines. 5-Aza-2' deoxycytidine and trichostatin-A treatment induced RASSF3 promoter demethylation, and restored its expression in GH3 and GT1.1 cell lines. RASSF3 overexpression in GH3 and GT1.1 cells inhibited proliferation, induced apoptosis accompanied by increased Bax, p53, and caspase-3 protein and decreased Bcl-2 protein expression. We also found that the antitumor effect of RASSF3 was p53 dependent, and p53 knockdown blocked RASSF3-induced apoptosis and growth inhibition. Taken together, our results suggest that hypermethylation-induced RASSF3 silencing plays an important role in the tumorigenesis of pituitary somatotroph adenomas.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Changzheng Hospital, Second Military Medical University, Shanghai, China.
authors.forename: Hu
authors.initials: H
authors.lastname: Peng
authors.forename: Huanhai
authors.initials: H
authors.lastname: Liu
authors.forename: Shuwei
authors.initials: S
authors.lastname: Zhao
authors.forename: Jian
authors.initials: J
authors.lastname: Wu
authors.forename: Jingping
authors.initials: J
authors.lastname: Fan
authors.forename: Jianchun
authors.initials: J
authors.lastname: Liao
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001374:Azacitidine / Q000494:pharmacology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D049912:Growth Hormone-Secreting Pituitary Adenoma / Q000235:genetics*; D006801:Humans; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: C454041:RASSF3 protein, human; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D020559:Monomeric GTP-Binding Proteins; D001374:Azacitidine
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