Wu Ting, Huang Xiao-Hua
Department of Basic Medical Sciences, Medical College, Xiamen University, Xiamen 361005, China.
Sheng Li Xue Bao. 2011 Dec 25;63(6):555-64.
Multiple endocrine neoplasia type 1 (MEN1) is a dominantly inherited tumor syndrome characterized by development of various combinations of tumors in multiple endocrine glands, including the pituitary, parathyroid or pancreas. MEN1 results from mutations in tumor suppressor gene Men1, which encodes nuclear protein menin. Menin has been shown to preferentially repress cell proliferation in endocrine tissues including pancreatic beta cells. Herein, the present study was to explore the potential mechanisms underlying menin in repressing cell proliferation in mice MEN1 insulinoma. In the Gene Set Enrichment Analysis (GSEA), Ccnb2 (encoding cyclin B2) was up-regulated in pancreatic islets of Men1-excised mice after 14-day tamoxifen-feeding. Immunofluorescence with antibody against cyclin B2 revealed that the expression of cyclin B2 was greatly increased in MEN1 insulinoma. In Men1(-/-) cells, Men1 ablation leaded to an increase in cyclin B2 expression. Immunofluorescent staining by phospho-H3S10 antibody revealed the increasing number of Men1(-/-) cells in mitosis. Cells were seeded at a density of 5 × 10(4), then counted on day 2, 4 and 6, and the cell growth curve revealed Men1 ablation increased the cell proliferation. In contrast, knockdown of cyclin B2 by shRNA diminished the number of cells in mitosis and reduced cell proliferation. Further, chromatin immunoprecipitation (ChIP) assay indicated that menin affected the histone modification of the promoter of Ccnb2 by reducing the level of histone H3 lysine 4 tri-methylation (H3K4me3) and histone H3 acetylation but not affecting the level of histone H3 lysine 9 tri-methylation (H3K9me3) or histone H3 lysine 27 tri-methylation (H3K27me3). Our results suggest that menin may inhibit MEN1 insulinoma by suppressing cyclin B2 expression via histone modification.
多发性内分泌腺瘤1型（MEN1）是一种常染色体显性遗传肿瘤综合征，其特征是在多个内分泌腺中发生各种组合的肿瘤，包括垂体、甲状旁腺或胰腺。MEN1是由肿瘤抑制基因Men1的突变引起的，该基因编码核蛋白menin。Menin已被证明优先抑制包括胰腺β细胞在内的内分泌组织中的细胞增殖。在此，本研究旨在探讨menin在抑制小鼠MEN1胰岛素瘤细胞增殖中的潜在机制。在基因集富集分析（GSEA）中，喂食他莫昔芬14天后，Men1基因敲除小鼠的胰岛中Ccnb2（编码细胞周期蛋白B2）上调。用抗细胞周期蛋白B2抗体进行免疫荧光检测显示，MEN1胰岛素瘤中细胞周期蛋白B2的表达显著增加。在Men1（-/-）细胞中，Men1缺失导致细胞周期蛋白B2表达增加。用磷酸化组蛋白H3丝氨酸10抗体进行免疫荧光染色显示，处于有丝分裂期的Men1（-/-）细胞数量增加。以5×10⁴的密度接种细胞，然后在第2、4和6天进行计数，细胞生长曲线显示Men1缺失增加了细胞增殖。相反，用短发夹RNA（shRNA）敲低细胞周期蛋白B2可减少有丝分裂期细胞数量并降低细胞增殖。此外，染色质免疫沉淀（ChIP）分析表明，menin通过降低组蛋白H3赖氨酸4三甲基化（H3K4me3）和组蛋白H3乙酰化水平来影响Ccnb2启动子的组蛋白修饰，但不影响组蛋白H3赖氨酸9三甲基化（H3K9me3）或组蛋白H3赖氨酸27三甲基化（H3K27me3）水平。我们的结果表明，menin可能通过组蛋白修饰抑制细胞周期蛋白B2的表达来抑制MEN胰岛素瘤。
