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多发性内分泌肿瘤1型(multiple endocrine neoplasia type1,MEN1)是一种常染色体显性遗传的肿瘤综合征,患者常表现出多发性的内分泌器官肿瘤,包括垂体瘤、甲状旁腺瘤和胰岛瘤。抑癌基因Men1的突变导致MEN1的发生,其编码的蛋白为核蛋白menin。Menin可以抑制包括胰岛β细胞在内的内分泌细胞增殖。本文探讨menin通过抑制细胞增殖来抑制MEN1胰岛瘤的可能机制。在基因芯片的分析中,喂养它莫西酚(tamoxifen)14d后诱导条件敲除Men1的小鼠胰岛中cyclin B2表达上升。免疫荧光的实验显示在小鼠MEN1胰岛瘤的组织切片中,cyclin B2表达量显著增加。细胞水平的研究显示,在Men1敲除的细胞中,cyclin B2表达量上升。以第10位丝氨酸磷酸化的组蛋白H3(phospho-H3S10)抗体对细胞进行免疫荧光实验,显示Men1敲除的细胞中处于有丝分裂的细胞数增加。以5×104的密度接种细胞,在第2天、第4天和第6天的时候分别对细胞计数,显示Men1敲除的细胞增殖加快。相反地,用shRNA敲低细胞中的cyclin B2,则细胞中处于有丝分裂的细胞数减少,细胞增长减慢。染色质免疫沉淀(chromatin immunoprecipitation,ChIP)分析显示,menin影响了cyclin B2启动子区组蛋白H3第4位赖氨酸的三甲基化水平及组蛋白H3的乙酰化水平,但不影响组蛋白H3第9位赖氨酸和第27位赖氨酸的三甲基化水平。上述结果提示menin可能通过组蛋白修饰而抑制cyclin B2的表达从而抑制了MEN1胰岛瘤的生长。
Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant tumor syndrome in which patients often exhibit multiple endocrine organ tumors including pituitary, parathyroid and insulinomas. The mutation of the tumor suppressor gene Men1 leads to the occurrence of MEN1, and the protein encoded by it is the nucleoprotein menin. Menin inhibits endocrine cell proliferation including islet beta cells. This article explores the possible mechanism by which menin suppresses MEN1 islets by inhibiting cell proliferation. In the gene chip analysis, cyclin B2 expression was increased in mouse islets induced by conditional knockout Menl after 14 days of feeding tamoxifen. Immunofluorescence experiments showed that the expression of cyclin B2 was significantly increased in the tissue sections of mouse MEN1 islets. Studies at the cellular level show that cyclin B2 expression is elevated in Men1 knockout cells. Immunofluorescent staining of cells with phosphoserone H3 (phospho-H3S10) antibody, phosphorylated at position 10 serine, showed an increase in the number of mitotic cells in the Men1 knockout cells. Cells were seeded at a density of 5x104, and cells were counted separately on day 2, day 4, and day 6 to show that the proliferation of Men1-knockout cells was accelerated. Conversely, knockdown of cyclin B2 in cells with shRNA reduced the number of mitotic cells in the cells and slowed cell growth. Chromatin immunoprecipitation (ChIP) analysis showed that menin affects the level of trimethylation of histone H3 at position 4 of histone H3 promoter and the acetylation level of histone H3, but does not affect histone Trimethylation levels of lysine at position 9 and lysine at position 27. The above results suggest that menin may inhibit the growth of MEN1 insulinoma by inhibiting the expression of cyclin B2 through histone modification.