BRAF activation induces transformation and then senescence in human neural stem cells: a pilocytic astrocytoma model.
BRAF activation induces transformation and then senescence in human neural stem cells: a pilocytic astrocytoma model.
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DOI：
10.1158/1078-0432.ccr-10-3349
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发表时间：
2011-06-01
期刊：
影响因子：
--
通讯作者：
Eberhart CG
中科院分区：
文献类型：
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作者：
Raabe EH;Lim KS;Kim JM;Meeker A;Mao XG;Nikkhah G;Maciaczyk J;Kahlert U;Jain D;Bar E;Cohen KJ;Eberhart CG
在最常见的儿童脑肿瘤毛细胞星形细胞瘤中，BRAF常被基因融合或点突变激活。我们研究了组成型BRAF激活在正常人神经干和祖细胞中的功能作用，以确定其在脑肿瘤诱导中的作用。将组成型活性BRAFV600E等位基因导入人神经球，检测其对MAPK（丝裂原活化蛋白激酶）信号传导、增殖、软琼脂糖集落形成、干细胞表型和细胞衰老诱导的影响。免疫组织化学检测毛细胞星形细胞瘤中p16INK4a水平。BRAFV600E的表达最初强烈促进了菌落的形成，但没有导致增殖的显著增加。表达brafv600e的细胞随后停止增殖，并诱导癌基因诱导的衰老标志物，包括酸性β-半乳糖苷酶、PAI-1和p16INK4a，而对照组则没有。衰老的开始与包括SOX2在内的神经干细胞标志物的表达减少有关。原代毛细胞星形细胞瘤培养也能诱导酸性β-半乳糖苷酶活性。66例毛细胞星形细胞瘤的免疫组化检查显示，大多数病例的p16INK4a免疫反应性，但p16INK4a阴性的肿瘤患者的总生存期明显缩短。BRAF在人神经干和祖细胞中的激活最初促进软琼脂糖的克隆生长，提示部分细胞转化，但随后癌基因诱导的衰老限制了增殖。BRAF诱导衰老可能有助于解释毛细胞星形细胞瘤的低级别病理生物学，而与缺乏p16INK4a表达的肿瘤相关的较差临床结果可能反映了诱导衰老失败或逃避癌基因诱导的衰老。
BRAF is frequently activated by gene fusion or point mutation in pilocytic astrocytoma, the most common pediatric brain tumor. We investigated the functional effect of constitutive BRAF activation in normal human neural stem and progenitor cells to determine its role in tumor induction in the brain. The constitutively active BRAFV600E allele was introduced into human neurospheres, and its effects on MAPK (mitogen-activated protein kinase) signaling, proliferation, soft agarose colony formation, stem cell phenotype, and induction of cellular senescence were assayed. Immunohistochemistry was used to examine p16INK4a levels in pilocytic astrocytoma. BRAFV600E expression initially strongly promoted colony formation but did not lead to significantly increased proliferation. BRAFV600E-expressing cells subsequently stopped proliferating and induced markers of oncogene-induced senescence including acidic β-galactosidase, PAI-1, and p16INK4a whereas controls did not. Onset of senescence was associated with decreased expression of neural stem cell markers including SOX2. Primary pilocytic astrocytoma cultures also showed induction of acidic β-galactosidase activity. Immunohistochemical examination of 66 pilocytic astrocytomas revealed p16INK4a immunoreactivity in the majority of cases, but patients with tumors negative for p16INK4a had significantly shorter overall survival. BRAF activation in human neural stem and progenitor cells initially promotes clonogenic growth in soft agarose, suggesting partial cellular transformation, but oncogene-induced senescence subsequently limits proliferation. Induction of senescence by BRAF may help explain the low-grade pathobiology of pilocytic astrocytoma, whereas worse clinical outcomes associated with tumors lacking p16INK4a expression could reflect failure to induce senescence or an escape from oncogene-induced senescence.