Oliver Trudy G, Grasfeder Linda L, Carroll Audra L, Kaiser Constanze, Gillingham Christine L, Lin Simon M, Wickramasinghe Rasika, Scott Matthew P, Wechsler-Reya Robert J
Department of Pharmacology and Cancer Biology and Bioinformatics Shared Resource, Duke University Medical Center, Durham, NC 27710, USA.
Proc Natl Acad Sci U S A. 2003 Jun 10;100(12):7331-6. doi: 10.1073/pnas.0832317100. Epub 2003 May 30.
Cerebellar granule cells are the most abundant neurons in the brain, and granule cell precursors (GCPs) are a common target of transformation in the pediatric brain tumor medulloblastoma. Proliferation of GCPs is regulated by the secreted signaling molecule Sonic hedgehog (Shh), but the mechanisms by which Shh controls proliferation of GCPs remain inadequately understood. We used DNA microarrays to identify targets of Shh in these cells and found that Shh activates a program of transcription that promotes cell cycle entry and DNA replication. Among the genes most robustly induced by Shh are cyclin D1 and N-myc. N-myc transcription is induced in the presence of the protein synthesis inhibitor cycloheximide, so it appears to be a direct target of Shh. Retroviral transduction of N-myc into GCPs induces expression of cyclin D1, E2F1, and E2F2, and promotes proliferation. Moreover, dominant-negative N-myc substantially reduces Shh-induced proliferation, indicating that N-myc is required for the Shh response. Finally, cyclin D1 and N-myc are overexpressed in murine medulloblastoma. These findings suggest that cyclin D1 and N-myc are important mediators of Shh-induced proliferation and tumorigenesis.
小脑颗粒细胞是大脑中数量最多的神经元，颗粒细胞前体细胞（GCPs）是儿童脑肿瘤髓母细胞瘤中常见的转化靶点。GCPs的增殖受分泌信号分子音猬因子（Shh）调控，但Shh控制GCPs增殖的机制仍未得到充分了解。我们使用DNA微阵列来鉴定这些细胞中Shh的靶点，发现Shh激活了一个促进细胞周期进入和DNA复制的转录程序。在Shh最强烈诱导的基因中，有细胞周期蛋白D1和N-myc。在存在蛋白质合成抑制剂环己酰亚胺的情况下，N-myc转录被诱导，所以它似乎是Shh的直接靶点。将N-myc逆转录病毒转导至GCPs中可诱导细胞周期蛋白D1、E2F1和E2F2的表达，并促进增殖。此外，显性负性N-myc可显著降低Shh诱导的增殖，表明N-myc是Shh反应所必需的。最后，细胞周期蛋白D1和N-myc在小鼠髓母细胞瘤中过表达。这些发现表明，细胞周期蛋白D1和N-myc是Shh诱导的增殖和肿瘤发生的重要介质。
