Department of Physiology, Keio University School of Medicine, Shinjuku, Tokyo, Japan.
PLoS One. 2012;7(3):e33431. doi: 10.1371/journal.pone.0033431. Epub 2012 Mar 12.
Musashi1 (MSI1) is an RNA-binding protein that plays critical roles in nervous-system development and stem-cell self-renewal. Here, we examined its role in the progression of glioma. Short hairpin RNA (shRNA)-based MSI1-knock down (KD) in glioblastoma and medulloblastoma cells resulted in a significantly lower number of self renewing colony on day 30 (a 65% reduction), compared with non-silencing shRNA-treated control cells, indicative of an inhibitory effect of MSI1-KD on tumor cell growth and survival. Immunocytochemical staining of the MSI1-KD glioblastoma cells indicated that they ectopically expressed metaphase markers. In addition, a 2.2-fold increase in the number of MSI1-KD cells in the G2/M phase was observed. Thus, MSI1-KD caused the prolongation of mitosis and reduced the cell survival, although the expression of activated Caspase-3 was unaltered. We further showed that MSI1-KD glioblastoma cells xenografted into the brains of NOD/SCID mice formed tumors that were 96.6% smaller, as measured by a bioluminescence imaging system (BLI), than non-KD cells, and the host survival was longer (49.3±6.1 days vs. 33.6±3.6 days; P<0.01). These findings and other cell biological analyses suggested that the reduction of MSI1 in glioma cells prolonged the cell cycle by inducing the accumulation of Cyclin B1. Furthermore, MSI1-KD reduced the activities of the Notch and PI(3) kinase-Akt signaling pathways, through the up-regulation of Numb and PTEN, respectively. Exposure of glioma cells to chemical inhibitors of these pathways reduced the number of spheres and living cells, as did MSI1-KD. These results suggest that MSI1 increases the growth and/or survival of certain types of glioma cells by promoting the activation of both Notch and PI(3) kinase/Akt signaling.
Musashi1（MSI1）是一种 RNA 结合蛋白，在神经系统发育和干细胞自我更新中发挥关键作用。在这里，我们研究了它在神经胶质瘤进展中的作用。在神经胶质瘤和髓母细胞瘤细胞中，基于短发夹 RNA（shRNA）的 MSI1 敲低（KD）导致第 30 天自我更新集落的数量明显减少（减少 65%），与非沉默 shRNA 处理的对照细胞相比，表明 MSI1-KD 对肿瘤细胞生长和存活具有抑制作用。对 MSI1-KD 神经胶质瘤细胞的免疫细胞化学染色表明，它们异位表达了中期标记物。此外，观察到 MSI1-KD 细胞在 G2/M 期的数量增加了 2.2 倍。因此，MSI1-KD 导致有丝分裂延长和细胞存活减少，尽管激活的 Caspase-3 的表达没有改变。我们进一步表明，MSI1-KD 神经胶质瘤细胞异种移植到 NOD/SCID 小鼠的大脑中形成的肿瘤比非 KD 细胞小 96.6%，通过生物发光成像系统（BLI）测量，宿主的存活时间更长（49.3±6.1 天 vs. 33.6±3.6 天；P<0.01）。这些发现和其他细胞生物学分析表明，通过诱导 Cyclin B1 的积累，MSI1 在神经胶质瘤细胞中的减少延长了细胞周期。此外，MSI1-KD 通过上调 Numb 和 PTEN，分别降低了 Notch 和 PI(3) 激酶-Akt 信号通路的活性。化学抑制剂暴露于这些通路会减少球体和活细胞的数量，MSI1-KD 也是如此。这些结果表明，MSI1 通过促进 Notch 和 PI(3) 激酶/Akt 信号通路的激活，增加某些类型的神经胶质瘤细胞的生长和/或存活。
