Department of Stem Cell Biology and Regenerative Medicine, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, United States of America.
PLoS Biol. 2010 Feb 23;8(2):e1000319. doi: 10.1371/journal.pbio.1000319.
Glioblastomas are deadly cancers that display a functional cellular hierarchy maintained by self-renewing glioblastoma stem cells (GSCs). GSCs are regulated by molecular pathways distinct from the bulk tumor that may be useful therapeutic targets. We determined that A20 (TNFAIP3), a regulator of cell survival and the NF-kappaB pathway, is overexpressed in GSCs relative to non-stem glioblastoma cells at both the mRNA and protein levels. To determine the functional significance of A20 in GSCs, we targeted A20 expression with lentiviral-mediated delivery of short hairpin RNA (shRNA). Inhibiting A20 expression decreased GSC growth and survival through mechanisms associated with decreased cell-cycle progression and decreased phosphorylation of p65/RelA. Elevated levels of A20 in GSCs contributed to apoptotic resistance: GSCs were less susceptible to TNFalpha-induced cell death than matched non-stem glioma cells, but A20 knockdown sensitized GSCs to TNFalpha-mediated apoptosis. The decreased survival of GSCs upon A20 knockdown contributed to the reduced ability of these cells to self-renew in primary and secondary neurosphere formation assays. The tumorigenic potential of GSCs was decreased with A20 targeting, resulting in increased survival of mice bearing human glioma xenografts. In silico analysis of a glioma patient genomic database indicates that A20 overexpression and amplification is inversely correlated with survival. Together these data indicate that A20 contributes to glioma maintenance through effects on the glioma stem cell subpopulation. Although inactivating mutations in A20 in lymphoma suggest A20 can act as a tumor suppressor, similar point mutations have not been identified through glioma genomic sequencing: in fact, our data suggest A20 may function as a tumor enhancer in glioma through promotion of GSC survival. A20 anticancer therapies should therefore be viewed with caution as effects will likely differ depending on the tumor type.
胶质母细胞瘤是致命的癌症，其表现出由自我更新的胶质母细胞瘤干细胞（GSCs）维持的功能细胞层次结构。GSCs 受不同于大块肿瘤的分子途径调控，这些分子途径可能是有用的治疗靶点。我们确定 A20（TNFAIP3），一种细胞存活和 NF-κB 途径的调节剂，在 GSCs 中的表达相对于非干细胞胶质母细胞瘤细胞在 mRNA 和蛋白质水平上均上调。为了确定 A20 在 GSCs 中的功能意义，我们使用慢病毒介导的短发夹 RNA（shRNA）靶向 A20 表达。抑制 A20 表达通过与细胞周期进程降低和 p65/RelA 磷酸化降低相关的机制降低 GSC 生长和存活。GSCs 中 A20 水平的升高导致凋亡抵抗：GSCs 比匹配的非干细胞神经胶质瘤细胞对 TNFalpha 诱导的细胞死亡的敏感性降低，但 A20 敲低使 GSCs 对 TNFalpha 介导的凋亡敏感。A20 敲低后 GSCs 的存活率降低导致这些细胞在原发性和继发性神经球形成测定中的自我更新能力降低。用 A20 靶向治疗降低 GSCs 的致瘤潜能导致携带人胶质母细胞瘤异种移植物的小鼠的存活率增加。对胶质母细胞瘤患者基因组数据库的计算机分析表明，A20 的过表达和扩增与存活率呈负相关。这些数据表明，A20 通过对神经胶质瘤干细胞亚群的影响促进神经胶质瘤的维持。尽管淋巴瘤中 A20 的失活突变表明 A20 可以作为肿瘤抑制因子，但通过神经胶质瘤基因组测序尚未鉴定出类似的点突变：事实上，我们的数据表明 A20 可能通过促进 GSC 存活在神经胶质瘤中起肿瘤增强剂的作用。因此，A20 抗癌疗法应谨慎看待，因为其效果可能因肿瘤类型而异。
