ASCL1 defines differentiation-competent GBM cells and directs neoplastic cells towards neuronal fate

We identified a subgroup of patient-derived glioblastoma (GBM) cells that express high levels of the neurogenic transcription factor, ASCL1, which predicts response to pharmacological inhibition of the Notch signaling pathway. Treatment of ASCL1hi GBM cells with a Notch signaling inhibitor induced a change in cell fate from neoplastic to neuronal. Importantly, acquisition of the neuronal fate was accompanied by a reduction in tumorigenic potential. Loss of ASCL1 in GBM cells rendered cells no longer responsive to Notch signaling inhibition and we determined ASCL1 is required for the competency of GBM cells to undergo neuronal differentiation. Enforced ASCL1 expression directed GBM cells towards a neuronal cell fate reminiscent of terminal differentiation. RNA-seq analysis of GBM cells treated with the Notch signaling inhibitor reveals neuronal target gene activation is associated with increased stoichiometric levels of ASCL1, suggesting threshold levels of ASCL1 in GBM cells governs neuronal differentiation. We demonstrate that neoplastic cells which retain expression of key neurogenic programs can have their fates redirected towards terminal differentiation. Directed fate specification to neuronal cell types by exploiting latent neurogenic programs may be a strategy to treat a subset of GBM patients. Our findings therefore highlight the potential of differentiation therapy for a subset of molecularly defined GBMs.

我们鉴定出一类源自患者的胶质母细胞瘤（glioblastoma, GBM）细胞亚群，该亚群高表达神经营养转录因子ASCL1，其表达水平可预测细胞对Notch信号通路（Notch signaling pathway）药理学抑制的响应效果。使用Notch信号通路抑制剂处理ASCL1高表达的胶质母细胞瘤细胞，可诱导其细胞命运从肿瘤性向神经元性转变。尤为重要的是，细胞获得神经元命运的同时，其致瘤潜能也随之降低。胶质母细胞瘤细胞中ASCL1的缺失会使细胞不再响应Notch信号通路抑制，且我们证实ASCL1是胶质母细胞瘤细胞获得神经元分化能力的必需因子。强制过表达ASCL1可将胶质母细胞瘤细胞导向神经元命运，该过程类似于终末分化（terminal differentiation）。对经Notch信号通路抑制剂处理的胶质母细胞瘤细胞进行RNA测序（RNA-seq）分析后发现，神经元靶基因的激活与ASCL1的化学计量水平升高相关，这提示胶质母细胞瘤细胞中ASCL1的阈值水平调控着神经元分化进程。我们证实，保留关键神经发生程序表达的肿瘤细胞，其命运可被重定向至终末分化状态。通过激活潜在神经发生程序，定向将细胞命运特化为神经元细胞类型，或可成为治疗一类胶质母细胞瘤患者的策略。因此，我们的研究结果凸显了分化疗法（differentiation therapy）针对一类经分子分型鉴定的胶质母细胞瘤的应用潜力。