Numb regulates glioma stem cell fate and growth by altering epidermal growth factor receptor and Skp1-Cullin-F-box ubiquitin ligase activity.

Glioblastoma contains a hierarchy of stem-like cancer cells, but how this hierarchy is established is unclear. Here, we show that asymmetric Numb localization specifies glioblastoma stem-like cell (GSC) fate in a manner that does not require Notch inhibition. Numb is asymmetrically localized to CD133-hi GSCs. The predominant Numb isoform, Numb4, decreases Notch and promotes a CD133-hi, radial glial-like phenotype. However, upregulation of a novel Numb isoform, Numb4 delta 7 (Numb4d7), increases Notch and AKT activation while nevertheless maintaining CD133-hi fate specification. Numb knockdown increases Notch and promotes growth while favoring a CD133-lo, glial progenitor-like phenotype. We report the novel finding that Numb4 (but not Numb4d7) promotes SCFFbw7 ubiquitin ligase assembly and activation to increase Notch degradation. However, both Numb isoforms decrease epidermal growth factor receptor (EGFR) expression, thereby regulating GSC fate. Small molecule inhibition of EGFR activity phenocopies the effect of Numb on CD133 and Pax6. Clinically, homozygous NUMB deletions and low Numb mRNA expression occur primarily in a subgroup of proneural glioblastomas. Higher Numb expression is found in classical and mesenchymal glioblastomas and correlates with decreased survival. Thus, decreased Numb promotes glioblastoma growth, but the remaining Numb establishes a phenotypically diverse stem-like cell hierarchy that increases tumor aggressiveness and therapeutic resistance.

胶质母细胞瘤包含一个干细胞样癌细胞层级结构，但这个层级结构是如何形成的尚不清楚。在此，我们表明不对称的Numb定位以一种不依赖Notch抑制的方式决定胶质母细胞瘤干细胞样细胞（GSC）的命运。Numb不对称地定位于CD133高表达的GSCs。主要的Numb异构体Numb4降低Notch并促进一种CD133高表达、放射状胶质细胞样表型。然而，一种新的Numb异构体Numb4Δ7（Numb4d7）的上调增加Notch和AKT的激活，同时仍然维持CD133高表达的命运决定。Numb的敲低增加Notch并促进生长，同时倾向于一种CD133低表达、胶质祖细胞样表型。我们报道了一个新的发现，即Numb4（但不是Numb4d7）促进SCF - Fbw7泛素连接酶的组装和激活以增加Notch的降解。然而，两种Numb异构体都降低表皮生长因子受体（EGFR）的表达，从而调节GSC的命运。小分子对EGFR活性的抑制模拟了Numb对CD133和Pax6的作用。临床上，纯合的NUMB缺失和低Numb mRNA表达主要发生在一个前神经元型胶质母细胞瘤亚组中。在经典型和间充质型胶质母细胞瘤中发现较高的Numb表达，且与生存率降低相关。因此，Numb的降低促进胶质母细胞瘤的生长，但剩余的Numb建立了一个表型多样的干细胞样细胞层级结构，增加了肿瘤的侵袭性和治疗抗性。