Colavito Sierra A, Zou Mike R, Yan Qin, Nguyen Don X, Stern David F
Breast Cancer Res. 2014 Sep 25;16(5):444. doi: 10.1186/s13058-014-0444-4.
The recently identified claudin-low subtype of breast cancer is enriched for cells with stem-like and mesenchymal-like characteristics. This subtype is most often triple-negative (lacking the estrogen and progesterone receptors (ER, PR) as well as lacking epidermal growth factor 2 (HER2) amplification) and has a poor prognosis. There are few targeted treatment options available for patients with this highly aggressive type of cancer.
Using a high throughput inhibitor screen, we identified high expression of glioma-associated oncogene homolog 1 (GLI1), the effector molecule of the hedgehog (Hh) pathway, as a critical determinant of cell lines that have undergone an epithelial to mesenchymal transition (EMT).
High GLI1 expression is a property of claudin-low cells and tumors and correlates with markers of EMT and breast cancer stem cells. Knockdown of GLI1 expression in claudin-low cell lines resulted in reduced cell viability, motility, clonogenicity, self-renewal, and reduced tumor growth of orthotopic xenografts. We observed non-canonical activation of GLI1 in claudin-low and EMT cell lines, and identified crosstalk with the NFκB pathway.
This work highlights the importance of GLI1 in the maintenance of characteristics of metastatic breast cancer stem cells. Remarkably, treatment with an inhibitor of the NFκB pathway reproducibly reduces GLI1 expression and protein levels. We further provide direct evidence for the binding of the NFκB subunit p65 to the GLI1 promoter in both EMT and claudin-low cell lines. Our results uncover crosstalk between NFκB and GLI1 signals and suggest that targeting these pathways may be effective against the claudin-low breast cancer subtype.
最近发现的乳腺癌紧密连接蛋白低表达亚型富含具有干细胞样和间充质样特征的细胞。该亚型最常为三阴性（缺乏雌激素和孕激素受体（ER、PR）且缺乏表皮生长因子2（HER2）扩增），预后较差。对于这种侵袭性很强的癌症患者，几乎没有可用的靶向治疗选择。
通过高通量抑制剂筛选，我们发现胶质瘤相关癌基因同源物1（GLI1）（刺猬信号通路（Hh）的效应分子）的高表达是经历上皮-间充质转化（EMT）的细胞系的关键决定因素。
GLI1高表达是紧密连接蛋白低表达细胞和肿瘤的特征，与EMT和乳腺癌干细胞标志物相关。在紧密连接蛋白低表达细胞系中敲低GLI1表达导致细胞活力、迁移能力、克隆形成能力、自我更新能力降低，以及原位异种移植瘤的生长减缓。我们在紧密连接蛋白低表达和EMT细胞系中观察到GLI1的非经典激活，并确定了与NFκB信号通路的相互作用。
这项工作突出了GLI1在维持转移性乳腺癌干细胞特征中的重要性。值得注意的是，用NFκB信号通路抑制剂治疗可重复性地降低GLI1表达和蛋白水平。我们进一步提供了直接证据，证明NFκB亚基p65在EMT和紧密连接蛋白低表达细胞系中均与GLI1启动子结合。我们的结果揭示了NFκB和GLI1信号之间的相互作用，并表明靶向这些信号通路可能对紧密连接蛋白低表达乳腺癌亚型有效。
