Cardinal Bernardin Cancer Center and Department of Pathology, Loyola University Chicago, Maywood, IL, USA.
Oncogenesis. 2013 Aug 5;2(8):e60. doi: 10.1038/oncsis.2013.26.
The Notch pathway is functionally important in breast cancer. Notch-1 has been reported to maintain an estrogen-independent phenotype in estrogen receptor α (ERα)+ breast cancer cells. Notch-4 expression correlates with Ki67. Notch-4 also plays a key role in breast cancer stem-like cells. Estrogen-independent breast cancer cell lines have higher Notch activity than estrogen-dependent lines. Protein kinase Cα (PKCα) overexpression is common in endocrine-resistant breast cancers and promotes tamoxifen (TAM)-resistant growth in breast cancer cell lines. We tested whether PKCα overexpression affects Notch activity and whether Notch signaling contributes to endocrine resistance in PKCα-overexpressing breast cancer cells.Analysis of published microarray data from ERα+ breast carcinomas shows that PKCα expression correlates strongly with Notch-4. Real-time reverse transcription PCR and immunohistochemistry on archival specimens confirmed this finding. In a PKCα-overexpressing, TAM-resistant T47D model, PKCα selectively increases Notch-4, but not Notch-1, expression in vitro and in vivo. This effect is mediated by activator protein-1 (AP-1) occupancy of the Notch-4 promoter. Notch-4 knockdown inhibits estrogen-independent growth of PKCα-overexpressing T47D cells, whereas Notch-4IC expression stimulates it. Gene expression profiling shows that multiple genes and pathways associated with endocrine resistance are induced in Notch-4IC- and PKCα-expressing T47D cells. In PKCα-overexpressing T47D xenografts, an orally active γ-secretase inhibitor at clinically relevant doses significantly decreased estrogen-independent tumor growth, alone and in combination with TAM. In conclusion, PKCα overexpression induces Notch-4 through AP-1. Notch-4 promotes estrogen-independent, TAM-resistant growth and activates multiple pathways connected with endocrine resistance and chemoresistance. Notch inhibitors should be clinically evaluated in PKCα- and Notch-4-overexpressing, endocrine-resistant breast cancers.
Notch 通路在乳腺癌中具有重要的功能。已有报道称 Notch-1 可维持雌激素受体 α（ERα）+乳腺癌细胞中的雌激素非依赖性表型。Notch-4 的表达与 Ki67 相关。Notch-4 也在乳腺癌干细胞样细胞中发挥关键作用。雌激素非依赖性乳腺癌细胞系的 Notch 活性高于雌激素依赖性细胞系。蛋白激酶 Cα（PKCα）过表达在内分泌抵抗性乳腺癌中很常见，并促进乳腺癌细胞系中他莫昔芬（TAM）耐药性的生长。我们检测了 PKCα 过表达是否会影响 Notch 活性，以及 Notch 信号是否有助于 PKCα 过表达的乳腺癌细胞中的内分泌抵抗。对 ERα+乳腺癌的已发表微阵列数据的分析表明，PKCα 的表达与 Notch-4 密切相关。对存档标本的实时逆转录 PCR 和免疫组织化学证实了这一发现。在 PKCα 过表达、TAM 耐药的 T47D 模型中，PKCα 选择性地增加了 Notch-4 的表达，而不是 Notch-1，无论是在体外还是体内。这种作用是由 Notch-4 启动子上的激活蛋白-1（AP-1）占据介导的。Notch-4 敲低抑制了 PKCα 过表达的 T47D 细胞的雌激素非依赖性生长，而 Notch-4IC 的表达则刺激了这种生长。基因表达谱显示，Notch-4IC 和 PKCα 表达的 T47D 细胞中诱导了与内分泌抵抗相关的多个基因和途径。在 PKCα 过表达的 T47D 异种移植物中，在临床相关剂量下，一种口服活性的 γ-分泌酶抑制剂单独使用和与 TAM 联合使用，均可显著降低雌激素非依赖性肿瘤生长。总之，PKCα 过表达通过 AP-1 诱导 Notch-4。Notch-4 促进雌激素非依赖性、TAM 耐药性生长，并激活与内分泌抵抗和化疗耐药相关的多个途径。在 PKCα 和 Notch-4 过表达、内分泌抵抗的乳腺癌中，应临床评估 Notch 抑制剂。
