Triple-negative breast cancer (TNBC) has the worst prognosis of all breast cancers, and lacks effective targeted treatment strategies. Previously, we identified 33 transcription factors highly expressed in TNBC. Here, we focused on six sex determining region Y-related HMG-box (SOX) transcription factors (SOX4, 6, 8, 9, 10, and 11) highly expressed in TNBCs. Our siRNA screening assay demonstrated that SOX9 knockdown suppressed TNBC cell growth and invasion in vitro. Thus, we hypothesized that SOX9 is an important regulator of breast cancer survival and metastasis, and demonstrated that knockout of SOX9 reduced breast tumor growth and lung metastasis in vivo. In addition, we found that loss of SOX9 induced profound apoptosis, with only a slight impairment of G1 to S progression within the cell cycle, and that SOX9 directly regulates genes controlling apoptosis. On the basis of published CHIP-seq data, we demonstrated that SOX9 binds to the promoter of apoptosis-regulating genes (tnfrsf1b, fadd, tnfrsf10a, tnfrsf10b, and ripk1), and represses their expression. SOX9 knockdown upregulates these genes, consistent with the induction of apoptosis. Analysis of available CHIP-seq data showed that SOX9 binds to the promoters of several epithelial–mesenchymal transition (EMT)- and metastasis-regulating genes. Using CHIP assays, we demonstrated that SOX9 directly binds the promoters of genes involved in EMT (vim, cldn1, ctnnb1, and zeb1) and that SOX9 knockdown suppresses the expression of these genes. Implications: Our studies identified the SOX9 protein as a “master regulator” of breast cancer cell survival and metastasis, and provide preclinical rationale to develop SOX9 inhibitors for the treatment of women with metastatic triple-negative breast cancer.

中文翻译：

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SOX9 对于三阴性乳腺癌细胞的存活和转移至关重要

三阴性乳腺癌（TNBC）在所有乳腺癌中预后最差，缺乏有效的靶向治疗策略。以前，我们确定了 33 个在 TNBC 中高度表达的转录因子。在这里，我们专注于在 TNBC 中高度表达的六个性别决定区 Y 相关 HMG 盒（SOX）转录因子（SOX4、6、8、9、10 和 11）。我们的 siRNA 筛选试验表明，SOX9 敲低在体外抑制了 TNBC 细胞的生长和侵袭。因此，我们假设 SOX9 是乳腺癌存活和转移的重要调节因子，并证明敲除 SOX9 可减少体内乳腺肿瘤的生长和肺转移。此外，我们发现 SOX9 的缺失诱导了严重的细胞凋亡，细胞周期内 G1 到 S 的进程只有轻微的损害，并且 SOX9 直接调节控制细胞凋亡的基因。基于已发表的 CHIP-seq 数据，我们证明 SOX9 与凋亡调节基因（tnfrsf1b、fadd、tnfrsf10a、tnfrsf10b 和 ripk1）的启动子结合，并抑制它们的表达。SOX9 敲低上调这些基因，与细胞凋亡的诱导一致。对可用 CHIP-seq 数据的分析表明，SOX9 与几个上皮间充质转化 (EMT) 和转移调节基因的启动子结合。使用 CHIP 分析，我们证明 SOX9 直接结合参与 EMT 的基因（vim、cldn1、ctnnb1 和 zeb1）的启动子，并且 SOX9 敲低抑制了这些基因的表达。启示：我们的研究确定 SOX9 蛋白是乳腺癌细胞存活和转移的“主要调节因子”，