Centre for Cancer Therapeutics, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, ON, K1H 8L6, Canada.
Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON, K1H 8M5, Canada.
Breast Cancer Res. 2021 May 13;23(1):55. doi: 10.1186/s13058-021-01435-6.
Approximately 5-10% of HER2-positive breast cancers can be defined by low expression of the Ste20-like kinase, SLK, and high expression of SOX10. Our lab has observed that genetic deletion of SLK results in the induction of Sox10 and significantly accelerates tumor initiation in a HER2-induced mammary tumor model. However, the mechanism responsible for the induction of SOX10 gene expression in this context remains unknown.
Using tumor-derived cell lines from MMTV-Neu mice lacking SLK and biochemical approaches, we have characterized the signaling mechanisms and relevant DNA elements driving Sox10 expression.
Biochemical and genetic analyses of the SOX10 regulatory region in SLK-deficient mammary tumor cells show that Sox10 expression is dependent on a novel -7kb enhancer that harbors three SoxE binding sites. ChIP analyses demonstrate that Sox9 is bound to those elements in vivo. Our data show that AKT can directly phosphorylate Sox9 in vitro at serine 181 and that AKT inhibition blocks Sox9 phosphorylation and Sox10 expression in SLK(-/-) tumor cells. AKT-mediated Sox9 phosphorylation increases its transcriptional activity on the Sox10 -7kb enhancer without altering its DNA-binding activity. Interestingly, analysis of murine and human mammary tumors reveals a direct correlation between the levels of active phospho-Sox9 S181 and Sox10 expression.
Our results have identified a novel Sox10 enhancer and validated Sox9 as a direct target for AKT. As Sox10 is a biomarker for triple-negative breast cancers (TNBC), these findings might have major implications in the targeting and treatment of those cancers.
大约 5-10%的 HER2 阳性乳腺癌可以通过 Ste20 样激酶 SLK 的低表达和 SOX10 的高表达来定义。我们的实验室观察到，SLK 的基因缺失会导致 Sox10 的诱导，并显著加速 HER2 诱导的乳腺肿瘤模型中的肿瘤起始。然而，在这种情况下诱导 SOX10 基因表达的机制尚不清楚。
使用缺乏 SLK 的 MMTV-Neu 小鼠的肿瘤衍生细胞系和生化方法，我们已经描述了驱动 Sox10 表达的信号转导机制和相关 DNA 元件。
在 SLK 缺陷型乳腺肿瘤细胞中 Sox10 调控区的生化和遗传分析表明，Sox10 的表达依赖于一个新的-7kb 增强子，该增强子含有三个 SoxE 结合位点。ChIP 分析表明 Sox9 在体内结合这些元件。我们的数据表明 AKT 可以在体外直接在 Sox9 的丝氨酸 181 上磷酸化 Sox9，并且 AKT 抑制阻止了 SLK(-/-)肿瘤细胞中 Sox9 的磷酸化和 Sox10 的表达。AKT 介导的 Sox9 磷酸化增加了其对 Sox10-7kb 增强子的转录活性，而不改变其 DNA 结合活性。有趣的是，对鼠和人乳腺肿瘤的分析表明，活性磷酸化 Sox9 S181 的水平与 Sox10 的表达之间存在直接相关性。
我们的结果确定了一个新的 Sox10 增强子，并验证了 Sox9 是 AKT 的直接靶标。由于 Sox10 是三阴性乳腺癌（TNBC）的生物标志物，这些发现可能对这些癌症的靶向治疗具有重大意义。
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