Carpenter R L, Paw I, Dewhirst M W, Lo H-W
Division of Surgical Sciences, Department of Surgery, Duke University School of Medicine, Durham, NC, USA.
1] Department of Radiation Oncology, Duke University School of Medicine, Durham, NC, USA [2] Duke Cancer Institute, Duke University School of Medicine, Durham, NC, USA.
Oncogene. 2015 Jan 29;34(5):546-57. doi: 10.1038/onc.2013.582. Epub 2014 Jan 27.
Epithelial-mesenchymal transition (EMT) is an essential step for tumor progression, although the mechanisms driving EMT are still not fully understood. In an effort to investigate these mechanisms, we observed that heregulin (HRG)-mediated activation of HER2, or HER2 overexpression, resulted in EMT, which is accompanied with increased expression of a known EMT regulator Slug, but not TWIST or Snail. We then investigated how HER2 induced Slug expression and found, for the first time, that there are four consensus HSF sequence-binding elements (HSEs), the binding sites for heat shock factor-1 (HSF-1), located in the Slug promoter. HSF-1 bound to and transactivated the Slug promoter independent of heat shock, leading to Slug expression in breast cancer cells. Mutation of the putative HSEs ablated Slug transcriptional activation induced by HRG or HSF-1 overexpression. Knockdown of HSF-1 expression by siRNA reduced Slug expression and HRG-induced EMT. The positive association between HSF-1 and Slug was confirmed by immunohistochemical staining of a cohort of 100 invasive breast carcinoma specimens. While investigating how HER2 activated HSF-1 independent of heat shock, we observed that HER2 activation resulted in concurrent phosphorylation of Akt and HSF-1. We then observed, also for the first time, that Akt directly interacted with HSF-1 and phosphorylated HSF-1 at S326. Inhibition of Akt using siRNA, dominant-negative Akt mutant, or small molecule inhibitors prevented HRG-induced HSF-1 activation and Slug expression. Conversely, constitutively active Akt induced HSF-1 phosphorylation and Slug expression. HSF-1 knockdown reduced the ability of Akt to induce Slug expression, indicating an essential role that HSF-1 plays in Akt-induced Slug upregulation. Altogether, our study uncovered the existence of a novel Akt-HSF-1 signaling axis that leads to Slug upregulation and EMT, and potentially contributes to progression of HER2-positive breast cancer.
上皮-间质转化（EMT）是肿瘤进展的关键步骤，尽管驱动EMT的机制仍未完全明确。为了探究这些机制，我们观察到，这里调节蛋白（HRG）介导的HER2激活或HER2过表达会导致EMT，同时已知的EMT调节因子Slug的表达增加，但TWIST或Snail的表达并未增加。随后，我们研究了HER2如何诱导Slug表达，并首次发现Slug启动子中有四个热休克因子1（HSF-1）的共有序列结合元件（HSEs），即HSF-1的结合位点。HSF-1与Slug启动子结合并在无热休克的情况下激活它，从而导致乳腺癌细胞中Slug的表达。假定的HSEs发生突变会消除HRG或HSF-1过表达诱导的Slug转录激活。通过小干扰RNA（siRNA）敲低HSF-1的表达会降低Slug的表达以及HRG诱导的EMT。对100例浸润性乳腺癌标本进行免疫组织化学染色，证实了HSF-1与Slug之间呈正相关。在研究HER2如何在无热休克的情况下激活HSF-1时，我们观察到HER2激活会导致Akt和HSF-1同时磷酸化。随后，我们也首次观察到Akt直接与HSF-1相互作用，并在S326位点使HSF-1磷酸化。使用siRNA、显性负性Akt突变体或小分子抑制剂抑制Akt可阻止HRG诱导的HSF-1激活和Slug表达。相反，组成型激活的Akt会诱导HSF-1磷酸化和Slug表达。敲低HSF-1会降低Akt诱导Slug表达的能力，表明HSF-1在Akt诱导的Slug上调中起关键作用。总之，我们的研究发现了一种新的Akt-HSF-1信号轴，该信号轴导致Slug上调和EMT，并可能促进HER2阳性乳腺癌的进展。
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