SKI knockdown inhibits human melanoma tumor growth in vivo.
SKI knockdown inhibits human melanoma tumor growth in vivo.
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DOI：
10.1111/j.1755-148x.2009.00603.x
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发表时间：
2009-12
影响因子：
4.3
通讯作者：
Medrano EE
中科院分区：
文献类型：
--
作者：
Chen D;Lin Q;Box N;Roop D;Ishii S;Matsuzaki K;Fan T;Hornyak TJ;Reed JA;Stavnezer E;Timchenko NA;Medrano EE
SKI蛋白通过与Smad转录因子相关而抑制TGF-β肿瘤抑制通路。SKI在人类恶性黑色素瘤中以疾病进展方式上调，其过表达促进体外黑色素瘤细胞的增殖和迁移。SKI在体内拮抗TGF-β信号传导的机制尚未完全阐明。在这里，我们发现内源性SKI表达被RNAi敲低的人黑色素瘤细胞产生最小的原位肿瘤异种移植物结节，显示出低有丝分裂率和明显的凋亡。这些微小的肿瘤表现出活跃的TGF-β信号的关键特征，包括高水平的核Smad3和p21Waf - 1，这些在亲代黑色素瘤中没有发现。为了了解SKI如何促进肿瘤生长，我们使用了功能增益和功能损失方法，发现在阻断TGF-β生长抑制途径的同时，SKI在黑色素瘤细胞中促进Smad3连接区域的磷酸化，从而促进Smad3从肿瘤抑制到肿瘤发生的转变，而在正常的人类黑色素细胞中则没有。在这种情况下，SKI需要阻止TGF-β介导的癌蛋白c-MYC的下调，并诱导纤溶酶原激活物抑制剂-1，一种肿瘤生长和血管生成的介质。总之，结果表明SKI利用TGF-β通路的多个调控水平，尽管黑色素瘤肿瘤中可能存在致癌突变，但其缺乏恢复TGF-β肿瘤抑制和凋亡活性。
The SKI protein represses the TGF-β tumor suppressor pathway by associating with the Smad transcription factors. SKI is upregulated in human malignant melanoma tumors in a disease-progression manner and its overexpression promotes proliferation and migration of melanoma cells in vitro. The mechanisms by which SKI antagonizes TGF-β signaling in vivo have not been fully elucidated. Here we show that human melanoma cells in which endogenous SKI expression was knocked down by RNAi produced minimal orthotopic tumor xenograft nodules that displayed low mitotic rate and prominent apoptosis. These minute tumors exhibited critical signatures of active TGF-β signaling including high levels of nuclear Smad3 and p21Waf�1, which are not found in the parental melanomas. To understand how SKI promotes tumor growth we used gain- and loss-of-function approaches and found that simultaneously to blocking the TGF-β-growth inhibitory pathway, SKI promotes the switch of Smad3 from tumor suppression to oncogenesis by favoring phosphorylations of the Smad3 linker region in melanoma cells but not in normal human melanocytes. In this context, SKI is required for preventing TGF-β-mediated down-regulation of the oncogenic protein c-MYC, and for inducing the plasminogen activator inhibitor-1, a mediator of tumor growth and angiogenesis. Together, the results indicate that SKI exploits multiple regulatory levels of the TGF-β pathway and its deficiency restores TGF-β tumor suppressor and apoptotic activities in spite of the likely presence of oncogenic mutations in melanoma tumors.