Adhesion control of cyclin D1 and p27Kip1 levels is deregulated in melanoma cells through BRAF-MEK-ERK signaling
Adhesion control of cyclin D1 and p27Kip1 levels is deregulated in melanoma cells through BRAF-MEK-ERK signaling
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DOI：
10.1038/sj.onc.1208544
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发表时间：
2005-05-12
期刊：
影响因子：
8
通讯作者：
Aplin, AE
中科院分区：
文献类型：
--
作者：
Bhatt, KV;Spofford, LS;Aplin, AE
BRAF突变是细胞外信号调节激酶1和2 （ERK）级联的一个组成部分，在黑色素瘤中很常见。了解BRAF突变如何导致包括锚定和生长因子不依赖性在内的恶性性状是很重要的。我们之前已经表明，正常人类表皮黑色素细胞（NHEM）中ERK的有效激活需要同时粘附细胞外基质和生长因子。突变体V599E BRAF足以促进ERK的激活，不依赖于粘附和生长因子。在这里，我们分析了NHEM和人类黑色素瘤细胞中G1细胞周期事件的调节。我们发现NHEM的S期进入需要通过MEK-ERK途径的粘附和生长因子信号。这种控制与诱导cyclin D1和下调p27（Kip1）相关，这是G1细胞周期的两个关键事件。在表达V599E BRAF的黑色素瘤细胞中，cyclin D1的组成性表达不依赖于粘附，但依赖于MEK的激活和ERK的核积累。通过RNA干扰降低细胞周期蛋白D1水平可抑制黑色素瘤细胞进入S期。重要的是，在没有粘附的情况下，NHEM中V599E BRAF的表达足以促进cyclin D1启动子的活性。此外，p27（Kip1）水平在表达V599E BRAF的黑色素瘤细胞中下调，活跃的BRAF足以下调血清饥饿NHEM中的p27（Kip1）水平。因此，粘附-生长因子的协同作用，导致ERK的有效激活，调节人类黑素细胞中cyclin D1和p27（Kip1）的水平，突变BRAF在黑素瘤中覆盖了粘附-生长因子对这两种G1细胞周期蛋白的控制。这些发现为BRAF突变如何导致人类黑素细胞异常增殖提供了重要的见解。
Mutations in BRAF, a component of extracellular signal-regulated kinases 1 and 2 (ERK) cascade, are frequent in melanoma. It is important to understand how BRAF mutations contribute to malignant traits including anchorage- and growth factor-independence. We have previously shown that effficient activation of ERK in normal human epidermal melanocytes (NHEM) requires both adhesion to the extracellular matrix and growth factors. Mutant V599E BRAF is sufficient to promote ERK activation independent of adhesion and growth factors. Here, we analysed regulation of G1 cell cycle events in NHEM and human melanoma cells. We show that S phase entry in NHEM requires both adhesion and growth factor signaling through the MEK-ERK pathway. This control correlates with induction of cyclin D1 and downregulation of p27(Kip1), two key G1 cell cycle events. In melanoma cells expressing V599E BRAF, cyclin D1 was constitutively expressed independent of adhesion but dependent upon MEK activation and nuclear accumulation of ERK. Reduction of cyclin D1 levels by RNA interference inhibited S phase entry in melanoma cells. Importantly, express ion of V599E BRAF in NHEM was sufficient to promote cyclin D1 promoter activity in the absence of adhesion. Additionally, p27(Kip1) levels were downregulated in V599E BRAF-expressing melanoma cells and active BRAF was sufficient to downregulate p27(Kip1) in serum-starved NHEM. Thus, adhesion-growth factor cooperation, leading to efficient activation of ERK, regulates cyclin D1 and p27(Kip1) levels in human melanocytes and mutant BRAF overrides adhesion-growth factor control of these two G1 cell cycle proteins in melanomas. These findings provide important insight into how BRAF mutations contribute to aberrant human melanocyte proliferation.