Opposing Effects of KLF5 on the Transcription of MYC in Epithelial Proliferation in the Context of Transforming Growth Factor β
Opposing Effects of KLF5 on the Transcription of MYC in Epithelial Proliferation in the Context of Transforming Growth Factor β
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DOI：
10.1074/jbc.m109.036160
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发表时间：
2009-10-09
影响因子：
4.8
通讯作者：
Dong, Jin-Tang
中科院分区：
文献类型：
--
作者：
Guo, Peng;Dong, Xue-Yuan;Dong, Jin-Tang
原癌基因MYC在细胞增殖和肿瘤发生中起重要作用，通过转化生长因子β信号下调MYC的表达是转化生长因子β抑制细胞增殖所必需的。另一方面，KLF5是一种促增殖的碱性转录因子，在上皮细胞动态平衡的情况下，在转化生长因子β的刺激下，逆转其功能成为抗增殖的转化生长因子β辅助因子。在这项研究中，我们研究了在转化生长因子β基因敲除KLF5显著降低HaCaT表皮细胞MYC表达的背景下，KLF5是否直接调节上皮细胞中MYC的转录。然而，当应用转化生长因子β时，虽然MYC的表达被显著抑制，但KLF5的敲除增加了MYC的表达。此外，KLF5的重新表达恢复了转化生长因子β对两种癌细胞MYC表达的抑制作用。染色质免疫沉淀和寡核苷酸下拉实验表明，KLF5与KLF5结合元件(KBE)和转化生长因子β抑制元件(TIE)DNA元件的结合是MYC转录所必需的，而与KBE的结合被TGFβ降低，而与TIE的结合被增加。这些结果表明KLF5不仅对增殖上皮细胞的MYC转录是必需的，而且还介导了转化生长因子β对MYC转录的抑制作用。此外，不同的结合部位介导了KLF5在转化生长因子β中的不同作用。
The proto-oncogene MYC plays a critical role in cell proliferation and tumorigenesis, and its down-regulation by transforming growth factor beta (TGF beta) signaling is necessary for TGF beta to inhibit cell proliferation. KLF5, on the other hand, is a pro-proliferative basic transcription factor that reverses function to become an anti-proliferative TGF beta cofactor upon TGF beta stimulation in epithelial homeostasis. In this study we investigated whether KLF5 directly regulates MYC transcription in epithelial cells in the context of TGF beta Knockdown of KLF5 significantly reduced MYC expression in the HaCaT epidermal epithelial cells. When TGF beta was applied, however, whereas MYC expression was significantly inhibited, knockdown of KLF5 increased MYC expression. Furthermore, re-expression of KLF5 restored the inhibitory effect of TGF beta on MYC expression in two cancer cell lines. Chromatin immunoprecipitation and oligo pulldown experiments demonstrated that whereas binding of KLF5 to both KLF5 binding element (KBE) and TGF beta inhibitory element (TIE) DNA elements was necessary for MYC transcription, binding to KBE was decreased by TGF beta and binding to TIE was increased by TGF beta These results suggest that KLF5 is not only essential for MYC transcription in proliferating epithelial cells but also mediates the inhibitory effect of TGF beta on MYC transcription. Furthermore, different binding sites mediate different effects of KLF5 in the context of TGF beta.