Transforming growth factor beta 1 induces proliferation in colon carcinoma cells by Ras-dependent, smad-independent down-regulation of p21cip1.
Transforming growth factor beta 1 induces proliferation in colon carcinoma cells by Ras-dependent, smad-independent down-regulation of p21cip1.
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转化生长因子 β 1 通过 Ras 依赖性、smad 独立的 p21cip1 下调诱导结肠癌细胞增殖。
DOI：
10.1074/jbc.m107646200
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Friedman,Eileen
中科院分区：
文献类型：
--
作者：
Yan,Zhongfa;Kim,Geum-Yi;Deng,Xiaobing;Friedman,Eileen
转化生长因子β1（Transforming growth factor β 1，TGFβ1）可作为肿瘤抑制因子或肿瘤促进因子，这取决于恶性细胞的特性。我们最近证明，用致癌细胞K-rasV 12而不是致癌细胞H-rasV 12转染的结肠癌细胞从TGFβ1不敏感转变为TGFβ1生长刺激的，并且也变得更具侵袭性（Yan，Z.，邓，X. Friedman，E.（2001）J.Biol.Chem.276，1555-1563）。我们现在证明，TGFβ1对结肠癌细胞的生长刺激是Ras依赖性的，而不是Smad依赖性的。在U9结肠癌细胞中，通过生长刺激对TGFβ1产生反应，在thesmad 4基因中发现Gln-311处的截短突变。在这些细胞中检测到非常少的smad 4蛋白。功能研究证实了smad 4蛋白的缺失。在U9细胞中，共转染野生型mad 4而非突变型mad 4介导了3 TP-lux和pSBE启动子报告基因构建体对TGFβ1的应答。TGFβ1在U9细胞中启动的增殖需要Ras介导的p21 cip 1蛋白下调。在TGFβ1处理的U9细胞中，p21 cip 1与cdk 2·cyclin复合物的结合减少，而cdk 2复合物的激酶活性增加。p21 cip 1水平升高可降低对TGFβ1的增殖反应。表达DN-N17 ras的U9细胞对TGFβ1无增殖反应，也不下调cdk抑制剂p21 cip 1的表达，DN-N17 ras呈剂量依赖性抑制TGFβ1对U9细胞3 TP lux的激活。TGFβ1还可降低p21 cip 1的水平，并刺激表达突变型K-Ras但不表达smad 4蛋白的SW 480细胞的增殖。TGFβ1在U9细胞中不激活或抑制p21 cip 1启动子构建体，即使在存在共转染的smad 4的情况下，也不改变p21 cip 1 mRNA水平。因此，p21 cip 1水平的降低是由TGFβ启动的Ras依赖性但不依赖于smad的转录后机制介导的。
Transforming growth factor β1 (TGFβ1) can act as a tumor suppressor or a tumor promoter depending on the characteristics of the malignant cell. We recently demonstrated that colon carcinoma cells transfected with oncogenic cellularK-rasV12, but not oncogenic cellularH-rasV12, switched from TGFβ1-insensitive to TGFβ1-growth-stimulated and also became more invasive (Yan, Z., Deng, X., and Friedman, E. (2001)J. Biol. Chem.276, 1555–1563). We now demonstrate that TGFβ1 growth stimulation of colon carcinoma cells is Ras-dependent and smad-independent. In U9 colon carcinoma cells, which are responsive to TGFβ1 by growth stimulation, a truncating mutation at Gln-311 was found in thesmad4gene. Very little smad4 protein was detected in these cells. Loss of smad4 protein was confirmed by functional studies. In U9 cells co-transfected wild-typesmad4, but not mutantsmad4, mediated response of the 3TP-lux and pSBE promoter reporter constructs to TGFβ1. Proliferation initiated by TGFβ1 in U9 cells required Ras-mediated down-regulation of p21cip1 protein. Less p21cip1 was associated with cdk2·cyclin complexes in TGFβ1-treated U9 cells, and the cdk2 complexes had increased kinase activity. Elevation of p21cip1 levels diminished proliferative response to TGFβ1. U9 cells expressing DN-N17ras neither proliferated in response to TGFβ1 nor down-regulated the cdk inhibitor p21cip1, and TGFβ1 activation of 3TP-lux in U9 cells was inhibited by DN-N17ras in a dose-dependent manner. TGFβ1 also decreased p21cip1 levels and stimulated proliferation in SW480 cells, which express mutant K-Ras but no smad4 protein. TGFβ1 did not activate or inhibit the p21cip1 promoter construct in U9 cells even in the presence of co-transfected smad4, or alter p21cip1 mRNA levels. Thus the decrease in p21cip1 levels was mediated by a TGFβ-initiated Ras-dependent, but smad-independent post-transcriptional mechanism.