Lee Mi-Sook, Ko Seong-Gyu, Kim Hwang-Phill, Kim Yong-Bae, Lee Sung-Yul, Kim Sang-Gyun, Jong Hyun-Soon, Kim Tae-You, Lee Jung Weon, Bang Yung-Jue
National Research Laboratory for Cancer Epigenetics, Cancer Research Institute, Department of Tumor Biology, College of Medicine, Seoul National University, Seoul 110-799, Korea.
Int J Oncol. 2004 May;24(5):1229-34.
Integrin-mediated cell adhesion enables cells to respond to extracellular stimuli for diverse cellular functions including proliferation, leading to differential biological activities from cells in suspension. Integrins can transduce signals (directly) to intracellular molecules and also collaborate with other membrane receptor-mediated signal pathways, including TGF-beta1 pathway. TGF-beta1 induces growth inhibition in epithelial cells and is known to transduce intracellular signaling in Smad-dependent or -independent manner. Currently effects of cell adhesion status on the TGF-beta1-mediated Erk1/2 regulation and on its Smad-(in)dependency are not known. In this study, we examined effects of cell adhesion status on the TGF-beta1-mediated Erk1/2 regulation, and roles of Smad proteins on the cell adhesion-mediated effects, using a gastric carcinoma cell variant. First, we found that cell adhesion-dependent Erk1/2 activation responded differentially to TGF-beta1, depending on cell adhesion status; TGF-beta1 treatment resulted in activation of Erk1/2 in suspended cells, whereas a decrease was noted in adherent cells. This activation of Erk1/2 by TGF-beta1 in suspension was more enhanced by an overexpression of Smad2, but not of other Smads 2, 4, and 7, but abolished by a Smad2 reduction via an introduction of its siRNA. In contrast, PKB/Akt regulation by TGF-beta1 was not different in suspension or in adhesion, and Smad7, but not the other Smads, activated PKB/Akt phosphorylation on TGF-beta1 treatment, indicating a specificity of Smad2-mediated and cell adhesion status-dependent activation of Erk1/2 activity.
整合素介导的细胞黏附使细胞能够对细胞外刺激做出反应，以实现包括增殖在内的多种细胞功能，从而导致悬浮细胞产生不同的生物学活性。整合素可以（直接）将信号转导至细胞内分子，还能与其他膜受体介导的信号通路协作，包括转化生长因子-β1（TGF-β1）通路。TGF-β1可诱导上皮细胞生长抑制，并且已知其以Smad依赖或非依赖的方式转导细胞内信号。目前，细胞黏附状态对TGF-β1介导的细胞外信号调节激酶1/2（Erk1/2）调控及其Smad依赖性的影响尚不清楚。在本研究中，我们使用一种胃癌细胞变体，研究了细胞黏附状态对TGF-β1介导的Erk1/2调控的影响，以及Smad蛋白在细胞黏附介导效应中的作用。首先，我们发现细胞黏附依赖的Erk1/2激活对TGF-β1的反应因细胞黏附状态而异；TGF-β1处理导致悬浮细胞中Erk1/2激活，而贴壁细胞中则出现下降。TGF-β1在悬浮细胞中对Erk1/2的这种激活作用在Smad2过表达时增强，但其他Smad2、4和7过表达时则不然，而通过引入其小干扰RNA（siRNA）降低Smad2水平可消除这种激活作用。相比之下，TGF-β1对蛋白激酶B/蛋白激酶B（PKB/Akt）的调控在悬浮或黏附状态下并无差异，并且在TGF-β1处理时，Smad7而非其他Smad激活了PKB/Akt磷酸化，这表明Smad2介导的以及细胞黏附状态依赖的Erk1/2活性激活具有特异性。
