Program in Nutrition and Exercise Physiology, Washington State University, Spokane, WA, 99210-1495, USA.
Clin Exp Metastasis. 2011 Aug;28(6):551-65. doi: 10.1007/s10585-011-9391-y. Epub 2011 May 1.
The murine EL4 lymphoma cell line exists in variants that are either sensitive or resistant to phorbol 12-myristate 13-acetate (PMA). In sensitive cells, PMA causes Erk MAPK activation and Erk-mediated growth arrest. In resistant cells, PMA induces a low level of Erk activation, without growth arrest. A relatively unexplored aspect of the phenotypes is that resistant cells are more adherent to culture substrate than are sensitive cells. In this study, the roles of the protein tyrosine kinases FAK and Pyk2 in EL4 phenotype were examined, with a particular emphasis on the role of these proteins in metastasis. FAK is expressed only in PMA-resistant (or intermediate phenotype) EL4 cells, correlating with enhanced cell-substrate adherence, while Pyk2 is more highly expressed in non-adherent PMA-sensitive cells. PMA treatment causes modulation of mRNA for FAK (up-regulation) and Pyk2 (down-regulation) in PMA-sensitive but not PMA-resistant EL4 cells. The increase in Pyk2 mRNA is correlated with an increase in Pyk2 protein expression. The roles of FAK in cell phenotype were further explored using transfection and knockdown experiments. The results showed that FAK does not play a major role in modulating PMA-induced Erk activation in EL4 cells. However, the knockdown studies demonstrated that FAK expression is required for proliferation and migration of PMA-resistant cells. In an experimental metastasis model using syngeneic mice, only FAK-expressing (PMA-resistant) EL4 cells form liver tumors. Taken together, these studies suggest that FAK expression promotes metastasis of EL4 lymphoma cells.
鼠源 EL4 淋巴瘤细胞系存在对佛波醇 12-肉豆蔻酸 13-乙酸酯（PMA）敏感或耐药的变体。在敏感细胞中，PMA 导致 Erk MAPK 激活和 Erk 介导的生长抑制。在耐药细胞中，PMA 诱导低水平的 Erk 激活，但没有生长抑制。耐药细胞比敏感细胞对培养底物具有更高的粘附性，这是表型中一个相对未被探索的方面。在本研究中，研究了蛋白酪氨酸激酶 FAK 和 Pyk2 在 EL4 表型中的作用，特别强调了这些蛋白在转移中的作用。FAK 仅在 PMA 耐药（或中间表型）EL4 细胞中表达，与增强的细胞-底物粘附相关，而 Pyk2 在非粘附的 PMA 敏感细胞中表达更高。PMA 处理导致 PMA 敏感但不耐药的 EL4 细胞中 FAK（上调）和 Pyk2（下调）的 mRNA 发生调节。Pyk2 mRNA 的增加与 Pyk2 蛋白表达的增加相关。使用转染和敲低实验进一步研究了 FAK 在细胞表型中的作用。结果表明，FAK 在外源基因转染的 EL4 细胞中不主要参与调节 PMA 诱导的 Erk 激活。然而，敲低研究表明，FAK 表达对于耐药细胞的增殖和迁移是必需的。在使用同源小鼠的实验性转移模型中，只有表达 FAK（耐药）的 EL4 细胞形成肝肿瘤。总之，这些研究表明 FAK 表达促进了 EL4 淋巴瘤细胞的转移。
