Huang C, Ma W Y, Young M R, Colburn N, Dong Z
The Hormel Institute, University of Minnesota, Austin, MN 55912, USA.
Proc Natl Acad Sci U S A. 1998 Jan 6;95(1):156-61. doi: 10.1073/pnas.95.1.156.
The JB6 mouse epidermal cell system, which includes tumor promotion-sensitive (P+) and tumor promotion-resistant (P-) cells, is a well-established and extensively used cell culture model for studying the mechanism of late-stage tumor promotion. Tumor promoters, such as 12-O-tetradecanoylphorbol 13-acetate (TPA) or epidermal growth factor (EGF), induce high levels of activator protein 1 (AP-1) activity and large, tumorigenic, anchorage-independent colonies in soft agar at a high frequency in JB6 P+ cells, but not in JB6 P- cells. We report here a molecular explanation for the defect in the AP-1 activation and promotion-resistant phenotype of P- cells. We demonstrate that the lack of AP-1 activation and cell transformation responses to TPA and EGF in P- cells appears attributable to the low level of mitogen-activated protein kinase (MAPK) (extracellular signal-regulated protein kinase, Erk) in these cells. TPA and EGF induce transactivation of AP-1 activity in P+ cells but not in P- cells. Nonphosphorylated forms and TPA- or EGF-induced phosphorylated forms of Erks (Erk1 and Erk2) in P- cells were much lower than those in P+ cells. Stable transfection of wild-type MAPK (Erk2) into P- cells restored its response to TPA and EGF for both AP-1 activation and cell transformation. These results suggest that the shortage of MAPK (Erk1 and Erk2) appears to be an important contributor to the tumor promotion-resistant phenotype in JB6 cells.
JB6小鼠表皮细胞系统包括对肿瘤促进敏感的（P+）细胞和对肿瘤促进有抗性的（P-）细胞，是一种成熟且广泛应用的细胞培养模型，用于研究晚期肿瘤促进机制。肿瘤促进剂，如12-O-十四酰佛波醇-13-乙酸酯（TPA）或表皮生长因子（EGF），在JB6 P+细胞中可高频诱导高水平的活化蛋白1（AP-1）活性以及在软琼脂中形成大量致瘤性、不依赖贴壁的集落，但在JB6 P-细胞中则不会。我们在此报告对P-细胞中AP-1激活缺陷和促进抗性表型的分子解释。我们证明，P-细胞中对TPA和EGF缺乏AP-1激活及细胞转化反应似乎归因于这些细胞中丝裂原活化蛋白激酶（MAPK）（细胞外信号调节蛋白激酶，Erk）水平较低。TPA和EGF可诱导P+细胞中AP-1活性的反式激活，但不能诱导P-细胞中的反式激活。P-细胞中未磷酸化形式以及TPA或EGF诱导的磷酸化形式的Erks（Erk1和Erk2）远低于P+细胞中的水平。将野生型MAPK（Erk2）稳定转染到P-细胞中可恢复其对TPA和EGF的AP-1激活及细胞转化反应。这些结果表明，MAPK（Erk1和Erk2）的短缺似乎是JB6细胞中肿瘤促进抗性表型的一个重要促成因素。
