Tuhácková Z, Sovová V, Sloncová E, Proud C G
Institute of Molecular Genetics, Academy of Sciences of Czech Republic, Prague.
Int J Cancer. 1999 Jun 11;81(6):963-9. doi: 10.1002/(sici)1097-0215(19990611)81:6<963::aid-ijc20>3.0.co;2-c.
Increased phosphorylation of the translational repressor protein 4E-BP1 was found in the cell line derived from the tumor induced in Syrian hamster by Rous sarcoma virus (RSV). This was accompanied by its dissociation from the complex with initiation factor eIF4E. The ribosomal S6 protein kinase p70S6k is supposed to be regulated by the same or a closely related rapamycin-sensitive signalling pathway to that which modulates 4E-BP1. Phosphorylation and activity of p70S6k were found to be also increased in RSV-transformed H19 cells that express significantly higher amounts of the Src protein (p60src) relative to the non-transformed hamster fibroblasts NIL-2. The increased activity and phosphorylation of p70S6k were blocked by rapamycin, indicating that the rapamycin-sensitive pathway is involved in its regulation in v-src-transformed hamster fibroblasts. In agreement with this, rapamycin reduced the expression of elongation factor eEF1alpha (whose translation is regulated by a rapamycin-sensitive mechanism thought to involve p70S6k) and did not affect the production of a housekeeping protein, alpha-tubulin, in these cells. Synthesis of Src protein was also inhibited in cells treated with rapamycin. However, treatment of cells with a concentration of rapamycin sufficient to completely inhibit the activity and phosphorylation of p70S6k resulted in only partial de-phosphorylation of 4E-BP1 and its re-association with eIF4E in the transformed cells, indicating that additional rapamycin-insensitive mechanisms/pathways are implicated in the control of 4E-BP1 phosphorylation in RSV-transformed hamster fibroblasts. Over-expression of eIF4E favours cell proliferation and can lead to a transformed phenotype, while over-expression of 4E-BP1 has the opposite effect. The altered signalling to the phosphorylation of 4E-BP1 in RSV-transformed cells, which leads to its dissociation from eIF4E and thus relief of inhibition of eIF4E function, may therefore represent an important regulatory mechanism in malignant cell growth.
在源自叙利亚仓鼠经劳氏肉瘤病毒（RSV）诱导产生的肿瘤的细胞系中，发现翻译阻遏蛋白4E - BP1的磷酸化增加。这伴随着它与起始因子eIF4E复合物的解离。核糖体S6蛋白激酶p70S6k被认为受与调节4E - BP1相同或密切相关的雷帕霉素敏感信号通路调控。相对于未转化的仓鼠成纤维细胞NIL - 2，在表达显著更高量Src蛋白（p60src）的RSV转化的H19细胞中，也发现p70S6k的磷酸化和活性增加。p70S6k活性和磷酸化的增加被雷帕霉素阻断，表明雷帕霉素敏感通路参与其在v - src转化的仓鼠成纤维细胞中的调节。与此一致，雷帕霉素降低了延伸因子eEF1α（其翻译受被认为涉及p70S6k的雷帕霉素敏感机制调控）的表达，并且不影响这些细胞中管家蛋白α - 微管蛋白的产生。雷帕霉素处理的细胞中Src蛋白的合成也受到抑制。然而，用足以完全抑制p70S6k活性和磷酸化的雷帕霉素浓度处理细胞，仅导致转化细胞中4E - BP1部分去磷酸化及其与eIF4E重新结合，表明在RSV转化的仓鼠成纤维细胞中，额外的雷帕霉素不敏感机制/通路参与4E - BP1磷酸化的控制。eIF4E的过表达有利于细胞增殖并可导致转化表型，而4E - BP1的过表达则具有相反的作用。因此，RSV转化细胞中4E - BP1磷酸化信号的改变，导致其与eIF4E解离，从而解除对eIF4E功能的抑制，可能代表恶性细胞生长中的一种重要调节机制。
