Zhan X, Hu X, Friesel R, Maciag T
Department of Molecular Biology, Jerome H. Holland Laboratory for the Biomedical Sciences, American Red Cross, Rockville, Maryland 20855.
J Biol Chem. 1993 May 5;268(13):9611-20.
The importance of growth factor-mediated immediate-early cellular events to the cell cycle has influenced the development and identity of oncogenes and tumor suppressor genes as well as the concept that growth factors commit mammalian cells to enter a biochemical program that ultimately yields DNA synthesis. However, the mid and late events involved in the regulation of growth factor-induced signal transduction remain largely unknown. In this report we demonstrate that BALB/c 3T3 cells require continuous exposure to fibroblast growth factor (FGF)-1 for a minimum of 12 h to achieve near maximal DNA synthesis. This correlates with the continuous internalization of radiolabeled FGF-1 into the cytosol and nucleus of BALB/c 3T3 cells and the maintenance of a low level of FGF receptors on the cell surface during the entire G1 phase of the cell cycle. Further analysis demonstrates the maintenance of a continuous series of differential FGF-1-induced tyrosine phosphorylation events including the phosphorylation of phospholipase C-gamma as well as novel FGF receptor polypeptide substrates, p60, p85, p90, and p130 throughout the G1 phase of the BALB/c 3T3 cell cycle. The tyrosine phosphorylation events are biphasic during the 12-h period after the administration of FGF-1, and the second phase is characterized by hyper-tyrosine phosphorylation of p60, p85, and p130. Interestingly, NIH 3T3 cells which overexpress the FGF receptor-1 polypeptide demonstrate exaggerated tyrosine phosphorylation of p60 and p85 but not p90 and exhibit growth factor-independent cell proliferation. These results suggest that the initiation of DNA synthesis in BALB/c 3T3 cells by FGF-1 is regulated by a complex biochemical program that involves the continuous tyrosine phosphorylation of known and novel polypeptides throughout the G0 to G1 transition period of the cell cycle.
生长因子介导的早期细胞事件对细胞周期的重要性影响了癌基因和肿瘤抑制基因的发展与特性，以及生长因子使哺乳动物细胞进入最终导致DNA合成的生化程序这一概念。然而，生长因子诱导的信号转导调控中涉及的中期和晚期事件在很大程度上仍不清楚。在本报告中，我们证明BALB/c 3T3细胞需要持续暴露于成纤维细胞生长因子（FGF）-1至少12小时才能实现接近最大程度的DNA合成。这与放射性标记的FGF-1持续内化到BALB/c 3T3细胞的细胞质和细胞核中以及在细胞周期的整个G1期细胞表面维持低水平的FGF受体相关。进一步分析表明，在BALB/c 3T3细胞周期的整个G1期，持续存在一系列不同的FGF-1诱导的酪氨酸磷酸化事件，包括磷脂酶C-γ以及新的FGF受体多肽底物p60、p85、p90和p130的磷酸化。在给予FGF-1后的12小时内，酪氨酸磷酸化事件呈双相性，第二阶段的特征是p60、p85和p130的过度酪氨酸磷酸化。有趣的是，过表达FGF受体-1多肽的NIH 3T3细胞表现出p60和p85的酪氨酸磷酸化增强，但p90没有，并且表现出不依赖生长因子的细胞增殖。这些结果表明，FGF-1在BALB/c 3T3细胞中启动DNA合成受一个复杂的生化程序调控，该程序涉及在细胞周期从G0到G1的过渡期内已知和新多肽的持续酪氨酸磷酸化。
