Korcz A, Soprano D R, Soprano K J
Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
J Cell Biochem. 1995 Sep;59(1):42-52. doi: 10.1002/jcb.240590106.
We have used the WI-38 cell long-term quiescent model system to study the regulation of cell cycle progression at the molecular level. By modulating the length of time that WI-38 cells are density arrested, it is possible to proportionately alter the length of the prereplicative or G-1 phase which the cell traverses after growth factor stimulation in preparation for entry into DNA synthesis. Stimulation of long- and short-term density arrested WI-38 cells with different growth factors or higher concentrations of individual growth factors does not alter the time required by long-term cells to enter S after stimulation. However, the time during the prereplicative period for which these growth factors are needed is different. Long-term quiescent WI-38 cells require EGF to traverse the G-0/G-1 border but do not need and apparently cannot respond to IGF-1 during the first 10 h after EGF stimulation, the length of the prolongation of the prereplicative phase. This suggests that EGF stimulation of long-term quiescent WI-38 cells initiates a series of molecular events which make these cells "competent" to respond to the "progression" growth factor, IGF-1. In light of the well-established role of protein tyrosine kinases in signal transduction, we set out to identify, clone, and analyze the expression of receptor and non-receptor tyrosine kinases which potentially could play a role during the prolongation of the prereplicative phase in making the long-term quiescent WI-38 cells competent to respond to IGF-1. We obtained 49 clones representing 11 different receptor and non-receptor type protein tyrosine kinases. Analysis of expression of these clones revealed a variety of different patterns of expression. However, the most striking pattern was exhibited by IGF-1 receptor. Our results suggest that induction of IGF-1 receptor mRNA by EGF may be an important event in the establishment of competence by EGF in long-term density arrested WI-38 cells.
我们利用WI-38细胞长期静止模型系统在分子水平上研究细胞周期进程的调控。通过调节WI-38细胞密度停滞的时间长度，可以相应地改变细胞在生长因子刺激后为进入DNA合成做准备时所经历的复制前期或G-1期的长度。用不同生长因子或更高浓度的单个生长因子刺激长期和短期密度停滞的WI-38细胞，不会改变长期细胞在刺激后进入S期所需的时间。然而，这些生长因子在复制前期所需的时间是不同的。长期静止的WI-38细胞需要表皮生长因子（EGF）来跨越G-0/G-1边界，但在EGF刺激后的前10小时内不需要胰岛素样生长因子-1（IGF-1），显然也不能对其作出反应，这10小时正是复制前期延长的时间。这表明EGF刺激长期静止的WI-38细胞引发了一系列分子事件，使这些细胞“有能力”对“促进”生长因子IGF-1作出反应。鉴于蛋白酪氨酸激酶在信号转导中已确立的作用，我们着手鉴定、克隆和分析受体及非受体酪氨酸激酶的表达，这些激酶可能在复制前期延长过程中发挥作用，使长期静止的WI-38细胞有能力对IGF-1作出反应。我们获得了49个克隆，代表11种不同的受体和非受体型蛋白酪氨酸激酶。对这些克隆表达的分析揭示了多种不同的表达模式。然而，最显著的模式是由IGF-1受体呈现的。我们的结果表明，EGF诱导IGF-1受体mRNA可能是EGF在长期密度停滞的WI-38细胞中建立反应能力的一个重要事件。
