Donigan A M, Cavalli R C, Pena A A, Savage C R, Soprano D R, Soprano K J
Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
J Cell Physiol. 1993 Apr;155(1):164-70. doi: 10.1002/jcp.1041550121.
WI-38 cells, density arrested for short periods of time, can be stimulated to re-enter the cell cycle by epidermal growth factor (EGF) alone. However, cells density arrested for longer periods have a prolonged prereplicative phase when serum stimulated and cannot be stimulated by EGF alone. Radio-ligand binding studies performed on WI-38 cells showed that actively growing cells bind [125I]EG at relatively low levels that increase to a maximum as the cells become contact inhibited. As the cells enter a state of deeper quiescence, EGF binding falls to one-third to one-fifth the short-term growth arrested levels, remaining constant thereafter. The EGF-receptor complexes internalize more slowly in long-term growth arrested cells, and the rate of ligand association to the receptor is lower than short-term growth arrested cells. The amount of EGF receptor protein in lysates of equal numbers of both short- and long-term quiescent cells remains the same. These results suggest that the failure of long-term growth arrested cells to respond to EGF is not due to dramatic changes in the amount of receptor protein during prolonged quiescence but more likely to an alteration in the ability of these receptors to bind ligand and/or activate the EGF signal transduction pathway.
短期处于密度抑制状态的WI-38细胞，仅通过表皮生长因子（EGF）就能被刺激重新进入细胞周期。然而，长期处于密度抑制状态的细胞在血清刺激时具有延长的复制前期，且不能仅被EGF刺激。对WI-38细胞进行的放射性配体结合研究表明，活跃生长的细胞以相对较低的水平结合[125I]EGF，随着细胞受到接触抑制，结合水平会增加到最大值。当细胞进入更深的静止状态时，EGF结合水平降至短期生长受抑制水平的三分之一至五分之一，此后保持恒定。在长期生长受抑制的细胞中，EGF受体复合物的内化更慢，配体与受体结合的速率低于短期生长受抑制的细胞。等量的短期和长期静止细胞裂解物中EGF受体蛋白的量保持相同。这些结果表明，长期生长受抑制的细胞对EGF无反应，并非由于长期静止期间受体蛋白量的显著变化，而更可能是由于这些受体结合配体和/或激活EGF信号转导途径的能力发生了改变。
