Larsson O, Zetterberg A, Engström W
J Cell Sci. 1985 Feb;73:375-87. doi: 10.1242/jcs.73.1.375.
We have previously shown that Swiss 3T3 cells located in the first part of G1 (post-mitotic G1 cells younger than 4.0 h or G1pm cells) were arrested after 9-10 h in the cell cycle by a short (1-8 h) exposure to serum-free medium or by a short (2-4 h) exposure to low doses of the protein synthesis inhibitor cycloheximide (CH). Kinetic data indicate that such G1pm cells rapidly return to G0 during this brief treatment and thereafter require a preparatory period of 8 h before continuing to G1. Cells older than 4 h, i.e. cells in mid or late G1 are already committed to DNA synthesis (presynthesis or G1ps cells). These cells as well as S and G2 cells were consequently unaffected by the brief serum starvation or the brief treatment with cycloheximide. In the present paper we show that the 10-h intermitotic delay that follows a 1-2 h exposure to serum-free medium can be completely counteracted by the presence of any one of the purified growth factors, epidermal growth factor (EGF), insulin or platelet-derived growth factor (PDGF). In contrast, the intermitotic delay following a longer exposure (8 h) to serum-free medium could no longer be counteracted by EGF or insulin. However, PDGF was still active in this respect. Most interestingly, the 12 h gross intermitotic delay induced by a 4h exposure to CH could be efficiently counteracted by EGF, PDGF or insulin. However, this effect on CH-treated cells could be counteracted by the growth factor only in the presence of 10% serum. This indicates the existence of a cooperative effect between PDGF, EGF or insulin and an unidentified serum factor. The effects on the cell cycle time of brief serum starvation and exposure to CH were compared with the effects on rate of protein synthesis and degradation. Although the effects of serum starvation on protein synthesis and degradation were found to be partially normalized by growth factors, we suggest that growth factors prevent cells from leaving the cell cycle by another mechanism and not merely by affecting the level of overall protein accumulation.
我们之前已经表明，位于G1期第一部分的瑞士3T3细胞（有丝分裂后G1期细胞，年龄小于4.0小时，即G1pm细胞），在细胞周期中经过9 - 10小时的停滞，这是通过短期（1 - 8小时）暴露于无血清培养基，或短期（2 - 4小时）暴露于低剂量的蛋白质合成抑制剂环己酰亚胺（CH）实现的。动力学数据表明，此类G1pm细胞在此短暂处理期间迅速回到G0期，此后在继续进入G1期之前需要8小时的准备期。年龄大于4小时的细胞，即处于G1期中期或后期的细胞，已经致力于DNA合成（合成前或G1ps细胞）。因此，这些细胞以及S期和G2期细胞不受短暂血清饥饿或环己酰亚胺短暂处理的影响。在本文中，我们表明，在暴露于无血清培养基1 - 2小时后出现的10小时有丝分裂间期延迟，可以通过任何一种纯化的生长因子，即表皮生长因子（EGF）、胰岛素或血小板衍生生长因子（PDGF）的存在而完全抵消。相比之下，在更长时间（8小时）暴露于无血清培养基后出现的有丝分裂间期延迟，不再能被EGF或胰岛素抵消。然而，PDGF在这方面仍然有效。最有趣的是，由4小时暴露于CH诱导的12小时总细胞分裂间期延迟，可以被EGF、PDGF或胰岛素有效抵消。然而，这种对CH处理细胞的影响，只有在存在10%血清的情况下，生长因子才能抵消。这表明PDGF、EGF或胰岛素与一种未鉴定的血清因子之间存在协同作用。将短暂血清饥饿和暴露于CH对细胞周期时间的影响，与对蛋白质合成和降解速率的影响进行了比较。尽管发现生长因子可部分恢复血清饥饿对蛋白质合成和降解的影响，但我们认为生长因子通过另一种机制阻止细胞离开细胞周期，而不仅仅是通过影响总体蛋白质积累水平。
