Robinson R A, Branum E L, Volkenant M E, Moses H L
Cancer Res. 1982 Jul;42(7):2633-8.
Previous studies have shown that the nontransformed AKR-2B cells when arrested in the G1 phase of the cell cycle due to low-molecule-weight nutrient (amino acid) deficiency exhibit a 5- to 10-fold lower level of epidermal growth factor (EGF) receptor activity than do the same cells in the rapidly growing state or arrested in G1 due to growth factor deficiency. The chemically transformed AKR-MCA and C3H/MCA-58 cell lines spontaneously arrest growth in G1 due to nutrient deficiency when grown to saturation density in medium with 10% fetal bovine serum. An examination of 125I-labeled EGF binding in rapidly growing and G1-arrested AKR-MCA and C3H/MCA-58 cells showed that the G1-arrested chemically transformed cells also have a 10- to 20-fold reduction in the amount of 125I-labeled EGF binding relative to the same cells in the rapidly growing state. Stimulation of DNA synthesis in the arrested cells by the addition of serum-free medium caused a 6- to 10-fold increase in 125I-labeled EGF binding. This recovery of receptor activity was inhibited by actinomycin D and cycloheximide, suggesting that new messenger RNA synthesis as well as increased protein synthesis is necessary for the recovery of EGF binding. A comparison of EGF binding in C3H/MCA-58 cells and the nontransformed parent line (C3H/10T 1/2) in the rapidly growing state showed the same approximate level of receptor activity. However, the rapidly growing AKR-MCA cells had approximately one-tenth the amount of EGF binding as did the rapidly growing nontransformed parent line (AKR-2B). Scatchard analysis of binding data showed a 10-fold greater number of receptors in the AKR-2B cells relative to the AKR-MCA cells with a lesser difference in apparent receptor affinity. The chemically transformed BP-3T3, like the other two chemically transformed lines, was also demonstrated to arrest growth spontaneously due to nutrient deficiency with an associated 100-fold decrease in EGF binding. Rapidly growing BP-3T3 cells had only slightly less 125I-labeled EGF binding than did the nontransformed parent line (BALB-3T3) in the rapidly growing state. The data indicate that one mechanism for reduction of EGF binding in chemically transformed cells is the propensity of these cells to arrest growth in G1 at saturation density due to low-molecular-weight nutrient deficiency, a state associated with decreased EGF binding.
先前的研究表明，未转化的AKR - 2B细胞在因低分子量营养素（氨基酸）缺乏而停滞于细胞周期的G1期时，其表皮生长因子（EGF）受体活性水平比处于快速生长状态或因生长因子缺乏而停滞于G1期的相同细胞低5至10倍。化学转化的AKR - MCA和C3H/MCA - 58细胞系在含10%胎牛血清的培养基中生长至饱和密度时，会因营养缺乏而自发地在G1期停滞生长。对快速生长和G1期停滞的AKR - MCA及C3H/MCA - 58细胞中125I标记的EGF结合情况的检测表明，与处于快速生长状态的相同细胞相比，G1期停滞的化学转化细胞中125I标记的EGF结合量也减少了10至20倍。通过添加无血清培养基刺激停滞细胞中的DNA合成，导致125I标记的EGF结合增加了6至10倍。受体活性的这种恢复受到放线菌素D和环己酰亚胺的抑制，这表明新信使RNA的合成以及蛋白质合成的增加对于EGF结合的恢复是必要的。对处于快速生长状态的C3H/MCA - 58细胞和未转化的亲代细胞系（C3H/10T 1/2）中的EGF结合情况进行比较，结果显示受体活性水平大致相同。然而，快速生长的AKR - MCA细胞的EGF结合量约为快速生长的未转化亲代细胞系（AKR - 2B）的十分之一。对结合数据进行Scatchard分析表明，相对于AKR - MCA细胞，AKR - 2B细胞中的受体数量多10倍，而表观受体亲和力的差异较小。与其他两个化学转化细胞系一样，化学转化的BP - 3T3细胞也被证明会因营养缺乏而自发地停滞生长，同时EGF结合量下降100倍。快速生长的BP - 3T3细胞在快速生长状态下的125I标记的EGF结合量仅略低于未转化的亲代细胞系（BALB - 3T3）。这些数据表明，化学转化细胞中EGF结合减少的一种机制是，这些细胞在饱和密度时因低分子量营养缺乏而倾向于在Gz期停滞生长，这种状态与EGF结合减少相关。
