McClain D A, D'Eustachio P, Edelman G M
Proc Natl Acad Sci U S A. 1977 Feb;74(2):666-70. doi: 10.1073/pnas.74.2.666.
Cellular microtubules, microfilaments, and surface receptors have been postulated to form a surface modulating assembly that regulates surface receptor mobility and cell growth. To test this hypothesis, we examined three agents known to affect cell growth [colchicine, concanavalin A (Con A), and the src gene product of Rous sarcoma virus] for their effects on chick embryo fibroblasts. Individual cells from serum-starved normal fibroblast populations became committed to enter S phase at various times over a 12 hr period after exposure to serum. Colchicine and other microtubule-disrupting agents blocked entry into S phase at a point close to the commitment point for each cell. The lectin Con A also blocked entry into the S phase when present in doses sufficient to modulate surface receptor mobility. In contrast, succinyl-Con A, which does not induce surface modulation, had no effect. Both Con A and colchicine blocked the appearance of cytoplasmic factors capable of stimulating DNA replication in a cell-free system. To study endogenous effects on the surface modulating assembly, we infected fibroblasts with a Rous sarcoma virus (tsNY68) having a temperature-sensitive mutation in the transforming (src) gene. We have previously shown that microtubular and microfilamentous structures of the surface modulating assembly are direct or indirect targets of the src gene product with consequent reduction in the capacity of Con A to induce surface modulation. TsNY68-infected fibroblasts shifted to the non-permissive temperature acquired normal microtubular morphology more rapidly (2 hr) than cells grown at the permissive temperature in the presence of protein synthesis inhibitors (7.5 hr). This suggests that the src gene product acts directly on the surface modulating assembly rather than via the nucleus or at the level of protein synthesis. Furthermore, "transformation" of the surface modulating assembly was partly blocked by treatment of the infected cells with Con A but not succinyl-Con A. Both Con A and colchicine inhibited entry into the S phase following a shift from nonpermissive to permissive growth conditions. All of these observations are in accord with the hypothesis that the surface modulating assembly acts as a signal regulator in growth control.
细胞微管、微丝和表面受体被假定形成一个调节表面受体流动性和细胞生长的表面调节组件。为了验证这一假设，我们研究了三种已知影响细胞生长的试剂[秋水仙碱、刀豆球蛋白A（Con A）和劳氏肉瘤病毒的src基因产物]对鸡胚成纤维细胞的影响。血清饥饿的正常成纤维细胞群体中的单个细胞在暴露于血清后的12小时内，会在不同时间进入S期。秋水仙碱和其他破坏微管的试剂在每个细胞接近进入S期的时间点阻止其进入。当刀豆凝集素Con A以足以调节表面受体流动性的剂量存在时，也会阻止进入S期。相比之下，不诱导表面调节的琥珀酰-Con A则没有效果。Con A和秋水仙碱都能阻止在无细胞系统中刺激DNA复制的细胞质因子的出现。为了研究对表面调节组件的内源性影响，我们用一种在转化（src）基因中有温度敏感突变的劳氏肉瘤病毒（tsNY68）感染成纤维细胞。我们之前已经表明，表面调节组件的微管和微丝结构是src基因产物的直接或间接靶点，从而导致Con A诱导表面调节的能力下降。tsNY68感染的成纤维细胞转移到非允许温度后，比在允许温度下存在蛋白质合成抑制剂的情况下生长的细胞更快（2小时）恢复正常微管形态（7.5小时）。这表明src基因产物直接作用于表面调节组件，而不是通过细胞核或在蛋白质合成水平上起作用。此外，用Con A而不是琥珀酰-Con A处理感染细胞，部分阻断了表面调节组件的“转化”。从非允许生长条件转变为允许生长条件后，Con A和秋水仙碱都抑制进入S期。所有这些观察结果都与表面调节组件在生长控制中作为信号调节器的假设一致。
