Takada K, Amino N, Tada H, Miyai K
Department of Laboratory Medicine, Osaka University Medical School, Japan.
J Clin Invest. 1990 Nov;86(5):1548-55. doi: 10.1172/JCI114874.
The mechanism of cell proliferation by a combination of thyroid-stimulating hormone (TSH) and insulin-like growth factor-I (IGF-I) was studied in rat thyroid (FRTL-5) cells. IGF-I stimulated an approximately 3.5-fold increase in the rate of Ca2+ influx sustained for at least 6 h in TSH-pretreated cells but not in quiescent cells. The significant cell proliferation was observed when TSH-primed cells were incubated with IGF-I for 24 h but not for 12 h. IGF-I stimulated the rate of Ca2+ influx in a dose-dependent manner that was similar to that for induction of DNA synthesis. Both Ca2+ influx and DNA synthesis observed in response to IGF-I in TSH-primed cells were inhibited by cobalt. In addition, the stimulations of Ca2+ influx and DNA synthesis by IGF-I were dependent on extracellular Ca2+ in TSH-pretreated cells. When TSH-primed cells were pretreated with pertussis toxin, both IGF-I-induced Ca2+ influx and DNA synthesis were abolished. However, pertussis toxin did not block the priming action of TSH or forskolin. When calcium entry was induced by Bay K8644, it stimulated cell growth in TSH-primed cells but not in quiescent cells. Moreover, cobalt and lanthanum inhibited DNA synthesis even when added several hours after the addition of Bay K8644 but not when added 24 h after the growth factor in TSH-primed cells. These findings suggest that at least two important mechanisms may work in response to IGF-I only in the TSH-primed G1 phase of the cell cycle: first, IGF-I can activate directly or indirectly the Ca2+ channel via a pertussis toxin-sensitive substrate in TSH-primed cells; and second, a long lasting calcium entry by IGF-I may be a cell cycle-dependent mitogenic signal.
在大鼠甲状腺（FRTL-5）细胞中研究了促甲状腺激素（TSH）和胰岛素样生长因子-I（IGF-I）联合作用促进细胞增殖的机制。IGF-I可使经TSH预处理的细胞中Ca²⁺内流速率增加约3.5倍，并至少持续6小时，但对静止细胞无此作用。当用IGF-I孵育经TSH预处理的细胞24小时而非12小时时，可观察到明显的细胞增殖。IGF-I以剂量依赖方式刺激Ca²⁺内流速率，这与诱导DNA合成的方式相似。钴可抑制经TSH预处理的细胞中由IGF-I引起的Ca²⁺内流和DNA合成。此外，在经TSH预处理的细胞中，IGF-I对Ca²⁺内流和DNA合成的刺激依赖于细胞外Ca²⁺。当用百日咳毒素预处理经TSH预处理的细胞时，IGF-I诱导的Ca²⁺内流和DNA合成均被消除。然而，百日咳毒素并不阻断TSH或福斯可林的启动作用。当用Bay K8644诱导钙内流时，它可刺激经TSH预处理的细胞生长，但对静止细胞无此作用。此外，即使在添加Bay K8644数小时后添加钴和镧，也会抑制DNA合成，但在经TSH预处理的细胞中在生长因子添加24小时后添加则无此作用。这些发现表明，至少有两种重要机制可能仅在细胞周期的TSH启动的G1期对IGF-I起作用：第一，IGF-I可通过经TSH预处理的细胞中对百日咳毒素敏感的底物直接或间接激活Ca²⁺通道；第二，IGF-I引起的持久钙内流可能是一种细胞周期依赖性的促有丝分裂信号。
