Regulation of IGF-I mRNA and signal transducers and activators of transcription-3 and-5 (Stat-3 and-5) by GH in C2C12 myoblasts
Regulation of IGF-I mRNA and signal transducers and activators of transcription-3 and-5 (Stat-3 and-5) by GH in C2C12 myoblasts
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DOI：
10.1210/en.143.2.492
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发表时间：
2002-02-01
期刊：
影响因子：
4.8
通讯作者：
Lang, CH
中科院分区：
文献类型：
--
作者：
Frost, RA;Nystrom, GJ;Lang, CH
GH 和 IGF-I 是调节人体纵向生长和维持瘦体重的关键激素。肝细胞中 GH 对 IGF-I 表达的调节已有充分记录。然而，人们对于 IGF-I 在外周组织（如肌肉）中的调节知之甚少。我们检查了 C2C12 成肌细胞中 GH 和 IGF-I 对 IGF-I mRNA 的调节。 GH 刺激 IGF-I mRNA 的积累，呈剂量和时间依赖性。当 GH 剂量低至 0.75 ng/ml 且暴露于 GH 短短 1 小时后，观察到 IGF-I mRNA 的升高，并且这种升高需要持续的转录和翻译。以脉冲方式施加 GH 10 分钟，然后是 8 小时的脉冲间隔，与连续暴露相比，IGF-I mRNA 的增加程度更大。 GH 刺激 GH 受体、信号转导器和转录激活剂 3 (Stat3) 和 Stat5 的酪氨酸磷酸化。如果细胞在上次 GH 暴露后 2 小时内接受 GH 脉冲，Stat5 对额外的磷酸化具有抵抗力。不应期持续4小时，6小时后细胞可再次受到最大刺激。在从先前施用 GH 中恢复的细胞中，Stat3 磷酸化也得到增强。酪氨酸激酶抑制剂金雀异黄素、PP1 和 AG-490 以及 MAPK 激酶抑制剂 PD98059 不会阻断 Stat3 或 Stat5 磷酸化。相比之下，WHI-P154（一种 Janus 激酶 3 抑制剂）可剂量依赖性地阻止 Stat3 磷酸化，但不能阻止 Stat5 磷酸化。 Stat3 的 GH 诱导核转运同样被 WHI-P164 抑制。最重要的是，GH 依赖性 IGF-I mRNA 表达被 WHIP154 抑制。相反，IGF-I mRNA表达被IGF-I肽抑制，且IGF-I的作用优于GH。 IGF-I mRNA 受 PI3K 和 MAPK 信号转导途径调节，但 IGF-I 肽主要通过渥曼青霉素敏感途径发出信号，下调其自身 mRNA。我们的数据表明 Janus 激酶（Jak2 或 Jak3）及其下游靶标（Stat3 和 Stat5）可能在 IGF-I mRNA 的表达和成肌细胞对 GH 的反应中发挥重要作用。此外，C2C12 细胞似乎是检查 GH 对 Janus 激酶/Stat 信号传导的调节和 IGF-I mRNA 调节的良好模型系统。
GH and IGF-I are critical hormones for the regulation of longitudinal growth and the maintenance of lean body mass in humans. The regulation of IGF-I expression by GH in hepatocytes is well documented; however less is known about the regulation of IGF-I in peripheral tissues such as muscle. We have examined the regulation of IGF-I mRNA by GH and IGF-I in C2C12 myoblasts. GH stimulated the accumulation of IGF-I mRNA dose- and time-dependently. An elevation of IGF-I mRNA was observed with GH doses as low as 0.75 ng/ml and after exposure to GH for as little as 1 h, and the increase required ongoing transcription and translation. GH applied in a pulsatile fashion for 10 min followed by an 8-h interpulse interval increased IGF-I mRNA to a greater extent than continuous exposure. GH stimulated tyrosine phosphorylation of the GH receptor, signal transducer and activator of transcription-3 (Stat3), and Stat5. Stat5 was resistant to additional phosphorylation if cells were given a GH pulse within 2 h of a previous GH exposure. The refractory period lasted for 4 h, and cells could be maximally stimulated again after 6 h. Stat3 phosphorylation was also enhanced in cells that were allowed to recover from a previous application of GH. The tyrosine kinase inhibitors, genistein, PP1, and AG-490, and the MAPK kinase inhibitor, PD98059, did not block Stat3 or Stat5 phosphorylation. In contrast, WHI-P154, a Janus kinase-3 inhibitor, dose-dependently prevented Stat3, but not Stat5, phosphorylation. GH-inducible nuclear transport of Stat3 was likewise inhibited by WHI-P164. Most importantly, GH-dependent IGF-I mRNA expression was inhibited by WHIP154. In contrast, IGF-I mRNA expression was inhibited by IGF-I peptide, and the effect of IGF-I was dominant over that of GH. IGF-I mRNA was regulated by both PI3K and MAPK signal transduction pathways, but IGF-I peptide signaled predominantly through a wortmannin-sensitive pathway to down-regulate its own mRNA. Our data suggest that Janus kinases (Jak2 or Jak3) and their downstream targets (Stat3 and Stat5) may play important roles in the expression of IGF-I mRNA and the myoblast response to GH. In addition, C2C12 cells appear to be a good model system to examine GH regulation of Janus kinase/Stat signaling and the regulation of IGF-I mRNA.