IDIS-Neoplasia and Endocrine Differentiation, Department of Physiology, CIMUS, School of Medicine, University of Santiago de Compostela USC, Santiago de Compostela, Spain.
Oncogene. 2012 Jun 7;31(23):2824-35. doi: 10.1038/onc.2011.458. Epub 2011 Oct 24.
Somatotrophs produce growth hormone (GH) and are the most abundant secretory cells of the pituitary. Somatotrophs express the transcription factor Pit-1 and the dependence receptor RET, its co-receptor GFRa1 and ligand GDNF. Pit-1 is a transcription factor essential for somatotroph proliferation and differentiation and for GH expression. GDNF represses excess Pit-1 expression preventing excess GH. In the absence of GDNF, RET behaves as a dependence receptor, becomes intracellularly processed and induces strong Pit-1 expression leading to p53 accumulation and apoptosis. How accumulation of Pit-1 leads to p53 expression is unknown. We have unveiled the relationship of Pit-1 with the p19Arf gene. There is a parallel correlation of RET processing, Pit-1 increase and ARF protein and mRNA expression. Interfering the pathway with RET, Pit-1 or p19Arf siRNA blocked apoptosis. We have found a Pit-1 DNA-binding element within the ARF promoter. Pit-1 directly regulates the CDKN2A locus and binds to the p19Arft promoter inducing p19Arf gene expression. The Pit-1-binding element is conserved in rodents and humans. RET/Pit-1 induces p19Arf/p53 and apoptosis not only in a somatotroph cell line but also in primary cultures of pituitary somatotrophs, where ARF siRNA interference also blocks p53 and apoptosis. Analyses of the somatotrophs in whole pituitaries supported the above findings. Thus Pit-1, a differentiation factor, activates the oncogene-induced apoptosis (OIA) pathway as oncogenes exerting a tight control in somatotrophs to prevent the disease due to excess of GH (insulin-resistance, metabolic disease, acromegaly).
生长激素细胞（GH）是脑垂体中分泌生长激素（GH）的最主要细胞，它们表达转录因子 Pit-1 和依赖性受体 RET、其共同受体 GFRa1 和配体 GDNF。Pit-1 是生长激素细胞增殖和分化以及 GH 表达所必需的转录因子。GDNF 抑制 Pit-1 过度表达，防止 GH 过量。在缺乏 GDNF 的情况下，RET 作为依赖性受体，被细胞内加工，并诱导强烈的 Pit-1 表达，导致 p53 积累和细胞凋亡。Pit-1 如何导致 p53 表达尚不清楚。我们揭示了 Pit-1 与 p19Arf 基因的关系。RET 加工、Pit-1 增加和 ARF 蛋白和 mRNA 表达之间存在平行相关性。用 RET、Pit-1 或 p19Arf siRNA 干扰该途径可阻断细胞凋亡。我们在 ARF 启动子内发现了一个 Pit-1 DNA 结合元件。Pit-1 直接调节 CDKN2A 基因座，并结合 p19Arf 启动子，诱导 p19Arf 基因表达。Pit-1 结合元件在啮齿动物和人类中是保守的。RET/Pit-1 不仅在生长激素细胞系中，而且在垂体生长激素细胞的原代培养物中诱导 p19Arf/p53 和细胞凋亡，而 ARF siRNA 干扰也可阻断 p53 和细胞凋亡。对整个垂体中的生长激素细胞进行的分析支持了上述发现。因此，作为一种分化因子的 Pit-1，激活了癌基因诱导的凋亡（OIA）途径，因为癌基因在生长激素细胞中发挥严格的控制作用，以防止因 GH 过量而导致的疾病（胰岛素抵抗、代谢疾病、肢端肥大症）。
