Kihara Sachiko, Yamamoto Hideyuki, Ohba Takashi, Shimasaki Shunichi, Okamura Hitoshi
Department of Reproductive Medicine and Surgery, Graduate School of Medical Sciences, Kumamoto University, Japan.
Endocr J. 2006 Apr;53(2):225-35. doi: 10.1507/endocrj.53.225.
Follistatin (FS) is produced and secreted from gonadotroph cells in pituitary gland as well as granulosa cells in the ovary. In the present study, we found that the FS promoter is activated by GnRH in the gonadotroph cell line, LbetaT2. Therefore, we examined the signal transduction pathways involved in the mechanism. The activation of the FS promoter by GnRH was inhibited by calphostin C, a protein kinase C inhibitor, and U0126, a MAP kinase kinase (MEK) inhibitor. Phosphorylation by protein kinase C of myristoylated alanine-rich C kinase substrate (MARCKS) in LbetaT2 cells was observed after 3-min treatment with GnRH and declined after 30 min. The subsequent activation of MAP kinase was also transient, and down-regulation of protein kinase C completely inhibited the MAP kinase activation by GnRH, suggesting that the transient activation of protein kinase C led to the transient activation of MAP kinase. Although phorbol 12-myristate 13-acetate treatment increased phosphorylation of MARCKS and activated MAP kinase, it did not activate the FS promoter. Genistein, a tyrosine kinase inhibitor, completely inhibited the GnRH-induced activation of the FS promoter, while no inhibition of the MAP kinase pathway was observed. These results suggest that the activations of both the protein kinase C and tyrosine kinase pathways are necessary for the activation of the FS promoter in gonadotroph cells.
卵泡抑素（FS）由垂体促性腺激素细胞以及卵巢颗粒细胞产生并分泌。在本研究中，我们发现促性腺激素释放激素（GnRH）可激活促性腺激素细胞系LbetaT2中的FS启动子。因此，我们研究了该机制中涉及的信号转导途径。蛋白激酶C抑制剂钙泊三醇C和丝裂原活化蛋白激酶激酶（MEK）抑制剂U0126可抑制GnRH对FS启动子的激活。用GnRH处理LbetaT2细胞3分钟后，观察到富含肉豆蔻酰化丙氨酸的C激酶底物（MARCKS）被蛋白激酶C磷酸化，30分钟后下降。随后丝裂原活化蛋白激酶的激活也是短暂的，蛋白激酶C的下调完全抑制了GnRH对丝裂原活化蛋白激酶的激活，表明蛋白激酶C的短暂激活导致了丝裂原活化蛋白激酶的短暂激活。尽管佛波酯12 -肉豆蔻酸酯13 -乙酸酯处理增加了MARCKS的磷酸化并激活了丝裂原活化蛋白激酶，但它并未激活FS启动子。酪氨酸激酶抑制剂染料木黄酮完全抑制了GnRH诱导的FS启动子激活，而未观察到对丝裂原活化蛋白激酶途径的抑制。这些结果表明，蛋白激酶C和酪氨酸激酶途径的激活对于促性腺激素细胞中FS启动子的激活都是必需的。
