Menon K M J, Menon Bindu
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA.
Indian J Med Res. 2014 Nov;140 Suppl(Suppl 1):S112-9.
A specific luteinizing hormone receptor (LHR) mRNA binding protein (LRBP) has been identified and purified. This LH receptor mRNA binding protein selectively binds to the polypyrimidine rich bipartite sequence in the coding region of the LHR mRNA and accelerates its degradation. In response to preovulatory LH surge, the LH receptor expression in the ovary undergoes downregulation by accelerated degradation of LH receptor mRNA through the involvement of this RNA binding protein. Here we describe the intracellular mechanism triggered by LH/hCG (human chorionic gonadotropin) that leads to the regulated degradation of LH receptor mRNA. Downregulation of LH receptor mRNA was induced by treatment of cultured human granulosa cells with 10 IU of hCG. Activation of downstream target, extracellular signal-regulated protein kinase 1 and 2 (ERK 1/2) showed an increase within five min and sustained up to 1 h. Confocal analysis showed that ERK1/2 translocates to the nucleus after 15 min of hCG treatment. This leads to an increase in LRBP expression which then causes downregulation of LH receptor mRNA by accelerating its degradation. Treatment with UO126 or transfection with ERK specific siRNA (small interfering RNA) resulted in the abolishment of ERK activation as well as LHR mRNA downregulation. RNA electrophoretic mobility gel shift assay of the cytosolic fractions showed that hCG-induced increase in the LH receptor mRNA binding activity was also abrogated by these treatments. These results show that LH/hCG-induced LH receptor mRNA downregulation is initiated by the activation of ERK1/2 pathway by regulating the expression and activity of LH receptor mRNA binding activity.
一种特异性促黄体生成素受体（LHR）mRNA结合蛋白（LRBP）已被鉴定和纯化。这种促黄体生成素受体mRNA结合蛋白选择性地结合促黄体生成素受体mRNA编码区富含多嘧啶的双联体序列，并加速其降解。在排卵前促黄体生成素激增的反应中，卵巢中促黄体生成素受体的表达通过这种RNA结合蛋白的参与，通过促黄体生成素受体mRNA的加速降解而发生下调。在此，我们描述了由促黄体生成素/人绒毛膜促性腺激素（hCG）触发的细胞内机制，该机制导致促黄体生成素受体mRNA的调控降解。用10 IU的hCG处理培养的人颗粒细胞可诱导促黄体生成素受体mRNA的下调。下游靶点细胞外信号调节蛋白激酶1和2（ERK 1/2）的激活在5分钟内增加，并持续长达1小时。共聚焦分析显示，hCG处理15分钟后ERK1/2转位至细胞核。这导致LRBP表达增加，进而通过加速其降解导致促黄体生成素受体mRNA下调。用UO126处理或用ERK特异性小干扰RNA（siRNA）转染导致ERK激活以及促黄体生成素受体mRNA下调的消除。对胞质部分进行的RNA电泳迁移率凝胶迁移试验表明，这些处理也消除了hCG诱导的促黄体生成素受体mRNA结合活性的增加。这些结果表明，促黄体生成素/ hCG诱导的促黄体生成素受体mRNA下调是通过调节促黄体生成素受体mRNA结合活性的表达和活性，由ERK1/2途径的激活引发的。
