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Endocrinology. 2013 Dec;154(12):4826-34. doi: 10.1210/en.2013-1619. Epub 2013 Sep 24.
LH receptor (LHR) expression in the ovary is regulated by the RNA binding protein, (LHR mRNA binding protein [LRBP]), which has been identified as being mevalonate kinase. This study examined the role of microRNA miR-122 in LRBP-mediated LHR mRNA expression. Real-time PCR analysis of ovaries from pregnant mare serum gonadotropin/human chorionic gonadotropin (hCG)-primed female rats treated with hCG to down-regulate LHR expression showed that an increase in miR-122 expression preceded LHR mRNA down-regulation. The expression of miR-122 and its regulation was confirmed using fluorescent in situ hybridization of the frozen ovary sections using 5'-fluorescein isothiocyanate-labeled miR-122 locked nucleic acid probe. The increased expression of miR-122 preceded increased expression of LRBP mRNA and protein, and these increases were followed by LHR mRNA down-regulation. Inhibition of protein kinase A (PKA) and ERK1/2 signaling pathways by H89 and UO126, respectively, attenuated the hCG-mediated up-regulation of miR-122 levels. This was also confirmed in vitro using human granulosa cells. These results suggest the possibility that hCG-mediated miR-122 expression is mediated by the activation of cAMP/PKA/ERK signaling pathways. Inhibition of miR-122 by injection of the locked nucleic acid-conjugated antagomir of miR-122 abrogated the hCG-mediated increases in LRBP protein expression. Because it has been previously shown that miR-122 regulates sterol regulatory element-binding proteins (SREBPs) and SREBPs, in turn, regulate LRBP expression, the role of SREBPs in miR-122-mediated increase in LRBP expression was then examined. The levels of active forms of both SREBP-1a and SREBP-2 were increased in response to hCG treatment, and the stimulatory effect was sustained up to 4 hours. Taken together, our results suggest that hCG-induced down-regulation of LHR mRNA expression is mediated by activation of cAMP/PKA/ERK pathways to increase miR-122 expression, which then increases LRBP expression through the activation of SREBPs.
黄体生成素受体 (LHR) 在卵巢中的表达受 RNA 结合蛋白（黄体生成素 mRNA 结合蛋白 [LRBP]）调控，该蛋白已被鉴定为甲羟戊酸激酶。本研究探讨了 microRNA miR-122 在 LRBP 介导的 LHR mRNA 表达中的作用。实时 PCR 分析显示，在接受人绒毛膜促性腺激素 (hCG) 处理的怀孕母马血清促性腺激素/人绒毛膜促性腺激素 (hCG) 诱导的雌性大鼠的卵巢中，miR-122 表达的增加先于 LHR mRNA 的下调。使用冷冻卵巢切片的荧光原位杂交，用 5'-荧光素异硫氰酸酯标记的 miR-122 锁定核酸探针，对 miR-122 的表达及其调控进行了验证。miR-122 的表达增加先于 LRBP mRNA 和蛋白的表达增加，随后 LHR mRNA 下调。分别用 H89 和 UO126 抑制蛋白激酶 A (PKA) 和 ERK1/2 信号通路，减弱了 hCG 介导的 miR-122 水平上调。在体外使用人颗粒细胞也得到了证实。这些结果表明，hCG 介导的 miR-122 表达可能是通过激活 cAMP/PKA/ERK 信号通路介导的。注射 miR-122 锁定核酸偶联的抗 miR-122 可阻断 hCG 介导的 LRBP 蛋白表达增加。因为先前已经表明 miR-122 调节固醇调节元件结合蛋白 (SREBPs)，而 SREBPs 又调节 LRBP 的表达，所以随后研究了 SREBPs 在 miR-122 介导的 LRBP 表达增加中的作用。SREBP-1a 和 SREBP-2 的活性形式都因 hCG 处理而增加，并且刺激作用持续至 4 小时。综上所述，我们的结果表明，hCG 诱导的 LHR mRNA 表达下调是通过激活 cAMP/PKA/ERK 途径增加 miR-122 表达来介导的，miR-122 表达增加通过激活 SREBPs 增加 LRBP 表达。
