The identification of new mechanism for controlling LH receptor expression

雌激素被认为可以增强卵巢中卵泡刺激素的作用，包括诱导黄体生成素受体（LHR）。在本研究中，我们阐明了雌激素对FSH诱导大鼠颗粒细胞LHR的作用机制。雌二醇明显增强了FSH诱导的LHR mRNA的增加，并呈时间和剂量依赖性，与FSH单独诱导的LHR mRNA水平相比，在72小时时最大增幅约为3.5倍。然后，我们研究了雌激素对LHR mRNA的影响是否由于转录增加和/或mRNA稳定性的改变。用含有LHR 5'-侧翼区域的质粒进行的荧光素酶测定没有显示雌二醇增加FSH诱导的启动子活性。相比之下，LHR mRNA的衰减曲线显示FSH和雌二醇的半衰期显著增加，表明LHR mRNA稳定性的增加至少与雌激素对LHR mRNA的调节有关。最近，甲羟戊酸激酶（mevalonate kinase, Mvk）被发现是一种与卵巢中LHR mRNA结合并改变LHR mRNA稳定性的反式因子。我们发现雌二醇和FSH可以降低大鼠颗粒细胞培养中Mvk mRNA的水平，导致LHR mRNA的上调，而LHR mRNA的表达与Mvk mRNA的表达呈负相关。此外，在雌激素存在的情况下，fsh诱导的LHR表达的增强被瞬时转染Mvk的过表达所消除。综上所述，这些数据表明，当雌激素负性控制Mvk时，LHR mRNA的上调是由于稳定性增加。

Estrogen has been considered to enhance FSH actions in the ovary including the induction of the LH receptor (LHR). In this study, we elucidated the mechanism underlying the effect of estrogen on the induction of LHR by FSH in rat granulosa cells. Estradiol clearly enhanced the FSH-induced LHR mRNA increase in a time- and dose-dependent manner, with a maximum increase of approximately 3.5-fold at 72 hr compared to the level of LHR mRNA solely induced by FSH. We then investigated whether the effect of estrogen on LHR mRNA was due to increased transcription and/or altered mRNA stability A luciferase assay with the plasmid containing the LHR 5'-flanking region did not show that estradiol increased the promoter activity induced by FSH. In contrast, the decay curves for LHR mRNA showed a significant increase in half-life with FSH and estradiol, suggesting that the increased stability of LHR mRNA is at least responsible for the regulation of LHR mRNA by estrogen. Recently, mevalonate kinase (Mvk) was identified as a trans-factor that binds to LHR mRNA and alters LHR mRNA stability in the ovary. We found that estradiol, with FSH, decreased Mvk mRNA levels in rat granulosa cell culture, resulting in up-regulation of LHR mRNA that was inversely correlated to Mvk mRNA expression. Furthermore, the augmentation of FSH-induced LHR expression in the presence of estrogen was erased with the overexpression of Mvk by transient transfection.Taken together, these data indicate that LHR mRNA is upregulated due to increased stability when estrogen negatively controls Mvk.