The identification of new mechanism for controlling LH receptor expression

雌激素被认为可以增强卵泡刺激素在卵巢中的作用，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FSH诱导的LHR mRNA表达，且呈时间和剂量依赖关系，72小时时最大值约为单独FSH诱导的3.5倍。我们进一步研究了雌激素对LHR基因表达的影响是否是由于转录增加和/或改变了基因的稳定性。用含有LHR 5‘-侧翼区的质粒进行的荧光素酶活性检测表明，雌激素并没有增加FSH诱导的启动子活性。相反，LHR mRNA的衰减曲线在FSH和雌二醇的作用下半衰期显著延长，提示LHR mRNA稳定性的提高至少与雌激素对LHR mRNA的调节有关。近年来发现甲氧戊酸激酶(MVK)是一种反式因子，能与LHR基因结合，改变LHR基因在卵巢中的稳定性。我们发现，在FSH的作用下，雌二醇降低了培养的大鼠颗粒细胞MVK基因的表达水平，导致LHR基因的表达上调，而LHR基因的表达与MVK基因的表达呈负相关。此外，在雌激素存在的情况下，FSH诱导的LHR表达的增加随着MVK的瞬时表达而被消除。综上所述，这些数据表明，当雌激素负性控制MVK时，LHR mRNA的上调是因为稳定性增加。

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.