The identification of new mechanism for controlling LH receptor expression

雌激素被认为可以增强FSH在卵巢中的作用，包括诱导LH受体（LHR）。在这项研究中，我们阐明了雌激素对FSH诱导大鼠颗粒细胞LHR的作用机制。与FSH单独诱导的LHR mRNA水平相比，雌二醇以时间和剂量依赖性方式明显增强FSH诱导的LHR mRNA增加，在72 h时最大增加约3.5倍。然后，我们研究了雌激素对LHR mRNA的影响是否是由于转录增加和/或mRNA稳定性改变。用含有LHR 5 '侧翼区的质粒进行荧光素酶测定，没有显示雌二醇增加FSH诱导的启动子活性。相反，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的稳定性增加至少是雌激素调节LHR mRNA的原因。最近，甲羟戊酸激酶（Mvk）被确定为一个反式因子，结合LHR mRNA和改变LHR mRNA的稳定性在卵巢。我们发现，雌二醇，FSH，降低Mvk mRNA水平在大鼠颗粒细胞培养，导致LHR mRNA的上调，Mvk mRNA的表达呈负相关。此外，FSH诱导的LHR表达在雌激素存在下的增强被Mvk通过瞬时转染的过表达所消除。总之，这些数据表明，由于当雌激素负控制Mvk时稳定性增加，LHR mRNA上调。

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.