In vivo and in vitro regulation of pituitary transcription factor-1 (Pit-1) by changes in the hormone environment.
In vivo and in vitro regulation of pituitary transcription factor-1 (Pit-1) by changes in the hormone environment.
复制标题
通过激素环境的变化对垂体转录因子 1 (Pit-1) 进行体内和体外调节。
作者：
S. González‐Parra;J. Chowen;L. Garcia;J. Argente
垂体前叶转录因子-1（Pit-1或GHF-1）是垂体前叶特异性的转录因子，并且参与生长激素（GH）、催乳素（PRL）和促甲状腺激素（TSH）β亚基基因的表达和调节。这三个基因的表达可以通过激素环境的变化来调节，并且认为其中一些作用是通过Pit-1介导的，但是关于该转录因子的生理调节知之甚少。因此，我们首先询问Pit-1基因表达是否由于体内性腺类固醇环境的变化而被修改，以及这是否与GH和/或PRL mRNA水平的变化相关。其次，我们试图确定性类固醇是否通过作用于垂体水平来影响这三种肽的mRNA水平，以及这些作用是雄激素还是雌激素介导的。最后，分析了性类固醇激素如何调节这三个基因对下丘脑神经肽生长激素释放激素（GHRH）和生长抑素（SS）的反应。为此，我们比较了完整的，去势的，去势睾酮替代成年雄性大鼠垂体前叶的Pit-1，GH和PRL mRNA水平。此外，成年男性垂体的原代培养物用于研究雄激素和雌激素对Pit-1、GH和PRL mRNA水平的直接影响。采用原位杂交组织化学方法比较Pit-1、GH和PRL mRNA的相对水平。体内研究的光密度分析表明，去势导致Pit-1、GH和PRL mRNA信号水平分别下降57%、40%和55%。此外，在去势时用睾酮（T）替代完全阻止了所有三种mRNA种类的下降（ANOVA：Pit-1 mRNA，p < 0.0001; GH mRNA，p < 0.0001; PRL mRNA，p < 0.0001）。在体内，T（10（-7）M）和雌二醇（10（-9）M）都能刺激Pit-1 mRNA和PRL mRNA的水平，而双氢睾酮（DHT; 10（-7）M）则无此作用。这些类固醇治疗对体外GH mRNA水平没有影响。此外，GHRH的文化增加GH mRNA水平，以及那些Pit-1和PRL，和SS对GH mRNA水平有相反的效果。然而GH对GHRH的反应并没有被暴露于性类固醇显著改变，SS的作用是。性类固醇的存在能够修改Pit-1和PRL对GHRH和SS的反应。这些结果清楚地表明，性类固醇的循环水平的变化调节垂体前叶的Pit-1的表达，这些变化可以与GH和PRL mRNA水平的相应修改。此外，对Pit-1和PRL mRNA水平的影响至少部分发生在垂体前叶水平，并且是雌激素受体介导的事件。相比之下，性腺类固醇激素对GH mRNA水平的影响不那么直接，最有可能是在下丘脑水平介导的，以及通过调节生长激素对下丘脑因子的反应。我们的结论是，转录因子Pit-1的积极调节生理，并可能参与介导的一些性类固醇和下丘脑因子对某些垂体前叶激素的合成的影响。
Pituitary transcription factor-1 (Pit-1 or GHF-1) is a transcription factor specific to the anterior pituitary and is involved in the expression and regulation of the growth hormone (GH), prolactin (PRL) and thyroid-stimulating hormone (TSH) beta-subunit genes. The expression of these three genes can be modulated by changes in the hormone environment and it is thought that some of these effects are mediated through Pit-1, but little is known about the physiological regulation of this transcription factor. Therefore, we first asked whether Pit-1 gene expression is modified as a result of changes in the in vivo gonadal steroid environment and if this could be correlated with changes in GH and/or PRL mRNA levels. Secondly, we sought to determine if sex steroids affect the mRNA levels of these three peptides by acting at the level of the pituitary and whether these effects are androgen or estrogen mediated. Finally, how sex steroids modulate the response of these three genes to the hypothalamic neuropeptides growth hormone-releasing hormone (GHRH) and somatostatin (SS) was analyzed. To this end, we compared Pit-1, GH and PRL mRNA levels in the anterior pituitary of intact, castrated, and castrated testosterone-replaced adult male rats. In addition, primary cultures of adult male pituitaries were used to study the direct effects of both androgens and estrogens on Pit-1, GH, and PRL mRNA levels. In situ hybridization histochemistry was used to compare relative levels of Pit-1, GH and PRL mRNA. Densitometric analysis of the in vivo studies showed that castration resulted in a 57, 40 and 55% decline in Pit-1, GH and PRL mRNA signal levels, respectively. Furthermore, replacement with testosterone (T) at the time of castration completely prevented the decline in all three mRNA species (ANOVA: Pit-1 mRNA, p < 0.0001; GH mRNA, p < 0.0001; PRL mRNA, p < 0.0001). In vivo, both T (10(-7) M) and estradiol (10(-9) M) were capable of stimulating Pit-1 mRNA and PRL mRNA levels, while dihydrotestosterone (DHT; 10(-7) M) had no effect. There was no effect of any of these steroid treatments on GH mRNA levels in vitro. Addition of GHRH to the cultures increased GH mRNA levels, as well as those of Pit-1 and PRL, and SS had the opposite effect on GH mRNA levels. Whereas the GH response to GHRH was not significantly modified by exposure to sex steroids, the effect of SS was. The presence of sex steroids was capable of modifying the Pit-1 and PRL responses to both GHRH and SS. These results clearly indicate that changes in circulating levels of sex steroids modulate the expression of Pit-1 in the anterior pituitary and that these changes can be correlated with commensurate modifications in GH and PRL mRNA levels. Furthermore, the effect on both Pit-1 and PRL mRNA levels occurs, at least in part, at the level of the anterior pituitary and is an estrogen-receptor-mediated event. In contrast, the effects of gonadal steroids on GH mRNA levels are less direct and are most likely mediated at the level of the hypothalamus, as well as through modulation of the response of the somatotroph to hypothalamic factors. We conclude that the transcription factor Pit-1 is actively regulated physiologically and may be involved in mediating some of the effects of sex steroids and hypothalamic factors on the synthesis of certain anterior pituitary hormones.