Mitchner N A, Garlick C, Ben-Jonathan N
Department of Cell Biology, University of Cincinnati Medical School, Ohio 45267-0521, USA.
Endocrinology. 1998 Sep;139(9):3976-83. doi: 10.1210/endo.139.9.6181.
The pituitary gland is a heterogeneous tissue comprised of several hormone secreting and supporting cells, most of which are targeted by estrogens. Estrogen-induced changes in the pituitary are presumably mediated via the classical estrogen receptor, ER alpha. However, a novel receptor, ER beta, and pituitary-specific truncated estrogen receptor products (TERPs) were recently identified. The objectives of this study were to examine the distribution of these receptors in the rat pituitary and compare their regulation by estradiol in Sprague-Dawley and the estrogen-sensitive Fischer 344 rats. Pituitary cryosections were subjected to immunocytochemistry for specific cell types, followed by in situ hybridization for ER alpha or ER beta. ER alpha was expressed by approximately 45% of the lactotrophs and melanotrophs, 35% of the corticotrophs and folliculo-stellate cells, and 25% of the gonadotrophs. The expression of ER beta showed a similar pattern but was generally lower than ER alpha. In two cell types, melanotrophs and gonadotrophs, ER beta expression was significantly lower than ER alpha. In the second experiment, pituitary sections were immunostained for ER alpha, followed by in situ hybridization for ER beta. Only a minute population (6-10%) of either anterior or intermediate lobe cells coexpressed ER alpha and ER beta. In the next experiment, Fischer 344 and Sprague-Dawley rats were injected with oil or estradiol for 24 h. Total RNA from dissected anterior and posterior (neurointermediate) pituitaries was subjected to RT-PCR for ER alpha, ER beta, or TERPs. Interestingly, ER alpha and ER beta were unchanged by estradiol in either lobe of the pituitary. In contrast, estradiol increased pituitary TERP messenger RNA levels 4- to 7-fold. A 20-kDa TERP protein was detected by Western blots in the pituitary but not the uterus. There were no differences in the estradiol-induced expression of any of the receptors between the two strains of rats. We conclude that: 1) ER beta is expressed in all anterior and intermediate lobe cell types examined, albeit at a lower level than ER alpha; 2) no more than 10% of pituitary cells coexpress ER alpha and ER beta; and 3) estradiol markedly increases TERP messenger RNA levels but does not alter the expression of ER alpha or ER beta. We propose that estrogen receptor heterogeneity contributes to the diversity of pituitary cell responsiveness to estrogens.
垂体是一种异质性组织，由几种分泌激素的细胞和支持细胞组成，其中大多数细胞都受雌激素作用。雌激素诱导的垂体变化可能是通过经典雌激素受体α（ERα）介导的。然而，最近发现了一种新的受体——雌激素受体β（ERβ）以及垂体特异性截短雌激素受体产物（TERP）。本研究的目的是检测这些受体在大鼠垂体中的分布，并比较它们在斯普拉格-道利大鼠和雌激素敏感的费希尔344大鼠中受雌二醇调节的情况。垂体冰冻切片针对特定细胞类型进行免疫细胞化学检测，随后进行ERα或ERβ的原位杂交。约45%的催乳素细胞和促黑素细胞、35%的促肾上腺皮质激素细胞和滤泡星状细胞以及25%的促性腺激素细胞表达ERα。ERβ的表达呈现相似模式，但总体低于ERα。在两种细胞类型，即促黑素细胞和促性腺激素细胞中，ERβ的表达显著低于ERα。在第二个实验中，垂体切片先进行ERα免疫染色，随后进行ERβ原位杂交。在前叶或中叶细胞中，只有极少部分（6 - 10%）同时表达ERα和ERβ。在接下来的实验中，给费希尔344大鼠和斯普拉格-道利大鼠注射油剂或雌二醇24小时。从分离出的垂体前叶和后叶（神经中间叶）提取的总RNA进行ERα、ERβ或TERP的逆转录聚合酶链反应（RT-PCR）。有趣的是，雌二醇对垂体任何一叶中的ERα和ERβ均无影响。相反，雌二醇使垂体TERP信使核糖核酸水平增加4至7倍。通过蛋白质免疫印迹法在垂体而非子宫中检测到一种20 kDa的TERP蛋白。两种品系大鼠之间，雌二醇诱导的任何一种受体表达均无差异。我们得出以下结论：1）在所检测的垂体前叶和中叶所有细胞类型中均有ERβ表达，尽管其水平低于ERα；2）不超过10%的垂体细胞同时表达ERα和ERβ；3）雌二醇显著增加TERP信使核糖核酸水平，但不改变ERα或ERβ的表达。我们认为雌激素受体的异质性导致了垂体细胞对雌激素反应的多样性。
