Shupnik M A, Pitt L K, Soh A Y, Anderson A, Lopes M B, Laws E R
Department of Internal Medicine, University of Virginia Health Science Center, Charlottesville 22908, USA.
J Clin Endocrinol Metab. 1998 Nov;83(11):3965-72. doi: 10.1210/jcem.83.11.5236.
The physiological effects of estrogen on the pituitary, including cellular proliferation and regulation of hormone synthesis, are mediated by the nuclear estrogen receptor (ER). The ER acts as a dimer to modulate gene transcription and contains specific functional domains encoded in different exons. Two separate, but related, forms of the receptor (ERalpha and ERbeta) exist, with distinct tissue and cell patterns of expression. Additional ER isoforms, generated by alternative messenger ribonucleic acid (mRNA) exon splicing, have been defined in several tissues and are postulated to play a role in tumorigenesis or in modulating the estrogen response. We examined 71 human pituitary adenomas of varying phenotypes and 6 normal pituitary specimens for ER mRNA forms by RT-PCR and hybridization blotting analysis. All prolactinomas (n = 14) contained ERalpha, and several contained ERbeta (5 of 14) mRNA. In comparison, 6 tumors that expressed PRL and GH expressed ERbeta (4 of 6) more frequently than ERalpha (3 of 6). ERbeta mRNA was also found more frequently in null cell (8 of 24 ERalpha and 14 of 24 ERbeta) and gonadotrope (13 of 21 ERalpha and 18 of 21 ERbeta) tumors. Additionally, ERbeta was found in 4 of 6 tumors that contained only GH, although ERalpha was not observed in this tumor type. Expression of the two ER forms within a tumor type was overlapping, but some tumors contained only 1 isoform. Expression of ERalpha mRNA splice variants also varied with cell type. All normal pituitaries contained ERalpha deletions of exon 4, 5, and 7, whereas only 2 of 6 samples contained the exon 2 deletion variant. Although the same ERalpha mRNA variants were observed among the various tumor types, the proportion of specific splice variants expressed varied. For example, most ER-positive prolactinomas expressed ERalpha variants with deletions of exon 2, 4, or 5, whereas gonadotropin tumors preferentially expressed the ERalpha exon 7 deletion variant. A novel ERbeta mRNA splice variant, missing exon 2, was observed in a majority of all ERbeta-positive tumors. Immunoblotting analysis of ERalpha and ERbeta proteins supported the mRNA results. Because ERalpha and ERbeta have different biological responses to selective ER modulators, and the ER deletion variants have biological effects distinct from those of the full-length ER, expression of these isoforms may influence the biological properties of these tumors and affect their ability to respond to estrogen and antiestrogen therapies.
雌激素对垂体的生理作用，包括细胞增殖和激素合成的调节，是由核雌激素受体（ER）介导的。ER作为二聚体调节基因转录，并包含由不同外显子编码的特定功能域。存在两种独立但相关的受体形式（ERα和ERβ），具有不同的组织和细胞表达模式。通过选择性信使核糖核酸（mRNA）外显子剪接产生的其他ER亚型已在多个组织中得到定义，并推测在肿瘤发生或调节雌激素反应中发挥作用。我们通过逆转录聚合酶链反应（RT-PCR）和杂交印迹分析，检测了71例不同表型的人垂体腺瘤和6例正常垂体标本中的ER mRNA形式。所有催乳素瘤（n = 14）均含有ERα，部分还含有ERβ（14例中的5例）mRNA。相比之下，6例同时表达催乳素（PRL）和生长激素（GH）的肿瘤中，表达ERβ（6例中的4例）的频率高于ERα（6例中的3例）。在无功能细胞肿瘤（24例ERα中有8例，24例ERβ中有14例）和促性腺激素细胞肿瘤（21例ERα中有13例，21例ERβ中有18例）中，ERβ mRNA也更常见。此外，在6例仅含GH的肿瘤中，有4例发现了ERβ，而在该肿瘤类型中未观察到ERα。同一肿瘤类型中两种ER形式的表达有重叠，但有些肿瘤仅含有1种亚型。ERα mRNA剪接变体的表达也因细胞类型而异。所有正常垂体均含有外显子4、5和7缺失的ERα，而6个样本中只有2个含有外显子2缺失变体。虽然在各种肿瘤类型中观察到相同的ERα mRNA变体，但特定剪接变体的表达比例不同。例如，大多数ER阳性催乳素瘤表达外显子2、4或5缺失的ERα变体，而促性腺激素肿瘤则优先表达外显子7缺失的ERα变体。在大多数ERβ阳性肿瘤中观察到一种缺失外显子2的新型ERβ mRNA剪接变体。ERα和ERβ蛋白的免疫印迹分析支持了mRNA结果。由于ERα和ERβ对选择性ER调节剂有不同的生物学反应，且ER缺失变体具有与全长ER不同的生物学效应，这些亚型的表达可能会影响这些肿瘤的生物学特性，并影响它们对雌激素和抗雌激素治疗的反应能力。
