Qian X, Jin L, Lloyd R V
Department of Laboratory Medicine and Pathology, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.
Endocrine. 1999 Oct;11(2):123-30. doi: 10.1385/ENDO:11:2:123.
The anterior pituitary gland produces neuronal nitric oxide synthase (nNOS) and nitric oxide regulates secretion of various anterior pituitary hormones. Estrogen has many functions in anterior pituitary cells including stimulation of prolactin (PRL) cell proliferation and secretion of various anterior pituitary hormones. However, the role of estradiol-17beta (E2) in regulating pituitary nNOS expression has not been previously examined. We studied the regulation of nNOS in normal pituitaries, and neoplastic GH3 pituitary tumors in order to analyze the effects of E2 on nNOS in pituitary cells. GH3 tumors expressed higher levels of nNOS proteins compared to normal pituitaries. Estrogen downregulated nNOS mRNA and protein in both estrogen-treated pituitaries with PRL cell hyperplasia and in GH3 tumors implanted into the flank of rats treated with E2 in silastic tubing. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated three alternatively spliced nNOS transcript isoforms--nNOSa, nNOSb, and nNOSc mRNAs--with distinct 5' untranslated first exons that arose from alternative splicing to a common second exon. All three spliced isoforms were found in the normal rat pituitary, whereas nNOSa and nNOSb, but not nNOSc, were expressed in GH3 tumors implanted into Wistar-Furth rats. E2 also downregulated the nNOSa alternative mRNA transcript isoform in vivo. These results indicate that the biological activity of nNOS in the normal rat anterior pituitary and in pituitary tumors is regulated by a complex pattern of alternative splicing and that some of these mRNA isoforms as well as nNOS protein are regulated by estrogen. Our results also indicate that the levels of nNOS and the alternatively spliced nNOS transcript between normal and GH3 pituitary tumors are different.
腺垂体产生神经元型一氧化氮合酶（nNOS），一氧化氮可调节腺垂体各种激素的分泌。雌激素在腺垂体细胞中有多种功能，包括刺激催乳素（PRL）细胞增殖以及腺垂体各种激素的分泌。然而，此前尚未研究过17β-雌二醇（E2）在调节垂体nNOS表达中的作用。我们研究了正常垂体以及垂体肿瘤GH3中nNOS的调节情况，以分析E2对垂体细胞中nNOS的影响。与正常垂体相比，GH3肿瘤中nNOS蛋白表达水平更高。在PRL细胞增生的经雌激素处理的垂体以及植入经E2硅橡胶管处理大鼠侧腹的GH3肿瘤中，雌激素均下调了nNOS mRNA和蛋白水平。逆转录聚合酶链反应（RT-PCR）分析显示有三种选择性剪接的nNOS转录异构体——nNOSa、nNOSb和nNOSc mRNA——具有不同的5'非翻译第一外显子，这些外显子由选择性剪接产生共同的第二外显子。在正常大鼠垂体中发现了所有这三种剪接异构体，而在植入Wistar-Furth大鼠的GH3肿瘤中表达的是nNOSa和nNOSb，而非nNOSc。E2在体内也下调了nNOSa选择性mRNA转录异构体。这些结果表明，正常大鼠腺垂体和垂体肿瘤中nNOS的生物活性受复杂的选择性剪接模式调节，并且这些mRNA异构体中的一些以及nNOS蛋白受雌激素调节。我们的结果还表明，正常垂体和GH3垂体肿瘤之间nNOS水平以及选择性剪接的nNOS转录本不同。
