Use of alternative promoters to express the aromatase cytochrome P450 (CYP19) gene in breast adipose tissues of cancer-free and breast cancer patients
Use of alternative promoters to express the aromatase cytochrome P450 (CYP19) gene in breast adipose tissues of cancer-free and breast cancer patients
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DOI：
10.1210/jc.81.11.3843
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发表时间：
1996-11-01
影响因子：
5.8
通讯作者：
Simpson, ER
中科院分区：
文献类型：
--
作者：
Agarwal, VR;Bulun, SE;Simpson, ER
脂肪组织中雌激素的生物合成在许多与雌激素有关的疾病中具有重要意义。最近的证据表明，雌激素在乳腺局部合成是一个独特的意义在老年妇女乳腺癌的发展。C-19类固醇合成雌激素是由细胞色素P450的一种特定形式催化的，即芳香酶细胞色素P450（P450 arom; CYP 19基因的产物）。人CYP 19基因包含9个编码外显子II-X，其转录本在卵巢、胎盘、睾丸、脂肪组织和脑中表达。CYP 19基因的组织特异性表达至少部分通过使用组织特异性启动子来确定，所述启动子产生具有独特5 '非编码末端的转录物。脂肪组织中的转录物含有来源于特定非翻译外显子的5 '末端，对应于来源于近端启动子II及其剪接变体I.3以及远端启动子I.4的表达。本研究的目的是确定这些不同的外显子特异性转录在乳腺脂肪组织中的分布，从无癌妇女接受乳房缩小术和乳腺癌患者，因为这将提供重要的线索，调节芳香酶在这些网站的表达的因素的性质。为了实现这一点，我们采用了竞争性RT-PCR，利用内标的每个外显子特异性转录的CYP 19基因，以及编码区，以评估总CYP 19基因转录。在癌症患者中（n = 18），总CYP 19基因转录水平显着较高的脂肪组织近端的肿瘤相比，脂肪组织远端的肿瘤，与以前的研究结果一致。此外，与无癌症个体（n = 9）的乳腺脂肪组织相比，癌症患者的乳腺脂肪组织中的总转录物水平更高，即使当来自癌症患者的脂肪组织取自没有可检测到的肿瘤的象限时。我们观察到外显子I.4特异性转录物在无癌妇女的乳腺脂肪中占主导地位。在该组织中，启动子II特异性和外显子I.3特异性转录本以低拷贝数存在。另一方面，在乳腺癌患者中，来自乳腺脂肪组织的CYP 19基因转录物主要具有启动子II特异性和外显子I.3特异性序列，而相对较少的转录物在5 '端具有外显子I.4特异性序列。我们的结论是，CYP 19基因在乳腺脂肪组织中的无癌个体的转录优选使用启动子I.4，暗示糖皮质激素和IL-6细胞因子家族的成员在这种表达的调节中的作用。另一方面，携带癌的乳腺脂肪组织中表达的增加是由启动子II和I.3的表达引起的，启动子II和I.3由通过增加cAMP形成起作用的未知因子调节，cAMP形成可能由肿瘤或相关细胞分泌。
Estrogen biosynthesis in adipose tissue has assumed great significance in terms of a number of estrogen-related diseases. Recent evidence suggests that estrogen synthesized locally in the breast is of singular significance in the development of breast cancer in elderly women. The biosynthesis of estrogen from C-19 steroids is catalyzed by a specific form of cytochrome P450, namely aromatase cytochrome P450 (P450arom; the product of the CYP19 gene). The human CYP19 gene comprises nine coding exons, II-X, and its transcripts are expressed in the ovary, placenta, testes, adipose tissue, and brain. Tissue-specific expression of the CYP19 gene is determined, at least in part, by the use of tissue-specific promoters, which give rise to transcripts with unique 5'-noncoding termini. Transcripts in adipose tissue contain 5'-termini derived from specific untranslated exons, corresponding to expression derived from the proximal promoter II and its splice valiant I.3, as well as a distal promoter, I.4. The object of the present study was to determine the distribution of these various exon-specific transcripts in breast adipose tissues from cancer-free women undergoing reduction mammoplasty and from patients with breast cancer, because this would provide important clues as to the nature of the factors regulating aromatase expression in these sites. To achieve this, we employed competitive RT-PCR, utilizing an internal standard for each exon-specific transcript of the CYP19 gene, as well as for the coding region, to evaluate total CYP19 gene transcripts. In cancer patients (n = 18), total CYP19 gene transcript levels were significantly higher in adipose tissue proximal to a tumor in comparison with adipose tissue distal to a tumor, in agreement with previous findings. Moreover, total transcript levels were higher in breast adipose tissue of cancer patients in comparison with those of cancer-free individuals (n = 9), even when the adipose tissue from the cancer patient was taken from a quadrant with no detectable tumor. We observed that exon I.4-specific transcripts were predominant in breast adipose obtained from cancer-free women. In this tissue, promoter-II-specific and exon I.3-specific transcripts were present in low copy number. On the other hand, in breast cancer patients, CYP19 gene transcripts from breast adipose tissue had primarily promoter-II-specific and exon I.3-specific sequence, whereas comparatively few transcripts had exon I.4-specific sequence at the 5'-terminus. We conclude that CYP19 gene transcription in breast adipose tissue of cancer-free individuals uses preferably promoter I.4, implicating a role of glucocorticoids and members of the IL-6 cytokine family in the regulation of this expression. On the other hand, the increased expression in breast adipose tissue bearing a carcinoma results from expression from promoters II and I.3, which are regulated by unknown factors acting via increased cAMP formation, which are presumably secreted by the tumor or associated cells.