AROMATASE IN ADIPOSE--RELATIONSHIP TO AGING AND CANCER

在人类中，雌激素是在许多组织部位合成的。 包括卵巢颗粒细胞和黄体，胎盘 合胞体滋养层，大脑中的各个部位，以及脂肪 组织.脂肪组织中雌激素的生物合成不仅随着 肥胖也与年龄有关。其生理意义尚不清楚，但 从病理生理学的角度来看，它与许多 人类疾病，特别是子宫内膜癌和乳腺癌。为了 研究我们克隆的雌激素生物合成的调节， 表征了编码人芳香化酶细胞色素P450的基因， （P450 arom），负责雌激素生物合成的酶。我们有 发现该基因长度超过70 kb，其组织特异性 通过使用替代启动子来调节表达。卵巢中 表达受翻译起始点附近的启动子调控 位点（启动子II）。在胎盘中， 其位于翻译起始点（启动子）上游至少40 kb处 I. I）。在原位脂肪组织中， 启动子（1.4），其在基因内的位置尚未确定。 出乎意料的是，当将人脂肪基质细胞置于培养物中时， 启动子的选择似乎由培养条件决定， 即是否存在cAMP、地塞米松和生长因子。 为了研究导致这种疾病的分子和细胞机制， 这种新的基因表达调控，我们提出的特点， 存在于每一个基因上游的基因区域中的调节元件， 启动子驱动脂肪基质细胞中的表达，以及 原地。与这些基因组相互作用的转录因子 调节元件将被表征，它们在激素和 组织特异性调节。特别是，我们希望确定 生长因子在细胞培养中启动子使用转换中的作用。 我们还将试图确定是否转录激活或 抑制本身足以决定启动子使用的转换 或者是否需要额外的机制，例如 选择性剪接因子决定优先使用 特定的5 '-剪接位点。最后，我们将确定相对 这些不同的因素和机制的重要性，在生理 调节脂肪组织中的雌激素生物合成，例如， 随着年龄的增长而增加， 区域脂肪分布特别是，我们将讨论的概念， 乳腺肿瘤的发展受肿瘤的区域分布的影响。 乳腺局部雌激素的生物合成及其机制 由此建立这种P450 arom表达梯度， 将继续进行调查。我们相信这些研究将 为哺乳动物基因表达的调控提供了新的见解， 一般以及P450 arom表达，特别是， 将有助于揭示年龄依赖性过程中雌激素的作用 在脂肪组织中的生物合成，即增加发生作为一个 衰老的作用以及脂肪组织雌激素的影响 生物合成在癌症发展中的作用。

In the human, estrogens are synthesized in a number of tissue sites including ovarian granulosa cells and corpus luteum, placental syncytiotrophoblast, various sites in the brain, as well as adipose tissue. Estrogen biosynthesis in adipose tissue increases not only with obesity but also with age. Its physiological significance is unclear, but from a pathophysiological standpoint it has been implicated in a number of human diseases, notably endometrial cancer and breast cancer. In order to study the regulation of estrogen biosynthesis we have cloned and characterized the gene encoding human aromatase cytochrome P450 (P450arom), the enzyme responsible for estrogen biosynthesis. We have found that this gene exceeds 70 kb in length and that its tissue-specific expression is regulated by the use of alternative promoters. In the ovary expression is regulated by a promoter proximal to the translational start site (promoter II). In the placenta, expression is regulated by a promoter which is at least 40 kb upstream from the start of translation (promoter I.l). In adipose tissue in situ, expression is regulated by a third promoter (1.4) whose position within the gene has yet to be ascertained. Unexpectedly, when human adipose stromal cells are placed in culture, promoter selection appears to be dictated by the culture conditions, namely the presence or absence of cAMP, dexamethasone and growth factors. In order to study the molecular and cellular mechanisms responsible for this novel regulation of gene expression, we propose to characterize the regulatory elements present in regions of the gene upstream of each of the promoters which drive expression in adipose stromal cells, as well as in situ. The transcription factors which interact with these genomic regulatory elements will be characterized and their role in hormonal and tissue-specific regulation defined. In particular, we wish to determine the role of growth factors in switching promoter use in cells in culture. We will also seek to establish whether transcriptional activation or inhibition per se is sufficient to determine the switching of promoter use or whether additional mechanisms are required, such as the regulation of alternative splicing factors which determine the preferential employment of specific 5'-splice sites. Lastly, we will determine the relative importance of these various factors and mechanisms in the physiological regulation of estrogen biosynthesis in adipose tissue, for example, the increase which occurs as a function of aging, and the variation with regional fat distribution. In particular we will address the concept that breast tumor development is influenced by the regional distribution of estrogen biosynthesis in local areas of the breast, and the mechanisms whereby such gradients of P450arom expression are established and maintained will be investigated. We believe that these studies will provide new insights into the regulation of mammalian gene expression in general as well as of P450arom expression in particular, but especially will throw light on age-dependent processes involving estrogen biosynthesis in adipose tissue, namely the increase that occurs as a function of aging, as well as the implication of adipose tissue estrogen biosynthesis in the development of cancer.