RETINOIC ACID RECEPTOR BETA AND BREAST CANCER

视黄酸受体β（RAR β），特别是RAR-β 2，RAR β 2是人乳腺组织的候选肿瘤抑制因子。 与RAR α和RAR γ相反，RAR β在mRNA和蛋白质水平的表达在乳腺肿瘤进展期间下降或丢失。 转录和蛋白质分析表明，这种表达下调或丢失的机制是多因素的，包括转录，转录后和潜在的翻译后修饰。 乳腺癌细胞可以利用RAR β功能的一种或多种调节控制来抑制正常的细胞功能。我们希望测试的假设，RAR β 2亚型是一种肿瘤抑制蛋白，最近发现的人类RAR β 4亚型具有显性负性转录因子的属性。 我们打算表征RAR β基因在正常人乳腺上皮细胞（HMEC）和恶性乳腺癌细胞中的表达和功能的关键调控机制。 我们将描述RAR β转录物和蛋白质产物以及蛋白质的细胞内定位。 我们将在乳腺癌细胞核中检测到的截短的RAR β 4转录物引入正常细胞，以研究核定位的生物学后果。 为了检验RAR β亚型的差异水平以及异常亚细胞定位是原发性乳腺癌特征的假设，我们将利用免疫细胞化学（ICC）检测RAR β蛋白对一组特征良好的乳腺癌标本。 为了确定乳腺癌细胞中抑制RAR β和随后的基因作用所必需的转录组分，我们将鉴定和表征影响乳腺肿瘤细胞中RAR β 2转录的转录机制的组分。这些研究将提供细胞学和分子学基础，以增强潜在的新型维甲酸定向治疗人类乳腺癌，以及RAR β作为诊断或预后工具的基础。

Retinoic acid receptor beta (RARbeta), and in particular RAR-beta2, RARbeta2 is a candidate tumor suppressor for human mammary gland tissue. RARbeta expression at the mRNA and protein level, in contrast to RARalpha and RARgamma, declines or is lost during breast tumor progression. Transcriptional and protein analysis suggests that the mechanism for this down-regulation or loss of expression is multi-factorial and includes transcriptional, post-transcriptional, and potential post-translational modifications. Breast cancer cells may exploit one or more of these regulatory controls of the RARbeta function in order to inhibit normal cellular functions. We wish to test the hypothesis that the RARbeta2 isoform is a tumor suppressor protein and that the recently identified human RARbeta4 isoform has the property of a dominant-negative transcription factor. We intend to characterize the critical regulatory mechanisms of RARbeta gene expression and function in normal human mammary epithelial cells (HMECs) and malignant breast carcinoma cells. We will characterize RARbeta transcripts and protein products as well as and the intracellular location of the proteins. We will introduce the truncated RARbeta4 transcripts, detected in breast cancer nuclei, into normal cells to study the biological consequences of nuclear localization. In order to test the hypothesis that differential levels, as well as aberrant subcellular localization, of RARbeta isoforms is a characteristic of primary breast cancers, we will utilize immunocytochemical (ICC) detection of RARbeta proteins against a panel of well-characterized breast cancer specimens. In order to determine transcriptional components necessary for repression of RARbeta and subsequent gene action in breast cancer cells, we will identify and characterize components of the transcriptional machinery influencing RARbeta2 transcription in breast tumor cells. These studies will provide the cytological and molecular basis for enhancing potential novel retinoid-directed therapies for human breast carcinoma as well as the basis for RARbeta as a diagnostic or prognostic tool.